United States Office of Solid Waste SW - 925
Environmental Protection and Emergency Response 1984
Agency Washington DC 20460
Solid Waste
Soil Properties, Draft
Classification,
and Hydraulic Conductivity
Testing
Technical Resource Document
for Public Comment
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SOIL PROPERTIES, CLASSIFICATION, AND
HYDRAULIC CONDUCTIVITY TESTING
Draft Technical Resource Document
for Public Comment
(SW-925)
MUNICIPAL ENVIRONMENTAL RESEARCH LABORATORY
OFFICE OF RESEARCH AND DEVELOPMENT
U.S. ENVIRONMENTAL PROTECTION AGENCY
CINCINNATI, OHIO 45268
OFFICE OF SOLID WASTE AND EMERGENCY RESPONSE
U.S. ENVIRONMENTAL PROTECTION AGENCY
WASHINGTON, D.C. 20460
March 1984
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DISCLAIMER
This report was prepared by D. W. Roberts of ABCDirt/Soil
Scientists, Seattle, Washington, under Contracts 68-03-2933 and
68-03-3068. The EPA Project Officer was M. H. Roulier of the
Municipal Environmental Research Laboratory, Cincinnati, Ohio.
This is a draft report that is being released by EPA for
public comment on the accuracy and usefulness of the
information in it. The report has received extensive technical
review but the Agency's peer and administrative review process
has not yet been completed. Therefore it does not necessarily
reflect the views or policies of the Agency. Mention of trade
names or commercial products does not constitute endorsement or
recommendtion for use.
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FOREWARD
The Environmental Protection Agency was created because of
increasing public and governmental concern about the dangers of
pollution to the health and welfare of the American people.
Noxious air, foul water, and spoiled land are tragic testimony
to the deterioration of our natural environment. The
complexity of the environment and the interplay between its
components require a concentrated and integrated attack on the
problem.
Research and development is the first necessary step in
problem solution; it involves defining the problem, measuring
its impact, and searching for solutions. The Municipal
Environmental Research Laboratory develops new and improved
technology and systems to prevent, treat, and manage wastewater
and the solid and hazardous waste pollutant discharges from
municipal and community sources; to preserve and treat public
drinking water supplies; and to minimize the adverse economic,
social, health, and aesthetic effects of pollution. This
publication is one of the products of that research—a vital
communications link between the researcher and the user
community.
This Technical Resource Document (TRD) is a compilation
of available laboratory and field testing methods for the
measurement of hydraulic conductivity (permeability) of soils
along with background information on relevant soil properties
and classification systems. The TRD was developed to assist
those involved in planning and construction of hazardous waste
disposal facilities and to support the Technical Guidance
Documents and Permit Guidance documents issued by EPA to assist
preparers and reviewers of applications for permits under
Subtitle C of the Resource Conservation and Recovery Act (RCRA),
This document is intended to supplement, and not replace, the
Technical Resource Document entitled, "Method 9100: Saturated
Hydraulic Conductivity, Saturated Leachate Conductivity, and
Intrinsic Permeability."
Francis T. Mayo, Director
Municipal Environmental
Research Laboratory
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PREFACE
Subtitle C of the Resource Conservation and Recovery Act
(RCRA) requires the Environmental Protection Agency (EPA) to
establish a Federal hazardous waste management program. This
program must ensure that hazardous wastes are handled safely
from generation until final disposition. EPA issued a series
of hazardous waste regulations under Subtitle C of RCRA that is
published in 40 Code of Federal Regulations (CFR) 260 through
265 and 122 through 124.
Parts 264 and 265 of 40 CFR contain standards applicable to
owners and operators of all facilities that treat, store, or
dispose of hazardous wastes. Wastes are identified or listed
as hazardous under 40 CFR Part 261. The Part 264 standards are
implemented through permits issued by authorized states or the
EPA in accordance with 40 CFR Part 122 and Part 124
regulations. Land treatment, storage and disposal (LTSD)
regulations in 40 CFR Part 264 issued on July 26, 1982,
establish performance standards for hazardous waste landfills,
surface impoundments, land treatment units, and waste piles.
The Environmental Protection Agency is developing three
types of documents for preparers and reviewers of permit
applications for hazardous waste LTSD facilities. These types
include RCRA Technical Guidance Documents, Permit Guidance
Manuals, and Technical Resource Documents (TRD's). The RCRA
Technical Guidance Documents present design and operating
specifications or design evaluation techniques that generally
comply with or demonstrate compliance with the Design and
Operating Requirements and the Closure and Post-Closure
Requirements of Part 264. The Permit Guidance Manuals are
being developed to describe the permit, application information
the Agency seeks and to provide guidance to applicants and
permit writers in addressing the information requirements.
These manuals will include a discussion of each step in the
permitting process, and a description of each set of
specifications that must be considered for inclusion in the
permit.
The Technical Resource Documents present state-of-the-art
summaries of technologies and evaluation techniques determined
by the Agency to constitute good engineering designs,
practices, and procedures. They support the RCRA Technical
iv
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Guidance Documents and Permit Guidance Manuals in certain areas
(i.e., liners, leachate management, closure covers, water
balance) by describing current technologies and methods for
designing hazardous waste facilities or for evaluating the
performance of a facility design. Although emphasis is given
to hazardous waste facilities, the information presented in
these TRD's may be used in designing and operating
non-hazardous waste LTSD facilities as well. Whereas the RCRA
Technical Guidance Documents and Permit Guidance Manuals are
directly related to the regulations, the information in these
TRD's covers a broader perspective and should not be used to
interpret the requirements of the regulations.
This document is a first edition draft being made available
for public review and comment. It has undergone review by
recognized experts in the technical areas covered, but Agency
peer review processing has not been completed yet. Public
comment is desired on the accuracy and usefulness of the
information presented in this manual. Comments received will
be evaluated, and suggestions for improvement will be
incorporated, wherever feasible, before publication of the
second edition. Communications should be addressed to Docket
Clerk, Room S-212(A) , Office of Solid Waste (WH-562), U.S.
Environmental Protection Agency, 401 M Street, S.W.,
Washington, D.C., 20460. The document under discussion should
be identified by title and number; e.g., "Soil Properties,
Classification, and Hydraulic Conductivity Testing (SW-925).
v
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ABSTRACT
This Technical Resource Document (TRD) is a compilation of
available laboratory and field testing methods for the
measurement of hydraulic conductivity (permeability) of soils
along with background information on relevant soil properties
and classification systems. This TRD was developed to assist
those involved in planning and construction of hazardous waste
disposal facilities and also supports the Technical Guidance
Documents and Permit Guidance Documents issued by EPA to assist
reviewers of application for permits under Subtitle C of the
Resource Conservation and Recovery Act (RCRA).
The review of the literature consisted of searches through
the National Technical Information Service network and several
professional data bases available through the University of
Washington. Technical reports were also obtained from the EPA
Region X library,, and some documents and recommended readings
forwarded to us by colleagues.
Background information on soil classification, soil water,
and soil compaction are included along with descriptions of
sixteen methods (laboratory and field) for determination of
saturated or unsaturated hydraulic conductivity.
The conclusions that can be drawn from this study are: (1)
The area of soil testing for hydraulic conductivity overlaps
several professions: geology, hydrology, soil engineering, and
soil science; (2) Most testing methods for hydraulic
conductivity have been developed for agricultural or
engineering purposes other than application to the feasibility
and design of solid or hazardous waste disposal sites; (3) All
laboratory tests suffer from possible misrepresentation of
field conditions due to sample disruption and small size; (4)
Most field tests are more applicable to situations of
coarse-textured soils rather than fine-grained soils that are
more appropriate for disposal sites; (5) It is difficult at
this time to discern the degree of variation in soil testing
results caused by variation inherent in the soil testing method
or by variation of spatial properties of the soils; and (6)
Determination of soil hydraulic conductivity values is the
limiting factor to further development of the applicability of
the saturated-unsaturated transport model.
This report was submitted in fulfillment of Contracts
68-03-2933 and 68-03-3068 by ABCDirt, Inc. under the
sponsorship of the U.S. Environmental Protection Agency. This
report covers the period from January 30, 1981 to June 15, 1982,
vi
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TABLE OF CONTENTS
Page
FOREWORD Hi
PREFACE iV
ABSTRACT vi
LIST OF FIGURES X
LIST OF TABLES xiii
ACKNOWLEDGEMENT xiv
SECTION 1 : INTRODUCTION 1
SECTION 2: SOIL CLASSIFICATION 3
2.1 Soil Taxonomy 4
Diagnostic Horizons 5
Order 6
Suborders 7
Great Groups 8
Subgroups 8
Soil Family 8
Soil series 8
2.2 Unified Soil Classification System 9
Field Classification 10
Laboratory Classification 13
Atterberg Limits 13
Shrinkage Limits 13
Plasticity 13
Plastic Limit 13
Liquid Limit and Plasticity Index 14
Activity 14
SECTION 3: SOIL WATER 16
3.1 The Solid Framework 16
3.2 The Porous Network 16
Porosity and Void Ratio 17
Pore Size Distribution 17
3.3 Soil Wetness or Moisture Content 18
3.4 Soil Moisture Potential 19
Pressure Potential 19
Gravitational Potential 19
Vll
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Other Potentials 20
Hydraulic Head. 21
3.5 Moisture Retention Curve, Moisture
Characteristics, or the Retentivity
Curve 21
3.6 Hystersis 22
3.7 Anisotropy 24
3.8 Water Movement in Soils 25
Saturated Flow 27
Unsaturated Flow 27
3.9 Hydraulic Conductivity and Soil Pore
Geometry , 29
3.10 Hydraulic Conductivity and Anisotropy.... 30
3.11 Hydraulic Conductivity and Permeant 32
The Soil Solution 32
Hazardous Waste Leachate. . . 33
Solvent Phase 33
Organic Acids 33
Organic Bases 34
Neutral Polar Organics... , 34
Neutral Nonpolar Organics.... 34
3.12 Hydraulic Conductivity Testing Errors.... 35
Laboratory Tests 35
Limitations of Laboratory Tests 35
Comparison of Laboratory to Field
Testing Results , „ 36
Field Tests ,. 36
Fabric 37
Spatial Variation (Anisotropy).. 38
SECTION 4 : SOIL COMPACTION 39
4.1 Compaction Tests , . 41
4.2 Compaction and Hydraulic Conductivity.... 42
Structure 42
Fabric 43
Porosity 46
4.3 Compaction/Hydraulic Conductivity
Testing Errors. 48
Effect of Compaction Water Content 48
Maximum Size of Soil Aggregates 48
Presence of Deleterious Substances 48
Method of Compaction 49
Compactive Effort. 50
Air in Sample. . 50
Excessive Hydraulic Gradients 50
Sample Size 51
SECTION 5: HYDRAULIC CONDUCTIVITY AND HAZARDOUS
WASTE DISPOSAL 53
5.1 Land Treatment/Landf arming. 53
5.2 Landfills and Surface Impoundments 54
5.3 The Unsaturated Zone... 55
V11J
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5.4 The Saturated Zone 56
SECTION 6: SOIL TESTING METHODS 58
6.1 Saturated Hydraulic Conductivity 58
Laboratory Tests 58
Pressure Cells 58
Compaction Molds 60
Consolidation Cells 64
Modified Triaxial Apparatus 66
Field Tests 70
Piezometers 70
Double Ring Infiltrometer/Permeameter.. 74
Modified Air-Entry Permeameter 78
Cube Method 81
6.2 Unsaturated Hydraulic Conductivity 85
Laboratory Tests 85
Steady State-Column 85
Unsteady State-Instantaneous Profile... 90
Thermocouple Psychrometer 97
Field Tests 101
Crust 101
Instantaneous Profile .105
Calculation Methods 109
Dif f usivity 112
Pressure Outflow 112
Hot-Air Method 116
SECTION 7: SUMMARY 121
REFERENCES 126
APPENDIX A: GLOSSARY OP TECHNICAL TERMS 138
IX
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LIST OF FIGURES
Number Page
3.1 Soil Moisture retention curves for four
different soil materials ............................ 22
3.2 Cross-section through an idealized void
illustrating the hysteresis phenomena ............... 23
3.3 The relationships between water content
and suction (h) ..... . ............. ............. . ..... 23
3.4 Influence of underlying layer on hydraulic
conductivity ........................... . ............ 24
3.5 Water retention curves and hydraulic
conductivity ............................. ..... ........ 26
3.6 Graphic representation of hydraulic
conductivity determination from diffusivity
measurements ................................. , ...... 28
4.1 Standard compaction test ...................... ...... 39
4.2 Dynamic compaction curves for a silty clay... ....... 40
4.3 Static compaction curves for a silty clay ........... 41
4.4 Effect of mixing on hydraulic conductivity -
Jamaica clay. .............. .......................... 42
4.5 Effect of dispersion on hydraulic conductivity ...... 43
4.6 Hydraulic conductivity as a function of
molding water content for samples of silty
clay prepared to constant density by
kneading compaction .............. ... ................ 44
4.7 Influence of the method of compaction on
the hydraulic conductivity of silty clay ............ 45
4.8 Hydraulic flow rates as a function of
porosity for illite ................ , ................. 46
4.9 Discrepancies between measured and
predicted hydraulic conductivities ....... , ............ 47
x
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4.10 Comparison of field and laboratory
compaction 49
5.1 Water and waste movement within the root zone 53
5.2 Water and waste movement through a soil liner 55
5.3 Water and waste movement in the unsaturated
zone 56
6.1 Apparatus for pressure cell method 59
6.2 Modified compaction permeameter 62
6.3 Apparatus for hydraulic conductivity in
conjunction with consolidation test 65
6.4 Schematic of modified triaxial apparatus 68
6.5 Apparatus set-up for piezometer method 71
6.6 Nomograph for the determination of the
hydraulic conductivity from data obtained
by the piezometer method 74
6.7 Cross-section of double ring infiltrometer
apparatus 75
6.8 Schematic diagram of equipment for
permeameter method in place 77
6.9 Modified air-entry permeamter 79
6.10 Diagram of the cube method 83
6.11 Diagram of apparatus for short column
steady state method 86
6.12 Alternative steady state method for
undisturbed samples 88
6.13 Diagram of long column version of steady
state method 89
6.14 Diagram of flow cell, tensiometer system
and gamma system 92
6.15 Variation of soil water suction with time at
several column elevations 93
6.16 Variation of moisture content with time at
several column elevations 94
xi
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6.17 Instantaneous velocity profiles ..................... 95
6.18 Instantaneous total potential profiles .............. 95
6.19 Instantaneous potential gradient profiles ........... 96
6.20 Water content - instantaneous nydraulic
conductivity relation (showing the
computed value) „<,...„.. ........... ,, . ................ 96
6.21 Cross - section of thermocouple psychrorneter
permeameter ........................... . .............. 98
6.22 Schematic of crust test apparatus ....... ..... ........ 102
6.23 Hydraulic conductivity versus pressure head
for Bt horizon of Batavia silt loam .......... ...... 104
6.24 Field set-up for instantaneous profile method ....... 106
6.25 Comparison of traditional instantaneous
profile method to Libardi method .................... 108
6.26 Diagram of apparatus for the outflow method
of soil water diffusivity determination ............. 113
6.27 Graph of volumetric water content versus
distance from evaporating surface ................... 118
XII
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LIST OF TABLES
Number Page
2.1 Comparison of Particle Size Classes for U.S.D.A.
and Unified Systems ». 4
2.2 Major Features of Diagnostic Horizons Used to
Differentiate at the Higher Levels of the U.S.D.A.
Classification Scheme .. .. 5
2.3 Orders of Taxonomy 7
2.4 Unified Soil Classification System (U.S.C.S.)........ 11
3.1 Data on the Ratio of Horizontal to Vertical
Hydraulic Conductivity of Fine-Textured Soils........ 31
3.2 Sources of Error in Laboratory Test my for
Saturated and Unsaturated FJ ow, 36
4.1 Effect of Fabric on Hydraulic Conductivity... 43
4.2 Summary of Sources of Error in Estimating Field
Hydraulic Conductivity of Compacted Clay Liners
from Laboratory Tests , 52
6.1 Confidence Limits Cor Hydraulic Conductivity
as a Function of Number of Samples.. 60
6.2 Summary of Laboratory Instantaneous Profile
Methods for Hydraulic Conductivity 91
6.3 Comparison of Measured and Computed Water Content
and Pressure Head Values 97
6.4 List of Literature Citations for Field
Instantaneous Profile Method 105
6.5 Reduced Diffusivity Dt/L2 Versus l-Q(t)/Q(oo)
for Construction of the Overlay. 115
7.1 Soil Testing Methods Matrix/Saturated
Hydraulic Conductivity . 122
7.2 Soil Testing Methods Matrix/Unsaturated
Hydraulic Conductivity 124
xiii
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ACKNOWLEDGEMENT
This document was prepared by ABCDirt, Inc. of Seattle,
Washington under a contract with the Municipal Environmental
Research Laboratory,, U. S. Environmental Protection Agency,
Cincinnati, Ohio. David W. Roberts was Project Director of this
report.
Other personnel of ABCDirt, Inc. that actively contributed to the
compilation of this document are Jack R. Kulawik and Mark D.
Sarles. Assistance was also provided by Michael A. Nichols
during the early phases of the contract.
Special thanks are also extended to Dr. Michael H. Roulier whose
valuable assistance as EPA Project Officer helped guide thistwork
to a successful completion. Also, Dr. Thomas F. Zi'mmie
(Rensselaer Polytechnic Institute), Dr. James L. Withiam and Dr.
Sirous Haji-Djafari (D'Appolonia), Mark D. Nickelson (U. S. Army
Environmental Hygiene Agency), R. Jefferey Dunn (University of
California - Berkeley), and Dr. Johan Bouma (Soil Survey
Institute - The Netherlands) provided comments during draft
revisions.
xiv
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SECTION 1
INTRODUCTION
In what seems an inevitable progression from an initial
demand for goods and services, there follows the extraction of
natural resources, production, consumption, and ultimately, the
disposal of residuals. While at many points in this
progression methods may be used which either reduce the overall
quantity or change the form of waste materials, the capacity of
the environment to assimilate final residuals is finite. The
quality of human life can be impaired when such capacity is
exceeded.
Any assessment of the capacity of the environment to
immobilize, attenuate, or transport applied waste materials
must, consider the rate of water and/or pollutant movement
through soils regardless of whether the wastes are applied onto
or injected into the surface soil, or the wastes are placed
into lined surface impoundments or buried in lined landfills.
Presently, there are not recognized U.S.A. standards for
determining the rate of water and/or pollutant movement in
fine-textured soils which are more desirable for waste disposal
facilities. This Technical Resource Document (TRD) is intended
to provide information and guidance on available soil testing
methods that are presently in use by scientists and engineers
to determine the rate of water and/or pollutant movement in
soils.
It should be noted that this TRD provides information on a
variety of methods without identifying a preferred method.
Recommended methods are described in the Technical Guidance
Documents and Permit Guidance Documents issued by EPA to assist
preparers and reviewers of applications for permits under
Subtitle C of the Resource Conservation and Recovery Act
(RCRA). See the Preface of this TRD (pages iv and v) for
further information on these two documents. The EPA
publication entitled "Test Methods for Evaluating Solid Waste:
Physical and Chemical Methods (SW-846) also describes a
recommended method (#9100) for measuring hydraulic
conductivity. Permit applicants may use other methods but must
demonstrate that they are appropriate for the specific
circumstances. This TRD is one source of information for
applicants who are considering use of other methods.
While there is much discussion and disagreement regarding
the use of the terms hydraulic conductivity versus
permeability, hydraulic conductivity is preferentially used in
this text and is defined as the flux of water per unit gradient
of hydraulic potential and is the proportionality factor in
Darcy's Law whereas permeability refers to the ease with which
gases, plant roots, or water pass through a bulk mass of soil.
In general usage, these two terms are used interchangeably. It
1
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can be noted that hydraulic conductivity is the most variable
property of soil with a range in values exceeding fourteen
orders of magnitude (Cedergren, 1977).
While the TRD is principally written for .use in connection
with hazardous waste land treatment, surface impoundments, and
landfill facilities; it can also be applied to other types of
landbased waste disposal systems where soil testing methods for
hydraulic conductivity are needed, such as: non-hazardous
waste landfills and surface impoundments, land treatment
(landfarming), land application of domestic wastewater, and
on-site sewage disposal systems.
Section 2 provides background information on how soils are
classified by soil scientists according to how soils are formed
and exist in the natural landscape, and by soil engineers
according to the physical properties of a soil material.
Section 3 provides a wide variety of informtion on factors
of the soil that affect water relations and movement. Darcy's
Law concerning the rate of liquid movement through a porous
medium is discussed, along with factors that affect such
movement through soils such as soil pore geometry, anisotropy,
and permeant. A general discussion of the types of errors
associated with testing for hydraulic conductivity is also
introduced.
Section 4 describes the relevant parameters of soil
compaction and how compaction relates to hydraulic
conductivity. One subsection also discusses the errors
commonly involved in testing the hydraulic conductivity of
compacted soil samples.
Section 5 provides a discussion of the types of water
movement flow regimes that are relevant to the different kinds
of waste disposal facilities used for hazardous waste disposal
such as land treatment, landfills, or surface impoundments.
Actual soil testing methods and procedures for
determination of hydraulic conductivity are described for both
saturated and unsaturated liquid flow in Section 6, It should
be noted that most of the test methods use water, rather than a
waste liquid, as the permeant.
In Section 7, important considerations and limitations of
laboratory and field testing methods are summarized. A soil
testing methods matrix is presented which offers information
for each method on: application to specific type of
problem/facility, precision and accuracy, limitations of test,
status of the method, and comments.
A glossary of technical soil terms used in the text is
provided as an appendix.
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SECTION 2
SOIL CLASSIFICATION
In current use in the United States there are two major
schemes for classifying soils for purposes of evaluation and
design of hazardous waste land disposal sites. One classifica-
tion scheme (used by the U.S. Department of Agriculture (USDA),
Soil Conservation Service and other Professional Soil Scientists)
is a system based on quantitatively measurable physical and
chemical properties as they exist in the field. This system's
development, since the early 1900's, has occurred alongside soil
mapping efforts that have yielded Soil Survey Reports for most
U.S. Counties. Such information is used in resource management,
land use planning, the agriculture sciences, and forestry.
The second classification scheme is the Unified Soil Classi-
fication System (USCS) which was developed after WWII and is a
system based on the grain (particle) size and response to
physical manipulation at various water contents. This system
serves engineering uses of soil in developing dams, roads,
liners, etc. Therefore, on a general level, the difference
between the two classification schemes is that the USDA system is
concerned with mapping of native soil bodies as they occur on the
landscape while the USCS system is concerned with the uses of
soil as a material and how it will react to outside forces.
Another point regarding the USCS and USDA systems is that
both systems may use the same term but have different meanings.
TLe most apparent example of this phenomenon is the difference in
the range of particle size classes for the particular soil
separates and subclasses of the two systems. This is shown
graphically in Table 2-1.
However, even though texture is an important soil property
that affects and influences other soil properties, its degree of
importance to soil classificaton is different for the two sys-
tems. Soil texture is a major criterion in the USCS while it is
a minor criterion for classification in the USDA system.
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TABLE 2-1
COMPARISON OF PARTICLE SIZE
SYSTEM
FOR USDA AND UNIFIED
•? 0) C
F o
o> a .r
|||
Q < J
in "o u
=> jj
C
o
o
\J
t£
t/>
o
u
'5
|
E
Clay
Silt
Very
fine
sand
Fines (silt or clay)
Fine
sand
Med-
iurn
sand
Fine
sand
~D
5
o
o
u
C
D
D
Q
O
X
0)
Medium
sand
Fine
gravel
Coarse
sand
Coarse
gravel
Fine
grave
Ccarse
grave!
Cobbles
Cobbles
Sieve sizes g 8 § §§S 2 ^ i?S5 "
CN C
N —
i I
I 1
O OOOOOO OOOOO ^_ CN)c--jTj-s3co'~" CNfO'-tOCO
Pa rticle si2e, mm
2.1 SOIL TAXONOMY
The soil classification system currently utilized by soil
scientists and agronomists to map the areal extent of native soil
bodies is called Soil Taxonomy (USDA, 1975). One of the
attributes of this system is that the primary elements for
discerning different classes in the system are the quantitative
physical and chemical properties of soils as they are found in
the field. Another attribute of this system is the nomenclature
used which is similar to other taxonomic classification schemes
as used in other natural sciences such as biology or zoology.
The names in Soil Taxonomy (especially for the broader classifi-
cation categories) give a definite connotation of the major
characteristics of the soils in question which can be understood
in many languages since Latin or Greek words are the basis for
the names.
The characteristics of the soil in any place are a result of
the combined influence of climate and living organisms on a
specific kind of parent material, conditioned by relief, over a
period of time. The combined effect of these factors is
reflected in most soils as soil horizons of unique kinds. Each
key soil horizon has a unique morphology that reflects its
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genesis and composition and a unique behavior due to its physical
and chemical properties (Bartelli, 1977). The presence or
absence of kinds of soil horizons is an important criteria in the
classification of soils by Soil Taxonomy (USDA, 1975).
A soil horizon is a layer that has some set of properties
that have been produced by soil-forming processes. It also has
some properties that distinguish it from the horizons just above
and below it. A soil horizon is usually differentiated in the
field by characteristics such as texture, structure, consistence,
color or other physical or chemical properties.
Diagnostic Horizons
Diagonostic horizons are used in Soil Taxonomy to differen-
tiate soil classes or categories. Surface diagnostic horizons
are called epipedons (Greek epi means over, pedon means soil)
which includes the upper part of the soil profile darkened by
organic matter, the upper eluvial horizons, or both. Six
epipedons are recognized as well as six subsurface horizons which
are shown in Table 2-2 along with their major features.
TABLE 2-2
Diagnostic
Horizon
Mollic
Umbric
Ochric
Histic
Anthropic
Plaggen
Argillic
Natric
Spodic
Cambic
Agric
Oxic
MAJOR FEATURES OF DIAGNOSTIC HORIZONS USED TO
DIFFERENTIATE AT THE HIGHER LEVELS OF THE USDA
CLASSIFICATION SCHEME
Major Features
Sur f ace Hor izon s (Epipedons)
Thick, dark-colored, high-base saturation, strong
structure
Same as Mollic except low-base saturation
Light colored, low organic content, may be hard and
massive when dry
Very high in organic content, wet during some part
of the year
Cultivated soil layer rich in N, P, K and bases
Manmade surface layer more than 20 in. thick caused
by continuous manuring
Subsurface Horizons
Silicate clay accumulation
Argillic, high in sodium, columnar or prismatic
structure
Organic matter, Fe and Al oxide accumulation
Changed or altered by physical movements or by
chemical reactions
Organic and clay accumulation just below the plow
layer
Primarily mixture of Fe, Al oxides, and l:l-type
minerals
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Soil Taxonomy is a six-category system that permits aggrega-
tion of soil data and interpretations at various levels of
generalization, whether they are displayed as maps or statistics.
It is the only soil classification system with a consistent,
systematic nomenclature that indicates location in the system and
something about the properties of the soils in each class
(Johnson and McClelland, 1977). The six categories are (1)
Order (the broadest category); (2) Suborder; (3) Great Group;
(4) Subgroup; (5) Family; and (6) Series (the most specific).
Currently in the U. S., there are more than 11,000 recognized
soil series.
Order
This category is based largely on the morphology of surface
and subsurface horizons with soil genesis as an underlying fac-
tor. Any given order includes soils whose properties suggest
that they are not too dissimilar in their genesis or soil-forming
factors. The ten orders are listed below in Table 2-3. Note
that all order names have the common ending "sol" from the Latin
"solum" meaning soil. A prevalent soil series in the Puget Sound
area of Washington is the Alderwood soil (which was glacially
derived) and belongs to the Inceptisol soil order.
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TABLE 2-3
ORDERS OP SOIL TAXONOMY
Formative
Alfisols
Aridisols
Entisols
Histosols
Inceptisols
Mollisols
Oxisols
Spodosols
Ultisols
Vertisols
Suborders
Derviation
Meaningless
syllable
L. "aridus",
dry
Meaningless
syllable
Gk. "histos",
tissue
L. "inceptum",
beginning
L. "mollis",
soft
F. "oxide",
oxide
Gk. "spodos",
wood ash
L. "ultimas",
last
L. "verto",
turn
alf
id
ent
ist
ept
oil
ox
od
ult
ert
Description
Gray to brown epipedons;
formed mostly in humid-
region areas under na-
tive deciduous forests
Desert or dry soils
with an ochric epipedon
Recent soils lacking
profile development;
found under wide varie-
ty of climatic condi-
tions
Organic soils
Young soils, more de-
veloped than Entisols
Dark (mollic) epipedons,
includes some of the
world's most important
agricultural soils
Oxic subsurface horizon
from intense leaching of
silica leaving Fe and Al
oxides
Light colored (usually
albic) horizon above
spodic horizon
Old,moist soils devel-
oped under warm to trop-
ical climates, argillic
horizons with low base
saturation
High content of swelling
clays which can develop
deep, wide cracks when
dry
The suborder category within each order emphasize genetic
homogeneity. Thus, wetness, climatic environment, and vegetation
are characteristics which help determine the suborder in which a
given soil is found. The names of suborders are obtained by
adding a prefix syllable to a formative element taken from that
order name. The suborder for the Alderwood soil series mentioned
previously is
soil ("ept").
an ochrept, meaning a light colored ("ochr") young
-------
Great Groups
The great groups are subdivisons of the suborders based on
kind and arrangement of diagnostic horizons or uses of the epipe-
don. The great groups are named by prefixing the suborder names
by an ... ditional 'descriptive syllable. Again for the Alderwood
series, rhich belongs to the Durochrept great group, it is a
light colored, young soil with a hardpan ("dur") subsurface
horizon which was formed due to the pressure of glacial ice.
Subgroups
Each great group can be divided into three subgroups: the
central (typic) concept of the great groups; the intergrades, or
transitional forms to other great groups; and the extragrades,
which have some properties that are representative of the great
groups but do not indicate transitions to any other known kind of
soil. Each subgroup is identified by one or more adjectives
preceding the name of the great group. The Alderwood soil is a
Dystric Entic Durochrept which means it is a durochrept with low
base saturation ("dystr") and recently developed ("ent").
Soil Family
The intent of this category has been to group soils within a
subgroup having similar physical and chemical properties that
affect their responses to management and manipulation for use.
Families are defined primarily,to provide groupings of soils with
restricted ranges in:
1) Particle-size distribution in horizons of major
biologic activity below the plow depth;
2) Mineralogy of the same horizons considered in naming
the particle-size classes;
3) Temperature regime;
4) Thickness of the soil penetrable by roots; and
5) A few other properties that are used in defining some
families to produce the needed homogeneity (USDA, 1975).
Thus, the Alderwood soil, which is a loamy-skeletal, mixed, mesic
dystric entic durochrept means a family of soils within the
subgroup dystric entic durochrept that posseses a particle size
class where rock fragments greater than 2 mm make up 35 percent
or more by volume (loamy-skeletal), has mixed mineralogy, and is
located in a temperate climate (mesic).
Soil Series
A soil series is a group of soils developed from the same
kind of parent material, by the same genetic combination of
processes, and whose horizons are quite similar in their arrange-
8
-------
ment and general characteristics. Soils of any one series pos-
sess a unique characteristic profile in some way different from
other series within the same family. Soil series are usually
named after cities, regions, rivers or other local geographic
conditions close to the place where the soils were originally
defined.
The soil type is a subdivision of the soil series and is
named according to the texture of the surface horizon. There-
fore, with our example of the Alderwood soil series (which is
named after an old town in Washington), the surface texture is
gravelly loam.
2.2 UNIFIED SOIL CLASSIFICATION SYSTEM
The Unified Soil Classification System (USCS) serves
engineering uses of soils. The criteria for soil types in the
system are based on the grain (particle) size and response to
physical manipulation at various water contents (Fuller, 1978).
The USCS is based on textural characteristics for those
soils with such a small amount of fines that the fines do not
affect the behavior. It is based on plasticity-compressibility
characteristics for those soils where the fines affect the
behavior. The plasticity-compressibility characteristics are
evaluated by plotting the plasticity index versus the liquid
limit on a standard plasticity chart. The position of the plot-
ted point yields information from which to predict behavior as an
engineering construction material (Asphalt Institute, 1969).
The following properties form the basis of USCS soil
classification:
1) Percentages of gravel, sand and fines (fraction passing
No. 200 sieve).
2) Shape of the grain-size-distribution curve.
3) Plasticity and compressibility characteristics.
Four soil fractions are recognized: cobbles, gravel, sand,
and fines (silt or clay). The limiting boundaries between the
various fractions are given in Table 2-1.
The soils are divided as (1) coarse-grained soils, (2) fine-
grained soils, and (3) highly organic soils. The coarse-grained
soils contain 50 percent or less material smaller than the No.
200 sieve, and fine-grained soils contain more than 50 percent
material smaller than the No. 200 sieve. Highly organic soils
can generally be identified visually. The USCS recognizes 15
soil groups and uses names and letter symbols to distinguish
between these groups. These symbols are derived either from the
terms descriptive of the soil fractions, their relative value of
-------
liquid limit (high or low), or relative gradation (well-graded or
poorly graded); and are used to form the group symbols which
correspond to the names of typical soils as seen in Table 2-4,.
The coarse grained soils are subdivided into gravels (G) and
sands (S). The gravels have a greater percentage of the coarse
fraction (that portion retained on the No. 200 sieve) retained on
the No. 4 sieve, while the sands have the greater portion passing
the No. 4 sieve. Both the gravel and sancl groups are divided
into four secondary groups (Table 2-4).
Fine-grained soils are subdivided into silts (M) and clays
(C), depending on their liquid limit and plasticity index. Silts
are those fine-grained soils with a liquid limit: and plasticity
index that plot below the "A" line in Table 2-4, under Laboratory
Criteria, while clays are those that plot above the "A" line.
Organic clays are the exception to the above rule, as the liquid
limits and plasticity indexes of those soils plot below the "A"
line. The silt, clay and organic fractions are further
subdivided on the basis of relatively low (I,) or high (H) liquid
limits. The arbitrary dividing line between the low and high
liquid limits has been set at 50. Representative soil types for
each of these groups (ML, MH, CL, CH, OL, and OH) can be found
under the "Typical Names" column in Table 2-4.
Field Classification
The USCS is designed so that most soils can easily be
classified into the three primary groups (coarse-grained, fine-
grained, and highly organic) by means of visual inspection and
simple field tests. Additionally, with some field experience,
classification into the subdivisions can be performed with a
considerable degree of success. Further, laboratory tests for
classification may be performed to provide greater accuracy and
precision and/or as back-up to field-derived information.
The field classification procedure consists of a process of
elimination and occurs by moving from left to right in Table 2-4
until the proper group name is obtained. The general procedure
followed is described as follows: (1) Obtain a representative
sample or the soil; (2) Estimate the size of the largest
particle; (3) Remove the boulders and cobbles and estimate the
amount (percentage by weight) represented by this fraction in the
total sample; (4) Spread the dry sample on a flat, surface or in
the palm of the hand, and classify as coarse-grained or fine-
grained; (5) If coarse-grained, classify as gravel or sand by
criteria in Table 2-4; (6) If gravel or sand, classify as
"clean" or "with appreciable fines" where fines are the fraction
smaller than 0.074 mm (No. 200 sieve); (7) If the gravel or sand
is clean, decide if it is well-graded (W) or poorly-graded (P),
and assign the appropriate group name (GW, GP, SW, or SP); (8) If
the gravel or sand contains appreciable fines, decide if the
10
-------
TABLE 2-4 UNIFIED SOIL CLASSIFICATION SYSTEM (U.S.C.S.)
(LAMBE AND WHITMAN, 1979).
1 " ' — • — • , . — — - -— _ - .
Laboratory Classification
Criteria
Typical Names
Group
Symbols
fication Pioceduics
han 75 ^m and basing trauions on
ated weights)
IP
Ti
Ct
c
3
'j
K
'OJ
Ct7 =* 7^ Greater than 4
^10
- - <°3»>2 « ,,
•>
».
i
<
X
c
Q
equirements for G W
"
Not meeting all gradation r
Above "A" line
with PI between
4 and 7 are
borderline cases
requiring use of
dual symbols
j!
M
Is.
oc J3
ji: c
Atterberg limits above
"A" line, with PI
greater than 7
f*
t
c
e
1 \
\.
t
\
L
1
i
Cd
sS
o
L
sjoquiXs [Bnp
jo asn Suuinbs-i SOSBO ywiJapjog
SMOJIOJ se psyissGp sap s|ios pauiejg 3<
D21S UIPlS IUOJJ PUPS pUB 13ABJ3 JO SO
uoneagijuapi pr
Is
n
t.
* c 2
1
Wide range in gram size and substantial
amounts of all intermediate particle
sizes
Pooriy graded graveis, gravel-
sand mixtures, little or no fines
tt.
Predominantly one size or a range of sizes
with some intermediate sizes missing
(s3ug
OU JO 3[U'D
Silty gravels, poorly graded
gravel- sand- si It mixtures
^
Nonplastic fines (for identification pro-
cedures see ML below)
Clayey gravels, poorly graded
gravel-sand-clay mixtures
<0
Plastic fines (for identification procedures,
see CL below)
. ..
(sauu
jo lunouiB
9[pei39jddB)
3ZIS ;>A31S LUUI t-
u«m .laSjei si UOUOBJJ
nSIPOn )O JJBq U\?lp 3JO^
_
1
equirements for SH'
' 0io * 060
Not meeting all gradation r
Above "A" line
with PI between
4 and 7 are
borderline cases
requiring use of
dual symbols
Atterberg limits below
"A" line or PI less than
5
Alterberg limits below
"A" line with PI
greater than 7
%l\ oi %S
JPO3 (32 IS 9A91S UJtY
SPlUMJdd 3UUUJ313Q
\
';;
t equal liquid limit
If
111
(
\
s
o S.
g J. JU
1 = y T \
jtsf- " - 4
1 1?
U =
liii tt
g
r + - °
JHo
iKo
a *-H
So o o o o o
in ««• ro CM —*
xapui ^oi;sey
in
Liquid limit
Plasticity chart
for laboratory classification of fine grained soi
»y aapun USAIJJ SB suomBJj 3qi 8uiA"jMU3pi ui SAJTID 32is uiBJ8 3Sfi
2
V
C
"c °
0
1
s
~
Wide range in gram sizes and substantial
amounts of all intermediate particle
sizes
11
s
M v
i!
« C
" M
a.
Predominantly one size or a range of sizes
with some intermediate sizes missing
OU JO 9IJJII)
SpUBS UB3Q
SiUy sands, poorly graded sand-
silt mixtures
5,
Nonplastic fines (for identification pro-
cedures, see ML below)
Clayey sands, poorly graded
sand-clay mixtures
&i
Plastic fines (for identification procedures,
see CL below)
jo lunoujB
saug
MUM spuss
321S 3A31S OILU f
ueqi J3j|pujs si UOUSPJJ
spues
(3\"0 pS^PU
M37IS 3A31S Ulrf C /. UBU.I
si 1BU3IBU1 jo jieq ueqi
01 ^iqisiA apiuPd is?i|p
5
i
c
c
>
<
f
T:
c
«
L
i
«
i
c
1
Identification Proceduies on fraction Snwllet than 380 mn Sieve Size
Toughness
(consistency
near plastic
limit)
Dilatancy
(reaction
to shaking)
f 3 rt tn
sands, rock flour, silty or
clayey fine sands with slight
plasticity
Inorganic clays ol low to
medium piast icily, gravelly
clays, sandy clays*, sjliy clays,
lean clays
Organic silts and organic silt-
•"-) fcj h.
1
e S
Z *s v
0 0 *
-1 «•§ ''
u 0 c j
§" |S "
2
^J= Er -
£ » 3 e* £
0$ UBqi SS3{
uuiii ptnbu
sXep pus sil'S
ciay:> of low plasticuy
Inorganic silts, micaceous or
diatomaceous fine sandy or
silly soils, elastic silts
j IG
: « d
a -C «
u5 E
0
- u
2 * o
1 5 C
1 *n
C !/) *"
"a
1
-C
o
Jl >
a -3
>2
£ »
n ~.
0 -
a;
z
o
Z
°f
J5-5
It
Organic clays oi medium to high
plasticity
I
Shftht to
medium
2|
>
Medium to
high
OS
ueqi J31MJ8
iiuiij pinbij
stop puB sins
UIS 3LJ1 inoqp SI 3ZIS 3A31S Ujr* 5^ 3M 1 )
32IS 3A3IS LU'* 5^ U\>\^\
J9]]nms si leuaieiu jo jjeq ueqi 3JOr^
SJIOS P3U1PJ8-3U1J
u
C
oc
0
L.
o
i1
s
Readily identified by colour, odour,
spongy feel and frequently by fibrous
texture
Highly Organic Soils
From Wagner, 1957.
a Boundary classifications Soils possessing characterises of iwo groups are designated by combinations of group symbols For example GW-GC, well graded gravel-sand mixture with clay binder.
b All sieve sizes on this chart are U.S. standard
11
-------
fines are silty (M) or clayey (C), and classify as GM, GC, SM, or
SC; (9) for fine-grained soils or the fine-grained portion of a
coarse-grained soil, the dilatancy (reaction to shaking), the dry
strength (crushing characteristics), and toughness (consistency
near plastic limit) are performed; (10) Highly organic soils (Pt)
are characterized by undecayed particles of leaves, sticks,
grass, and other vegetative matter giving the soil a fibrous
texture; and (11) Soils which have characteristics of two groups
are given boundary classification using a name most nearly
describing the soil, and the two group symbols are listed such as
GW-GC.
Although the use of letter symbols is convenient, it does
not describe a soil as completely as is normally required.
Therefore, descriptive terms should be used and arranged in
narrative form in addition to the letter symbols to produce a
more complete soil classification. Such descriptions differ
between coarse-grained and fine-grained soils and are shown below
with examples.
For Coarse-grained soils: Give typical name;
indicate approximate percentages of sand and
gravel, maximum size; angularity, surface condi-
tion, and hardness of the coarse grains; local or
geologic name and ether pertinent descriptive
information; and symbol in parentheses. For un-
disturbed soils add information on stratification,
degree of compactness, cementation, moisture
conditions and drainage characteristics.
Example: Silty sand, gravelly; about 20% hard,
angular gravel particles 1/2 inch maximum size;
rounded and sub-angular sand grains coarse to
fine; about 15% non-plastic fines with low dry
strength; well compacted and moist in places;
alluvial sand; (SM).
For Fine-grained soils: Give typical name, indi-
cate degree and character of plasticity, amount
and maximum size of coarse grains, color in wet
condition, odor if any, local or geologic name,
and other pertinent descriptive information; and
symbol in parentheses. For undisturbed soils add
information on structure, stratification, consis-
tency in undisturbed and remolded states, moisture
and drainage conditions.
Example: Clayey silt, brown, slightly plastic,
small percentage of fine sand, numerous vertical
root holes, firm and dry in place, loess, (ML).
12
-------
Laboratory Classification
The same descriptive information that is required for field
classification is also needed for laboratory classification. The
field classification is refined by employing laboratory equipment
to perform simple and routine tests to determine gradation and
the Atterberg Limits. The gradation of soil material is deter-
mined by sieve analysis, and a grain-size curve is usually plot-
ted as per cent finer (or passing) by weight against a log scale
of grain size in millimeters while the Atterberg Limits are
determined by measuring the amount of plasticity of the soil
fraction finer than the No. 40 sieve.
Atterberg Limits—
The Atterberg Limits are a useful and qualitative measure of
the mechanical properties of a particular soil. They are based
on the fact that a fine-textured soil material can exist in any
of four states depending on water content. The different states
are separated by 'limits' termed: (1) shrinkage limit; (2)
plastic limit; and (3) liquid limit. As the amount of liquid is
increased, the consistency of the soil material changes. Unlike
solid or fluid systems, soil material also behaves as a particu-
late system in the plastic state. These limits are by no means
absolute and are sensitive to several environmental and operative
factors.
Shrinkage Limits— The shrinkage limit defines the moisture
content of a soil material when it passes from the solid to the
semisolid state. ASTM D-427-61 is the standard method for
determining the shrinkage limit. Basically, the water content is
determined just after enough water has been added to fill all the
voids of a dry pot of soil in a special apparatus.
Plasticity— Plasticity is the ability of a soil material to
change shape continuously under the influence of an applied
stress, and to retain the new shape once the stress is removed.
In contrast, elastic material rebounds and fluid material has no
shape. It is mainly the clay-size particles that exhibit plastic
behavior.
For a soil material to be plastic, there must be sufficient
water content so that the particles are able to move or slide
past one another to take up new positions, and then retain these
new positions. The cohesion between particles must be
sufficiently low to allow this movement and yet sufficiently high
to allow the particles to maintain the new position (Yong and
Warkentin, 1975).
Plastic Limit— The plastic limit is the moisture content
where a soil material changes from the semisolid to the plastic
state. Generally, the plastic limit is the water content at
which a 3.2 mm diameter thread;of soil material begins to crack
13
-------
and crumble under continued rolling by hand. For complete proce-
dures, see ASTM D-424-59.
Liquid Limit and Plasticity Index— The liquid.limit is the
water content when a soil material changes'from the plastic to
the liquid state* The test is accomplished in a standard liquid
limit device. The liquid limit is the water content at which a
groove cut is closed in the device after 25 taps. For standard
methods, refer to ASTM D-423-66.
The plasticity index for a soil material is calculated by
subtracting the plastic limit from the liquid limit. Both the
plasticity index and the liquid limit values are used to deter-
mine the Unified Soil Classification of fine-grained soils.
Activity— Since both the type and amount of clay influence
the Atterberg Limits of a particular soil, the term Activity has
been developed (Skempton, 1953) to mean the ratio of the
plasticity index to the clay fraction (percentage by weight of
particles finer than 0.002 mm). For many claysf a graph of
plasticity index versus clay content for several samples will
give a straight line passing through the origin. The slope of
such a line yields the activity of that soil.
The laboratory criteria for classifying soils are presented
in Table 2-4 and listed below in narrative form: (1) Determine
if the soil is coarse-grained, fine-grained, or highly organic by
determining the amount of soil passing the No. 200 sieve; (2) If
coarse-grained: (a) Perform a sieve analysis and plot gradation
curve on a grain-size chart. Also determine percentage passing
the No. 4 sieve and classify as gravel or sand; (b) Determine
amount of material passing the No. 200 sieve and if the fine
fraction does not interfere with the soils' free-draining proper-
ties, examine shape of the grain-size curve, and if well-greided,
classify as GW or SW; if poorly graded, as GP or SP; (c) if
between 5 percent and 12 percent of the material passes the No.
200 sieve, it is a borderline case, and the classification should
have a double symbol approximate to grading and plasticity
characteristics (GW-GM, SW-SM, etc.); (d) If more than 12 percent
passes the No. 200 sieve, perform the liquid limit and plastic
limit tests on the minus No. 40 sieve fraction. Use the
plasticity chart to determine the correct classification; (3) If
fine-grained: (a) perform liquid limit and plastic limit tests on
minus No. 40 sieve material. If the liquid limit is less than
50, classify as "L" and if the liquid limit is greater than 50,
classify as "H"; (b) For "L": if limits plot below "A" line and
the hatched zone on the plasticity chart, determine by color,
odor, or the change in the liquid limit and plastic limit caused
by oven-drying the soil, whether it is organic (OL) or inorganic
(ML). If the limits plot in the hatched zone, classify as ML-CL.
If the limits plot above the "A" line and the hatched zone on the
plasticity chart, classify as CL; (c) For "H": if the limits
14
-------
plot below the "A" line on the plasticity chart, determine
whether organic (OH) or inorganic (MH). If the limits plot above
the "A" line, classify as CH.
15
-------
SECTION 3
SOIL WATER
The variable amount of water contained in a unit mass or
volume of soil and the energy state of that water affect many
physical and chemical soil properties such as: consistency,
plasticity, compactibility, shrinkage or swelling, soil creep,
erosion, and hydraulic conductivity.
3.1 THE SOLID FRAMEWORK
The solid phase of the soil water system consists of mineral
particles of many sizes and shapes, arranged in a multitude of
ways, with some organic materials intermingled throughout, and
comprises about 60% of the volume of a soil. It is the size,
shape, and arrangement of these mineral particles that determine
the size, shape and distribution of pores. Such pores, in turn,
influence the amount of fluids contained in the pores and the
rate of transfer of the fluids through the system. Another
complicating factor is that the fluids, especially water, can
alter the pore geometry by dislodging and moving solid particles
within the system and by causing swelling (or shrinking) of some
mineral particles. Freezing and thawing of the soil and root
action can also alter the pore geometry.
3.2 THE POROUS NETWORK
Every soil material is composed of solid particles with the
remaining spaces called voids or pores which make up the porous
network through which water in the soil moves. Although the
shape of the spaces resulting from the regular packing of the
spheres is known, pores in many soil materials demonstrate that
factors in addition to simple packing have influenced their
shape, size, and arrangement. In many soil materials a signifi-
cant proportion of the pore spaces consists of pores of
comparable size interconnected by very much smaller pores, while
other soils may have systems of interconnected planar voids which
meet at relatively sharp angles.
Pores found in natural soils range in dimensions from those
that would accommodate burrowing animals to those that would hold
no more than a few layers of water molecules. If one were to
dislodge a large soil fragment from the exposed face of a soil
16
-------
profile, the resultant soil aggregate would contain numerous
pores that usually would be smaller than a few millimeters in
diameter. In some cases, the line of weakness which allowed the
fragment to be dislodged would, in itself, be a pore of large
planar extent.
Po r o s ity Ln)_and Void Rat io (e1
The porosity is an index of the relative pore volume in a
given soil sample. Its value generally lies in the range of 0.3-
0.6 (usually expressed as a percentage, 30-60%). While coarse-
textured soils tend to be less porous than fine-textured soils,
they contain individual pores of larger mean diameter. The
porosity of fine-textured soils is highly variable as the soil
alternatively swells, shrinks, aggregates, disperses, compacts,
and cracks. A laboratory method for determining porosity can be
found in Vomocil (1965).
Porosity = Volume of Pores
Total Volume of Soil Mass
The void ratio is also an index of the fractional volume of
soil pores, but it relates the pore volume to the volume of pore
solids rather than to the total volume of the soil mass.
Generally the void ratio varies between 0.3-2.0 and is expressed
as a decimal value.
Void Ratio = Volume of Voids
Volume of Soil Particles
The difference between these two indices is that a change in
pore volume will change only the numerator in the Void Ratio
equation, whereas a change of pore volume in terms of the
Porosity equation will change both the numerator as well as the
denominator. Void ratio is the generally preferred index in
engineering uses of the soil, whereas porosity is the more
frequently used index in the agricultural sciences. The rela-
tionships between porosity (n) and void ratio (e) are shown
below.
n = e/(l + e) and e = n/(l - n)
Pore Size pi.s t r ib u t i on
While both porosity (n) and void ratio (e) are indices
determining the total amount of pore space in a soil, they do not
provide any information regarding the width, shape, continuity or
tortuosity of the pores. For this reason, the pore size distri-
bution is a common parameter used to describe pore geometry.
Morphometric techniques are available for measuring pore-
size distributions and shapes of pores in thin sections. A
17
-------
detailed description of these methods can be found in Brewer
(1976), Jongerius (1974), and Ismail (1975) which explain the
general principles of quantitative morphological measurements of
soil pores using conventional point count, techniques or modern
electro-optical image analysis.
Mechanical determinations of pore-size distribution are
possible in two ways: (1) by forced intrusion of a non-wetting
fluid such as mercury, and (2) by use of a pressure plate
apparatus. The mercury intrusion method has been applied to
clays (Diamond, 1970 and Ahmed, Lovell, and Diamond, 1974). The
basis of the method is that, a non,wetting fluid will not enter
pores without application of pressure. The volume of mercury
intruded into an evacuated dry sample of the order of 1 g. in
size using successively higher pressures is measured. The total
volume of mercury introduced at each pressure gives the total
volume of pores with an equivalent diameter larger than that
corresponding to that pressure. The pressure plate method is
based on the incremental increase of suction on a soil required
to remove water from progressively smaller pores. Brewer (1976)
has stated that the mercury intrusion method is more suitable on
clay soils than the pressure plate technique.
3.3 SOIL WETNESS OR MOISTURE CONTENT
The relative water content of the soil can be expressed as a
percentage by weight (w), or percentage by volume (9):
w = Mass ofWater x JQO
Oven Dry Weight of Soil
e = yplurne_Qf Water x 100
Volume of Soil Sample
These methods, which involve sampling, transporting to the
laboratory, and repeated weighings, entail some inherent errors
(Bouma, 1977). Also, they are laborious and time consuming since
a period of at least 24 hours is usually allowed for complete
drying. The laboratory method is also somewhat arbitrary since
some clays may still contain appreciable amounts of absorbed
water when oven-dried at. 105 degrees Centigrade. Additionally,
the sampling procedure for the laboratory method is destructive
and may disturb an experimental plot sufficiently to distort the
results. For these reasons, many workers prefer in situ methods
which permit frequent or continuous measurement of the same
points, and, once the equipment, is installed and calibrated, with
much less time and labor. Such methods include electrical resis-
tance of porus blocks, neutron scattering, and gamma-ray absorp-
tion. Descriptions of these in situ methods can be found in
Hillel (1980).
] 8
-------
3.4 SOIL MOISTURE POTENTIAL
The study and occurence of movement of water in the soil
relies completely on the basic concepts of the soil moisture
potential, which are essentially based on thermodynamic
principles. Water moves from points where it has a higher poten-
tial energy status to points where it has a lower potential
status. The total potential or energy per unit quanity of water
(V't) is defined as the mechanical work required to transfer a
unit quantity (e.g., unit mass weight or volume) of water from a
standard reference state (=0) to one where the potential has the
defined value. The total potential (^^) of water is composed of
several components, which will be elaborated separately. For a
more detailed analysis than is presented here, the reader can
consult: Rose (1966), Hillel (1971), Childs (1969), Baver et al.
(1972), ISSS (1976), or Hillel (1980).
Pressure Potential (^/p or h)
Soil wetness refers solely to the total amount of liquid in
a soil sample. Additionally, it is important to ascertain the
distribution of water in the soil at different moisture contents
and to understand the natural laws that govern it. As the mois-
ture content of the soil sample decreases, water leaves the
larger soil pores but remains in the finer ones because the
smallest pores can "pull" the strongest. This can be explained
by considering the basic phenomena of liquid surface tension and
capillarity.
Surface tension occurs typically at the interface of a
liquid and a gas. Molecules in the liquid attract each other
from ail sides. In the surface areas the molecules are attracted
into the denser liquid phase by a force greater than the force
attracting them into the gaseous phase. The resulting force
draws the surface molecules downward, which results in a tendency
for the liquid surface to contract.
Capillarity refers to the phenomenon of the rise of water
into a capillary tube inserted in water, due to its surface
tension. The finer the tube, the higher the capillary rise and
the greater the negative pressure below the water meniscus in the
tube.
Gravitational Potential (»|/g)
Each body on the earth's surface is attracted toward the
center of the earth by a gravitational force equal to its weight.
To raise the body against this attraction, work must be done, and
this work is stored in the raised body as gravitational potential
energy (Z) which is determined at each point by the elevation of
19
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the point relative to some arbitrary reference level,. Therefore:
«^g = mgZ
where <^g = The gravitational potential energy of a mass m of
water at a height Z above a reference, and
g = acceleration of gravity.
This potential, expressed per unit weight, becomes v// = z (cm).
Other Potentials
The potential energy of a body was defined as energy present
by virtue of its presence in a force field. Pressure forces and
gravitational forces have been discussed so far, and they are the
most important when water movement under field conditions is
considered in non-saline soils. The effect of solutes on the
total potential of soil water, expressed by the osmotic potential
«^o, becomes of primary significance if the water is separated by
a membrane whose permeability to water molecules differs from
that to the solute. This potential is important in water move-
ment into and through plant roots, in which there are layers of
cells which exhibit different permeabilities to solvent, and
solute.
Some concluding remarks'must be made regarding the pressure
potential v/p. This potential characterizes the state of water in
the soil (together with
-------
Hydraulic head (H)
The hydraulic head is the sum of the gravitational and
pressure potentials:
H = Z + h
where H = hydraulic head
Z = the height o£ the point under consideration
above a reference level, and
h = the height of a vertical water column which
would exert a pressure at its base
numerically equal to the soil-water pressure
(negative in unsaturated soil, zero or posi-
tive in saturated soil).
The hydraulic head is a very convenient concept for describing
water movement and is often used in the literature.
3.5 MOISTURE RETENTION CURVE, MOISTURE CHARACTERISTIC, OR THE
RETENTIVITY CURVE
In a saturated soil at equilibrium with free water at the
same elevation, the actual pressure is atmospheric and the soil
liquid pressure is zero. If a slight negative pressure is ap-
plied to this water, no outflow may occur until, as the pressure
is further decreased, a certain critical value is exceeded at
which the largest pore begins to empty. The value of this criti-
cal pressure is usually very small in coarse-textured or well-
aggregated soils where large pores will immediately lose their
water when only a very small negative pressure is applied. As
the pressure is decreased (suction increased), more water is
drawn out of the soil and more of the relatively large pores,
which cannot exercise an adequate capillary force to retain their
water against the pressure applied, will empty. A gradual
decrease in pressure will result in the emptying of progressively
smaller pores until, at high negative pressures, only the very
narrow pores retain water. A decreasing pressure is thus
associated with decreasing soil wetness. The rate of decrease is
characteristic for any particular porous medium because it is a
function of the pore-size distribution. The curve which shows
the relationship between the negative pressure and the water
content is a very important soil physical characteristic and is
known as the soil moisture retention curve, the soil moisture
characteristic, or the liquid retentivity curve (ISSS, 1976).
Retention curves relating water content to pressure potential for
four USDA textural classes is shown in Figure 3.1. Also, the
slope of the retentivity curve (d0/dh) is called the water
capacity [C(0)] which is the rate of change of water content (8}
with the soil matric potential (^m) expressed per unit volume.
21
-------
50
z
HI
O
o
HI
cc
s
40
30
20
10
20 40 60 80
SOIL MOISTURE (MBAR)
Figure 3.1
Soil moisture retention curves for four different
soil materials (SSWMP, 1978).
3.6 HYSTERESIS
Unfortunately, the moisture content is not a single function
of the pressure potential. The moisture content corresponding
with a certain pressure is higher when it has been reached by
desorption (drying) of an initially wetter sample than when
reached by wetting (adsorption) of an initially drier sample.
Said another way, it is harder to get water out of the soil once
it is in, than to get it back in once it is out. The phenomenon
of hysteresis can be illustrated by considering a schematic void
partly filled with water (Figure 3.2). The water-filled ideal-
ized void (Figure 3.2a) will drain in the course of a desorption
process if the negative pressure exceeds the relatively large
capillary force corresponding with the smallest pore diameter
(2r) in the system. The idealized air-filled void (Figure 3.2b)
will fill with water in the course of an adsorption process as
soon as the relatively small capillary force, corresponding with
the largest pore diameter (2R), is sufficiently strong to pull
the water in. This comparison shows that the water content of
the soil at a given moisture tension will be greater following
desorption (drying) than following adsorption (wetting) (Figure
3.3) .
22
-------
b
2r
DESORPTION
ADSORPTION
Figure 3.2 Cross-section through an idealized void illustrating
the hysteresis phenomenon (SSWMP, 1978).
0.35
E
o
E
o
0
0.30
2
LL1
K-
Z
O
O
cc
in
0.25
During drying
During wetting
I
J_
20 40 60
SUCTION h (cm of water)
Figure 3.3 The relations between water content (#) and suction
(h) (Tzimas, 1979).
23
-------
Since the moisture retention curves are usually determined
by a desorption process starting with a saturated soil, values
thus obtained may not apply to water contents and moisture poten-
tials occurring in the field when an initially dry soil is wet-
ting up. However, a physically correct characterization of the
extent of hysteresis on a given soil is a very elaborate
procedure (Gillham et al., 1976).
3.7 ANISOTROPY
Anisotropy is the term used to describe the fact that soil
properties can vary with depth as well as
basically the result of weathering of rocks
and of the reorganization, translocation,
the more mobile constituents due to
environment (Brewer, 1976). Unfortunately,
is the rule rather than the the
ramifications with regard to soil
horizontally. It is
or sedimentary bodies
and concentration of
the effects of the
anisotropy in soils
exception, which has severe
testing methods for hydraulic
conductivity arid interpretations of results.
Soils are stratified formations consisting of distinct
layers (horizons) which have differences in particle size distri-
butions, structure, boundary conditions, and other properties
which effect the hydraulic properties of each horizon on a macro-
scopic level (soil series) as well as on the microscopic level
(soil fabric). Such differences will influence both vertical and
lateral hydraulic conductivity.
At the soil series level, anisotropy is manifested in two
ways: 1) horizons vary in depth as well as thickness and can
exhibit anomalies such as vertical sand seams or clay lenses, and
2) boundary conditions between soil horizons can sometimes in-
fluence overall water movement more than the properties of the
mass of the horizon itself. This is shown graphically in Fiqure
3.4.
Sand
Clay
Clay
Sand
Clay
Clay
Figure 3,4
Influence of
conductivity
underlying layer on hydraulic
24
-------
In Case A, water added to the sand will flow quickly through
the sand into the clay, while in Case B, no water will enter the
sand layer until the clay layer is nearly saturated because the
water is held by the finer pores in the clay horizon. Therefore,
the clay horizon in Case B might hold up to two or three times as
much water as the upper clay horizon in Case C.
3.8 WATER MOVEMENT IN SOILS
Water movement in soils can be divided into types of flow
systems for general considerations: (I) saturated flow where all
pores are filled with water, and (2) unsaturated flow where both
air and water are present in the pores.
The basic equation for describing water flow through porous
materials, whether saturated or unsaturated flow, is expressed by
Darcy's Law:
J = K AH
where J = flux, volume of liquid moving through a
unit cross-sectional area of soil per unit
of time
K = hydraulic conductivity
AH = hydraulic gradient
The hydraulic conductivity, K, is not constant; rather, it
varies with changes in the water content as well as with changes
in pressure head. Therefore, K can be expressed as either a
function of water content,K(0),or as a function of pressure head,
K(h). For determination of either function, the soil moisture
characteristic (retentivity curve) usually must be known, also.
Fiqure 3.5 demonstrates two different cases: A) water capacity
functions for four soils with respective hydraulic conductivity
curves expressed as a function of pressure head, and B) water
capacity function for one soil and its hydraulic conductivity
relation expressed as a function of water content.
The hydraulic conductivity is one of the most variable soil
properties of importance to waste disposal concerns as it
exhibits a great range of values (up to fourteen orders of magni-
tude) from coarse to very fine-grained soils.
25
-------
* 50
Z
UJ
H
Z
o
o
Ul
DC
co
O
S
40
30
20
10
1000
(A)
20 40 60 80
SOIL MOISTURE (MBAR)
a
13
•x.
E
o
O
3
0
z
o
o
i
100
10
1.0
0.1
Drying
iSand
I
Sandy loam
Clay
_1_
20 40 60 80 100
SOIL MOISTURE TENSION (MBAR)
o
*
0.40
E
3 0.30
I-
z
UJ
z
O 0.20
-------
Saturated Flow
The determination of saturated hydraulic conductivity is
physically easier and conceptionally simpler than the determina-
tion ot unsaturated hydraulic conductivity because the purpose is
to find the hydraulic conductivity at one point, (h = 0, 9=
constant), rather than over the range of pressure heads or range
of water contents necessary for unsaturated flow, and because it
is assumed that the soil pores are constantly and completely
filled with water. Therefore, in the determination of saturated
flow, the hydraulic conductivity is considered to be constant.
However, in a given soil, K may not remain the same due to
such processes as particle arrangement within the soil matrix
over time. Also, depending on the mode of wetting, saturated
soils rarely have all soil pores completely filled with water.
It is not unusual to expect 2-12% air remaining in the soil pores
(Yong & Warkentin, 1975). This implies that attention should be
placed on the mode of saturation because if K is determined for
the situation with entrapped air, it is basically an unsaturated
flow situation, and unsaturated flow will always be less than
saturated flow. (See Figure 3.5(A), which demonstrates that
saturated K equals the intercept on the abscissa and that
hydraulic conductivity decreases (sometimes sharply) as the pres-
sure head decreases from saturation, h = 0.)
For saturated flow testing methods, the basic approach is to
measure flow and total pressure or hydraulic pressure gradient
and calculate the hydraulic conductivity from Darcy's equation.
LJnsaturated Flow
The situation for unsaturated hydraulic conductivity is much
more complex than for saturated flow because the purpose is to
determine a complete hydraulic conductivity function over a range
of water contents or pressure heads rather than just one point as
for saturated flow.
For saturated flow testing methods, there is quite a variety
of techniques that measure different parts of the water capacity,
3iffusivity, or hydraulic conductivity functions during steady or
transient (unsteady) state conditions. Such methods range from
transient state field methods that measure flow, pressure head,
and water content to steady state laboratory methods that measure
flow and pressure head or water content with other inferred to
transient state field methods that calculate hydraulic
conductivity from water content only.
The soil water diffusivity is defined as:
3H = *101
d8 C(6)
27
-------
where
D(0) = the soil water diffusivity function
K(0) = the hydraulic conductivity function
C(8) = the water capacity function
dh = reciprocal of slope of C(d) function at
d# a particular water content
Although soil water diffusivity is somewhat difficult to
visualize physically, it is mathematically simple, being the
product of the hydraulic conductivity at a given water content
and the reciprocal of the slope of the retentivity curve at the
same water content. Likewise, if hydraulic conductivity is to be
determined, the equation can be rewritten as:
K(0) =
dh
where
D(0)
dj9
dh
hydraulic conductivity function
soil water diffusivity function, and
slope of water capacity curve/soil
water characteristic at a particular
water content.
The situation for hydraulic conductivity determination is
graphically presented in Figure 3.6 (A), (B) , and (C). Given the
diffusivity function (A) and the retentivity curve (B) , the
hydraulic conductivity at a particular water content, 6^r is
equal to the diffusivity at 9-± times the slope of the retentivity
at 8±r cl#/dh 1. Doing this same procedure over the range of
water contents will determine (C) the hydraulic conductivity
function.
>
w
u.
Slope at this point:
>-
l-
o
o
WATER CONTENT
(cm3/cm3)
PRESSURE HEAD (cm)
WATER CONTENT
3 3
(cm /cm )
Figure 3.6
Graphic representation of hydraulic conductivity
determinations from diffusivity measurements.
28
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3.9 HYDRAULIC CONDUCTIVITY AND SOIL PORE GEOMETRY
Since hydraulic conductivity is a characteristic physical
property of a porous media, it would seem reasonable to assume
that it relates to specific measurable properties of the soil
pore geometry, e. g., porosity, pore-size distribution, internal
surface area, etc. However, the many attempts to develop a
functional relation of universal applicability for the range of
soils and soil materials, has been generally unsuccessful.
The simplest approach is to seek a correlation between
hydraulic conductivity and total porosity. However, it can be
concluded that such an approach is generally futile (except for
comparison of otherwise identical media) owing to the strong
dependence of flow rate upon width, continuity, shape, and tor-
tuosity of the conducting pores. This is the reason why coarse-
textured soils (with less total porosity and fewer individual
pores, but larger and more uniformly sized pores) will have
greater saturated hydraulic conductivity than fine-textured soils
(which have greater total porosity, but smaller, more
irregularly-sized, tortuous pores).
Numerous theoretical models have been introduced to repre-
sent porous media by a set of relationships that are amenable to
mathematical treatment. Scheidegger (1974) gave a comprehensive
review of such models, including the straight capillaric,
parallel, serial, and branching models and concluded that the
preferred model of a porous medium should be based upon
statistical models.
One of the most widely accepted theories on the relation of
saturated hydraulic conductivity to the geometric properties of
porous media is the Kozeny-Carman theory which is based on the
concept of hydraulic radius. The measure of hydraulic radius is
the ratio of the volume to the surface of the pore space, or the
average ratio of the cross-sectional area of the pores to their
circumferences. The Kozeny-Carman equation is shown below:
n3
where K = saturated hydraulic conductivity
k = pore shape factor (approximately equal
to 2.5)
T = tortuosity factor (approximately equal
to square root of 2)
S = specific surface area per unit volume
of particles
n = porosity
29
-------
Although the Kozeny-Carman equation works well for the des-
cription of saturated hydraulic conductivity in uniformly graded
sands and some silts, serious discrepancies are found in clays
(Michaels and Lin, 1954, Lambe, 1955, and Olsen, 1962). The
failure ot this theory steins from the original assumptions which
are: (1) no pores are sealed off, (2) pores are distributed at
random, (3) pores are reasonably uniform in size, (4) porosity
not too high, (5) diffusion phenomena are absent, and (6) fluid
motion occurs like motion through a batch of capillaries
(Scheidegger, 1974). Soil systems which can satisfy every
assumption are rare to nonexistent with the exception of
uniformily graded sands upon which the Kozieny-Carman equation was
founded.
A more promising approach to the prediction of hydraulic
conductivity from physical properties of the porous medium is to
seek a connection between hydraulic conductivity and pore-size
distribution. However, since it is difficult to determine the
pore-size distribution per se either physically or
morphologically, it is often preferred to work with parameters
based on the suction or capillary pressure versus sorption or
desorption. Since flow through an irregular pore is limited by
the narrow bottlenecks along the flow paths, it is necessary to
consider or estimate the number and size of such bottlenecks and
the interconnections of pores of different widths. Initial work
along these lines has been published by Childs and Collis-George
(1950), Marshall (1958), and Millington and Quirk (1960, 1961,
1964) and has been expanded upon with the use of matching factors
by numerous authors including Kunze (1968), Green and Corey
(1971), Roulier et al. (1972), Neilsen et al. (1973), Carvallo et
al. (1976), Simmons et al. (1979), Libardi et al. (1980), and
Dane (1980). However, the results of these procedures (while
more generally applicable than those based on earlier models)
still appear to be valid for only coarse-textured materials with
hydraulic conductivities greater than 0.0001 cm/sec.
3.10 HYDRAULIC CONDUCTIVITY AND ANISOTROPY
As discussed earlier in this section, anisotropy in soils is
defined as the condition where soil properties are different in
different directions and is generally thought to be due to the
structure of the soil, which may be laminar, or platy, or
columnar, etc., thus exhibiting a pattern of micropores or
macropores with a distinctly directional bias.
Anisotropic soil conditions will affect flow direction as
there are both horizontal and vertical components to the hydrau-
lic conductivity function. Table 3-1 shows ratios of horizontal
hydraulic conductivity to vertical hydraulic conductivity for
fine-textured soils as found in the literature. Generally, for
varved or stratified clays, the ratio may exceed ten whereas for
less stratified soils, the ratio is likely to be closer to one.
30
-------
TABLE 3-1 DATA ON THE RATIO OF HORIZONTAL TO VERTICAL HYDRAULIC
CONDUCTIVITY OF FINE-TEXTURED SOILS
Reference
Tsien (1955)
Mitchell (1956)
Basett and Brodie (1961)
Olsen (1962)
Lumb and Holt (1968)
Morgenstern and Tchalanko (1967)
Casagrande and Poulos (1969)
Haley and Aldrich (1969)
Chan and Kenney (1973)
Kenney and Chan (1973)
Subbaraju et al. (1973)
Wu et al. (1978)
Horizontal K/Vertical K
1.2 - 1.7
1.0 -
0.9 -
4.0 -
0.7 -
1.5 -
3.0 -
7.0
1.5
4.0
1.2
2.0
40.0
3.3
3.7
1.5
1.05
15.0
At the microscopic level, soil fabric will also exhibit
anisotropy which can cause substantial hydraulic conductivity
anisotropy. In a section on fabric and permeability, Mitchell
(1976) states, "Of the properties of importance in the analysis
of geotechnical problems in fine-grained soils, none is more
influenced by fabric than the hydraulic conductivity."
Further, fabric may be developed in initially homogenous
soils from shear or compression forces. The amount of shear or
compression required for development of anisotropic fabric varies
for mineral soils, and depends on such factors as soil
mineralogy, composition of pore fluid, and initial fabric
(Mitchell, 1976).
A practical ramification of soil fabric anisotropy is that
hydraulic conductivity of a clay soil is dependent on the struc-
ture and fabric to such an extent that analysis based on proper-
ties determined from the same material, but with a different
structure may be totally in error. That is, where fabric and
isotropy can affect a parameter being tested (such as the
hydraulic conductivity of clay soils), laboratory results often
may not reproduce field results due to sampling and preparation
procedures of laboratory methods which will change soil fabric.
As a result, many researchers have expressed doubts that
laboratory hydraulic conductivity tests are capable of
reproducing field conditions. Olson and Daniel (1981) noted that
the volume of soil samples used in laboratory tests are almost
always too small to contain statistically significant dis-
tributions of macrofeatures encountered in the field such as sand
lenses, channels, root holes, etc. They also noted that samples
taken in the field may be affected either by collection method or
selection of the most uniform or intact sample. Bowles (1978)
stated that "The soil in the permeability device is never in the
31
-------
same state as in the field - it is always disturbed to some
extent." Therefore, extrapolation of laboratory results to field
conditions should only be used with caution and supporting
justification.
3.11 HYDRAULIC CONDUCTIVITY AND PERMEANT
The hydraulic conductivity of a certain soil is not an
exclusive property of the soil alone since it depends on the
attributes of the soil and the permeating fluid (permeant)
together. Properties of the permeant that will affect hydraulic
conductivity of a soil are viscosity and density. The terms
hydraulic conductivity and permeability are often used
interchangeably.
In contrast to hydraulic conductivity (permeability) the
intrinsic permeability is an exclusive property of the soil and
is independent of the properties of the fluid, provided that the
fluid does not change the properties of the soil. The hydraulic
conductivity, intrinsic permeability, and fluid properties are
related as follows:
K = kng/p
Where: K = hydraulic conductivity(permeability) (cm sec"1)
k = intrinsic permeability (cm^)
TI = viscosity (g cm"1 sec"1)
g = gravitational constant (981 cm sec"2)
p = density (g cm~3)
The viscosity parameter normalizes resistance due to the fluid
cohesiveness, while the density parameter normalizes the effect
of gravity. As the above equation indicates, hydraulic
conductivity of a soil is directly proportional to density and
inversely proportional to the viscosity of the permeant.
The Soil Solution
Under normal conditions, the main permeant in soil is water.
However, in the situation of disposing of hazardous wastes on
land, other fluids besides water will move thru the soil. Be-
cause such fluids are physically and chemically different than
water, they can cause dramatic changes in soil properties which
can induce changes in the hydraulic conductivity of the soil.
The types of changes in soil characteristics as a result of
different permeants present in the soil from waste leachate are
listed below (Matrecon, 1980):
32
-------
(1) The dispersion/flocculation (aggregation) properties
of the soil;
(2) The alterations in the shrink/swell properties of the
soil;
(3) The change of pore-size distribution characteristics;
(4) The dissolution/precipitation of chemical species
which can induce changes in the proportion of soil
volume available for flow; and
(5) The modification of the absorption properties of the
soil.
Hazardous Waste Leachate
To determine the effect of a specific waste on the hydraulic
conductivity of a soil, two different leachates must be
investigated. These leachates include both the flowable
constituents of the waste (primary leachate) and flowables
generated from percolating water leaching through the waste
(secondary leachate). Both primary and secondary leachates can
be divided into a solvent phase (the predominant fluid component)
and a solute phase (the components dissolved in the solvent).
And while the solutes in a leachate can affect the hydraulic
conductivity of a soil, usually the solvent will exert a more
predominant influence.
Solvent Phase--
A high percentage of the available research on the behavior
of organic fluids and hazardous waste leachates relates to sys-
tems where water is the solvent (Goring and Hamaker, 1972; Chian
and DeWalle, 1977; and McDougall et al., 1979) with organic
chemicals considered to be present in only trace amounts. How-
ever, in the case of hazardous waste disposal on land, while
water will always be the solvent in the secondary leachate,
organic compounds will usually be the solvent in primary
leachate.
Organic fluids disposed in hazardous waste disposal sites
will cover the full spectrum of chemical species and can be
classified into four groups for evaluating the effects of such
fluids on the hydraulic conductivity of a given soil. These
groups are based on the physical and chemical properties that
govern their interactions with clay minerals. The four groups
are: (1) Organic acids; (2) Organic bases; (3) Neutral polar
organics; and (4) Neutral nonpolar organics.
Organic Acids— Organic acids are organic fluids with acidic
functional groups and can be subdivided into phenolic and
aliphatic acids. The proton donating properties of these acids
give these fluids potential to react with and dissolve clay
particles.
33
-------
Brown and Anderson (1982), in conductivity studies with
compacted soil specimens, reported that organic acids affected
hydraulic conductivity by dissolution of clay particles followed
by piping of the particle fragments through the soil. These
effects resulted in sharp initial hydraulic conductivity de-
creases as the migrating particle fragments clogged the fluid-
conducting pores. On some soils, the hydraulic conductivity
later gradually increased as the acid dissolved the soil
particles that had previously clogged the pores.
Organic Bases— Organic bases are organic fluids capable of
accepting a proton to become an ionized cation. Since these
components are positively charged, they absorb strongly onto the
negatively charged clay surfaces and can replace absorbed water
which alters the clay surface chemistry and changes the behavior
of a clay soil.
Organic bases have been implicated in the dissolution of
clay liners in waste impoundments. Haxo (1976) found in
preliminary tests that smectitic clay liners allow passage of
strong bases within a short period of time. Also, Brown and
Anderson (1982), reported that bases tended to cause hydraulic
conductivity increases via alterations in soil structural fabric.
Neutral Polar Organics— Neutral polar organics do not exhibit
any net charge but have an asymetrical distribution of electron
density resulting in an appreciable dipole movement. This
property allows these compounds to compete with water for
absorption sites on the negatively charged clay surfaces which,
like other organic cations, will change the behavior of a clay
soil. Examples are alcohols, aldehydes, alkyl halides, glycols,
and ketones.
Neutral polar organic fluids tend to decrease the surface
tension (and hence viscosity) of absorbed water on clay particles
which results in increased hydraulic conductivity. Brown and
Anderson (1982), reported that the neutral polar fluids showed
continuous hydraulic conductivity increases with no apparent
tendency to reach maximum values.
Neutral Nonpolar Organics— Neutral nonpolar organics are organic
fluids that have no charge and a small if any, dipole moment.
This group is further subdivided into aliphatic and aromatic
hydrocarbons. With low water solubilities and little polarity to
compete with water for absorption sites on clay particles, these
chemicals have the potential to move through soils very rapidly.
In a study of hydraulic conductivity of a clay subsoil
underlying a proposed landfill site, White (1976) reported that
the clay soil was highly impermeable to water while very
permeable to lighter hydrocarbons. Additionally, Brown and
34
-------
Anderson (1982), found neutral nonpolar fluids caused initial
hydraulic conductivity increases of nearly two orders of
magnitude before the soil would stabilize and the hydraulic
conductivity would remain relatively constant.
3.12 HYDRAULIC CONDUCTIVITY TESTING ERRORS
Testing for hydraulic conductivity can be divided according
to flow regime into saturated and unsaturated flow and each flow
regime can be tested either in the laboratory or in the field
according to methods described in detail in Section 6. In this
discussion of testing method errors, laboratory methods will be
compared to field methods.
Laboratory Tests
The main advantages of laboratory testing are economy and
convenience. Laboratory tests offer financial benefits accruing
from the fact that a large number of tests can be performed
routinely in a well-equipped soil testing laboratory. Also, such
testing can be performed by technicians, in contrast to the
generally higher level of skill required for the execution and
interpretation of field testing. Laboratory testing further
offers protection from adverse weather conditions as they can be
performed at all times, while field testing is necessarily
restricted to non-rainy, unfrozen seasons, which generally means
it must be performed during the summer. However, such advantages
are offset by an array of disadvantages.
Limitations of Laboratory Tests--
Olson and Daniel (1981) have listed potential sources of
error in laboratory tests for both saturated and unsaturated
flow. These lists are presented in Table 3-2.
Of these possible sources of error, of greatest concern is
the use of samples that may not be representative of field condi-
tions. Disturbed samples that are taken back to the laboratory
and repacked in the various types of apparati will not have the
same fabric, structure, or pore configuration as they did in
their undisturbed state. Additionally, the use of small samples
compounds the disturbed soils problems by omitting macroscopic
variations occurring at the field level such as sand lenses,
fissures and joints, and root holes. Therefore, because
laboratory tests are deficient v/ith regard to both microscopic
and macroscopic features of the soil in the field, extreme
caution is urged with regard to laboratory results' extrapolation
to the field scale level.
35
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TABLE 3-2 SOURCES OF ERROR IN LABORATORY TESTING FOR SATURATED
AND UNSATURATED FLOW (OLSEN AND DANIEL, 1979)
Saturated Unsaturated
(1) Non-representative samples (1) Non-representative samples
(2) Voids formed during (2) Smear zones
sample preparation
(3) Smear zones (3) Incorrect flow direction
(4) Alteration in clay chemistry (4) Growth of microorganisms
(5) Air in sample (5) Chemical effects
(6) Growth of microorganisms (6) Temperature effects
(7) Meniscii problems in (7) Filter impedance
capillary tubes
(8) Use of excessive hydraulic gradients
(9) Temperature affects
(10) Volume change due to stress change
(11) Flow direction
Comparison of Laboratory to Field Testing Results--
A comparison of corresponding laboratory and field hydraulic
conductivity test results will show the field hydraulic
conductivity to be considerable, but unpredictably higher than
values measured in the laboratory. Olson and Daniel (1981)
compared field and laboratory hydraulic conductivity values from
the literature and found that the range of the ratios ot field
K/laboratory K have been reported from 0.3 to 46,000 with 90% of
the oDservations in the range from 0.38 to 64 with field results
usually being higher than laboratory results. They report the
major causes of this effect as being (1) a tendency to run
laboratory tests on more clayey samples, (2) the presence of sand
seams, fissures, and other macrostructural features in the field
that are not represented properly in laboratory tests, (3) the
use ot laboratory K values backcalculated from consolidation
theory rather than directly measured values, (4) the measurement
of vertical flow K in the laboratory and of horizontal K in the
field, (5) the use of distilled water in the laboratory, and (6)
air entrapment in laboratory samples.,
Field Tests
While field tests have some sources of error similar to
problems encountered in laboratory testing, field testing has
some unique problems. One such difficulty arises from the fact
that most experience in field soil testing has been on coarse-
textured soils. Also, most of the field-scale experience of soil
engineers, geohydrologists, and soil scientists has been experi-
mental rather than standardized and has addressed problems such
36
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as ground water flow and soil - water - plant relations, and this
information is not always completely applicable to the problems
of hazardous waste landfills and surface impoundments.
Another problem associated with field-scale testing lies in
the use of Darcy's Law in the flow analyses, in the excessive
attention directed at the analysis rather than the value of K.
This is an unfortunate occurrence because no other soil parameter
is as likely to exhibit the wide range of values (from 10^ cm
sec~l to 10~10 cm sec~l) as does hydraulic conductivity.
Important considerations for quantification of field level
hydraulic conductivity are fabric and spatial variability, as
elaborated below.
Fabric—
Of the parameters of significance in the analysis of
environmental problems of fine-textured soils none is more in-
fluenced by fabric than the hydraulic conductivity (Mitchell,
1976). A simple example of this phenomenon is provided in a
consideration of two equal volumes of soil (A and B) with exactly
the same properties with the exception of one long continuous
pore in soil volume A and four discontinuous pores with total
equivalent pore volume equal to soil volume A in soil volume B.
Hydraulic conductivity will be dramaticlly different between
these two cases.
Therefore, it is of importance that the soil testing
required for site evaluation actually test the soil fabric that
will exist in the landfill or surface impoundment. The tested
soil fabric will be of two separate types: soil fabric of the
liner and soil fabric of the unsaturated zone between the liner
and ground water table or bedrock.
The importance of soil fabric to considerations of the
hydraulic conductivity of soil liners cannot be overstated. In a
chapter of Fabric, Structure, and Property Relationships,
Mitchell (1976) states that the main conclusion to be drawn from
the considerations of his chapter is that the geotechnical
properties of any given soil are dependent on the structure to
such an extent that analyses based on properties determined from
the same material but, with a different structure may be totally
in error. Therefore, considerations of use of a particular soil
for a liner must be based on soil testing methods that stimulate
the field compactive effort to the highest degree possible.
As mentioned earlier, one considerable failing of
laboratory tests is that the soil fabric of the tested sample
will not be the same as the fabric of the soil in situ. Lambe
and Whitman (1979) state that because hydraulic conductivity
depends very much on soil fabric (both microstructural - the
37
-------
arrangement of individual particles, and macrostructural - such
as stratification) and because of the difficulty of getting
representative soil samples, field determinations of hydraulic
conductivity are often required to get a good indication of the
average hydraulic conductivity.
Spatial Variation (Ansiotropy) —
The soil is not a static body, but rather a dynamic set of
processes always being affected by the soil-forming factors of
climate, parent material, topography, vegetation, and time.
Therefore, a soil body will vary in both the vertical and
horizontal directions. For example, vertical variation is
manifested in different hydraulic conductivities between succes-
sive soil horizons, and horizontal variation is manifested in
differing thickness of soil horizons between soil profiles of the
same soil series. Thus non-homogeneity (anisotropy) in soils is
the rule rather than the exception, and soil testing of
homogeneous or mixed samples for average conditions may be
totally in error in predicting conditions that will exist in the
field.
Additionally, during the site evaluation and review process,
attention must be devoted to a qualification of errors involved
in soil testing results. That is, some determination of whether
the variation in soil testing results is a consequence of the
soil's spatial variability or a variation inherent in the soil
testing method itself. At this time, excepting the information
included in the Precision and Accuracy subheading of each method
in the Soil Testing Methods Section (Section 6), little
information is available to quantify the components ot variation
in the results of many soil testing methods.
38
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SECTION 4
SOIL COMPACTION
If a cohesive soil is compacted with a given type and amount
of compactive effort at various water contents, a compaction
curve such as the one shown in Figure 4.1 is obtained. This
compaction curve shows that as the molding water content is
increased, the dry density increases to a peak and then
decreases. The density and moisture content at peak density are,
respectively, maximum dry density and optimum moisture content
for that particular type of compaction and compactive effort.
For the Compaction Test shown in Figure 4.1, the maximum dry
density (unit weight) is 18.7 kN/m^ and the optimum moisture
content is 11%.
^ 19.0
E
18.5
H
Z 18.0
tr
o
17.5
I
I
I
I
0.41
0.43
0.46
0.49
0.52
<
cr
O
>
6 8 10 12 14 16 18
WATER CONTENT w(%)
Figure 4.1 Standard compaction test (Lambe, 1951).
The computed relationship between water content and dry
density at a constant degree of saturation may also be plotted on
the same scale as the compaction curve. As can be seen in Figure
4.1, the degree of saturation increases with increasing water
content to a value slightly above that at optimum moisture con-
tent and then tends to remain approximately constant. The
moisture relationship for a specific soil depends on the amount
39
-------
and type of compaction, as shown by Figures 4.2 and 4.3. Figure
4.2 shows the results of four laboratory tests using impact
compaction. The compaction effort was decreased from Test 1
through Test 4. Thus, for a given type of compaction, the higher
the compactive effort the higher the maximum density and the
lower the optimum water content. Further, as the molding water
content increases, the influence of compactive effort on density
tends to decrease. The points of maximum dry density and optimum
water content for the various compactive efforts tend to fall
along a line that parallels the lines of a constant degree of
saturation.
19
CO
E 18
-x
z
"". 17
5 16
3
i is
14
'*
_L
10 15 20
WATER CONTENT (%)
25
NO.
1
2
3
4
Layers
5
5
5
3
Blows per Hammer Hammer
Layers Mass prop
55 4.54 kg 457 mm (mod. AASHO)
26 5.54 457
12 4.54 457 (std. AASHO)
25 2.50 305
Figure 4.2
Dynamic compaction curves for a silty clay (Lambe
and Whitman, 1979).
Figure 4.3 demonstrates the results of static compaction in
which the compacting stress is decreased going from Test 1 toward
Test 4. As shown in this figure, the higher the compactive
stress, the higher the maximum density and the lower the optimum
water content.
40
-------
to
E
tr
Q
19
18
17
16
15
\
-------
4.2 COMPACTION AND HYDRAULIC CONDUCTIVITY
Hydraulic conductivity of a compacted soil layer is
influenced by soil properties such as structure, fabric, and
porosity.
Structure
Test data which show the influence of structure on hydraulic
conductivity are presented in Figure 4.4 and 4.5. Figure 4.4
shows that physically mixinq or blending of a soil can have a
major effect on hydraulic conductivity. Figure 4.5 shows the
large influence on hydraulic conductivity obtained by mixing in
0.1% (based on dry soil weight) of a polyphosphate dispersant.
The dispersant, increasing the repulsion between fine particles,
permits them to move to positions of greater hydraulic stability,
resulting in a reduction in hydraulic conductivity.
E 1x10
o
~5
1x10-6
Q
Z
O
o
o
< 1x10"
Q
Q
III
l-
<
a: 1x10
_o
8
CO
Controlled
mixing
Complete mixing
10
12 14 16 18
WATER CONTENT
(% dry soil mass)
Figure 4.4 Effect of mixing on hydraulic conductivity - Jamaica
clay (Lambe, 1955).
42
-------
1x10
-5
o
0)
10
*-*
E
o
Q
O
O
o
rr
Q
>• 1x10
-6
-7
10 11 12 13 14 15
MOLDING WATER CONTENT
(% dry soil mass)
cr
Q
20.0
19.0
18.0
10 11 12 13 14 15
MOLDING WATER CONTENT
(% dry soil mass)
Figure 4.5 Effect of dispersion on hydraulic conductivity
(Lambe, 1955)
Fabric
The fabric component of structure is one of the most impor-
tant soil characteristics influencing hydraulic conductivity,
especially for fine-textured soils. To suggest how large the
effect of fabric on hydraulic conductivity can be,
gives test results obtained on a compacted clay.
Table 4-1
TABLE 4-1
Soil
Jamaica
clay
Viginia
sandy clay
EFFECT OF FABRIC ON HYDRAULIC CONDUCTIVITY (Lambe and
Whitman, 1979)
Dry Unit
Weight of
Mold Ratio
18.07 kN/m3
18.22 kN/m3
1.3
1.3
Degree of
Saturation
Approximately
same
100%
100%
Hydraulic
Conductivity
(cm/ sec)
4 x
7 x 108
1 x 103
2.7 x 104
43
-------
The first comparison, between a sample compacted dry of
optimum and one wet of optimum, shows two samples of essentially
the same void ratio and degree of saturation having a hydraulic
conductivity ratio of approximately 60. The second comparison,
also between samples at the same void ratio and degree of
saturation shows a hydraulic conductivity ratio of greater than
3.
Another example of the profound influence of compaction
water content on the hydraulic conductivity of a silty clay is
shown in Figure 4.6.
Kneading
compaction curve "••.
\
13 15 17 19
MOLDING WATER CONTENT (%)
Figure 4.6
Hydraulic conductivity as a function of molding
water content for samples of silty clay prepared
to constant density by kneading compaction
(Mitchell, 1976).
44
-------
This is typical for the variation of hydraulic conductivity
with water content in compacted fine-textured soils. For the
example shown, all samples were compacted to the same density.
For samples compacted using the same compactive effort, curves
such as those in Figure 4.7 are typical.
~ 1x1° 5
"o
o -6
« 5x10
e
0
> 1x10~6
§ 5X10"7
O
Z
o
o
O 7
3 1x10 '
< a
tr 5x10 8
Q
108
> 106
35 ^.
z «
S | 104
>- c
oc
Q 102
100
Optimum water content
Static compaction
Kneading compaction
15 17 19 21 23 25 27
MOLDING WATER CONTENT (%)
15 17 19 21 23 25 27
MOLDING WATER CONTENT (%)
o Kneading compaction 1" x 2.8" 0 mold
• Kneading compaction 3.5" x 1.4" 0 mold
v Static compaction 1" x 2.8" 0 mold
Figure 4.7 Influence of the method of compaction on the
hydraulic conductivity of silty clay (Mitchell,
1976) .
45
-------
For compaction dry of optimum, clay particles and aggregates
are flocculated, the resistance to rearrangement during compac-
tion is high, and a fabric with comparatively large pores is
formed. Since flow through one large channel will be much
greater than flow through a number of channels having the same
total channel area, it is readily apparent that the larger a
channel for a given compactive effort, the higher the hydraulic
conductivity. For higher water contents, the particle groups are
weaker, and fabrics with smaller average pore-sizes are formed.
Considerably lower values of hydraulic conductivity are obtained
wet of optimum in the case of kneading compaction than by static
compaction, because the high shear stains induced in the kneading
compaction method break down flocculated fabric units.
Porosity
Data from consolidation - hydraulic conductivity tests where
the hydraulic conductivity was measured at a number of porosities
during compression and rebound can be compared with values
predicted by the Kozeny-Carman equation. A typical result is
shown in Figure 4.8 for illite.
10
-7
o
a
O
o
o
DC
a
o
Ui
-------
Ratios of measured to predicted values as a function of
porosity for several systems are shown in Figure 4.9. Signifi-
cant points of these plots are: (1) The measured hydaulic
conductivity can be greater or less than the predicted value, (2)
For compression at porosities greater than about 40 percent, the
measured hydraulic conductivity decreases more rapidly with
decreasing porosity than predicted, (3) For compression at
porosities less than about 40 percent, the measured hydraulic
conductivity decreases less rapidly than predicted, and (4) For
rebound, the hydraulic conductivity increases less rapidly than
predicted (Mitchell, 1976). The major factor responsible for the
failure of the Kozeny-Carman equation in fine-textured soils is
that the fabrics of such materials do not contain uniform pore
sizes (Olsen, 1962). Additionally, Bouma, et al. (1979) point
out that it is the connection of the pores and pore path
configurations rather than the total number or volume of pores
that determines the hydraulic conductivity of fine-textured
soils.
tn
UJ
I-
o
_l
u.
Q
UJ
I-
o
Q
UJ
DC
a.
a
ui
oc
UJ
2
U-
O
O
I-
(T
100
10
0.1
1A Sodium Illite 10~1 N NaCI
18 Sodium Illite 10~4 N NaCI
2A Natural Kaolinite Distilled H20
2B Sodium Kaolinite
1.0% by wt. Sodium Tetraphosphate
3A Calcium Boston Blue Clay 10~3 N CaCI2
3B Sodium Boston Blue Clay 10 N NaCI
28
I I I I I I I
0.2
0.4 0.6
POROSITY
0.8
Figure 4.9 Discrepancies between measured and predicted hydrau-
lic conductivities (Olsen, 1962). (a) Compression
cycles (b) Rebound cycles
47
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4.3 COMPACTION/HYDRAULIC CONDUCTIVITY TESTING ERRORS
The normal procedure for determination of the hydraulic
conductivity of a compacted soil sample is to compact the soil in
a mold and then to test for hydraulic conductivity on that
sample. The samples so tested are usually cylindrical or disc-
shaped with diameters between 3 and 15 centimeters. However,
when trying to estimate field hydraulic conductivity from
laboratory compaction and hydraulic conductivity testing, there
are many sources of error possible during both laboratory compac-
tion procedures as well as during laboratory hydraulic
conductivity testing. The types and sources of these errors are
discussed below.
Effect of Compaction Water Content
It has been clearly established that hydraulic conductivity
of saturated samples is relatively high for samples compacted dry
of optimum water content while the hydraulic conductiivity is
relatively low for samples compacted wet of optimum water con-
tent. Daniel (1981) reported that the hydraulic conductivity of
soils compacted dry of optimum might typically be 10 to 1000
times larger than the hydraulic conductivity of soil compacted
wet of optimum. For this reason, gross errors in predicting
field hydraulic conductivity from laboratory determinations may
occur if the field compaction water content is not as
anticipated.
Maximum Size of Soil Aggregates
During laboratory tests, the soil aggregates from the field
sample are usually broken down into smaller chunks than exist in
the field. Such disturbance of the natural aggregation of soils
will influence hydraulic conductivity.
Daniel (1981) reported that during testing of the same soil
with maximum aggregate sizes of 3/8 inches, 3/16 inches, and 1/16
inch the hydraulic conductivity of the smallest size class was
nearly two orders of magnitude less than the hydraulic conduc-
tivity of the largest size class. This implies that if aggregate
sizes are much smaller in the laboratory sample than exist in the
field, the laboratory tests may determine hydraulic
conductivities that are much lower than true field values.
Presence of Deleterious Substances
Similar to the situation with differences in soil aggregate
sizes between laboratory specimens and field conditions, the
presence of. deleterious substances in the field such as roots
or rocks or any other material not included in the 3-15 cm
laboratory specimen may cause substantial discrepancies between
the hydraulic conductivity measured in the laboratory and what
will actually occur under field conditions.
48
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Method of Compaction
While most laboratory hydraulic conductivity tests on soils
are performed on samples prepared with impact compaction using a
drop hammer, such equipment bears no resemblance to any pieces of
field compaction machinery.
Figure 4.10 presents a comparison of field and laboratory
compaction on the same soil. The figure illustrates the
difficulty of choosing a laboratory test that reproduces a given
field compaction procedure. The laboratory curves generally
yield a somewnat lower optimum water content than the actual
field optimum.
19
18
a
(-
z
IT
Q
17
16
15
I
10 15 20 25
WATER CONTENT (%)
Figure 4.10
Comparison of field and laboratory compaction. (1)
Laboratory static compaction, 13.8 MN/m^ (2) Modi-
fied AASHO (3) Standard AASHO (4) Laboratory static
compaction 1.38 MN/m2 (5) Field compaction, rubber-
tired load, 6 coverages (6) Field compaction,
sheeps-foot roller, 6 passes. Note: Static compac-
tion from top and bottom of soil sample (Lambe and
Whitman, 1979).
Additionally, Mitchell et al. (1965) compared static compac-
tion and kneading compaction and reported that similar hydraulic
conductivities were found on samples compacted dry of optimum
while kneading compaction produced hydraulic conductivities
nearly five times less than static compaction when samples were
compacted wet of optimum.
49
-------
Compactive Effort
Many researchers have found that hydra'ulic conductivity of
compacted soils is very sensitive to compactive effort. Mitchell
et al. (1965) reported that in studies on compacted silty clay
soil that the hydraulic conductivity may decrease by two orders
of magnitude, with no change in density or moisture content,
simply by changing the compactive effort. Therefore, it is very
important to make certain that the compactive effort used in the
laboratory is reasonably close to the compactive effort that will
be used in the field.
in the Sample
In testing compacted samples, it is often assumed that
soaking the samples from the bottom, with the top open to the
atmosphere, will yield saturated samples. However, Jackson
(1963) reported that for loam soils, only 79-91% of the total
porosity was tillable by water. Because water cannot pass
through air pockets, such pockets will effectively reduce the
pore space tnat can be occupied by water and thus reduce
hydraulic conductivity. This phenomena is one of the main
reasons why laboratory hydraulic conductivity results are
generally lower than hydraulic conductivities under actual field
conditions.
Ex c e s s i ve Hy dr a u 1 i c gr a dj en t s
It is virtually impossible to duplicate field hydraulic
gradients (usually less than 1) in the laboratory as testing time
becomes excessive as well as it is difficult to obtain accurate
measurements of the low flows and heads associated with very low
hydraulic gradients.
Since Darcy's Law indicates a linear relationship between
flow rate and hydraulic gradient, many workers have used elevated
hydraulic gradients to reduce testing time. However, if hy-
draulic gradients become excessive, piping or particle migration
may occur and adversely affect hydraulic conductivity measure-
ments.
Criteria for selecting an appropriate hydraulic gradient
depends on the soil type and the proposed use of the hydraulic
conductivity study. In comparative studies where qualitative,
rather than quantitative analyses are needed, larger gradients
may be used. Wardell and Doynow (1980) used hydraulic gradients
of 48 and 67 in a triaxial cell, while Brown and Anderson (1982)
utilized hydraulic gradients of 61.1 and 361.6 in a rigid-wall
permeameter. In both studies, no piping, particle migration, or
non-Darcy behavior was observed.
However, where the objective is to quantitatively estimate
50
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field hydraulic conductivity values from laboratory results,
Olson and Daniel (1981) have suggested use of hydraulic gradients
as close to those encountered in the field as is economically
feasible. Likewise, Zimmie et al. (1981) have recommended use of
hydraulic gradients of 5-20 (with gradients nearer the lower end
of the range to be preferred) for laboratory studies attempting
to duplicate field conditions.
Sample Size
The measurement of hydraulic conductivity in small cores
offers many practical problems as such cores may not be represen-
tative of in situ conditions where root holes, cracks, and fis-
sures are present. Thus, the size of the sample used to test
hydraulic conductivity is important if such information is used
to predict field behavior.
Anderson and Bouma (1973) experimented with a series of
cores of different lengths to determine the effect on hydraulic
conductivity. They found that 17 cm long cores had hydraulic
conductivities that were half a magnitude less than 5 cm long.
Daniel (1981) measured the hydraulic conductivity of a com-
pacted clay liner on samples of various sizes in the laboratory
with one very much larger sample tested in the field. The re-
sults were: 3.8 cm diameter core, 1 x 10~^ cm sec~l; 6.4 cm
diameter core, 8 x 10~9 cm sec~l; and 243.8 cm diameter core, 3 x
10~5 cm sec~l. Additionally, the average hydraulic conductivity
of the liner was back-calculated from measured leakage rates and
found to be 1 x 10~5 cm sec-l. Such results demonstrate the
significance of sample size in predicting field hydraulic
conductivity values.
Table 4-2 is a summary of testing errors possible when
testing for the hydraulic conductivity of compacted soils
(Daniel, 1981). It also shows estimates of the possible magni-
tude of error associated with each problem and an indication of
whether the laboratory hydraulic conductivity is likely to be
higher or lower than the field value. The estimates of error are
based on available data and are intended to show trends rather
than precise values.
51
-------
TABLE 4-2 SUMMARY OF SOURCES OF ERROR IN ESTIMATING FIELD
HYDRAULIC CONDUCTIVITY OF COMPACTED CLAY LINERS FROM
LABORATORY TESTS
Possible Number
of Orders of
Laboratory K Magnitude of
Potenti&l sources of error Too High or Jjow? Error
Compaction at a higher water
content in laboratory than field Low 1 to 3
Maximum size of clay chunks smaller
in laboratory than field Low 1 to 2
Deleterious substances present in
the field but not in laboratory
samples Low 1 to 3
Use ot static or impact compaction
rather than kneading compaction to
prepare laboratory specimens High 0 to 1
Use of more compactive effort in
the laboratory than in the field Low 1 to 3
Air in laboratory samples Low 0 to 1
Use of excessive hydraulic gradients Low 0 to 1
Sample size Low 0 to 3
52
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SECTION 5
HYDRAULIC CONDUCTIVITY AND HAZARDOUS WASTE DISPOSAL
Having discussed soil classification, water movement, and
soil compaction to provide background information, this section
will describe the relevant aspects of hydraulic conductivity to
consideration of the different types of hazardous waste disposal
facilitities and their impact on the environment.
5.1 LAND TREATMENT/LANDFARMING
At land treatment facilities the waste material is applied
onto the plants and the soil surface or injected into the root
zone (Figure 5.1). The major advantage of these types of facili-
ties is in the way that plants and soil can utilize or immobilize
water, metals, and contaminants. Additionally, land treatment
operations are the only type of waste disposal facility that
offer the potential for return to other land uses including
agriculture or forestry after waste disposal activities have
ceased.
Root Zone
Figure 5.1 Water and waste movement within the root zone.
In land treatment systems considerations of both saturated
as well as unsaturated hydraulic conductivity are relevant.
Wastewater applied to the soil will infiltrate into and through
the soil in accordance with the principles of saturated flow.
However, after each application and once the liquid moves lower
in the soil profile and root zone, unsaturated conditions and
flow phenomena will prevail.
53
-------
Therefore, when evaluating the feasibility or developing the
design for such a land treatment facility, soil testing for
saturated as well as unsaturated hydraulic conductivity may be
necessary to predict the behavior of specific soil and site
conditions. Specific soil testing methods for accomplishing such
tasks are:
Saturated Hydraulic Conductivity Soil Testing Methods
A. Laboratory
1. Pressure Cells (Section 6, pp. 58)
B. Field
1. Double Ring Infiltrometer (Section 6, pp. 74)
2. Air-Entry Permeameter (Section 6, pp. 78)
3. Cube (Section 6, pp. 81)
4. Crust (Section 6, pp. 101)
Unsaturated Hydraulic Conductivity Soil Testing Methods
A. Laboratory
1. Long Column (Section 6, pp. 85)
2. Instantaneous Profile (Section 6, pp. 90)
3. Thermocouple Psychrometer 6, pp. 97)
B. Field
1. Crust (Section 6, pp. 101)
2. Instantaneous Profile (Section 6, pp. 105)
Because the soil surface and root zone horizons are very
accessible and offer the use in situ conditions and Icirger sam-
ples for testing which will more closely represent conditions
that will be present at an actual operating site, field testing
may be favored over laboratory determinations.
5.2 LANDFILLS AND SURFACE IMPOUNDMENTS
At landfill and surface impoundment facilities the waste
material is placed into an excavated pit that can be lined with
compacted soil (Figure 5.2). As no soil material is totally
impervious, and since such soil liners will have a waste liquid
or leachate ponded on top of them, saturated hydraulic
conductivity will be the flow regime of interest. Of special
note for this particular situation is that a liner developed from
disturbed or admixed soil materials will behave differently than
soil in its natural state with regard to its hydraulic
properties.
54
-------
Figure 5.2 Water and waste movement through a soil liner.
Because soil liners are constructed from disturbed or
admixed materials, there is no simple and reliable way to test
them in situ. Accordingly, hydraulic conductivity must be
performed on compacted laboratory specimens that will be used in
the field. Therefore, as the facility is constructed, the field
density should be checked to ascertain that density and
associated hydraulic conductivities are related to the laboratory
model.
Laboratory methods for determining saturated hydraulic con-
ductivity on compacted specimens are:
1. Compaction Molds (Section 6, pp. 60)
2. Consolidation Cells (Section 6, pp. 64)
3. Triaxial Apparatus (Section 6, pp. 66)
4. Thermocouple Psychrometers (Section 6, 97)
5.3 THE UNSATURATED ZONE
Another type of liquid movement that is relevant in all
types of land disposal facilities is movement in the unsaturated
zone between the root zone or liner and ground water table or
bedrock as depicted in Figure 5.3.
As described in Section 3, unsaturated hydraulic
conductivity is more difficult to measure than saturated
hydraulic conductivity due to the fact that the unsaturated
hydraulic conductivity varies with both moisture content and
pressure head and therefore must be determined over a range of
values while saturated hydraulic conductivity will be a constant
value.
Also, it can be noted that testing of the unsaturated zone
during feasibility and design stages will be of benefit later as
for most systems there will be the requirement for monitoring of
the unsaturated zone after construction of the facility. Good
decisions made during feasibility and design stages for types and
locations of unsaturated hydraulic conductivity tests will
facilitate the unsaturated zone monitoring requirements.
55
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Root Zone
Unsaturated Zone
Water table
Bedrock
Figure 5.3 Water and waste movement in the unsaturated zone
Types of tests for determination of unsaturated hydraulic
conductivity are:
Laboratory Tests
1. Long Column (Section 6, 58)
2. Instantaneous Profile (Section 6, 90)
3. Thermocouple Psychrometers (Section 6,
97)
B. Field Tests
1. Crust (Section 6, 101)
2. Instantaneous Profile (Section 6,
105)
5.4 THE SATURATED ZONE
A fourth
most types of
saturated zone
disposal site.
category of liquid movement that is relevant in
land disposal facilities is movement in the un-
or water table that occurs under a potential waste
As the saturated zone will often occur at great
depths below the soil surface, in situ tests utilizing boreholes
will be necessary. Generally, constant or falling head tests will
56
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be employed and examples of the variety of approaches are: (1)
Augerhole; (2) Cased borehole (no inserts); (3) Cased borehole
(with inserts): (i) sand filter plug, (ii) perforated/slotted
casing in lowest section, and (iii) well point placed in hole,
casing drawn back; (4) Piezometer/permeameters (with or without
casing): (i) suction bellows apparatus, (ii) short cell, and
(iii) piezometer tip pushed into soft deposits/placed in boring,
sealed, casing withdrawn/self-boring; and (5) Well-pumping tests.
As these tests are applicable to testing the saturated zone
below a water table, they are not specifically soil testing
methods. Rather, they are methods to ascertain the flow rate and
direction or the existing ground water. Therefore, such methods
are not described in this report, but can be found in most
geology/hydrology or engineering texts.
57
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SECTION 6
SOIL TESTING METHODS
6.1 SATURATED HYDRAULIC CONDUCTIVITY
6.1.1 Laboratory Tests
Pressure Cells —
General description — The pressure cell technique is a
method where an undisturbed core, or volume of soil, is placed in
a metal pressure cell. After the soil is initially saturated, it
is connected to a standpipe where a falling head procedure allows
water to move through the pressure cell.
Parameters measured — Saturated hydraulic conductivity (cm
sec"1) .
Method— (Klute, 1965a) .
Apparatus: The basic equipment involved is (1) pressure
cell, (2) standpipe, and (3) water supply as shown in Figure
6.1
Procedure:
(1) Saturate the soil column.
(2) Connect soil column to end caps containing porous
plates.
(3) Fill the standpipe with liquid to a height greater than
HI-
(4) Measure the time for hydraulic head difference to fall
from HI to H2.
(5) Measure the cross-sectional area of the standpipe, the
temperature of the water, and sample length and
diameter.
(6) Calculate the conductivity from
K = fll In Hl
At
58
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where a = cross-section area of standpipe
1 = length of soil column
A = cross section area of soil column
t = elapsed time for HI to decrease to H2-
To drain
Porous plate
Standpipe
"O" ring seals
Porous plate
Overflow (Fixed level)
To water source -
for filling standpipe
2-way stopcock
Figure 6.1 Apparatus for pressure cell method (Klute, 1965a).
Precision and Accuracy— The sampling error involved in
hydraulic conductivity measurements of this type has been repor-
ted by Mason et al. (1957). An analysis of variance was
performed on the conductivity rate measurements and found the
variation within a given pit or site ranged from 0.10 to 0.18.
59
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Confidence limits in terms of hydraulic conductivity were com-
puted using a variance of 0.10 and a t-di stribution value
appropriate to a 95% confidence level. The results are given in
Table 6-1. It shows that the confidence interval (AK) depends
upon tne number of samples and upon the mean value of the hydrau-
lic conductivity (K).
TABLE 6-1. CONFIDENCE LIMITS FOR HYDRAULIC CONDUCTIVITY AS A
FUNCTION OF NUMBER OF SAMPLES AND THE MEAN
CONDUCTIVITY (Mason et al., 1957)
Number of samples
2
3
5
8
16
Confidence limit
AK
2.00 K
1.90 K
1.45 K
1.11 K
0.76 K
Limitations of test— (1) Small sample can be unrepresenta-
tive of field conditions; (2) Test make take long periods of time
on fine-textured or remolded soils; and (3) Saturating the cores
by submerging one end in a pan of water with the other end open
to the air for 16 hours may not completely saturate the samples.
Other saturation techniques include vacuum wetting, fluctuating
external gas pressure, and preliminary flushing of the pores with
carbon dioxide followed by passage of air-free water (Reeve,
1957).
Status of the method— This method is the accepted standard
test for laboratory determination of saturated hydraulic conduc-
tivity in the agricultural sciences.
Compaction Molds—
General description— The general compaction mold technique
is a method where disturbed soil is compacted in a metal cell.
This metal cell is then placed in a pan of water to allow for
saturation. Then a falling head technique similar to the
described method for pressure cells is applied. Differences in
the height of the liquid in the standpipe are recorded over time.
However, the method described here is a modified compaction
permeameter technique as presented by Matrecon, Inc. wnich
utilizes a constant elevated pressure rather than a falling head
to speed up testing time.
Parameters measured— Saturated intrinsic hydraulic conduc-
tivity(cm2)
60
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Method — (Matrecon, 1980) .
Apparatus: Equipment needed will include: (1) Soil crusher;
(2) Soil grinder; (3) 2 mm Sieve; (4) Moisture cans; (5)
Balance for up to 20 kgs.; (6) 105°C Drying oven; (7) Com-
paction molds; (8) Compaction rammer; (9) Steel straight
edge; (10) Permeameter bases and top plates; (11) A source
of compressed air with a water trap, regulator, and pressure
meter; (12) A fraction collector with automatic timer for
collection of samples over time; (13) An airtight, cooled
chamber to limit volatile loss of samples during and after
sampling; and (14) A vented hood to hold the compaction
permeameters and the chamber containing fraction collector
(safety precaution).
The modified compaction permeameter is shown in Figure 6.2.
Procedure :
(1) Disaggregate soil and allow to air dry.
(2) Grind the air dried soil and pass it through a 2 mm
sieve.
(3) Mix the sieved soil thoroughly and divide into two lots
of equal weight. Each lot of soil should be placed in
airtight containers at room temperature until time of
use. Each lot should consist of enough soil to prepare
up to 10 compaction molds (50 kg will provide for some
spillage losses assuming a mold volume of about 1000
(4) Use one lot of the soil to determine the moisture
density relations of the soil by following the ASTM
Method D 698-78. This will determine the optimum mois-
ture content to obtain the maximum density at the
compactive effort to be used.
(5) Use a second lot of the soil to prepare compaction
molds at optimum moisture content.
(6) Fit a valve on top of the permeameter top plate with
pressure fittings and connect it to a source of air
pressure via copper tubing. Place a water trap, pres-
sure regulator, and pressure gauge in line between the
air pressure source and permeameter. The water trap
should go between the pressure source and regulator to
prevent buildup of debris on the membrane in the regu-
lator. The pressure gauge should be located between
the regulator and a pressure manifold to the permeame-
ters so that the hydraulic head being exerted on the
dry cores may be monitored.
61
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Pressure intake
Sealing gaskets
Pressure release
Top plate
Clamping stud
Outlet
Base plate
^
.V//////7/1
Porous stone insert
Figure 6.2 Modified compaction perraeameter (Matrecon, 1980)
(1) Place sufficient volume of the leaching solution in the
chamber above the compacted soil,
(8) Apply pressure to force at least one pore volume ot the
standard leachate (0.01 N CaSo4 or CaCl) through the
dry cores. After the intrinsic hydraulic conductivity
values are stable and below 10"^-^ cm^, release the
pressure, disassemble the permeameter, and examine the
core.
(9) If the clay core has shrunk,
liner.
it is unsuitable as a dry
(10) If the clay has expanded into the upper mold, remove
the excess soil with a straight edge by cutting so as
to not smear the clay surfaces. Reweigh the core to
determine its density, then remount it on the
permeameter.
(11) Repressurize the permeameter and pass standard leachate
through until the intrinsic hydraulic conductivity
value stabilizes again below 10"^^ cm^.
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(12) Remove the remaining standard leachate from eight of
the fluid chambers and replace it in duplicate cores
with each of the two wastes or waste leachates to be
tested.
(13) If, after passage of one pore volume of the various
leachates, the intrinsic hydraulic conductivity values
of the cores are still below 10~10 cm^, disassemble the
permeameter and reexamine the cores.
(14) If the dry core has shrunk, it is unsuitable as a clay
liner for that waste.
(15) If the clay core has expanded, repeat step 10, then
proceed to step 17.
(16) If the clay has not changed volume, remount it on the
permeameter.
(17) Repressurize the permeameter and pass at least one pore
volume of the standard leachate. If its intrinsic
hydraulic conductivtiy has climbed above 10~10 cm^
(circa 10"^ cms~l), the clay is not suitable for con-
taining the waste. If the intrinsic hydraulic conduc-
tivity values measured on a waste's primary and
secondary leachate have consistently stayed below 10"^^
cm2, proceed to Step 18.
(18) Examine the translucent teflon outlet tube for signs of
soil particle migration out of the core. If there is
evidence of soil migration, pass at least one more pore
volume to observe if this internal erosion of the core
continues. If it continues after the two pore volumes
of standard leachate have passed, the clay is
unsuitable for that waste. If the soil migration
stops, at least one pore volume of the standard
leachate should be passed to assure that the core
stabilization is permanent; then proceed to step 19.
(19) If there are no signs of soil migration, depressurize
the system and extrude the clay cores from their molds
to examine them for signs of cracking, internal
erosion, soil piping, clay dissolution, stuctural
changes, or any other differences from the control
cores (those having received only saturated leachate).
If there are no signs that the cores have deteriorated,
the clay should be suitable for lining the disposal
facility to contain the waste.
The equation used for calculation of the intrinsic hydraulic
conductivity (K) is:
63
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K = VnL
pg At (L + H)
where K = intrinsic hydraulic conductivity (cm^)
V = volume of flow (cm^) in time t
n = permeant viscosity (dyne sec cm~l)
p = permeant density (gm cm~3)
g = gravitational constant (cm sec~2)
A = cross sectional area of flow (cm^)
t = time (sec)
L = length of soil core (cm)
H = pressure (cm of H20)„
Precision and accuracy— Not known.
Limitations of test-- (1) Small sample can be unrepresenta-
tive or field conditions; (2) Use of excessive head pressures
may produce flow along side walls of permeameter; (3) Potential
for interaction between metal cell components and waste; (4) No
assurance of sample saturation during test; and (5) Test will
take 1 to 5 months.
Status of the method— Experimental. Recently developed for
particular application to use of an actual liquid waste (rather
than water) with compacted soil layer.
Consolidation Cells—
General description— The use of consolidometers is common
in the field of geotechnical engineering, to determine the com-
pressibility and rate of settlement of soil. Because consolida-
tion is largely caused by squeezing water out of the soil, it
follows that consolidation is a function of hydraulic
conductivity. The consolidation cell technique is a method that
employs direct measurement by means of a falling head permeameter
of special design used in conjunction with a conventional
consolidaton apparatus.
Parameters measured— Saturated hydraulic conductivity (cm
sec"1) .
Method— (Means and Parcher, 1963).
Apparatus: The basic equipment involved is (1) fixed-ring
consolidation cell, (2) an apparatus for applying the head
of water mounted on a board as shown in Figure 6.3.
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Mounting board
Water supply
Load
Consolidation cell
Porous plate
Hg Manometer
and scale
From gas pressure source
Figure 6.3
Apparatus for hydraulic conductivity in conjunction
with consolidation test (Means and Parcher, 1963).
Procedure:
(1) A soil sample is cut to fit snugly into the fluid-ring
consolidation cell so there is no leakage between the
sample and ring.
(2) Porous plates are placed above and below the sample to
allow water to flow freely through the sample.
(3) Water under the applied head is admitted to the bottom
of the sample through the lower porous plate and forced
upward through the sample. A load is applied to the
sample through the upper porous plate. This load
should remain long enough to produce complete consoli-
dation under this load.
65
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(4) Add water to the burette.
(5) Record the initial head applied, h]_; the final head,
\\2'i and the time between the measurements of h^ and \\2-
Since hj and \\2 are only a small portion ot the total
applied head, the test may be considered a constant
head test without appreciable error by using h = (hj +
h2)/2 + ha.
(6) Determine the hydraulic conductivity from:
K = _QL
hAt
where K = saturated hydraulic conductivity (cm sec~l)
Q = flow (cm3)
L = length of sample (cm)
h = head (cm)
A = cross sectional area of sample (cm~2)
t = time (sec)
Precision and accuracy— While precision and accuracy of this
method are not specifically known, it has been concluded (Zimmie
et al., 1979) that direct measurement of hydraulic conductivity
of a consolidated sample is much more precise than calculating
hydraulic conductivity from consolidation theory using the coef-
ficients of consolidation and compressibility along with void
ratio.
Limitations of test— (1) Small samples can be unrepresenta-
tive of field conditions; (2) falling-head procedure may take
long periods for measurement of hydraulic conductivity in clay
soils; and (3) sample saturation cannot be assured.
Status of the method— The consolidaton cell method is
routinely used for other engineering consolidation-hydraulic
conductivity problems such as earth dams, retaining walls, slurry
trenches, etc. The method has not been widely used in the
evaluation of soil and waste disposal problems.
Modified Triaxial Apparatus—
General description— The modified triaxial apparatus tech-
nique is a method where the key elements are a soil specimen
surrounded by a thin, flexible rubber membrane enclosed in a
fluid pressurized chamber. By the application of the proper
chamber pressure and vertical load on the piston, the specimen
can be stressed to in situ conditions. Drain holes at both ends
of the specimen allow the performance of hydraulic conductivity
tests.
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Parameters measured— Saturated hydraulic conductivity (cm
sec~l) .
Method— (Wardell and Doynow, 1980).
Apparatus: The triaxial cell is a standard low pressure
cell which utilizes 1.4 inch diameter samples. The cell
base is equipped with four drain holes each of which leads
externally to a no-volume change valve. Two of these
drains lead vertically into the base ot the sample, with one
used for applying back-pressure while the other is used for
measuring the amount of outflow. A third drain is the duct
for the confining liquid. The fourth drain is connected to
the top cap which is placed on top of the soil sample and is
used for applying back-pressure and to impose the head of
water during actual hydraulic conductivity testing.
A schematic diagram of the triaxial testing apparatus is
shown in Figure 6.4. The chamber fluid is pressurized by
applying air pressure to the water in tank 1. The actual
pressure is measured roughly using a pressure guage (PG 1),
and more accurately with a mercury manometer (Ml). The
fluid going to the top and bottom caps of the soil sample is
also pressurized with air and the pressure measured with a
mercury manometer (M2). The water in tank 2 is de-aired.
Using a series of three valves (V6, V7, V8) , it is easy to
direct the de-aired water in all the possible flow paths.
For example, pressure can be applied to the bottom of the
sample with the vacuum on the top for saturation; pressure
can be applied to both top and bottom to dissolve air into
the water (back-pressure); or hydraulic conductivity
measurements can be made with flow upwards or downwards.
For testing, the water flows downwards to atmospheric pres-
sure and is measurid using a standpipe with a diameter of
approximately 0.11 cm.
Procedure:
(1) The disturbed sample material is oven-dried at 105°C,
and then ground up to pass a number 200 sieve.
(2) The sample is prepared by mixing 1500 ml of de-aired
water with six pounds of clay. The water is added
slowly, with each amount being mixed by hand into a
slurry, making sure the clay has absorbed all of the
water.
(3) When the clay has a uniform consistency, it is placed
into a large Proctor mold that has holes in the base to
allow water to enter or exit.
67
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Air supply
Air supply
To water
supply
To water
supply
To vacuum-
Figure 6.4 Schematic of modified triaxial apparatus (Wardell and
Doynow, 1980).
(4) A piston with a similar hole pattern is placed on top
of the sample. Filter paper is placed on both top and
bottom of the sample to prevent the pore spaces from
clogging. The mold is placed in a pan to ensure that
68
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the mold had a large supply of water during consolida-
tion. The pan is filled with de-aired water at all
times.
(5) The Proctor mold is placed in a consolidation frame and
weights are applied slowly to the lever arm to allow
the sample to consolidate, and to limit the amount of
soil squeezing out the top and sides of the piston.
(6) Weights are added until the sample has an equivalent
overburden pressure of 30 psi and then the sample is
allowed to sit for three days to ensure full
consolidation.
(7) The sample is then taken out of the consolidation frame
and cut and prepared according to triaxial procedures
given by Bishop and Henkel (1962).
(8) The sample is loaded into the triaxial cell and sur-
rounded by a standard rubber membrane (0.008 inches
thick).
(9) After loading the sample into the triaxial apparatus, a
chamber pressure of 14 psi is applied to approximate
the low overburden pressure of typical hazardous waste
disposal sites as fifteen feet of overburden which would
be approximately equal to 14 psi. After application of
the chamber pressure, the drains are closed.
(10) Then backpressure is applied to fully saturate the sam-
ple. To apply backpressure, chamber pressure and back-
pressure have to be raised simultaneously. The back-
pressure and chamber pressure are increased the same at
all times. The pressures are increased in 5 psi incre-
ments and allowed to remain at that pressure for five
minutes. After the five minute period, the pressure is
raised until the backpressure reached 30 psi and the
chamber pressure is 44 psi. The specimen is allowed
to sit overnight.
(11) To initiate the hydraulic conductivity test, a head of
de-aired water is applied to the top of the sample and a
pressure gradient of 5-20 is superimposed. At the same
time the valve to the standpipe is opened to allow
measurement of the flow volumes.
(12) Immediately after the gradient is applied, the flow rate
will be due to a combination of both consolidation and
seepage. However, after 15-30 minutes, consolidation
effects are negligible. Therefore, hydraulic conductiv-
ity values should be determined from data obtained after
30 minutes.
69
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(13) For determination of hydraulic conductivity, equations
for constant head tests are used:
K =
hAt
where K = saturated hydraulic conductivity (cm sec"1)
Q = flow (cm3)
L = length of sample (cm)
h = head (cm)
A = cross-sectional area of sample (cm^)
t = time (sec)
Precision and accuracy — Work by Wardell and Doynow (1980)
demonstrates results that were reproducable and consistent on the
same soil under different hydraulic gradients which would indi-
cate good precision of the method. Also, Zimmie (1981) stated
that satisfactory precision can be obtained by using good labora-
tory techniques, typically within 10-30 percent.
Limitations of test — (1) Small samples can be unrepresen-
tative of field conditions; and (2) Hydraulic gradients used in
connection with this method should be limited to the range of 5-
20 (Zimmie, 1981).
Status of the method — While triaxial apparati are common
testing devices used by geotechnical engineers for the measure-
ment ot soil strength, with modifications the device can also be
used for measurement of hydraulic conductivity. Presently, this
method is probably the most common technique used for the deter-
mination of the low hydraulic conductivity of fine-textured
soils.
6.1.2 Field Tests
Piezometers—
General description— The piezometer method is based on the
measurement of flow into an unlined cavity at the lower end of a
lined hole. Water entering the unlined cavity and rising in the
lined hole is removed several times by pumping or bailing to
flush the soil pores along the cavity wall. After flushing is
completed, the water is allowed to come to equilibrium with the
water table.
It should be noted here that there are several varieties of
"piezometer" tests used, depending on the geometry and materials
located at the point of measurement. Besides the cylindrical
cavity outlined in this procedure, there are spherical cavities,
70
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sand-filled cavities, piezometer tips placed in sand-filled
cavities, or piezometer tips pushed directly into the soil. This
last method (Jezequel and Mieussens, 1975) looks especially
promising for evaluation of the low conductivities of clay soils.
Parameters measured— Saturated hydraulic conductivity (cm
sec"1) .
Method— (Boersma, 1965a).
Apparatus: (1) Auger: open-blade type; (2) Bailer or pump:
tubing diameter smaller than that of the hole, with a check-
valve at the lower end; (3) Probe: a measuring tape attach-
ed to a float that will fit the auger hole without touching
the sides; (4) Stop watch; and (5) Liner: a section of pipe
that will fit tightly in the auger hole should be used. The
length ot such pipe should be sufficient to extend from the
bottom of the auger hole to 15 cm or more above the soil
surface. This apparatus set-up is shown in Figure 6.5.
Pump tube-
n
Liner pipe
w
3
Reference level
Soil surface
Water table
Unlined cavity
Restricting layer
Figure 6.5
Apparatus
1965a)
set-up for piezometer method (Boersma,
71
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Procedure:
(1) Remove surface sod, trash, and loose soil from location
of the hole.
(2) Install the piezometer. Note: Piezometers are instal-
led by either driving by force or jetting with a stream
of water. In general, the driving method is limited to
relatively shallow depths (30 feet), whereas piezometers
may be jetted to depths of 100 to 150 feet or greater.
In this procedure the driving method is used with a 4,9
cm auger and a 5.08 cm liner of electrical conduit.
(3) Auger the hole 10 cm into the soil, remove the auger,
and tap the sharpened end of the liner into the hole to
the depth of the opening.
(4) Insert the auger into the liner, bore the hole 15 cm
deeper, and tap the liner down to the bottom of the
hole.
(5) Repeat this process until the bottom of the liner is at
the desired depth below the water table.
(6) Then carefully auger out a cavity 10.2 cm in length
below the end of the liner.
(7) Remove the water from the hole several times to reduce
or eliminate puddling effects.
(8) While removing water, estimate the order of magnitude of
the rate of rise for selection of increments of rise to
be used in the measurements.
(9) Record the following measurements:
length of piezometer (D)
height of piezometer above ground surface (F)
depth to water table (E)
cavity depth (W)
cavity radius (R)
depth ot piezometer below soil surface (H=D-F)
depth of water table (d=D-E).
(10) Remove the water from the pipe, and measure the time At
required for the water level to rise through the
distance Ah. If time permits, make three or more such
pairs of measurements as the water rises. Make no
measurements after the water has risen to a level 20 cm
below the water table.
72
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(11) Repeat the measurement of rate of rise of the water
level in the same hole after the water level in the hole
has risen to the level of the water table. If values of
Ah/At obtained in the second series of measurements are
not consistent with those of the first, repeat the
process until consistent results are obtained.
(12) To calculate hydraulic conductivity:
K = JEfii in
AAt
where K = hydraulic conductivity (cm sec"-'-),
R = inside radius of liner (cm),
E = distance from top of liner to the water table
(cm) ,
LI = distance (cm) from top of liner to water level
in liner at time t]_,
L2 = distance (cm) from top of liner to water level
in liner at time t2,
At = t2~t]_, time increment for water to rise from
LI to L2 (sec), and
A = geometry factor (cm) which is a function of R,
the distance (d) from the water table to the
bottom of the liner, the distance (W) from the
bottom of the liner to the bottom of the hole,
and the distances from the bottom of the hole
to a restricting layer.
In this particular case, with W = 10.2 cm and R = 2.45
cm, the A-factor is assumed to be constant and equal to
43.2 cm. Also, considering these same particular cavity
dimensions, a nomograph such as shown in Figure 6.6 can
be used to determine K.
Precision and accuracy— For the procedure given, an error
less than ± 8% is introduced by assuming A = 43.2 cm, as long as
d > W and S > 1/2 W (Boersma, 1965a).
Limitations of test-- (1) Occurence of errors and inconsis-
tencies due to smear adjacent to the piezometer pocket and air in
the piezometer pocket; (2) Only applicable to conductivity
measurement below water table; and (3) Measures both vertical and
horizontal conductivity. If the diameter of the cavity is small
and the length of the cavity is several times its diameter, the
horizontal permeability is measured. The wider the hole and the
shorter the length of the cavity, the more nearly the measurement
becomes one of vertical conductivity.
Status of the method— The piezometer methods of measuring
hydraulic conductivity are the standard methods used when
determining water flow rates in shallow ground water areas.
73
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0.1 _f
0.05 --
5x10 -
1x10
-5
10
10.000
Figure 6.6
Nomograph for the determination of the hydraulic
conductivity from data obtained by the piezometer
method (Boersma, 1965a). The nomograph is valid only
for conditions where the length of the cavity is 10.2
cm and the diameter is 4.9 cm.
Double Ring Infiltrometer/Permeameter—
General description— The double ring infiltrometer tech-
nique is a method where two open metal cylinders, (from a few
centimeters to several feet in size), are placed one inside the
other, then are driven into the soil and partially filled with
water that is maintained at a constant level in both rings. The
74
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amount of water added to maintain the constant water level is the
measure of the volume of water that infiltrates the soil. This
volume can be measured over time and thus be expressed in cm
sec" .
A modification of this method is the permeameter method
reported by Boersma (1965b). In this technique, the sides of a
hole are used as the outer ring with a smaller metal cylinder
positioned in the center. There is a constant water supply
system tnat maintains the water level in the cylinder and in the
surrounding hole. This method also employs the use of
tensiometers to indicate saturated conditions.
Parameters measured— Saturated hydraulic conductivity (cm
sec"1) .
Method I—
3385-75).
Double ring infiltrometer (Bertrand, 1965; ASTM D
Apparatus: (1) Infiltrometer rings: cylinders of cold-
rolled steel, aluminum alloy, or galvanized steel with the
bottom eage beveled to facilitate driving into soil (15-45
cm in diamaters); (2) Driving plate: a steel plate larger
than the largest ring cylinder; (3) Driving hammer: a
sledge hammer or other device to tamp on plate to drive
cylinder into ground; (4) Water supply: 5-gallon jugs to
55-gallon drums may be used; (5) Puddling protection device:
a piece of folded burlap, cloth, heavy paper, or any other
suitable material used to protect the soil surface from
puddling when water is first added; (6) Timing device, and
(7) Depth gauge: a hook gauge, steel tape, rule, or length
of heavy wire pointed on one end, for use in measuring and
controlling the depth of water (head) in the infiltrometer
ring. A manometer could also be used. Figure 6.7 shows the
set-up of the double rings, excluding the water supply.
Outer ring water level
Soil surface
Scale
Water level
Inner ring
Outer ring
Figure 6.7
Burlap (to prevent puddling)
Apparatus set-up for double ring infiltrometer
(EPA/Army Corps of Engineers/USDA, 1977).
75
-------
Procedure:
(1) Set outside cylinder in place and push it firmly into
the soil. Place the driving plate on the cylinder and
use the driving hammer to push cylinder 10-15 cm into
the soil.
(2) Repeat step 1 for the smaller ring centered in the outer
ring.
(3) Place burlap or other puddling protection material on
the soil within the inner cylinder,,
(4) Add water to outer ring to a depth of 5-10 cm and main-
tain this depth throughout the observation period.
(5) Add water to outer ring to a depth of 5-10 cm and main-
tain this depth after each observation period. Record
all volumes of water that are added to maintain a con-
stant head.
(6) Record water volumes used at 15 minute intervals for the
first hour, 30 minute intervals for the second hour, and
hourly after that until two or more hourly volume
measurements are equal.
(7) Calculate the hydraulic conductivity by:
K -
At
where V = volume of water (cm^)
A = area of inner ring (cm^)
t = time (sec)
Method II Permeameter (Boersma, 1956b).
Apparatus: (1) Infiltrometer ring: same as for the double
ring using larger diameter ring (45 cm); (2) Driving plate;
(3) Driving hammer; (4) Water supply; (5) Depth controlling
device: a hook gauge, manometer, constant level float valve,
or any other apparatus to maintain constant head in ring,
and (6) Tensiometers: four mercury tensiorneters that are
capable of measuring both positive and negative pressures.
This apparatus is shown in Figure 6.8.
76
-------
Tensiometer
Constant head
water supply
Outer ring
Inner ring
Figure 6.8
Schematic diagram of equipment for permeameter
method in place (Boersma, 1965b).
Procedure:
(1) Excavate a hole 1 m square to the horizon to be tested.
(2) Set cylinder in place and push firmly into the soil.
Place the driving plate on the cylinder and use the
driving hammer to push cylinder 15 cm into the soil.
(3) Spread about 2 cm of uniform, coarse sand over the area
inside the cylinder to avoid puddling of the soil sur-
face during the test.
(4) Space the four tensiometers at equal intervals around
the cylinder, each 10 cm outside the cylinder and 23 cm
below the level of the soil inside the cylinder.
(5) Install the depth-controlling device to maintain a con-
stant 15 cm head.
(6) Add water to inside and outside ring to a depth of 15
cm.
77
-------
(7) Record the time intervals and water volumes.
(8) Terminate the test when the tensiometers indicate zero
tension, and the water is moving through the test layer
at a constant rate.
(9) Calculate the hydraulic conductivity from:
K =
AH
where Q = flow rate (cm3 sec"-*-)
L = length of soil column inside the cylinder (cm)
A = cross-sectional area of cylinder (cm2)
H = height of the water level inside the cylinder
above the base (cm).
Precision and accuracy— Prom the work of Luxmoore, et al.
(1981) with double ring tests on a low level radioactive waste
disposal site, they reported the infiltration rate of the control
treatment to be 3.0 x 10~5 cm sec~l after 20 days, and 3.35 x
10"5 cm sec"1 after 259 days. Such results demonstrate that the
method offers reproducibility and good precision. However, in-
formation on the accuracy of the method for fine-textured soils,
or comparison of the double ring method to other methods, is not
available.
Limitations of test— (1) Care must be exercised in the
installation of ring cylinders to prevent shatter or compaction
of soil adjacent to border. (2) Air may become trapped below the
advancing water front which may have significant effect on
results obtained. (3) A considerable amount of time may be
required for fine-textured soils, and (4) Correction for evapora-
tion should be made.
Status of the method— (1) Double ring method is ASTM
Standard D 3385-75. (2) Permeameter method's extent of use is
not known.
Modified Air-Entry Permeameter—
General description— The air-entry permeameter technique is
a method where a 25 cm diameter cylindrical unit of undisturbed
soil is isolated within an infiltration cylinder driven into the
soil, and a head of water is applied to the upper end of the soil
unit, causing water to penetrate the soil with a wetting front.
The infiltration rate is measured until the wetting front is
close to the bottom of the cylinder which is determined by use of
an implanted tensiometer.
-------
Parameters measured — Saturated hydraulic conductivity (cm
Method — (Topp and Binns, 1976).
Apparatus: The basic equipment required and the experimen-
tal set-up for the air-entry permeameter test are shown in
Figure 6.9. The items required are: (1) 25 cm diameter
metal cylinder with flange of rolled angle iron with
attached foam-rubber gasket; (2) plastic sheeting lid with
C-clamps for attachment; (3) Water-supply reservoir; (4)
Vacuum gauge; (5) Tensiometer; (6) Air escape valve; and (7)
Disk used to dissipate energy of the water stream from the
water reservoir.
T
H,
Reservoir
Vacuum guage
Soil surface
>^>^
^
G
7
7
/" — "N ' jr
(\ \^ ^ Supply valve
v )
X.
lO-O-- ^
-
^y/K^
L
fr
r
ttl^——^—————
T
^^
\>
^
1 .. Tensiometer
P
^
-.
R-
s
^ ^" Air escape valve
1
iM
^
I
_T_
f I , f*m—e* 1 <» rrtr\
VL V. 1 v/"~vie»i'»K
^^
^^r1 Rank fit
rcrLJ
1j^^^*^/iO\^^/>'ii\ ^y/\. ^
/\C\^jf />v^' / jf)C**y s />.
Cylinder wan
— Wetting front
Figure 6.9 Modified air-entry permeameter (Topp and Binns,
1976) .
Procedure:
(1) A driver with a sliding weight and cylindrical base is
used to drive the cylinder to a predetermined depth.
79
-------
(2) The soil is lightly packed down against the cylinder
wall to ensure a good bond between cylinder-and soil.
(3) If the soil is bare, it should be covered with coarse
sand to act as a protective layer.
(4) A disk is then placed in the center of the cylinder to
dissipate the energy of the water stream from the supply
pipe.
(5) The lid assembly with the air valve open and the gauge
and supply valves closed is positioned on the cylinder
so that the air-escape valve is at the highest point.
(6) The lid is tightened with the C-clamps and lead weights
are placed on the lid to offset the hydrostatic lift
that will be developed by the elevation of the water-
supply reservoir.
(7) The tensiometer is inserted through a 8 cm long guide in
the lid of the permeameter.
(8) The water reservoir is filled and the supply line is
opened to quickly fill the apparatus while air is
allowed to move out of the air-escape valve.
(9) Once the apparatus is' filled with water and all air is
removed the air escape valve is closed,
(10) Immediately after the air valve is closed, the measure-
ment ot the rate of flow of water from the reservoir
is initiated and continued until the wetting front
causes the tensiometer reading to decrease toward zero.
(11) The water supply valve is then closed and the air-entry
pressure is determined on the vacuum gauge.
(12) The air entry valve is calculated from:
Pa = pmin + G + L
where Pa = air entry value of soil, expressed as pres-
sure head in cm water at point of air entry
pmin = minimum pressure head in cm water as deter-
mined by the maximum reading on the vacuum
gauge
G = height of gauge above soil surface in cm
L = depth of wet front (depth of tensiometer) in
cm
80
-------
(13) Saturated hydraulic conductivity is then calculated
from:
2 (dH/dt) L (Rr/Rc)2
Ht + L +
where dH = rate of fall of water level in reservoir
dt just before closing supply valve, in cm
sec~l
Ht = height above soil surface of water level in
reservoir at time supply valve is closed, in
cm.
Rr = radius of reservoir in cm.
Re = radius of cylinder in cm.
Precision and accuracy — TOpp and Binns (1976) found that
the air-entry permeameter gave reproducible values of hydraulic
conductivity at various depths in a number of different soils.
In comparison with other methods, they found that results were
consistent with values obtained from determinations made on
laboratory cores, although the laboratory core result was
generally lower than the hydraulic conductivity determined by the
air-entry permeameter which was probably due to lack of worm
holes or cracks in the laboratory samples. Topp and Binns (1976)
also found that extrapolated results from the crust method
compared favorably with the values obtained from the air-entry
permeameter. Aldabagh and Beer (1971) found the method to be
consistent and reasonable with equipment variability
substantially less than the natural variation of soil.
Limitations of test — (1) Care must be exercised in the
installation of cylinder to prevent shatter or compaction of soil
adjacent to border; (2) Cannot be performed very adequately on
initially wet or nearly saturated soils because the induced
wetting front from the addition of water is not very clear or
well-defined; (3) Will be difficult on soils with gravel or
stones.
Status of the method — Relatively new method but its use is
increasing due to advantage that it takes relatively short time
periods (approximately 1 hour) to conduct test.
Cube Method —
General description — The cube technique is a method for
measuring both the vertical and horizontal saturated hydraulic
conductivity of a cube of soil (25 x 25 x 25 cm) which is carved
out in situ and covered with gypsum. The vertical saturated
81
-------
hydraulic conductivity is measured by infiltrating water into the
exposed upper surface and by collecting it below the exposed
lower surface ot the cube. To obtain horizontal saturated
hydraulic conductivity, the cube is then turned. The two pre-
viously open surfaces are covered with gypsum, which is removed
from the other two vertical sides. These turn into surfaces for
percolation after again turning the cube. A vertical saturated
hydraulic conductivity is now measured which represents the
horizontal saturated hydraulic conductivity of the cube in its
original position in the soil. The set-up of the field operation
to ootain the cube is shown in Figure 6.10.
Parameters measured-— Saturated hydraulic conductivity (cm
sec"1) .
Method— (Bouma and Dekker, 1981).
Apparatus: Basically, the only apparatus is a hinged wooden
box with inside dimensions of 35 x 35 x 35 cm along with
tools to dig a soil pit, carve a cube, and gypsum.
Procedure:
(1) A soil pit with a pedestal is dug in naturally wet or
very moist soil (so that maximum swelling has occurred).
(2) A horizontal plane is exposed and a cube of soil (25 x
25 x 25 cm) is carved out in situ by removing at least
20 cm of soil along its four sides using a sharp knife
and removing only small fragments at a time to avoid any
compaction of the cube.
(3) The square wooden box that is open at its upper and
lower surface is placed around the cube of soil in the
pit. A metal rim is attached to the bottom of the box
to support the gypsum between the sides of the cube and
inner walls of the box.
(4) A gypsurn slurry is then prepared and poured into this
space as soon as its starts to become viscous.
(5) After approximately 20 minutes and when the gypsum has
hardened, the box with soil and gypsum is removed from
the pit by pulling a metal wire along the outside bottom
area of the box.
(6) The upper and lower soil surfaces of the cube in the box
are then cleaned and exposed outside the pit by chipping
away soil fragments with a small knife.
82
-------
-35cm
Soil column —
25cm
Soil
cube
Cut to
remove cube
Sidewall
- Gypsum
Metal rim
Excavation and retrieval
Sidewall
P
Gypsum
rim added
Infiltrative
surface
Soil
cube
Hinge
Sidewall
Gypsum
Soil
cube
Cube detail
Sidewalls removed
Funnel-
Cylinder-
Apparatus for measurement
Initial (Vertical)
infiltrative surface
to be sealed
Second (Horizontal)
infiltrative surface
to be exposed
Figure 6.10 Diagram of the cube method.
83
-------
(7) The box is then placed on a funnel which channels the
percolated water to a measuring device.
(8) Then water is shallowly ponded on top of the cube,
creating a hydraulic head gradient across the sample
close to one. To facilitate such ponding, a small rim
of gypsum must be applied on top of the gypsum which
already encases the cube.
(9) Fluxes are measured by periodically collecting the
percolated volume of water and by considering the cross-
sectional area of flow. Such fluxes are identical to
saturated hydraulic conductivity, due to the low head on
top of the cube.
(10) The measurement is terminated as soon as the fluxes are
constant.
(11) The box is now turned on its side and is removed from
the gypsum-covered cube by loosening its hinges.
(12) The two exposed sides of the turned cube are then
covered with a viscous gypsum slurry.
(13) Two new surfaces for infiltration and drainage are pre-
pared by removing the gypsum covers of the two other
sides of the turned cube. Removal should be done such
that a 5 cm wide gypsum rim with a height of 5 cm is
left on each side which allows ponding on top and
supports the cube when it is placed on the funnel.
Removal of the gypsum should be initiated by sawing,, as
knives may cause the gypsum to fracture,,
(14) The gypsum-covered cube is now turned 90 degrees and is
placed on the funnel to allow the measurement that
represents the horizontal saturated hydraulic
conductivity of the sample in its original position by
repeating Steps (8) through (10).
Precision and accuracy— While the method is quite new and
not widely used presently, its advantages over other methods will
provide for its greater use in the future. That is, the cube
method offers advantages over other laboratory determinations as
the size of the sample is much larger than other methods and
therefore will include some macropores as they occur in the
field. Also the mode of isolating the sample in the cube method
is nondestructive as compared to some field techniques which may
cause compaction of the sample due to punching or pounding
cylinders or infiltrometers into moist or wet clay soils.
Another advantage of the cube method is that both vertical and
horizontal saturated hydraulic conductivity are obtained from the
84
-------
same sample. A final advantage of the cube is that the method
is very inexpensive and does not require specialized equipment.
Limitations of test— (1) Method may require relatively
long periods of time to perform test on clay soils; (2) Sample
saturation cannot be assured; (3) Swelling of sample may occur
which may affect hydraulic conductivity measurment.
Status of the method— Very new method but use will increase
due to ease and low expense of procedure.
6.2 UNSATURATED HYDRAULIC CONDUCTIVITY
6.2.1 Laboratory Tests
Steady State—
General description— Steady state techniques are methods
where the hydraulic conductivity is measured by applying a con-
stant hydraulic head difference across the sample contained in a
soil core and measuring the resulting steady state flux of water.
The flow rate, Q, and tensiometer matric potentials (pressure
head) are recorded.
Parameters measured— Unsaturated hydraulic conductivity (cm
sec~l). Apparatus can also be used to determine saturated
hydraulic conductivity (see "Pressure Cells", Section 6.1.1).
Method I— Short column (Klute, 196 5b).
Apparatus: A generalized set-up of the equipment required
is shown in Figure 6.11. The volume of the soil chamber can
vary depending on size and shape of the sample.
This sample core of soil is held between two porous plates,
P^ and P^, which may be made of plastic, fritted glass
beads, cellulose acetate filters, or ceramic. Installed and
sealed into the side of this core are two tensiometers, T^
and T?. Water is added from a hanging water-column supply
system at hydraulic head H^. Flow occurs through the first
porous plate, the soil core (which is maintained at a con-
stant head via a manometer (M)}, the lower porous plate, and
outflow is via the drip point into a chamber or graduated
cylinder.
85
-------
Constant head
water supply
Pressure measurement
system for tensiometers
FT
"3
H
Permeameter
Soil
VT
r
Drip point —
H4
7 Hydraulic head reference level 7
From gas
pressure source
H
Manometer
Figure 6.11
Diagram of apparatus for short column steady state
method of (Klute, 1965b).
86
-------
Procedure:
(1) Fill the tensiometers, water supply, and water removal
systems with de-aired water by filling them under vacuum
or by flushing them following prolonged soaking.
(2) Clamp the sample between the end caps and install the
tensiometers.
(3) Measure distance between two tensiometers, L. Calculate
cross-sectional area, A, of soil core.
(4) With the outflow tubing clamped off, apply water to wet
the sample. Note: It is suggested that 0.01N CaSC-4
should be used, and collected outflow should be recycled
through core.
(5) When the sample has been wetted, establish a hydraulic
gradient across the sample at a mean pressure-head near
zero.
(6) Maintain a constant hydraulic head until steady flow is
attained. Flow is considered steady state when (1)
time-invariant readings of two tensiometers appear, and
(2) inflow rates equal outflow rates.
(7) Record the volume of flow, Q, which occurs over time, t.
(8) Record the height of the fluid column of manometer M,
(9) Record the hydraulic heads #3 and H^.
(10) Record the pressure heads h^ and 114.
(11) Decrease the water content of the sample by increasing
the gas pressure on the cell, or by reducing the mean
value of EI and H2-
(12) Repeat steps 6 through 11 as needed to obtain informa-
tion for calculation of the hydraulic conductivity at a
series of decreasing pressure heads and water contents.
(13) Maintain a complete record of the volumes of inflow and
outflow, as well as the volume of water involved in
changes in the readings of the tensiometers.
(14) After the final run through steps 6-11, the soil core
should be removed and water content should be
determined for the whole sample gravimetrically. This
will permit calculation of water content at each mean
pressure head from the first water content and volumes
of inflow and outflow.
87
-------
(15) Calculate the hydraulic conductivity at each mean pres-
sure head and water content from:
K =
QL
At(H3 - H4)
(16) Calculate the mean pressure head h corresponding to the
above conductivity value from:
h = (Pjm/e) + (h-3 + h,a)
... ^ ,
where m is the gauge pressure in the cell expressed
as a column of fluid of length m,
Pl is the density of the manometer fluid,
e is the density of water,,
(17) Plot the K(h) function.
Variations: For undisturbed samples, a pressure chamber
apparatus similar to Figure 6.12 is used.
Pressure chamber
From constant head
water supply
To pressure
measurement
system for
tensiometers
From gas
pressure source
control system
To constant head
drip point
Figure 6.12 Alternative steady state method for undisturbed
samples (Klute, 1965b).
-------
Method II— Long column (Klute, 1972).
The long column version of the steady state method uses a
column length on the order of 50-200 cm whereas the short columns
are on the order of 10-15 cm. Further, more than two tensiome-
ters are encased along the side of the longer column as shown in
Figure 6.13.
To pressure measurement
system for tensiometers
To constant head drip point and guage
From constant head
water supply
Long column
permeameter
Figure 6.13
Diagram of long column version ot steady state
method (Boersma et al., 1972).
By starting at saturation and proceeding through a series of
progressively decreasing flow rates, a series of points can be
determined for the drainage K(h) function similar to short column
version. An advantage of the long column method is that the use
of several tensiometers at convenient intervals along the column
will allow the determination of the head difference across each
interval and thus the hydraulic conductivity function for each
section or layer.
Variations: Watson (1967) describes a long column variation
in which a zone of entrapped air (an
The column is initially saturated and
to obtain the saturated conductivity.
allowed to occur and at an appropriate
the upper end. This procedure traps a
air lens) is established.
steady state flow is used
Then partial drainage is
time water is reapplied at
lens of air in the middle
89
-------
of the column. The hydraulic conductivity is calculated in the
usual steady state manner.
Another variation in this procedure is water content
measurement by gamma attenuation in addition to the pressure head
measurements via tensiometry. Thus both the K(h) and K(0) can be
determined from measured values.
Precision and accuracy— Klute (1965b) states that the
variability of results from the short column method will be as
large or larger than those from the measurement of hydraulic
conductivity of saturated soil by the Pressure Cell method (Table
6-1) .
It is believed that a large portion of this variation can be
attributed to the length of the core used (SSWMP, 1978).
Anderson and Bouma (1973) showed that variation in hydraulic
conductivity decreased significantly for cores that were greater
than 15 cm in length.
Limitations of test— (1) Steady state methods require
relatively long times to establish steady state flow; (2) Small
samples may not be representative of field conditions; (3) The
usual steady state procedures yield a hydraulic conductivity
pressure head relationship, K(h). If the measurement of the
hydraulic conductivity-water content function K(0) is desired,
additional procedures such as gamma attenuation or neutron
attenuation will have to be employed to determine water content
of the sample at each steady state (or determine water content-
pressure head function on separate sample). The short column
method outlined could estimate the K(6>) function using final
water content and inflow and outflow volumes to back-calculate
water contents at each steady state; (4) Hydraulic conductivity
versus suction or degree of saturation is established from wet to
dry but not dry to wet as will occur at the actual waste site;
(5) Maximum suction limited to available range of tensiometer
unless pressure offset method can be utilized.
Status of the method— Since this method can determine both
saturated and unsaturated hydraulic conductivity, it is a widely
employed procedure by soil physicists who require analysis of
steady state conditions (as compared to transient or unsteady
state conditions).
Unsteady State: Instantaneous Profile—
General description— The instantaneous profile technique is
a method that can be used in the laboratory or in the field. In
the laboratory, a flow system (usually a soil column) is
established whereby the flow or outflow, water content, and
pressure head are measured or inferred.
90
-------
Basically, there are three options with respect to measure-
ments made on the flow system: (1) the water content and pres-
sure head distribution may both be measured, (2) the water con-
tent distribution may be measured and the pressure head inferred
from water retention data, or (3) the pressure head distribution
may be measured and the water content inferred from water
retention data.
Table 6-2 shows the variety of approaches.
TABLE 6-2 SUMMARY
METHODS
Reference;
Watson (1966)
Wind (1966)
Vachaud (1967)
Weeks and
Richards (1967)
Flocker
et al. (1968)
Cassel
et al. (1968)
Vauchaud and
Thorny (1971)
Rogers and
Klute (1971)
Gillham
et al. (1976)
Gillham
et al. (1979)
OF LABORATORY INSTANTANEOUS PROFILE
FOR HYDRAULIC CONDUCTIVITY
Water Content From;
Gamma attenuation
Inferred from
-------
Gamma system/source
Flow cell
Lead shield
Lead shield —
Tensiometer system
Vent
Lucite top cap
From constant gas
pressure source
Burette
From constant head
water supply
Gamma system/detector
137
Tensiometers (to switch/transducer/output)
Flow cell cross-section
Source
— Lead shield
Flow cell
Lead shield
Detector
Amplifier/analyzer
Top view
Figure 6.14
Diagram of flow cell, tensiometer, and gamma
system. (Gillham et al., 1976).
92
-------
Procedure:
(1) A steady-state condition is achieved at the start of the
experiment by supplying excess water (distilled and
boiled) to the surface of the column such that a very
small head of water (1 mm) is maintained there.
(2) After the column is saturated and the water supply
stopped, the drainage experiment commences with the
disappearance of ponded water through the upper soil
surface.
(3) Water content and water suction values over short time
periods are recorded at different depths throughout the
experiment.
(4) After the experiment is terminated, plot (a) soil water
suction (cm) versus time on the abscissa for the various
depths of measurements. Examples of these graphs are
presented in Figure 6.15 and Figure 6.16.
1 so
o
z
o
o
-------
Z
UJ
o
o
oc
HI
t-
0.40 -
0.35
0.30 -
0.25 -
0.20 -
0.15 ->
0.10 —
0.05 -
I
l
I
10 14
TIME (minutes)
18
Figure 6.16
Variation of moisture content with time at
several column elevations (Watson, 1966).
(5) Using the information in Figure 6.16 for the variations
of water content with time for several column
elevations, it is a straight foward matter to find the
relation between 9w/9t and z at several required times
through the use of the equation:
where
v
w
z
Ow/at) = -Ov/3z)t
flow velocity (cm sec"-'-)
volumetric water content (cm^ cm~l)
elevation above the datum plane defined
positive in the upward direction
as
The velocity profiles are obtained by integrating the
3w/9t profile curves graphically with respect to z.
Examples of the resulting velocity profiles are shown in
Figure 6.17 for times of 1, 3, 5, 10, and 20 minutes.
Such profiles represent the instantaneous velocities
down the column at the times stated.
94
-------
E
o
LU
<
s
Q
Ul
>
O
to
I
57
55 —
50 -
45 —
40 —
35 -
30 -
25 -
o
o
d
i
CM
o
p
o
I
co
o
o
6
i
o
p
6
I
in
o
o
d
i
-------
40 —'
35
0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8
POTENTIAL GRADIENT
Figure 6.19 Instantaneous potential gradient profiles. (Watson,
1966).
(8) The instantaneous hydraulic conductivity for any
elevation and time can be determined from Figures 6.17
and 6.19 by dividing the velocity value at that point in
space/time by the corresponding potential gradient
value, with due note being taken of the signs. Then the
curve relating hydraulic conductivity can be plotted
versus the water content as shown in Figure 6.20.
INSTANTANEOUS HYDRAULIC CONDUCTIVITY
(cm/sec)
Figure 6.20
Water content-instantaneous hydraulic conductivity
relation showing the computed value (Watson, 1966).
Precision and accuracy— A comparison between measured and
computed water content and pressure head values, including ef-
fects of hysteresis, has been provided by Gillham et al. (1979)
for variations in the laboratory instantaneous profile method.
This is shown in Table 6-3.
96
-------
TABLE 6-3 COMPARISON OF MEASURED AND COMPUTED WATER CONTENT AND
PRESSURE HEAD VALUES (Gillham et al., 1979)
Average difference between measured
and computed results
Pressure head Water Content
Slow drainage-rewetl h(cm) (01
Hysteretic-nonuniform 0.72 6.5 x
Nonhysteretic-nonuniform 0.72 2.2 x 102
Hysteretic-uniform 1.80 1.7 x 102
Rapid drainage-rewet2
Hysteretic-nonuniform 1.00 1.2 x 102
^Calculated using data at t = 45, 68, 90, and 125 minutes
Calculated using data at t = 11, 22, 45, and 68 minutes
Limitations of test— (1) The time required to obtain data
for the calculation of the water content versus hydraulic
conductivity curve is a function of the pore size of the porous
material and will increase with decreasing pore size; (2) Small
sample size; and (3) Results are limited to tensiometer range of
measurement.
Status of the method— Main laboratory method for un-
saturated hydraulic conductivity in agricultural sciences.
Thermocouple Psychrometers—
General description— The thermocouple psychrometer techni-
que is a method very similar to the instantaneous profile method
except thermocouple psychrometers are used instead of
tensiometers. Psychrometers measure the relative humidity of the
pore air which can be translated into soil suction. In the
testing procedure a soil sample is compacted into a plastic tube
into wnich the calibrated psychrometers are positioned and
sealed. Flow is initiated and measurements recorded. A moisture
retention curve for the sample soil must also be determined.
Parameters measured— Unsaturated hydraulic conductivity (cm
sec"1) .
Method— (Hamilton et al., 1981).
Apparatus: The basic equipment involved is: (1) plastic
tube; (2) thermocouple psychrometers; (3) psychrometer
instrumentation which includes: (a) a microvolt meter, (b) a
strip-chart recorder, (c) a source of electric current for
cooling the measuring junction, and (d) a switchbox when
more than one psychrometer is used; (4) hypodermic syringes;
(5) controlled humidity and temperature vessel; and (6) a
water supply as shown in Figure 6.21.
97
-------
To psychrometer switching/instrumentation
Water
supply
^222222222.
^2222222^
Thermocouple
psychrometer
Controlled atmosphere
vessel
To psychrometer switching/instrumentation
Figure 6.21 Cross-section of thermocouple psychrometer perme-
ameter.
Procedure:
(1) The sample soil is sieved through a No. 40 sieve and
then water is added to obtain a gravimetric water con-
tent of 5.0%.
(2) Samples are then compacted into a plastic tube with an
inside diameter of 50 mm and length of 114 mm at a
density of 107 pcf.
(3) Psychrometers are inserted and sealed in seven ports
along the tube that are spread at a distance of 13 mm.
(4) The ends are closed using plastic end plates with 0-ring
seals.
98
-------
(5) The outflow end is provided with a hypodermic needle to
act as an air vent and a sheet of filter paper to help
maintain a uniform head.
(6) The inflow end is provided with a 5 cc capacity
hypodermic syringe for inflowing water and several discs
of filter paper are used to help distribute the flow
across the entrance face. The plunger of the syringe is
pushed at a controlled rate using a standard mechanical
loading press (sprew jack driven by electric motor
through a variable speed gear box).
(7) The entire cell is then placed into a vessel of high
humidity and controlled temperature.
(8) Flow is then initiated (typical rates of 0.7 cc/day)
with psychrometer readings taken every 24 hours.
(9) Flow is continued until the suction at the inflow has
decreased to about 4 atmospheres, and the leading edge
of the wetting front has at least reached the farthest
psychrometer.
(10) Inflow is then stopped and the psychrometers are removed
with a water content sample taken from the soil around
each psychrometer hole.
(11) The sample is then extruded and cut into discs to obtain
another measurement of water content.
(12) Such values of volumetric water content (Q) are
evaluated from the suction measurements and from the
moisture retention curve (water content versus suction),
which are either measured on a duplicate sample or are
obtained from measurements of water content taken at the
beginning and end of a test and matched to the measured
suctions.
(13) Then plots of suction versus horizontal position are
prepared with values of the hydraulic conductivity
gradient (dp/dx) computed for each probe and each time
where p is defined as the negative of the pore water
pressure.
(14) Volumetric water content is then plotted versus
horizontal position with the total volume of water
downstream of each point determined for each time by
integration:
V.., = I0A dx
99
-------
where
Vw = total volume of water downstream of each point
9 = volumetric water content
A = total cross-sectional area of sample
x = position coordinate
(15) Then the rate of flow past a point (dvw/dt) is computed
for each probe location and each time.
(16) Hydraulic conductivity is computed from the equation:
K = Jk dVw/dt
A dp/dx
where k = hydraulic conductivity
Vw = unit weight of water
A = total cross-sectional area of sample
dvw/dt = rate of flow past each point
dp/dx = hydraulic gradient
(17) From calculations of hydaulic conductivity, plots may be
developed of K versus suction, water content, or degree
of saturation.
Precision and accuracy-- The precision and accuracy of this
method hinges on obtaining an accurate water content-versus-
suction relationship and accuracy of suction measurements during
the hydraulic conductivity test. The accuracy of the moisture
curve is variable due to the hysteresis phenomena which makes the
wetting (absorption) moisture retention curve different than the
drying (desorption) moisture retention curve. The accuracy of
suction measurements by psychrometers for the range of 1 to 75
atmospheres has been suggested by Daniel (197$)) to be between 5
and 30% provided there are no extreme fluctuations in tempera-
ture, corrosion problems, or any gross blunders during calibra-
tion of the psychrometers or during the actual test procedure.
Limitations of test— (1) Small sample may be unrepresenta-
tive of field conditions; (2) Applicable to suctions between 1
and 80 atmospheres which translates to clays with degrees of
saturation between approximately 30 and 90 percent, and sands
with degrees of saturation less than 50 percent (Daniel et al.,
1981) (3) Susceptibility of psychrometer corrosion in acidic
soils; (4) Cannot be used to measure unsaturated hydraulic con-
ductivity near saturation (less than 1 atm); (5) Requires roughly
three weeks per test not including calibration of the
psychrometers or determination of the moisture retention curve.
Status of the method— The thermocouple psychrometer method
for measurement of unsaturated hydraulic conductivity is a
100
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recently developed testing procedure that is meant to be applied
to compacted, relatively dry arid soils where suctions exist that
cannot be measured by tensiometers or pressure plate apparati.
6.2.2 Field Tests
Crust Test—
general description— The crust technique is a field adapta-
tion of the laboratory procedure for flow through an impeding
layer. The crust test can be used to determine both saturated
and unsaturated conductivity.
The crust test method requires carving out a cylindrical
pedestal of soil, whose upper surface is at the depth where the
hydraulic conductivity rate is desired. A ring infiltrometer of
the same diameter as the pedestal is firmly affixed to the top of
the pedestal so that the soil's horizontal surface is enclosed by
the ring. A paste consisting of gypsum and sand, mixed with a
small amount ot water, is spread over the entire horizontal
surface and is allowed to harden, forming a crust. When water is
introduced through the infiltrometer and maintained at a constant
head, flow into the soil is restricted by the crust. A constant,
steady state flow rate is established, inducing a nearly uniform
moisture potential (measured by tensiometers) and the steady
state flow rate (measured at the infiltrometer with a burette)
defines a plot of infiltration versus soil moisture tension (the
K(h) curve). Crusts of different resistances yield different
points on the K(h) curve. A series of crusts ranging from
greater to lower resistance assures that the data points fall on
the wetting curve.
The technique can be extended to include measurement of
saturated hydraulic conductivity which requires the addition of a
barrier to flow around the sides of the soil pedestal. This is
usually done with the soil pedestal thoroughly wetted and with a
slurry of dental grade plaster applied to the sides. No crust is
applied to the surface in this case.
Parameters measured— Saturated and unsaturated hydraulic
conductivity (cm sec~l).
Method— (SSWMP, 1978) .
Apparatus: The basic equipment required and the
experimental set-up for the crust test are shown in Figure
6.22. The items required are: (1) Ring infiltrometer (24
cm diameter); (2) Tensiometers; (3) Constant water supply;
and (4) Crust made from gypsum, sand and water.
101
-------
Manometer
-Water supply system
Figure 6.22
Schematic of
1978) .
the crust test apparatus. (SSWMP,
Procedure:
(1) A hole is
interest.
dug to a level just above the horizon of
(2) A free-standing soil pedestal is carved down several
centimeters to facilitate placement of the ring
infiltrometer on the pedestal. It should be noted that,
at first, the pedestal is made four or five centimeters
larger than the ring.
(3) The infiltrometer is then placed on the top of the
pedestal and carefully pushed into the soil with excess
soil around the outside of the ring cut away with a
knife. The ring is pushed down until about 1.5 cm of
side wall remains above the soil.
102
-------
(4) The soil pedestal must be carved to a height of at least
one ring diameter. With a 24 cm ring, a height of 30 cm
is recommended.
(5) After the pedestal is formed, it is wrapped with
aluminum foil to reduce evaporation from sidewalls.
(6) A horizontal hole is augered into the side of the
pedestal at a depth of 2-5 cm under the infiltrative
surface in the middle of the pedestal. The diameter of
the hole should be slightly less than the diameter of
the porous cup to assure a tight fit. After the
tensiometer cup is in place, the hole should be sealed
with mud or glue to prevent evaporation.
(7) The free end of the tensiometer runs through a manometer
board to a mercury reservior. A graduated scale is used
to read potential as centimeters of water when mercury
rises on this scale. The difference in elevation
between the porous cup and the surface of the mercury in
the reservior is referred to as the correction factor or
CF, which can be determined in the field with two meter
sticks and a level. It is subtracted from the total
tension to yield matric soil tension.
(8) Once in place, the tensiometer is filled with de-aired
water using a 50-ml syringe with a 22-gauge needle.
(9) With the pedestal instrumented, a crust is made from the
appropriate proportions of sand, gypsum, and water. A
higher sand content in the mixture will produce a crust
of less resistance and higher rates of flow. Generally,
the first crust to be used will be the most resistant.
(10) After the crust has hardened, the gasket and cover plate
of the ring infiltrometer are bolted into place so that
the air escape position is at the highest elevation
possible. The water supply system is activated and
allowed to fill the chamber and, when all air is purged,
the Mariotte tube and stopper are placed into the
burette to reduce the hydraulic head, and the air
escape port is capped. When air bubbles begin to rise
from the tip of the Mariotte tube, the first volume
measurement can begin.
(11) Volume measurements are recorded periodically until
equilibrium is reached. Tension measurements are
recorded simultaneously. The hydrauliuc conductivity at
that tension is equal to the constant inflow rate.
(12) After equilibrium has been reached, the first crust is
removed and replaced by a less resistant one and steps
103
-------
10 and 11 are repeated. Each succeeding crust yields a
point on the K curve. The results for the &22^ horizon
of the Batavia silt loam are shown"in Figure 6.23.
0)
•o
-*
o
l-
O
Q
Z
O
o
o
-------
Limitations of, test— (1) Large time requirement is
necessary to achieve steady state flow under crusts of high
resistance; (2) It is difficult to assure that good contact
between ring and pedestal is made; and (3) Results limited to
range of tensiometer measurement.
Status of the method-- The method was first developed around
1970 (Hillel & Gardner, 1970). Since that time a great deal of
research effort has been conducted by the Small Scale Waste
Management Project at the University of Wisconsin (SSWMP, 1978)
under the sponsership of EPA.
Instantaneous Profile—
General description— The traditional instantaneous profile
technique in situ is a method where a nearly level plot of soil
is diked to pond 2-3 cm of water. After addition of water the
plot is covered to prevent evaporation, and drainage occurs. At
frequent intervals both pressure head and water content values
are measured. From these measurements, instantaneous values of
the pressure gradients and fluxes can be determined, which will
also provide hydraulic conductivity values.
As with the laboratory instantaneous profile method, there
have been various applications by several authors. These
citations are listed in Table 6-4.
TABLE 6-4
LIST OF LITERATURE CITATIONS FOR FIELD INSTANTANEOUS
PROFILE METHOD
Richards et al., 1957
Ogata and Richards, 1957
Nielson et al., 1962
Rose et al., 1965
Rose and Krishnam, 1967
Van Bavel et al., 1968
Davidson etal., 1969
Renger et al., 1970
Hillel et al., 1972
Roulier et al., 1972
Nielson et al., 1973
Baker et al., 1974
Cheng et al., 1975
Nagpal and DeVries, 1976
Carvallo et al., 1976
SSWMP, 1978
Simmons et al., 1979
Dane, 1980
Libardi et al., 1980
sec
Parameters measured—
~; diff usivity (cm 2
Unsaturated hydraulic conductivity (cm
105
-------
Method— Traditional instantaneous profile (SSWMP, 1978).
Apparatus:: Equipment required consists of a neutron probe
to measure water content and tensiometers to measure pres-
sure head. A diagram of this set-up is shown in Figure
6.24.
Neutron probe
^
Tensiometers
Dike (to pond water)
12 cm
Figure 6.24
Field set-up for instantaneous profile method
(SSWMP, 1978).
Procedure:
(1) Once the plot has been prepared and the instruments are
in place, the plot should be wetted a day or two be;fore
the start of actual measurements.
(2) Water is then ponded on the surface until the tensio-
meters remain constant.
(3) As soon as the water is no longer visible on the sur-
face, the plot is covered by plastic, and the first
measurements are taken at time = zero.
(4) As the internal drainage process proceeds, periodic
measurements are made of water content and hydraulic
head throughout the profile. These readings must be
taken frequently (every hour or two) but can be taken at
greater time intervals (daily) as the internal drainage
process slows down.
106
-------
(5) Plot volumetric moisture content variation with time at
each depth from neutron-meter data.
(6) Prepare a table with the following headings:
t Z d0 dZdfl =Yd2d0
dt dt M Z, dt
(days) (cm) (days~l) (cm day~l) (cm day~l)
It should be noted that d#/dt are the slopes at particu-
lar points of time from the graph of step 5.
(7) Plot matric suction variation with time for each depth
from tensiometric data.
(8) Prepare a table with the following headings:
Z q da K 9
dZ
(cm) (cm/day) (cm/cm) (cm/day) (%)
K is calculated by dividing q by dH/dZ for each time.
It should be noted that dH/dZ are the slopes for parti-
cular depths in the graph of step 7.
(9) Plot hydraulic conductivity against volumetric moisture
content and draw best-fit curves for the different
layers by use of semi-log paper (i.e., log K versus 9).
(10) Evaluate whether the entire profile can be characterized
by a single curve or whether each depth has a separate
K(0) curve.
Method II — Unit gradient-drainage.
In a uniformly draining soil profile, the hydraulic gradient
is often unity, and the water content is a function of time and
nearly independent of depth. This relation can be expressed as:
D = Ldh
dt
where D = diffusivity (cm^ sec~-M
L = length (cm)
h = average hydraulic head (cm)
This method differs from the traditional instantaneous pro-
file method in that instead of measuring both water content and
pressure head in the field, only pressure head is measured in the
field, and water content from laboratory-determined water reten-
107
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tion curves is used to calculate hydraulic conductivity from the
equation K = Dd#/dt. Description of the unit, gradient-drainage
has been reported by: Black et al., 1969; Davidson et al., 1969;
Gardner, 1970; Klute, 1972; Nielson et al., 1973; and Simmons et
al., 1979.
Method III— Libardi method (Libardi et ai., 1980).
The Libardi method is a recent attempt to simplify the field
determination of hydraulic conductivity by means of a modified
instantaneous profile method. Similar to the unit-gradient
drainage method, it measures only one parameter rather than both
water content and pressure head. However, unlike the unit-
gradient drainage method, the other parameter is not measured in
the laboratory. In fact, in the Libardi method, only the neutron
probe device is used for water content measurement, and hydraulic
conductivity is determined without any further information.
Precision and accuracy— Dane (1980) compared the Libardi
method to the traditional instantaneous profile method and found
good agreement subject to a modification of the Libardi method at
higher values of water content. The results are shown in Figure
6.25.
o
o
0.50
0.00
-0.50
-1.00
-1.50
-2.00
-2.50
-3.00
-3.50
-4.00
Modified Libardi Method
Instantaneous Profile Method
q
o
CO
o
to
-------
Precision is only fair to good on fine-textured soils where
water movement is slower. The instantaneous profile method is
probably one of the most accurate methods because of large sample
size.
Limitations of test— (1) Values of matric suction measured
are limited to tensiometer range of less than about 0.9 atm
(Olson and Daniel, 1981); (2) Field plot must be level; (3) It is
not applicable to cases where lateral flow is appreciable (Hillel
et al.f 1972); (4) Plots (3 m x 3 m) may not be large enough to
assure one-dimensional vertical flow at the center of plot if
surrounding area is vegetated and strongly evapotranspiring
(Baker et al.f 1974); and (5) May take weeks to perform test on
soils with low hydraulic conductivities or restricting layers.
Status of the method— Has been regularly used in the agri-
cultural sciences as it is the most accurate method for predic-
tion of field behavior. Several variations of the method exist,
including more recent attempts to streamline the procedure and
time requirements.
6.2.3 Calculation Methods
Because of various difficulties involved in the direct
measurement of the hydraulic conductivity function, there has
been considerable interest in the potential of calculating the
conductivity from other properties of the medium that may be
easier to measure such as pore size distribution or the water
retention curve. The basic concepts are given by Childs and
Collis-George (1950), Marshall (1958), and Millington-Quirk
(1960, 1961, 1964). Because there is quite a variety in the
approaches, brief summaries are provided for a number of research
efforts.
Nielson et al. (1960) compared the conductivity calculated
by the Childs Collis-George and Marshall methods with measured
conductivity values on four soils in the pressure-head range 0 to
-100 cm of water. The Childs Collis-George method gave the best
results, in part due to the matching factor used, while the
Marshall method gave results that were too high.
Jackson et al. (1965) used a matching factor with the
Millington and Quirk method, calculating conductivity from both
the drying and wetting curves to examine the effect of
hysteresis. Results showed that hydraulic conductivity relations
for both curves were similar.
Laliberte and Corey (1967) presented an equation for calcu-
lating the hydraulic conductivity of unsaturated materials which
utilized an empirical functional relationship between relative
hydraulic conductivity, K, and the capillary pressure, P.
109
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Kunze et al. (1968) also used a matching factor with a
modified Millington and Quirk method.
Brust et al. (1968) used the Millington-Quirk method with a
matching factor, and the Laliberte-Brooks-Corey method to calcu-
late the hydraulic conductivity water content function for
several horizons of a clay loam soil with laboratory determined
water retention curves. The calculated hydraulic conductivity
relations obtained by the Millington-Quirk and Laliberte-Brooks-
Corey methods were compared to field conductivity by the instan-
taneous profile method.
Green and Corey (1971) developed a computational method
based on the pore-interaction model of Marshall which seemed to
offer no particular advantage over either the Marshall equation
with matching factor or the Millington-Quirk equation with
matching factor. From their results, they concluded that such
methods appeared sufficiently reliable for field applications.
Bruce (1972) compared the hydraulic conductivity from labor-
atory outflow data to procedures for calculating hydraulic con-
ductivity from Childs Collis-George (1950), Marshall (1958),
Millington-Quirk (1961), and Laliberte et al. (1966). He con-
cluded that all methods for describing the transport system can
be used with discrimination to calculate the hydraulic con-
ductivity of many soil materials with adequate accuracy.
Roulier et al. (1972) compared field-measured hydraulic
conductivity by the instantaneous profile method to three
different laboratory methods: (1) conductivity by the laboratory
instantaneous profile method, (2) calculated hydraulic conduc-
tivity by the Marshall equation from laboratory moisture curves
on intact core.3 and from field data, and (3) calculated conduc-
tivity by the: Millington-Qui rk method from laboratory and field
moisture curves. They concluded that the laboratory instan-
taneous profile method, the Marshall equation method, and the
Millington-Quirk method were qualitatively similar because all
methods require the use of a matching factor to simulate field
hydraulic conductivity. However, without such matching factors,
the laboratory or calculated hydraulic conductivity was found to
range from 2 to 20 times the hydraulic conductivity determined in
the field. They also recommended that the hydraulic conductivity
value used to calculate the matching factor for these three
methods be measured in the field within the soil-water content
range under question.
One of the many objectives of Nielson et al. (1973) was to
evaluate the suitability of various soil-water equations for
predicting hydraulic conductivity under field conditions. Using
the calculation techniques of Childs and Collis-George (1950),
Marshall and Millington-Quirk (1960, 1961, 1964), and Kunze et
al. (1968), they concluded that the accuracy of the calculated
110
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hydraulic conductivity was strongly related to the accuracy of
the matching factor.
Campbell (1974) proposed a modified Childs and Collis-George
method which was compared to measured hydraulic conductivity as
well as to coventionally-calculated hydraulic conductivity by the
Millington-Quirk method. Agreement between the three methods was
good for the Botany sand, the Guelph loam, and the Ap horizon of
the Cecil sandy loam. Agreement was not good for the 62 and 63
horizons of the Cecil sandy loam.
Carvallo et al. (1976) compared the measured hydraulic con-
ductivity from the unit-gradient drainage field method to the
calculated hydraulic conductivity by a modified Green and Corey
method. They concluded that agreement of the calculated K values
and in situ K values was best when the matching factor was
selected at the lowest water content for which in situ K was
measured.
Simmons et al. (1979), in a broad study of spatial
variability of field-measured soil-water properties, included the
calculation of hydraulic conductivity by the Millington-Quirk
method. They concluded that the error in the Millington-Quirk
method of estimating hydraulic conductivity on the sample soil
was dependent on the matching factor KS/KSC (where Ks = actual
hydraulic conductivity at saturation, and Ksc = calculated hy-
draulic conductivity at saturation), and the errors in two
scaling factors, Km and a.
Libardi et al. (1980) proposed two new methods of estimating
hydraulic conductivity that are called the Water Content Method
and the Flux Method, which are compared to a third method
developed by Chong et al. (1979), and measured K values. Their
results suggest that all three methods provide comparable esti-
mates of hydraulic conductivity and can be applicable to situa-
tions where soil horizons do not differ dramatically in hydraulic
conductivity. They also believe that a better characterization
of hydraulic conductivity can be achieved by using simple methods
at a greater number of sites than more rigorous methods at just a
few sites.
Dane (1980) compared four methods for determining hydraulic
conductivity: (1) traditional field determination by the instan-
taneous profile method, (2) the Van Genuchten (1979) analytical
model using laboratory water retention curves, (3) the Van
Genuchten analytical model using field-dervied water retention
curves, and (4) a modified field instantaneous profile method for
fine-textured soils developed by Libardi et al. (1980). The
results of this analysis showed good agreement among all four
methods.
Ill
-------
Integration of this information illuminates several points:
(1) Most of the soils used in these experiments have been
coarse-textured with relatively high hydraulic conductivities
(usually 10~4 Cm sec~l or greater); (2) Roulier et al. (1972),
Carvallo et al. (1976), and Simmons et al. (1979) support the
recommendation that the K selected in determining the matching
factor should be measured in the field (rather than the labora-
tory) within the suction range being studied, (3) Recent work of
Dane (1980) and Libardi (1980) show great potential for providing
simplified methods for hydraulic conductivity determination, and
(4) Calculations of unsaturated hydraulic conductivity can be
used to estimate saturated hydraulic conductivity. In fact,
matching factors of K actual/K calculated are most often
determined at or near saturation.
6.2.4 Diffusivity
Pressure Outflow—
general description— In the pressure outflow method, the
time dependence of the outflow of water from a soil core on a
porous plate or membrane in a pressure cell is used to determine
the soil-water diffusivity (D).
Hydraulic equilibrium is first established in a layer of
soil (usually 1-5 cm in depth), with the gas phase pressure in
the cell at a given level. Beginning at or near saturation, step
increases of gas pressure are applied to produce an outflow of
water, and the volume of outflow as a function of time is mea-
sured. Paired values of diffusivity and water content are ob-
tained from each pressure increment and thus the drainage func-
tion, D(#), can be plotted. Because the total volume of outflow
and the pressure head increment corresponding to each gas phase
pressure increment are known, the water capacity (C) can be
obtained and used to calculate hydraulic conductivity from the
relationship:
K = DC
where K = unsaturated hydraulic conductivity (cm sec-1)
D = diffusivity (cm^ sec~l)
C = water capacity (cm~l).
Parameters measured— Diffusivity (cm^ sec"l).
Method— (Klute, 1965c) .
Apparatus: The essential components of this laboratory set-
up are shown in Figure 6.26. The components are: (1)
pressure chamber with a porous plate or membrane; (2) an
112
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outflow-volume-measurement system; (3) a system for control
of the gas-phase pressure in the chamber; (4) a system for
removal of gas bubbles from beneath the porous plate or
membrane; and (5) a timing device.
To suction or pressure as
needed for flushing operation
From gas pressure source Clamp
m
Permeameter
— Burettes
for flushing and
storage of water
Reservoir-
Reference mark
I
Horizontal capillary
tube and scale
Grooved porous plate
Figure 6.26 Diagram of apparatus for the outflow method of soil
water diffusivity determination (Klute, 1965c).
Procedure:
(1) Saturate the porous plate by wetting it under vacuum or
soaking it for a long time in de-aired water.
(2) Assemble the lower end-cap and the set-up for measuring
the volume of outflow. Remove all air bubbles from the
ouflow system.
(3) Place the sample upon the porous plate, and assemble the
cell. Saturate the sample by soaking it in water.
(4) After saturation, close the cell and apply the lowest
gas-phase pressure desired. When outflow equilibrium
113
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has been reached, carry out the flushing operation to
remove any air from beneath the plate and check again
for equilibrium. Equilibrium is indicated when the
meniscus in the horizontal tube does not move.
(5) Adjust the position of the meniscus in the horizontal
tube to the starting mark. Record the burette readings.
(6) Close the clamp on the air pressure line and raise the
pressure in the line by the desired amount. Record the
initial and final pressures.
(7) Simultaneously, open the clamp on the pressure line and
start the timing device. Record the position of the
meniscus as a function of time. Take frequent readings
in the beginning of outflow and fewer toward the end.
(8) Continue to record the outflow until equilibrium is
attained. Make the necessary measurements to obtain the
total volume of water Q(oo) removed from the sample as a
result of the increase in pressure. Flush any gas from
beneath the plate before the final volume readings are
taken,
(9) Repeat steps 4-8 at as many levels of gas pressure as
are desired. The number of steps will be determined by
the range of soil water content to be covered, by the
amount of time available for the measurements, and by
the desired delineation of the diffusivity function.
(10) Determine by gravimetric means the water content of the
entire sample after the last equilibrium has been
attained.
(11) Construct a plot of the quanitities log (1-Q (t) /Q (CD) )
versus log (Dt/4L,2) from the following equation:
xv^ I _ _ I
1 - Q(t) =
Q(oo)
m=0
where
Q(t) = volume of outflow at time t
Q(oo) = total volume of outflow from applied pressure
increment
m = initial cell pressure
The plot will be referred to as the overlay or theoretical
curve. The data for the construction of the overlay is presented
in Table 6-5.
114
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TABLE 6-5 REDUCED DIFFUSIVITY Dt/L2 VERSUS l-Q(t)/Q(oo)
FOR CONSTRUCTION OF THE OVERLAY (Klute, 1965c)
l-0m/0(oo) Dt/L^. l-0(t)/0(oo)
0.000 1,0000 0.040 0.7743
0.001 0.9643 0.070 0.7014
0.002 0.9495 0.100 0.6433
0.004 0.9286 0.200 0.4959
0.007 0.9056 0.400 0.3022
0.010 0.8872 0.700 0.1390
0.020 0.8404 1.000 0.0690
1.4185 0.0245
(12) From the experimentally determined volume-outflow data,
calculate the quantity l-Q(t)/Q(oo). If it was possible
to hold all the outflow due to a given pressure incre-
ment in the horizontal tube, use the scale readings for
the position of the meniscus to calculate the outflow
ratio. Absolute values of volume are not needed because
the units of quantity cancel. (However, it will be
necessary to use the cross-sectional areas of the tube
when calculations of the water content of the sample are
to be made.)
(13) On another sheet of the same lot of log/log graph paper
used for the overlay, construct a plot of log 1-
Q(t)/Q(oo) versus log t, using the experimental data.
(14) Place the theoretical curve over the experimental curve,
match the log l-Q(t)/Q(oo) scales, and, by translation
along the log (Dt/4L^) axis only, bring the theoretical
and experimental curves into coincidence.
(15) Select any convenient value of Dt/4L2 from the overlay
and read the corresponding value of t from the experi-
mental curve. If the chosen value of Dt/4L2 is
represented as w, then the diffusivity is given D =
w4L2/t where t is the experimental value of time corres-
ponding to the chosen value of w.
(16) The water content - pressure head curve can be calcu-
lated from the final water content of the sample and
from the outflow volumes corresponding to each pressure
increment. If the volume of the sample is V, the speci-
fic water capacity C is given by C = Q(oo)/vAh.
(17) The hydraulic conductivity is calculated by K = DC.
Precision and accuracy— Many authors, including Olson and
Daniel (1981), have criticisms relating to the assumption that a
value of the hydraulic conductivity is constant over the small
115
-------
increments of gas pressure and conclude that the difficulty in
the interpretation of the data and lack of replicated results
present serious application difficulties. -On the other hand,
Klute (1972) maintains that a number of investigators have ob-
tained hydraulic conductivity values, at least to within half an
order of magnitude.
Limitations of test— (1) As mentioned above, there remain
both experimental and theoretical difficulties in the method
affecting accuracy and precision of results. (2) Again, the
limitations of laboratory tests for predicting field conditions
are often particularly applicable to this method where soil core
length is usually 1-5 cm (more often nearer the 1 cm end). (3)
The test has many variations beyond the short column-small incre-
ment method described. Either disturbed or undisturbed cores have
been used. Inflow rather than outflow has been measured; suction
has been applied to the bottom rather than pressure to the top;
one large pressure increment rather than several small ones has
been used; as have tests for pressures under 1 atmosphere com-
pared to tests for pressures from 1-15 atmospheres.
Status of method— This method has been widely used in the
agricultural sciences for difficulties associated with soil-water
problems other than hydraulic conductivity. A pressure membrane
apparatus for pressures betwe'en 1 and 15 atmospheres has been
accepted by the American Society of Testing Materials as Standard
D 3152-72.
Hot Air Method—
General description— In this quick method, an undisturbed
small column of soil in a cylinder (diameter 5 cm, height 10 cm)
is saturated with water by capillary action. Then hot air (130-
250 degrees C) is blown towards the exposed upper surface of the
otherwise entirely closed core. This happens while the cylinder
is standing on a balance, which allows very frequent measurements
of total weight. For validity of the mathematical assumptions
used in the calculations, the loss of weight must be proportional
to the square root of time as well as the lower part of the core
should remain at the original water content. As soon as the hot
air is turned off, the core is gently pushed from the cylinder
and is cut in small, 2-5 cm thick sections from which the gravi-
metric moisture content is determined. A graph of water content
versus depth is used in calculating diffusivity.
Parameters measured— Diffusivity (cin2 sec~l)
116
-------
Method— (Arya et al., 1975).
Apparatus: The only equipment required for this method are:
(1) hot air gun, (2) brass cylinders 10 cm high and 5 cm in
diameter, and (3) a balance.
Procedure:
(1) Field soils are sampled by pushing brass cylinders ver-
tically into the soil, which are then excavated and
carefully trimmed at both ends.
(2) Samples are then placed on porous ceramic discs in the
laboratory in contact with free water to allow satura-
tion by capillary action.
(3) Samples are then sealed at both ends and positioned
horizontally to equilibrate for several days.
(4) Then the core is opened on one end and placed on a
balance. Hot air is then blown on the open wet surface
for 10 - 25 minutes to achieve maximum evaporation.
(5) Water loss due to evaporation is determined by subse-
quent weighing of the soil core during the procedure.
Such loss in weight as a function of time serves as a
check of one condition presupposed by the method, which
says that a cumulative evaporation must be proportional
to the square root of time.
(6) At the conclusion of each test the bottom seal of the
core is broken and the soil is pushed out of the brass
cylinder with a suitably designed piston.
(7) Within minutes the core is sliced into several (12 - 15)
2-5 mm lengths which are weighed and oven dried to
determine the gravimetric water content distribution and
the average bulk density. The water contents of the
lower segments proved if a second condition is met, i.
e., that the original water content of the soil column
was maintained unchanged at the closed end during the
evaporation procedure.
(8) Next, the volume of each sample is estimated by dividing
its dry weight by the mean bulk density of the soil
core. Sample length is obtained by dividing the sample
volume by the internal cross-sectional area of the brass
cylinder
(9) With this information the following graph can be
developed:
117
-------
4>
z
LU
t-
z
o
oc e
lil o
3
O
cc
t-
LU
5
s
o
DISTANCE FROM EVAPORATING SURFACE. X (cm)
Figure 6.27
Graph of volumetric water content versus distance
from evaptorating surface.
(10) From such a smoothed water content distribution curve,
diffusivity can be calculated according to the equation
(Bruce and Klute, 3956):
D(0X) =
2t
(dx/d0)
/
xd0
where
D(0
t
x
the diffusivity as a function of the
volumetric water content, 0 , in cm^ sec"-'-
time, in seconds
the distance from the evaporating surface,
in cm
the initial water content, in cm^/cm^
Boundary conditions are:
0= Si x > 0
0= #o x = 0
t = 0
t > 0
where 0O is the air dry water content.
Precision and accuracy-- The precision of this method is
only fair because of the dependence on the slope of the graph,
the determination of gravimetric moisture contents, and small
sample size. The accuracy is good for strictly matrix flow, but
only fair overall because of small sample size.
118
-------
Limitations of test— (1) Small sample size can be unrepre-
sentative of field conditions; (2) Requires moisture retention
curve to calculate unsaturated hydraulic ocnductivity; (3) Method
is not very reliable near saturation due to difficulties in
determining slopes of d0/dx lines in the lower part of the core;
and (4) The method seems to be limited to soils and soil struc-
tures with relatively low conductivities in the low tension
range.
Status of the method— Relatively new test but its use is
increasing due to the fact that the method is simple, rapid, and
inexpensive.
119
-------
This page intentionally left blank so that Table 7-1 (pages 122
and 123) and Table 7-2 (pages 124 and 125) will occupy facing
pages.
120
-------
SECTION 7
SUMMARY
The conclusions that can be drawn from this study are: (1) The
area of soil testing for hydraulic conductivity overlaps the
professions of geology, hydrology, soil engineering, and soil
science as all these disciplines have made attempts to measure
the rate of liquid movement thru soil materials; (2) A high
percentage of the testing methods for hydraulic conductivity
determination have been developed for agricultural or engineering
purposes other than the application to the feasibility and/or
design of hazardous waste disposal sites; (3) All laboratory
methods suffer from potential misrepresentation of actual field
conditions due to small size of samples and/or disruption of
samples when transported or remixed; (4) Experience with field
testing techniques has generally been limited to more coarse-
textured soils rather than fine-grained soils that are more
appropriate for hazardous waste disposal sites; (5) It is not
possible at this time to discern the degree of variation in soil
testing results caused by the variation inherent in the soil
testing method compared to the variation of the spatial proper-
ties of the soil itself; and (6) Determination of soil hydraulic
conductivity values is the limiting factor to further development
of an applicable saturated - unsaturated transport model for
prediction or estimation of behavior of a proposed hazardous
waste disposal site.
Important considerations and limitations of laboratory and field
testing methods are summarized in the Soil Testing Methods Matrix
which are shown in Tables 7.1 and 7.2. Table 7.1 summarizes
information for laboratory and field methods for the determina-
tion of saturated hydraulic conductivity while Table 7.2 is
directed at unsaturated hydraulic conductivity methods, calcula-
tion methods, and diffusivity methods.
121
-------
TABLE 7-1 SOIL TESTING METHODS MATRIX/SATURATED HYDRAULIC
CONDUCTIVITY
METHOD
APPLICATION
PRECISION AND ACCURACY
O
*<
to
t_
O
a
(0
o
ui
H
PRESSURE CELL
Land treatment
Fair-many samples necessary
to obtain 95% confidence
limits
COMPACTION MOLDS
Liner evaluation
Not available (new metiod)
CONSOLIDATION CELL
Liner evaluation
Fair-direct measurement of
consolidated sample is much
more precise than K computed
from consolidation and
compression data
MODIFIED TRIAXIAL
APPARATUS
Liner evaluation
Good-reproducible results
PIEZOMETERS
Land treatment
Fair-measure average of
vertical and horizontal
components of K in all
soil layers below water
table
x>
w
il
o
ui
cc
3
(0
DOUBLE RING
INFILTROMETER
/PERMEAMETER
Land treatment
Good-reproducible results
AIR-ENTRY
PERMEAMETER
Land treatment
Good-reproducible results
that compare favorably
other methods
CUBE
Land treatment
Good-large size of sample
more representative of in
situ conditions, can
measure vertical and
horizontal K separately
CRUST
Land treatment
Good-large sample size
and reproducible results,
can measure both saturated
and unsaturated K
122
-------
LIMITATIONS OF TEST
(1) Small sample may be unrepresentative
of actual field conditions, (2) several
days required for fine-textured soils,
and (3) saturation of sample not assured
(1) Small sample, (2) excessive gradients
may cause sidewall flow, (3) interaction
between metal cell and waste, (4) satur-
ation of sample not assured, and (5)
test will take 1-5 months
(1) Small sample, (2) falling head pro-
cedure may require many days to perform
test, and (3) saturation of sample not
assured
(1) Small sample, and (2) recommended
hydraulic gradients in range of 5-20
(1) Errors due to smear zones, (2) re-
quires presence of water table, and (3)
measures both vertical and horizontal
hydraulic conductivity
(1) Care must be taken during placement
of rings into soil, (2) air trapped be-
low wetting front will effect results,
(3) a few days required for fine-tex-
tured soils, and (4) if uncovered,
correction for evaporation should be
made
(1) Care must be taken during placement
of cylinder into soil, (2) will not
work well on initially wet soils, and
(3) difficult on soils with gravel or
stones
(1) Method will require a few days for
clay soils, (2) sample saturation can-
not be assured, and (3) swelling of
sample may effect measurement
(1) Difficult to assure good contact
between soil pedestal and ring
METHOD STATUS
Agricultural
standard
Experimental
Engineering
standard for
consolidation
data
Engineering
standard,
common for clay
soils with low
hydraulic
conductivity
Standard test
for areas with
shallow depths
to water table
ASTM standard,
also commonly
used in agri-
culture and
irrigation
Relatively new
method, use in-
creasing due to
ease of proce-
dure
Relatively new
method, use in-
creasing due to
ease of proce-
dure
Relatively new
method, devel-
oped in connec-
tion with EPA
sponsered
university
research
COMMENTS
Simple and inex-
pensive equip-
ment
Special equipment
developed for use
of particular
waste and
compacted soil
Slight modifica-
tion of common
engineering
laboratory
equipment
Major modification
of common engi-
neering laboratory
equipment
Many variations
in equipment and
and procedures
Simple and inex-
pensive equip-
ment, easy method
to perform
Moderately inex-
pensive equipment
Very inexpensive
equipment and
materials
Moderately inex-
pensive equipment,
easy to perform
for saturated K
123
-------
TABLE 7-2 SOIL TESTING METHODS MATRIX/UNSATURATED HYDRAULIC
CONDUCTIVITY
METHOD
APPLICATION
PRECISION AND ACCURACY
o
a
o
jQ
a
a
u
oc
3
0>
3
STEADY STATE
/ COLUMN
Unsaturated zone
Fair-variability de-
creases as length of
column increases
UNSTEADY STATE
/ INSTANTANEOUS
PROFILE
Unsaturated zone
Fair-many variations of
method, field method
more accurate
THERMOCOUPLE
PSYCHROMETERS
Un8aturated zone
Good-accuracy of, and range
of suction of psychrometers
makes method particularly
applicable to compacted
arid soils
9
\L
a
LLJ
tc
3
CRUST
Unsaturated zone
Good-large sample size
and reproducible results,
can measure both saturated
and unsaturated K
INSTANTANEOUS
PROFILE
Unsaturated zone
Good-probably the most
accurate field method
because of the large
sample size
W
=>Z0
o2§
-JI-K-
<< ui
0-15
VARIOUS
PROCEDURES
Unsaturated zone
Fair-calculated values
never as good as measured
values
PRESSURE OUTFLOW
Unsaturated zone
(0
U.
Fair-disagreement among
authors regarding precision
and accuracy
HOT AIR
Unsaturated zone
Fair-because of dependence
on the slope of the water
content curve and determina-
tion of water contents
gravimetrically
124
-------
LIMITATIONS OF TEST
(1) Method will require longer time for
clay soils, (2) small sample, (3) pro-
cedure yields K(h), not KW, (4) K
determined from desorption rather than
absorption data, and (5) suction lim-
ited to range of tensiometer measure-
ment
(1) Method will require longer time for
clay soils, (2) small sample, and (3)
results limited to range of tensiometer
measurement
(1) Small sample, (2) applicable to clays
with degrees of saturation between 30-
90%, and sands less than 50%, (3) psy-
chrometer corrosion in acid soils, and
(4) cannot measure K near saturation
(1) Several days required to achieve
steady state flow under crusts of high
resistance, (2) difficult to assure good
contact between soil pedestal and ring,
and (3) results limited to range of
tensiometer measurement
(1) Results limited to range of tensio-
meter measurement, (2) field plot must
be level, (3) not applicable in soils
with high lateral flow, and (4) plots
should be larger if surrounding area
is strongly evapotranspiring
(1) Limited to more coarse-textured soils,
(2) matching factors must be determined,
and (3) matching factors most often deter-
mined at or near saturation
(1) Small sample, and (2) many variations
of method using disturbed and undisturbed
samples, inflow rather than outflow mea&-
ured, or one large pressure increment used
instead of several small ones
(1) Small sample, (2) requires moisture
retention curve to calculate K, (3) not
very reliable near saturation, and (4)
limited to soils with relatively low
conductivities in the low tension range
1 METHOD STATUS
Agricultural
standard
Agricultural
standard
Experimental
Relatively
new method,
developed in
connection
with EPA
sponsored
university
research
Agricultural
standard
Experimental
Agricultural
and ASTM
standard
Relatively new
method, use in-
creasing due to
short time
period for test
COMMENTS
Inexpensive
equipment
Expensive and
potentially dan-
gerous equipment,
detailed procedure
Moderately expen-
sive equipment,
detailed proce-
dure
Moderately inex-
pensive equipment,
repetitive proce-
dure with crusts
of different
resistance
Moderately expen-
sive equipment,
easy procedure
once set up
Large variety of
methods
Moderately inex-
pensive equipment,
detailed procedure
Inexpensive equip-
ment, easy proce-
dure
125
-------
REFERENCES
Ahmed, S., C.W. Lovell Jr., and S. Diamond. 1974. Pore Sizes
and Strength ot Compacted Clay. Journal of the Geotechnical
Engineering Division, A.S.C.E. 100: 407-425.
Aldabagh, A.S.Y. and C.E. Beer. 1971. Field Measurement of
Hydraulic Conductivity Above a Water Table with an Air-Entry
Permeameter. Trans. Amer. Soc. Agric. Eng. 14: 29-31.
Anderson, J.L. and J. Bouma. 1973. Relationships Between Satur-
ated Hydraulic Conductivity and Morphometric Data of an Argillic
Horizon. Soil Sci. Soc. Amer. Proc. 37: 408-413.
Arya, L.M., D.A. Farrell, and G.R. Blake. 1975. A Field Study
of Soil Water Depletion Patterns in Presence of Growing Soybean
Roots: I. Determination of Hydraulic Properties of the Soil.
Soil Sci. Soc. Amer. Proc. 39: 424-430.
Asphalt Institute, The. 1969. Soils Manual for Design of As-
phalt Pavement Structures. The Asphalt Institute. Madison,
Wisonsin. 265 pp.
ASTM D 423-66. 1979. Standard Test Method for Liquid Limit of
Soils, ASTM Committee D-18, Annual Book of ASTM Standards, Part
19. Philadelphia, Pennsylvania. pp. 123-126.
ASTM D 424-59. 1979. Standard Test Method for Plastic Limit and
Plasticity Index ot Soils, ASTM Committee D-18, Annual Book of
ASTM Standards, Part 19. Philadelphia, Pennsylvania, pp. 127-
128.
ASTM D 427-61. 1979. Standard Test Method for Shrinkage Factors
of Soils, ASTM Committee D-18, Annual Book of ASTM Standards,
Part 19. Philadelphia, Pennsylvania. pp. 132-134.
ASTM D 698-78. 1979. Standard Test Method for Moisture-Density
Relations ot Soils and Soil Aggregate Mixtures Using 5.5 Ib.
(2.49 kg.) Rammer and 12 in. (305 mm.) Drop, ASTM Committee D-18,
Annual Book or ASTM Standards, Part 19. Philadelpnia,
Pennsylvania. pp. 201-207.
ASTM D 1556-64. 1979. Standard Test Method for Density of Soil
in Place by the Sand Cone Method, ASTM Committee D-18, Annual
Book or ASTM Standards, Part 19. Philadelphia, Pennsylvania.
pp. 266-269.
126
-------
ASTM D 1557-78. 1979. Standard Test Method for Moisture-Density
Relations of Soils Using a 10 Ib. (4.53 kg.) Rammer and 18 in.
(457 mm.) Drop, ASTM Committee D-18, Annual Book of ASTM
Standards, Part 19. Philadelphia, Pennsylvania. pp. 270-276.
ASTM D 1561-76. 1979. Compaction of Test Specimens of
Bituminous Mixtures by Means of California Kneading Compactor,
ASTM Committee D-18, Annual Book of ASTM Standards, Part 19«
Philadelphia, Pennsylvania. pp. 279-282.
ASTH D 2922-78. 1979. Density of Soil and Soil Aggregates in
Place by Nuclear Methods (Shallow Depth, Test for), ASTM Commit-
tee D-18, Annual Book of ASTM Standards, Part 19. Philadelpnia,
Pennsylvania. pp. 422-429.
ASTM D 3152-72. 1979. Standard Test Method for Capillary
Moisture Relationships for Fine-Textured Soils by Pressure-
Membrane Apparatus, ASTM Committee D-18, Annual Book of ASTM
Standards, Part 19. Philadelphia, Pennsylvania. pp. 478-485.
ASTM D 3385-75. 1979. Standard Test Method for Infiltration
Rate of Soils Using Double-Ring Infiltrometers, ASTM Committee D-
18, Annual Book ot ASTM Standards, Part 19. Philadelpnia,
Pennsylvania. pp. 497-502.
Baker, F.G. 1977. Factors Influencing the Crust Test for In
Situ Measurement of Hydraulic Conductivity. Soil Sci. Soc. Amer.
J. 41: 1029-1032.
Baker, F.G., P.L.M. Veneman, and J. Bouma. 1974. Limitations of
the Instantaneous Profile Method for Field Measurement of
Unsaturated Hydraulic Conductivity. Soil Sci. Soc. Amer. Proc.
38: 885-888.
Bartelli, L.J. 1977. Diagnostic Soil Horizons in Soil Taxonomy.
Trans. Res. Record 642, Transportation Res. Board, National Res.
Coun. pp. 6-9.
Basett, D.J. and A.F. Brodie. 1961. A Study of Matabitchual
Varved Clay. Ontario Hydro Res. News 13: 1-6.
Baverr L.D., W.H. Gardner and W.R. Gardner. 1972. Soil Physics.
John Wiley Publishing, New York, New York. 498 pp.
Bertrand, A.R. 1965. Rate of Water Intake in the Field. In:
Method of Soil Analysis. C.A. Black, Ed. Amer. Soc. of
Agronomy, Madison, Wisonsin. pp. 197-208.
Bishop, A.W. and D.J. Henkel. 1962. The Measurement of Soil
Properties In the Triaxial Test. Edward Arnold Ltd., London,
Second Edition.
127
-------
Black, T.A., W.R. Gardner, and G.W. Thurtell. 1969. The Pre-
diction of Evaporation, Drainage, and Soil Water Storage for a
Bare Soil. Soil Sci. Soc. Amer. Proc. 33: 655-660.
Boersma, L. 1965a. Field Measurement of Hydraulic Conductivity
Below A water Table. In: Methods of Soil Analysis, C.A. Black,
Ed. Amer. Soc. of Agronomy, Madison, Wisconsin., pp. 222-233.
Boersma, L. 1965b. Field Measurement of Hydraulic Conductivity
Above A Water Table. In: Methods of Soil Analysis, C.A. Black,
Ed. Amer. Soc. of Agronomy, Madison, Wisconsin., pp. 234-252.
Boersma, L., J.W. Gary, D.D. Evans, A.H. Ferguson, W.H. Gardner,
R.J. Hanks, R.D. Jackson, W.D. Kemper, D.E. Miller, D.R. Nielsen,
and G. Uehara. 1972. Soil Water. Amer, Soc. of Agronomy/Soil
Sci. Soc. of Amer., Madison, Wisconsin. 175 pp.
Bouma, J. 1977. Soil Survey and the Study of Water in Un-
disturbed Soil. Soil Survey Papers, No. 13. Soil Survey
Institute, Wageningen, The Netherlands. 107 pp.
Bouma, J., A. Jongerius, and D. Schoonderbeek. 1979. Calcula-
tion of Saturated Hydraulic Conductivity of Some Pedal Clay Soils
Using Micromorphometric Data. Soil Sci. Soc. Amer. J. 43: 261-
264.
Bouma, J. and L.W. Dekker. '1981. A Method of Measuring the
Vertical and Horizontal Saturated Hydraulic Conductivity of Clay
Soils with Macropores. Soil Sci. Soc. Amer. J. 45: 662-663.
Bowles, J.E. 1978. Engineering Properties of Soils and Their
Measurement. McGraw-Hill Book Co., New York, New York.
Brewer, R. 1976. Fabric and Mineral Analysis of Soils. R.E.
Krieger Publishing Co., Huntington, New York. 482 pp.
Brown, K.W. and D.C. Anderson. 1982. Effects of Organic Sol-
vents on the Permeability of Clay Soils. Draft Report in
Fulfillment of EPA Grant No.: R 806825010, Cincinnati, Ohio. 188
pp.
Bruce, R.R. 1972. Hydraulic Conductivity Evaluation of the Soil
Profile from Soil Water Retention Relations. Soil Sci. Soc.
Amer. Proc. 36: 555-561.
Brust, K.J., C.H.M. van Bavel, and G.B. Stirk. 1968. Hydraulic
Properties of a Clay Loam Soil and Field Measurement of Water
Uptake by Roots. II. Comparison of Field and Laboratory Data on
Retention and of Measured and Calculated Conductivities. Soil
Sci. Soc. Amer. Proc. 32: 322-326.
128
-------
Campbell, G.S. 1974. A Simple Method for Determining Un-
saturated Conductivity from Moisture Retention Data. Soil Sci.
117: 311-314.
Casagrande, L. and S.J. Poulos. 1969. On the Effectiveness of
Sand Drains. Can. Geotech. J. 6: 287-326.
Cassel, D.K., A.W. Warrick, D.R. Nielsen, and J.W. Biggar. 1968.
Soil Water Diffusivity Values Based Upon Time Dependent Soil
Water Content Distributions. Soil Sci. Soc. Amer. Proc. 32: 774-
777.
Carvallo, H.O., O.K. Cassel, J. Hammond, and A. Bauer. 1976.
Spatial Variability of In Situ Unsaturated Hydraulic Conductivity
of Maadock Sandy Loam. Soil Sci. 121: 1-8.
Cedergren, H.R. 1977. Seepage, Drainage, and Flow Nets. John
Wiley and Sons, Inc., New York, New York. 534 pp.
Chan, H.T. and T.C. Kenney. 1973. Laboratory Investigation of
Permeability Ratio of New Liskeard Varved Soil. Can. Geotech. J.
10: 453-472.
Cheng, J.D., T.A. Black, and R.P. Willington. 1975. A Technique
for the Field Determination of the Hydraulic Conductivity of
Forest Soils. Can. J. Soil Sci. 55: 79-82.
Chian, E.S.K. and F.B. DeWalle. 1977. Evaluation of Leachate
Treatments. Vol. I & II, EPA 600/2-77-186 a & b, U.S. Environ-
mental Protection Agency, Cincinnati, Ohio.
Childs, E.G. 1969. The Physical Basis of Soil Water Phenomena.
John Wiley Publishing, New York, New York. 493 pp.
Childs, E.G. and N. Collis-George. 1950. The Permeability of
Porous Materials. Royal Soc. (London), Proc., A. 201: 392-405.
Chong, S.K., R.E. Green, and L.R. Ahuja. 1979. Infiltration
Prediction Based on In Situ Soil Water Redistribution
Measurements: 1. Hydraulic Conductivity and Diffusivity
Determination. Submitted for publication in Water Resources
Research.
Dane, J.H. 1980. Comparison of Field and Laboratory Determined
Hydraulic Conductivity Values. Soil Sci. Soc. Amer. J. 44: 228-
231.
Daniel, D.E. 1979. Thermocouple Psychrometers for Measuring
Suction in Unsaturated Soils. A Report for the Project: A Study
of Shallow Land Burial of Low-Level Radioactive Waste, Sponsored
by Los Alamos Scientific Laboratory. 94 pp.
129
-------
Daniel, D.E. 1981. Problems in Predicting the Permeability ot
Compacted Clay Liners. In: Proceedings of Symposium on Uranium
Mill Tailings Management, Geotechnical Engineering Program, Civil
Engineering Department, Colorado State University, Fort Collins,
Colorado, October 26-27, 1981. pp. 665-675.
Daniel, D.E., J.M. Hamilton and R.E. Olson. 1981. Suitability
of Thermocouple Psychrometers for Studying Moisture Movement in
Unsaturated Soils. Permeability and Groundwater Transport, ASTM
STP 746, T.F. Ziinmie and C.O. Riggs, Eds. Amer. Soc. for Testing
and Materials, Philadelphia, Pennsylvania. pp. 84-100.
Davidson, J.M., L.R. Stone, D.R. Nielsen, and M.E. LaRue. 1969.
Field Measurement and Use of SoJl-Water Properties. Water
Resources Res. 5: 1312-1321.
Diamond, S. 1970. Pore Size Distributions in Clays. Clays and
Clay Minerals 18: 7-23.
EPA/Army Corps of Engineers/USDA. 1977. Process Design Manual
for Land Treatment of Municipal Wastewater. EPA 625/1-77-008,
U.S. Environmental Protection Agency, Washington, D.C. 506 pp.
Flocker, W.J., M. Yamaguchi, and D.R. Nielsen. 1968. Capillary
Conductivity and Soil-Water Diffusivity Values from Vertical Soil
Columns. Agron. J. 60: 605-610.
Fuller, W.H. 1978. Investigation of Landfill Leachate Pollutant
Attenuation by Soils. EPA 600/2-78-158, Appendix A. U.S.
Environmental Protection Agency, Muricipal Environmental Research
Laboratory, Cincinnati, Ohio. pp. 122-137.
Gardner, W.R. 1970. Field Measurement of Soil Water
Diffusivity. Soil Sci. Soc. Amer. Proc. 34: 832-833.
Gillham, R.W., A. Klute, and D.F. Heerman. 1976. Hydraulic
Properties of a Porous Medium: Measurement and Empirical Repre-
sentation. Soil Sci. Soc. Amer. J. 40: 203-207.
Gillham, R.W., A.Klute, and D.F. Heerman. 1979. Measurement and
Numerical Simulation ot Hysteretic Flow in a Heterogeneous Porous
Medium. Soil Sci. Soc. Amer. J. 43: 1061-1067.
Goring, C.A.I, and J.W. Hamaker. 1972. Organic Chemicals in the
Soil Environment, Vol. I & II. Marcel Dekker, Inc., New York,
New York.
Green, R.E. and J.C. Corey. 1971. Calculation of Hydraulic
Conductivity: A Further Evaluation of Some Predictive Methods.
Soil Sci. Soc. Amer. Proc. 35: 3-8.
130
-------
Haley and Aldrich. 1969. Report No. 1 - Engineering Properties
of Foundation Soils at Long Creek - Fore River Areas and Back
Cove. Report to Maine State Highway Commission.
Hamilton, J.M., D.E. Daniel and R.E. Olson. 1981. Measurement
of Hydraulic Conductivity of Partially Saturated Soils.
Permeability and Groundwater Contaminant Transport, ASTM STP 746,
T.F. Zimmie and C.O. Riggs, Eds. Amer. Soc. for Testing and
Materials, Philadelphia, Pennsylvania. pp. 182-196.
Haxo, Jr., H.E. 1976. Evaluation of Selected Liners When
Exposed to Hazardous Wastes. In: Proceedings of Hazardous Waste
Research Symposium, Residual Management by Land Disposal, Tuscon,
Arizona, EPA 600/9-76-015, U.S. Environmental Protection Agency,
Cincinnati, Ohio.
Hillel, D.I. 1971. Soil and Water: Physical Principles and
Processes. Academic Press, New York, New York. 288 pp.
Hillel, D.I. 1980. Fundamentals of Soil Physics. Academic
Press, New York, New York. 413 pp.
Hillel, D.I. and W.R. Gardner. 1970. Measurement of Unsaturated
Conductivity and Diffusivity by Infiltration through an Impeding
Layer. Soil Sci. 109: 149-153.
Hillel, D.I., V.D. Krentos, and Y. Stylianou. 1972. Procedure
and Test of an Internal Drainage Method for Measuring Soil
Hydraulic Characteristics In Situ. Soil Sci. 114: 395-400.
Ismail, S.N.A. 1975. Micromorphic Soil-Porosity Characteriza-
tion by Means ot Electro-Optical Image Analysis (Quantimet 720).
Soil Survey Papers, No. 9. Soil Survey Institute, Wageningen,
The Netherlands. 104 pp.
ISSS (International Society of Soil Science). 1975. Soil
Physics Terminology. Bull. ISSS, No. 48. pp. 16-22.
Jackson, R.D. 1963. Porosity and Soil-Water Diffusivity
Relations. Soil Sci. Soc. Amer. Proc. 27: 123-126.
Jackson, R.D., R.J. Reginato, and C.H.M. van Bavel. 1965.
Comparison of Measured and Calculated Hydraulic Conductivities of
Unsaturated Soils. Water Resources Res. 1: 375-380.
Jezequel, J.F. and C. Mieussens. 1975. In Situ Measurement of
Coefficients of Permeability and Consolidation in Fine Soils.
In: Proceedings of the Conference on In Situ Measurement of Soil
Properties, A.S.C.E., New York, New York, Vol. I, pp. 208-224.
131
-------
Johnson, W.M. and J.E. McClelland. 1977. Soil Taxonomy: An
Overview. Transportation Res. Record 642, Transportation Re-
search Board, National Research Council. pp. 2-6.
Jongerius, A. 1974. Recent Developments in Soil Micrornor-
phometry. In: Soil Microscopy. Proc. of the Fourth Int. Working
Meeting on Soil Micromorphology, G.K. Rutherford, Ed. Kingston,
Canada, pp. 67-83.
Kenney, T.C. and H.T. Chan. 1973. Field Investigation ot
Permeability Ratio of New Liskeard Varved Soil. Canadian
Geotechnical J. 10: 473-488.
Kluter A. 1965a. Laboratory Measurement of Hydraulic Con-
ductivity of Saturated Soil. In: Methods of Soil Analysis, C.A.
Black, Ed. Amer. Soc. of Agronomy, Madison, Wisconsin. pp. 210-
220.
Klute, A. 1965b. Laboratory Measurement of Hydraulic Con-
ductivity of Unsaturated Soil. In: Methods of Soil Analysis.
C.A. Black, Ed. Amer. Soc. of Agronomy, Madison, Wisconsin. pp.
253-261.
Klute, A. 1965c. Water Diffusivity. In: Methods ot Soil
Analysis, C.A. Black, Ed. Amer. Soc. of Agronomy, Madison,
Wisconsin. pp. 262-272.
Klute, A. 1972. The Determination of the Hydraulic Conductivity
of Unsaturated Soils. Soil Sci. 113: 264-276.
Kunze, R.J., G. Uehara, and K. Graham. 1968. Factors Important
in the Calculation of Hydraulic Conductivity. Soil Sci. Soc.
Amer. Proc. 32: 760-765.
Laliberte, G.E. and A.T. Corey. 1967. Hydraulic Properties of
Disturbed and Undisturbed Soils. In: Permeability and Capil-
larity of Soils, ASTM STP 417, Amer. Soc. for Testing and
Materials, Philadelphia, Pennsylvania. pp. 56-71.
Laliberte, G.E., A.T. Corey, and R.H. Brooks. 1966. Properties
of Unsaturated Porous Media. Hydrology Paper No. 17, Colorado
State Univ., Fort Collins, Colorado.
Lambe, T.W. 1955. The Permeability of Fine-Grained Soils. ASTM
STP 163, Amer. Soc. for Testing and Materials, Philadelphia,
Pennsylvania. pp. 56-67.
Lambe, T.W. and R.V. Whitman. 1979. Soil Mechanics, SI Version.
John Wiley and Sons, Inc., New York, New York. 553 pp.
132
-------
Libardi, P.L.f K. Reichardt, D.R. Nielsen, and J.W. Biggar.
1980. Simple Field Methods for Estimating Soil Hydraulic Con-
ductivity. Soil Sci. Soc. Amer. J. 44: 3-7.
Lumb, P. and J.K. Holt. 1968. The Undrained Shear Strength of a
Soft Marine Clay from Hong Kong. Geotechnique 18: 25-36.
Luxmoore, R.J., B.P. Spalding, and I.M. Munro. 1981. Areal
Variation and Chemical Modification of Weathered Shale Infiltra-
tion Characteristics. Soil Sci. Soc. Amer. J. 45: 687-691.
Marshall, T.J. 1958. A Relation Between Permeabaility and Size
Distribution of Pores. J. Soil Sci. 9: 1-8.
Mason, D.D., J.F. Lutz, and R.G. Petersen. 1957. Hydraulic
Conductivity as Related to Certain Soil Properties in a Number of
Great Soil Groups - Sampling Errors Involved. Soil Sci. Soc.
Amer. Proc. 21: 554-561.
Matrecon, Inc. 1980. Lining of Waste Impoundment and Disposal
Facilities Manual (Draft). U.S. Environmental Protection Agency,
Cincinnati, Ohio. 595 pp.
McDougall, W.J., R.A. Fusco, and R.P. O'Brien. 1979. Con-
tainment and Treatment of the Love Canal Landfill Leachate. Pre-
sented at the Annual Water Pollution Control Federation Meeting,
October 11, 1979.
Means, R.E. and J.V. Parcher. 1963. Physical Properties of
Soils. Charles E. Merrill Books Inc., Columbus, Ohio. 464 pp.
Michaels, A.S. and C.S. Lin. 1954. The Permeability of
Kaolinite. Industrial and Eng. Chem. 46: 1239-1246.
Millington, R.J. and J.P. Quirk. 1960. Transport in Porous
Media. Trans, of 7th Int. Congr. Soil Sci., Madison, Wisconsin,
I: 97-106.
Millington, R.J. and J.P. Quirk. 1961. Permeability of Porous
Solids. Trans. Faraday Soc. 57: 1200-1207.
Millington, R.J. and J.P. Quirk. 1964. Formation Factor and
Permeability Equations. Nature 202: 143-145.
Mitchell, J.K. 1956. The Fabric of Natural Clay and Its Rela-
tion to Engineering Properties. Proc. Highway Res. Board 35:
693-713.
Mitchell, J.K. 1976. Fundamentals of Soil Behavior. John Wiley
and Sons, Inc., New York, New York. 422 pp.
133
-------
Mitchell, J.K., D.R. Hooper and R.G. Campanella. 1965.
Permeability of Compacted Clay. J. of the Soil Mechanics and
Foundation Division, A.S.C.E. 91: 41-65.
Morganstern, H.R. and J.S. Tchalenko. 1967., The Optical Deter-
mination of Preferred Orientation in Clays and Its Application to
the Study of Microstructure in Consolidated Kaolin. Proc. of the
Royal Soc. (London) 300: 218-250.
Nagpal, N.K. and J. deVries. 1976. An Evaluation of the Instan-
taneous Profile Method for In Situ Determination of Hydrologic
Properties of Layered Soil. Can. J. Soil Sci. 56: 453-461.
Nielsen, D.R., D. Kirkham, and E.R. Perrier. 1960. Soil
Capillary Conductivity: Comparison of Measured and Calculated
Values. Soil Sci. Soc. Amer. Proc. 24: 157-160.
Nielsen, D.R., J.M. Davidson, J.W. Biggar, and R.J. Miller.
1962. Water Movement through Panoche Clay Loam Soil. Hilgardia
-
Neilsen, D.R., J.W. Biggar, and K.T. Erh. 1973. Spatial
Variability of Field-Measured Soil-Water Properties. Hilgardia
42: 215-259.
Ogata, G. and L.A. Richard^. 1957. Water Content Changes
Following Irrigation of Bare Pield Soil that is Protected from
Evaporation. Soil Sci. Soc. Amer. Proc. 21: 355-356.
Olsen, H.W. 1962. Hydraulic Flow Through Saturated Clays.
Proc. of the Ninth National Conf. on Clays and Clay Minerals.
pp. 131-161.
Olson, R.E. and Daniel, D.E. 1981. Measurement of the Hydraulic
Conductivity of Fine-Grained Soils. In: Permeability and Ground-
water Transport, ASTM STP 746, T.F. Zimmie and C.O. Riggs, Eds.
Amer. Soc. for Testing and Materials, Philadelphia, Pennsylvania.
pp. 18-64.
Reeve, R.C. 1957. The Measurement of Permeability in the
Laboratory. Agron. 7: 414-419.
Renger, M., W. Giesel, O. Strebel, and S. Lorch. 1970. Erste
Ergebnisse zur Quanti tativen Erfassung der Wasserhaushalts-
komponenten in der Ungesattig ten Bodenzone. Zeitschrift fur
Pf lanzenernahrung und Broderkunde 126: 15-35.
Richards, L.A., W.R. Gardner, and G. Ogata. 1956. Physical
Processes Determining Water Loss from Soil. Soil Sci. Soc. Amer.
Proc. 20: 310-314.
134
-------
Rogers, J.S. and A. Klute. 1971. The Hydraulic Conductivity
Water Content Relationship during Non-Steady Flow through a Sand
Column. Soil Sci. Soc. Amer. Proc. 35: 695-700.
Rose, C.W. 1966. Agricultural Physics. Pergamon Press.
Oxford, England.
Rose, C.W. and A. Krishnan. 1967. A Method of Determining
Hydraulic Conductivity Characteristics for Non-Swelling Soils In
Situ and of Calculating Evaporation from Bare Soil. Soil Sci.
103: 369-373.
Rose, C.W., W.R. Stern, and J.E. Drummond. 1965, Determination
of Hydraulic Conductivity as a Function of Depth and Water Con-
tent for Soil In Situ. Aust. J. Soil Res. 3: 1-9.
Roulier, M.H., L.H. Stolzy, J. Letey, and L.V. Weeks. 1972.
Approximation ot Field Hydraulic Conductivity by Laboratory Pro-
cedures on Intact Cores. Soil Sci. Soc. Amer. Proc. 36: 387-393.
Scheidegger, A.E. 1974. The Physics of Flow Through Porous
Media. University of Toronto Press, Toronto, Canada. 353 pp.
Simmons, C.S., D.R. Nielsen, and J.W. Biggar. 1979. Scaling of
Field-Measured Soil-Water Properties. I. Methodology, II.
Hydraulic Conductivity and Flux. Hilgardia 47: 77-153.
Skempton, A.W. 1953. The Colloidal Activity of Clay. In: Proc.
of the Third International Conf. on Soil Mechanics and Foundation
Engineering (Switzerland), Vol. I, pp. 57-6.1.
Small Scale Waste Management Project (SSWMP). 1978. Management
of Small Waste Flows. EPA 600/2-78-173, U.S. Environmental Pro-
tection Agency, Cincinnati, Ohio. 764 pp.
Subbaraju, B.H. et al. 1973. Field Performance of Drain Wells
Designed Expressly for Strength Gain in Soft Marine Clays. In:
Proc. of 8th International Conf. Soil Mech. and Foun. Eng.,
Moscow. pp. 217-220.
Topp, G.C. and M.R. Binns. 1976. Field Measurement of Hydraulic
Conductivity with a Modified Air-Entry Permeameter. Can. J. Soil
Sci. 56: 139-147.
Tsien, S.I. 1955. Stabilization of Marsh Deposit. Highway Res.
Board, Bull. 115. pp. 15-43.
Tzimas, E. 1979. The Measurement of Soil-Water Hysteretic
Relationships on a Soil Monolith. J. Soil Sci. 30:529-534.
135
-------
U.S.D.A. (U.S. Department of Agriculture). 1975. Soil Taxonomy:
A Basic System of Soil Classification for Making and Interpreting
Soil Surveys. Soil Survey Staff, Soil Conservation Service,
Washington, D.C. 754 pp.
Vachaud, G. 1967. Determination of the Hydraulic Conductivity
of Unsaturated Soils from an Analysis of Transient Flow Data.
Water Resources Res. 3: 697-705.
Vachaud, G. and J. Thony. 1971. Hysteresis During Infiltration
and Redistribution in a Soil Column at Different Initial Water
Contents. Water Resources Res. 7: 111-127.
van Bavel, C.H.M,, G.B. Stirk, and K.J. Brust. 1968. Hydraulic
Properties of a Clay Loam Soil and the Field Measurement of Water
Uptaken by Roots. I. Interpretation of Water Content and Pres-
sure Profiles. Soil Sci. Soc., Amer. Proc. 32: 310-317,,
Van Genuchten, M. Th. 1979. Calculating the Unsaturated
Hydraulic Conductivity with a New Closed-Form Analytical Model.
Research Rep. No. 78-WR-08, Pr inceton University,. Princeton, New
Jersey.
Vomocil, J.A. 1965. Porosity. In: Methods of Soil Analysis,
C.A. Black, Ed., Amer. Soc. of Agronomy, Madison, Wisconsin, pp.
299-314.
Wardell, J.T. and J.S. Doynow. 1980. Laboratory Permeability
Testing of Fine Grained Soils for Hazardous Waste Disposal Siting
Studies. M.S. Thesis, Rensselaer Polytechnic Institute, Troy,
New York. 53 pp.
Watson, K.K. 1966. An Instantaneous Profile Method for
Determining the Hydraulic Conductivity of Unsaturated Porous
Materials. Water Resources Res. 2: 709-715.
Watson, K.K. 1967. The Measurement of the Hydraulic
Conductivity of Unsaturated Porous Matrials Using a Zone of
Entrapped Air. Soil Sci. Soc. Amer. Proc. 31: 716-721.
Weeks, L.V. and S.J. Richards. 1967. Soil Water Properties
Computed from Transient Flow Data. Soil Sci. Soc. Amer. Proc.
31: 721-725.
White, R. 1976. Remolded Soil Samples from Proposed Waste
Landfill Site North of Three Rivers, Texas. Performed by Trinity
Engineering Testing Corporation for the City of Corpus Christi,
Texas. Rep. No. 76791, 8 pp.
Wind, G.P. 1966. Capillary Conductivity Data Estimated by a
Simple Method. In: Water in the Unsaturated Zone, Vol. I: 181-
191.
136
-------
Wu, T.H., N.Y. Chang and E.M. All. 1978. Consolidation and
Strength Properties of a Clay. J. Geot. Eng. Div., A.S.C.E. 104:
899-905.
Yongf R.N. and B.P. Warkentin. 1975. Soil Properties and
Behavior. Elsevier Scientific Publishing Co., New York, New
York. 449 pp.
Zimmie, T.F. 1981. Geotechnical Testing Considerations in the
Determination of Laboratory Permeability for Hazaradous Waste
Disposal Siting. Hazardous Solid Waste Testing: First
Conference, ASTM STP 760, R.A. Conway and B.C. Malloy, Eds.,
Amer. Soc. for Testing and Materials, Philadelphia, Pennsylvania.
pp. 293-304.
Zimmie, T.F., J.S. Doynow and J.T. Wardell. 1981. Permeability
Testing of Soils for Hazardous Waste Disposal Sites. In: Proc.
of Tenth International Conf. on Soil Mechanics and Foundation
Engineering, Stockholm, Sweden. 4 pp.
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APPENDIX A
GLOSSARY OF TECHNICAL TERMS
absorption: The process by which one substance is taken into and
included within another substance, as the absorption of water
by soil or nutrients by plants. (2)
acidity, total: The total acidity in a soil or clay. Usually it
is estimated by a buffered salt determination of (cation-
exchange minus exchangeable bases) = total acidity. (1)
adsorption: The increased concentration of molecules or ions at
a surface, including exchangeable cations and anions on soil
particles. (2)
aggregation: The act of soil particles cohering so as to behave
mechanically as a unit, (2)
air-dry: (a) The state of dryness (of a soil) at equilibrium
with the moisture content in the surrounding atmosphere. The
actual moisture content will depend upon the relative humidity
and the temperature of the surrounding atmosphere. (b) To
allow to reach equilibrium in moisture content with the sur-
rounding atmosphere. (1)
alkaline soil: Any soil having a pH > 7.0. (1)
anisotropic mass: A mass having different properties in dif-
ferent directions at any given point. (5)
available water: The portion of water in a soil that can be
readily absorbed by plant roots. Considered by most workers
to be that water held in the soil against a pressure of up to
approximately 15 bars. (1)
bar: A unit of pressure equal tc one million dynes per square
centimeter. (1)
base-saturation percentage: The extent to which the adsorption
complex of a soil is saturated with exchangeable cations other
than hydrogen. It is expressed as a percentage of the total
cation-exchange capacity. (1)
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bearing capacity: Ability of a material to support a load normal
to the surface. (6)
bedrock: The more or less continuous body of rock which under-
lies the overburden soils. (7)
bentonite: An expansive clay formed from the decomposition of
volcanic ash. (6)
bulk density, soil: The mass of dry soil per unit bulk volume.
The bulk volume is determined before drying to constant weight
at 105 degrees Centigrade. (])
bulk specific gravity: The ratio of the bulk density of a soil
to the mass of unit volume of water. (1)
bulk volume: The volume, including the solids and the pores, of
an arbitrary soil mass. (1)
California bearing ratio: The ratio of: (1) The force per unit
area required to penetrate a soil mass with a 3 square inch
(8 cm) circular piston (approximatelly 1.95 inch (51 mm)
diameter) at the rate of 0.05 inches (1.3 mm)/minute, to (2)
That required for corresponding penetration of a standard
material. The ratio is usually determined at 0.1 inch
(12.7 mm). Corps of Engineers' procedures require determina-
tion of the ratio at 0.1 inch and 0.2 inch (5.1 mm). Where
the ratio of 0.2 inch is consistently higher that at 0.1 inch,
the ratio at 0,2 inch is used. (5)
capillary attraction: A liquid's movement over or retention by a
solid surface due to the interaction of adhesive and cohesive
forces. (1)
capillary conductivity: (Obsolete) See soil water - B: hydrau-
lic conductivity.
capillary fringe: A zone just above the water table (zero gauge
pressure) that remains almost saturated. (The extent and the
degree of definition of the capillary fringe depends upon the
size-distribution of pores). (1)
capillary migration (capillary flow): The movement of water by
capillary action. (5)
cation-exchange: The interchange between a cation and solution
and another cation on the surface of any surface-active
material such as clay colloid or organic colloid. (1)
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cation-exchange capacity (CEC): The sum total of exchangeable
cations that a soil can absorb. Expressed in milliequivalents
per 100 grams or per gram of soil (or of other exchangers such
as clay). (1)
channels: Voids that are significantly larger than packing
voids. They are generally cylindrically shaped and smooth
walled, have regular conformation, and have relatively uniform
cross-sectional size and shape. (4)
clay: (a) A soil separate consisting of particles > 0.002 mir in
equivalent diameter. (b) A textural class. (1)
clay films: Coating of clay on the surfaces of soil peds and
mineral grains and in soil pores. (Also called clay skins,
clay flows, illuviation cutans, argillans or tonhautchen.)
(1)
clay mineral: Naturally occurring inorganic crystalline material
found in soils and other earthy deposits, the particles being
clay sized; that is, > 0.002 mm in diameter. (1)
clod: A com pact, coherent mass of soil ranging in size from 5 to
100 mm to as much as 20 to 25 cm and is produced artificially
usually by the activity of man by plowing, digging, etc.,
especially when these operations are performed on soils that
are either too wet or too dry for normal tillage operations.
(1)
coarse fragments: Rock or mineral particles > 2.0 mm in
diameter. (1)
coarse texture: The texture exhibited by sand, loamy sands, and
sandy loams except very fine sandy loams. (1)
cohesionless soil: A soil that when unconfined has little or no
strength when air-dried and that has little or no cohesion
when submerged. (5)
cohesive soil: A soil that when unconfined has considerable
strength when air-dried and that has significant cohesion when
submerged. (5)
colloidal particles: Particles that are so small that the sur-
face activity has an appreciable influence on the properties
of the particle. (1)
compaction: The densification of a soil by means of mechanical
manipulation. (5)
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compaction curve (Proctor curve) (moisture-density curve): The
curve showing the relationship between the dry unit weight
(density) and the water content of a soil for a given compac-
tive effort. (5)
\vaciiiajLL.jr/ u.jju i_ la ^,
tive effort. (5)
compaction test (moisture-density test): A laboratory compacting
procedure whereby a soil at a known water content is placed in
a specified manner into a mold of given dimensions, subjected
to a compactive effort of controlled magnitude, and the
resulting unit weight is determined. The procedure is re-
peated for various water contents sufficient to establish a
relation between water content and unit weight. (5)
compressibility: Property of a soil or rock pertaining to its
susceptibility to decrease in volume when subjected to load.
(5)
compression curve: See pressure-void ratio curve.
compressive strength (unconfined or uniaxial compressive
strength): The load per unit area at which an unconfined
cylindrical specimen of soil or rock will fail in a simple
compression test. Commonly the failure load is the maximum
that the specimen can withstand in the test. (5)
conductivity, hydraulic: See soil water.
consistency: (a) The resistance of a material to deformation or
rupture. (b) The degree of cohesion or adhesion of the soil
mass. (1)
consolidation: The gradual reduction in volume of a soil mass
resulting from an increase in compressive stress. (a) initial
consolidation (initial compression): A comparatively sudden
reduction in volume of a soil mass under an applied load due
principally to expulsion and compression of gas in the soil
voids preceding primary consolidation. (b) primary consolida-
tion (primary compression) (primary time effect): The reduc-
tion in volume of a soil mass caused by the application of a
sustained load to the mass and due principally to a squeezing
out of water from the void spaces of the mass and accompanied
by a transfer of the load from the soil water to the soil
solids. (c) secondary consolidation (secondary compression)
(secondary time effect): The reduction in volume of a soil
mass caused by the application of a sustained load to the mass
and due principally to the adjustment of the internal struc-
ture of the soil mass after most of the load has been trans-
ferred from the soil water to the soil solids. (5)
consolidation test: A test in which the specimen is laterally
confined in a ring and is compressed between porous plates.
(5)
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consolidation-time curve (time curve) (consolidation curve)
(theoretical time curve): A curve that shows the relation, be-
tween: (1) The degree of consolidation, and (2) The elapsed
time after the application of a given increment of load. (5)
creep: Slow mass movement of soil and soil material down
relatively steep slopes primarily under the influence of
gravity, but facilitated by saturation with water and by
alternate freezing and thawing. (1)
crust: A surface layer on soils, ranging in thickness from a few
millimeters to perhaps as much as an inch, that is much more
compact, hard, and brittle, when dry, than the material
immediately beneath it. (1)
cutan: A modification of the texture, structure, or fabric at
natural surfaces in soil materials due to concentration of
particular soil constituents or 'in-situ1 modification of the
plasma; cutans can be composed of any of the component
substances of the soil material. (4)
Darcy's law: (a) A law describing the rate of flow of water
through porous media. (Named for Henry Darcy of Paris who
formulated it in 1856 from extensive work on the flow of water
through sand filter beds.) As formulated by Darcy the law is:
Q = kS(H + e)
e
where
Q is the volume of water passed in unit time,
S is the area of the bed,
e is the thickness of the bed,
H is the height of the water on top of the bed, and
"k is a coefficient depending on the nature of the sand" and
for cases where the pressure "under the filter is equal to
the weight of the atmospheres"
(b) Generalization for three dimensions: The rate of viscous
flow of water in isotrophic porous media is proportional to,
and in the direction of, the hydraulic gradient. (c)
Generalization for other fluids: The rate of viscous flow of
homogenous fluids through isotrophic porous media is propor-
tional to, and in the direction of, the driving force. (1)
deflocculate: (a) To separate the individual components of com-
pound particles by chemical and/or physical means. (b) To
cause the particles of the disperse phase of a colloidal
system to become suspended in the dispersion medium. (1)
deformation: A change in the shape or size of a solid body. (7)
142
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degradation: The breakdown of substances by biological action.
(2)
degree o± consolidation (percent consolidation): The ratio,
expressed as a percentage of: (1) The amount of consolidation
at a given time within a soil mass, to (2) The total amount of
consolidation obtainable under a given stress condition. (5)
degree of saturation: The extent or degree to which the voids in
rock contain fluid (water, gas, or oil). Usually expressed in
percent related to total void or pore space. (7)
deposit: Material left in a new position by a natural tran-
sporting agent such as water, wind, ice, or gravity, or by the
activity of man. (1)
depression curve: Record of profile of water table as a result
of pumping. (6)
discontinuity: (a) Boundary between major layers of the Earth
which have different seismic velocities. (b) Interruption of
the homogeneity of a rock mass (e.g. joints, faults, etc.).
(5)
disperse: (a) To break up compound particles, such as aggre-
gates, into the individual component particles. (b) To
distribute or suspend fine particles, such as clay, in or
throughout a dispersion medium, such as water . (1)
disturbed samples: Soil samples obtained in a manner which des-
troys the original orientation and some of the physical pro-
perties of the naturally disposed material. (6)
drawdown curve: The trace of the top surface of the water table
in an aquifer or of the free water surface, when a new or
changed means of extraction of water takes place. (6)
dry-weight percentage: The ratio of the weight of any
constituent (of a soil) to the oven-dry weight of the soil.
See oven-dry soil. (1)
ductility: The condition in which material can sustain permanent
deformation without losing its ability to resist load. (7)
duripan: A mineral soil horizon that is cemented by silica,
usually opal or micro-crystalline forms of silica, to the
point that air-dry fragments will not slake in water or HC1.
A duripan may also have accessory cement such as iron oxide or
calcium carbonate. (1)
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elastic limit: Point on stress-strain curve at which transition
from elastic to inelastic behavior takes place. (7)
eolian: Pertaining to material transported and deposited by the
wind. Includes earth materials ranging from dune sands to
silty loess deposits. (3)
equivalent diameter: In sedimentation analysis, the diameter
assigned to a non-spherical particle, it being numerically
equal to the diameter of a spherical particle of the same
density and velocity of fall. (1)
erode: To wear away or remove the land surface by wind, water,
or other agents. (1)
evapotranspiration: The combined loss of water from a given
area, and during a specified period of time, by evaporation
from the soil surface and by transpiration from plants. (.1)
fabric (soils): The physical constitution of a soil material as
expressed by the spatial arrangement of the solid particles
and associated voids. Fabric is the element of structure
which deals with arrangement. (4)
failure (in rocks): Exceeding the maximum strength of the rock
or exceeding the stress or strain requirement of a specific
design. (7)
fault: A fracture or fracture zone along which there has been
displacement of the two sides relative to one another parallel
to the fracture (this displacement may be a few centimeters or
many kilometers). (7)
field capacity (field moisture capacity): (Obsolete in technical
work.) The percentage of water remaining in a soil 2 or 3
days after having been saturated and after free drainage has
practically ceased. (The percentage may be expressed on the
basis of weight or volume.) See moisture tension. (1)
fill: Man-made deposits of natural soils or rock products and
waste materials. (5)
film water: A layer of water surrounding soil particles and
varying in thickness from 1 or 2 to perhaps 100 or more
molecular layers. Usually considered as that water remaining
after drainage has occurred because it is not distinguishable
in saturated soils. (1)
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fine texture: Consisting of or containing large quantities of
the fine fractions, particularly of silt and clay. (Includes
all clay loams and clays; that is, clay loams, sandy clay
loam, silty clay loam, sandy clay, silty clay, and clay
textural classes. Sometimes subdivided into clayey texture
and moderately fine texture.) See soil texture. (1)
firm: A term describing the consistency of a moist soil that
offers distinctly noticeable resistance to crushing but can be
crushed with moderate pressure between the thumb and fore-
finger. See consistency. (1)
fissure flow: Flow of water through joints and larger voids.
(5)
flow curve: The locus of points obtained from a standard liquid
limit test and plotted on a graph representing water content
as ordinate on an arithmetic scale and the number of blows as
abscissa on a logarithmic scale. (5)
flow line: The path that a particle of water follows in its
course of seepage under laminar flow conditions. (5)
flow net: A graphical representation of flow lines and equipo-
tential (piezometric) lines used in the study of seepage
phenomena. (5)
fracture: A break in the mechanical continuity of a body of rock
caused by stress exceeding the strength of the rock. Includes
joints and faults. (5)
fragipan: A natural subsurface horizon with high bulk density
relative to the solum above, seemingly cemented when dry, but
when moist showing a moderate to weak brittleness. The layer
is low in organic matter, mottled, slowly or very slowly
permeable to water, and usually shows occasional or frequent
bleached cracks forming polygons. It may be found in profiles
of either cultivated or virgin soils but not in calcareous
material. (1)
free water (gravitational water) (ground water) (phreatic wa-
ter): Water that is free to move through a soil or rock mass
under the influence of gravity. (5)
friable: A consistency tei'm pertaining to the ease of crumbling
of soils. See consistency. (1)
geohydrology: Science of the occurrence, distribution, and move-
ment of water below the surface of the Earth. (6)
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geomorphology: The description of the present exposed surfaces
of the crust of the Earth., and seeks to interpret these sur-
faces in terms of natural processes (chiefly erosion) which
lead or have led to their formation. (6)
geophysics: The study of all the gross physical properties of
the Earth and its parts, particularly associated with the
detection of the nature and shape of unseen subsurface rock
bodies by measurement of such properties and property con-
trasts. Small scale applied geophysics is now a major aid in
geological reconnaissance. (6)
geotechnical: Pertaining to geotechnics, which is the applica-
tion of scientific methods to problems in engineering geology.
(6)
glacial drift: Rock debris that has been transported by glaciers
and deposited, whether directly from the ice or from the melt-
water. The debris may or may not be heterogeneous. (1)
glacial geology: The study of the direct Affects of the forma-
tion and flow under gravity of large ice masses on the Earth's
surface. Glaciology is concerned with the physics of ice
masses. (6)
glacial outwash: Stratified sand and gravel produced by glaciers
and carried, sorted, and deposited by water that originated
mainly from the melting of glacial ice. Outwash deposits may
occur in the form of valley fills (valley trains and/or out-
wash terraces) or as widespread outwash plains. (3)
glaciofluvial deposits: Material moved by glacier and sub-
sequently sorted and deposited by streams flowing from the
melting ice. (3)
glaciolacustrine deposits: Material ranging from fine clay to
sand derived from glaciers and deposited in glacial lakes by
water originating mainly from the melting of glacial ice.
Many are bedded or laminated with varves. (3)
glacial till: Unsorted and unstratified glacial drift, generally
unconsolidated, deposited directly by a glacier without subse-
quent reworking by water from the glacier, and consisting of a
heterogeneous mixture of clay, silt, sandf gravel, and
boulders varying widely in size and shape. (3)
gleying: Formation of gray or green material in soil when
stagnation of water results in exclusion of air and reduction
of iron. (6)
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gradation (grain-size distribution) (texture): The proportions
by mass of a soil or fragmented rock distributed in specified
particle-size ranges. (5)
grading: A 'well-graded' sediment containing some particles of
all sizes in the range concerned. Distinguish from 'well-
sorted1, which describes a sediment with grains of one size.
(6)
grain-size analysis (mechanical analysis) (particle-size analy-
sis): The process of determining grain-size distribution.
(5)
granule: A natural soil aggregate or ped which is relatively
nonporous. See soil structure and soil structure types. (1)
gravel: Round or seroirounded particles of rock that will pass a
3-in. (76.2 mm) sieve and.be retained on a No. 4 (4.75 mm)
U.S. standard sieve. (5)
gravitational potential: See soil water.
ground water: The portion of the total precipitation which at
any particular time is either passing through or standing in
the soil and the underlying strata and is free to move under
the influence of gravity. (1)
ground water level: The level below which the rock and subsoil,
to unknown depths, are saturated. (7)
hardpan: A hardened soil layer, in the lower A or in the B
horizon, caused by cementation of soil particles with organic
matter or with materials such as silica, sesquioxides, or
calcium carbonate. The hardness does not change appreciably
with changes in moisture content and pieces of the hard layer
do not slake in water. (1)
head: The energy, either kinetic or potential, possessed by each
unit weight of a liquid, expressed as the vertical height
through which a unit weight would have to fall to release the
average energy possessed. It is used in various compound
terms such as pressure head, velocity head, and loss of head.
(2)
heave: Upward movement of soil caused by expansion or displace-
ment resulting from phenomena such as: moisture absorption,
removal of overburden, driving of piles, frost action, and
loading of an adjacent area. (5)
heterogeneity: Having different properties at different points.
(7)
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homogeneous mass: A mass that exhibits essentially the same
physical properties at every point throughout the mass. (5)
horizon: See soil horizon.
hydration: The physical binding of water molecules to ions,
molecules, particles, or other matter. (2)
hydraulic conductivity: See soil water.
hydraulic gradient: The loss of hydraulic head per unit distance
of flow. (5)
hydrogeology: The study of the natural (and artificial) distri-
bution of water in rocks, and its relationship to those rocks.
Inasmuch as the atmosphere is a continuation of the hydro-
sphere, and is in physical and chemical balance with it, there
is a close connection with meteorology. (6)
hydrostatic pressure: A state of stress in which all the princi-
pal stresses are equal (and there is no shear stress). (7)
hygroscopic water: Water adsorbed by a dry soil from an atmos-
phere of high relative humidity, water remaining in the soil
after "air-drying" or water held by the soil when it is in
equilibrium with an atmosphere of a specified relative
humidity at a specified temperature, usually 98% of relative
humidity at 25 degrees Centigrade. (1)
igneous rock: Rock formed from the cooling and solidification of
magma, and that has not been changed appreciably since its
formation. (1)
immobilization: The conversion of an element from the inorganic
to the organic form in microbial tissues or in plant tissues.
(1)
impervious: Resistant to penetration by fluids or by roots. (1)
infiltration: The downward entry of water into the soil. (1)
infiltration rate: A soil characteristic determining or descri-
bing the maximum rate at which water can enter the soil under
specified conditions, including the presence of an excess of
water. (1)
integral sampling: A technique of core drilling which provides
knowledge of the original orientation of the samples re-
covered. (6)
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intergrade: A soil that possesses moderately well-developed
distinguishing characteristics of two or more genetically
related soil Great Groups. (1)
internal friction (shear resistance): The portion of the
shearing strength of a soil or rock that is usually considered
to be due to the interlocking of the soil or rock grains and
the resistance to sliding between the grains. (5)
ion exchange: A chemical process involving reversible
interchange of ions between a liquid and a solid but no
radical change in structure of the solid. (2)
isochrome: A curve showing the distribution of the excess hydro-
static pressure at a given time during a process of consolida-
tion. (5)
isomorphous substitution: The replacement of one atom by another
of similar size in a crystal lattice without disrupting or
changing the crystal structure of the mineral. (1)
isotropic: Having the same properties in all directions. (6)
joint: A break of geological origin in the continuity of a body
of rock occurring either singly, or more frequently in a set
or system, but not attended by a visible movement parallel to
the surface of discontinuity. (7)
kame: A moundlike hill of ice-contact glacial drift, composed
chiefly of stratified sand and gravel. (3)
karst: A type of topography that is characterized by closed
depressions or sink holes, and is dependent upon underground
solution and the diversion of surface waters to underground
routes. It is formed over limestone, dolomite, gypsum and
other soluble rocks as a result of differential solution of
these materials and associated processes of subsurface
drainage, cave formation, subsidence, and collapse. (3)
laminar flow (streamline flow) (viscous flow): Flow in which the
head loss proportional to the first power of the velocity.
(5)
landform: Any physical, recognizable form or feature of the
Earth's surface, having a characteristic shape, and produced
by natural causes. (3)
landscape: All the natural features, such as fields, hills,
forests, and water that distinguish one part of the Earth's
surface from another part; usually that portion of land or
territory which the eye can comprehend in a single view,
including all of its natural characteristics. The distinct
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association of landforms, especially as modified by geologic
forces, that can be seen in a single view. (3)
leach: To cause water or other liquid to percolate through soil.
(2)
line of seepage (seepage line) (Phreatic line): The upper free
water surface of the zone of seepage. (5)
liquefaction: Act or process of liquefying or of rendering or
becoming liquid; reduction to a liquid state. (2)
liquid limit: The minimum percentage (by weight) of moisture at
which a small sample of soil will barely flow under a standard
treatment. Synonymous with "upper plastic limit". See
plastic limit. (1)
liquidity index (water-plasticity ratio) (relative water con-
tent): The ratio, expressed as a percentage, of (1) The
natural water content of a soil minus its plastic limit, to
(2) its plasticity index. (5)
lithologic: Pertaining to the physical character of a rock. (3)
loading: The time rate at which material is applied to a treat-
ment device involving length, area, volume or other design
factor. (1)
loess: Material transported and deposited by wind and consisting
of predominantly silt-sized particles. (1)
lysimeter: (a) A device for measuring percolation and leaching
losses from a column of soil under controlled conditions. (b)
A device for measuring gains (precipitation and condensation)
and losses (evapotranspiration) by a column of soil. (1)
manometer: An instrument for measuring pressure. It usually
consists of a U-shaped tube containing a liquid, the surface
of which in one end of the tube moves proportionally with
changes in pressure on the liquid in the other end. Also, a
tube type of differential pressure gauge. (2)
matric potential: See potential, soil water.
mechanical analysis: (Obsolete) See particle-size analysis and
particle-size distribution.
mesh: One of the openings or spaces in a screen. The value of
the mesh is usually given as the number of openings per linear
inch. This gives no recognition to the diameter of the wire
and thus mesh number does not always have a definite relation
to the size of the hole. (2)
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metamorphic rock: Rock derived from pre-existing rocks but that
differ from them in physical, chemical, and mineralogical
properties as a result of natural geological processes,
principally heat and pressure, originating in the Earth. The
pre-existing rocks may have been igneous, sedimentary, or
another form of metamorphic rock. (1)
modulus of elasticity (modulus of deformation): The ratio of
stress to strain for a mineral under given loading condition;
numerically equal to the slope of the tangent or the secant of
a stress-strain curve. (5)
moisture content (water content): The ratio, expressed as a
percentage, of: (a) The weight of water in a given soil mass,
to (b) The weight of solid particles. (5)
moisture-retention curve: A graph showing the soil moisture
percentage (by weight or by volume) versus applied tension (or
pressure). Points on the graph are usually obtained by in-
creasing (or decreasing) the applied tension or pressure over
a specified range. (1)
moraine: An accumulation of drift, with an initial topographic
expression of its own, built chiefly by the direct action of
glacial ice. Examples are end, ground, lateral, recessional,
and terminal moraines. (3)
morphology: See soil morphology.
N-value: The number of blows required to drive the sampler of
the Standard Penetration test its last 12 inches (300 mm).
(6)
negative pressure: A pressure less than the local atmospheric
pressure at a given point. (3)
normally consolidated soil deposit: A soil deposit that has
never been subjected to an effective pressure greater than the
existing overburden pressure. (5)
optimum moisture content (optimum water content): The water
content at which a soil can be compacted to a maximum dry unit
weight by a given compactive effort. (5)
osmotic pressure: See soil water.
outwash plain: An extensive lowland area forming the surface of
a body of coarse textured, glaciofluvial material. An outwash
plain is commonly smooth; where pitted, due to melt-out of in-
corporated ice masses, it is generally low in relief. (3)
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oven-dry soil: Soil which has been dried at 105 degrees Centi-
grade until it reaches constant weight. (1)
overburden: The loose soil, sand, silt, or clay that overlies
bedrock. (7)
overburden load: The load on a horizontal surface underground
due to the column of material located vertically above it.
(7)
overconsolidated soil deposit: A soil deposit that has been
subjected to an effective pressure greater than the present
overburden pressure. (5)
oxidation-reduction potential: The potential required to trans-
fer electrons from the oxidant to the reductant and used as a
qualitative measure of the state of oxidation in wastewater
treatment systems. (2)
parent material: The unconsolidated and more or less chemically
weathered mineral or organic matter from which the solum of
soil is developed by pedogenic processes. (1)
particle density: The mass per unit volume of the soil
particles. In technical work, usually expressed as grams per
cubic centimeter. See bulkeny, soil. (1)
particle size: The effective diameter of a particle measured by
sedimentation, sieving, or micrometric methods. (1)
particle-size analysis: Determination of the various amounts of
the different separates in a soil sample, will usually be
sedimentation, sieving, micrometry, or combinations of these
methods. (1)
particle-size distribution: The amounts of the various soil
separates in a soil sample, usually expressed as weight per-
centages. (1)
ped: An individual natural soil aggregate consisting of a clus-
ter of primary particles, and separated from adjoining peds by
surfaces of weakness which are recognizable as natural voids
or by the occurrence of cutans. (4)
pedology: (a) The description of those parts of the present
Earth surface which have become weathered or otherwise
modified 'in-situ' by solar energy and by the effects of
organisms to form a soil which is of primary importance to man
in agriculture. (6) (b) The science of soils, that is, the
study of the origin, classification, description and use of
natural soil bodies. (4)
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pedon: A three-dimensional body of soil with lateral dimensions
large enough to permit the study of horizon shapes and rela-
tions. Its area ranges from 1 to 10 square meters. Where
horizons are intermittent or cyclic, and recur at linear
intervals of 2 to 7 m, the pedon includes one-half of the
cycle. Where the cycle is less than 2 m, or all horizons are
continuous and of uniform thickness, the pedon has an area of
approximately 1 square meter. If the horizons are cyclic, but
recur at intervals greater than 7 m, the pedon reverts to the
1 square meter size, and more than one soil will usually be
represented in each cycle. (1)
penetrability: The ease with which a probe can be pushed into
the soil. (May be expressed in units of distance, speed,
force, or work depending on the type of penetrometer used.
(1)
penetration resistance (standard penetration resistance) (Proctor
penetration resistance): (a) A number of blows of a hammer of
specified weight falling a given distance required to produce
a given penetration into soil of a pile, casing, or sampling
tube. (b) Unit load required to maintain constant rate of
penetration into soil of a probe or instrument. (c) Unit load
required to produce a specified penetration into soil at a
specified rate of a probe or instrument. For a Proctor
needle, the specified penetration is 2.5 in. (63.5 mm) and the
rate is 0.5 in. (12.7mm)/sec. (5)
penetration resistance curve (Proctor penetration curve): The
curve showing the relationship between: (a) The penetration
resistance, and (b) The water content. (5)
percent compaction: The ratio, expressed as a percentage, of:
(a) Dry unit weight of a soil, to (b) Maximum unit weight ob-
tained in a laboratory compacton test. (5)
percent saturation (degree of saturation): The ratio, expressed
as a percentage, of: (a) The volume of water in a given soil
or rock mass, to (b) The total volume of intergranular space
(voids). (5)
perched water table: A water table usually of limited area
maintained above the normal free water elevation by the pres-
sure of an intervening relatively impervious confining stra-
tum. (5)
percolation: The flow or trickling of a liquid downward through
a contact or filtering medium. The liquid may or may not fill
the pores of the medium. (2)
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permanent strain: The strain remaining in a solid with respect
to its initial condition after the application and removal of
stress greater than the yield stress (commonly also called
"residual" strain). (7)
permeability, soil: (a) The ease with which gases, liquids, or
plant roots penetrate or pass through a bulk mass of soil or a
layer of soil. Since different soil horizons vary in perme-
ability, the particular horizon under question should be
designated. (b) The property of a porous medium itself that
relates to the ease with which gases, liquids, or other sub-
stances can pass through it,. Previously, frequently
considered the "k" in Darcy's law. See Darcy's law and soil
water. (1)
pH, soil: The negative logarithm of the hydrogen-ion activity of
a soil. The degree of acidity (or alkalinity) of a soil as
determined by means of a glass, quinhydrone, or other suitable
electrode or indicator at a specified moisture content or
soil-water ratio, and expressed in terms of the pH scale. (1)
physical properties (of soil): Those characteristics, processes,
or reactions of a soil which are caused by physical forces and
which can be described by, or expressed in, physical terms or
equations. Sometimes confused with and difficult to separate
from chemical properties; hence, the terms "physical-chemical"
or "physiochemical". Examples of physical properties are bulk
density, water-holding capacity, hydraulic conductivity,
porosity, pore-size distribution, etc. (1)
piezometer: An instrument for measuring pressure head. (5)
piezometric surface: (a) The surface at which water will stand
in a series of piezometers. (5) (b) An imaginary surface
that everywhere coincides with the static level of the water
in the aquifer. (7)
piping: An underground flow of water with a sufficient pressure
gradient to cause scour along a preferred path. (6)
piston sampler: A tube with an internal piston used for
obtaining relatively undisturbed samples from cohesive soils,
(6)
plane of weakness: Surface or narrow zone with a (shear or
tensile) strength lower than that of the surrounding material.
(7)
plane stress (strain): A state of stress (strain) in a solid
body in which all stress (strain) components normal to a
certain plane are zero. (7)
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plastic equilibrium: State of stress within a soil or rock mass
or a portion thereof, which has been deformed to such an
extent that its ultimate shearing resistance is mobilized.
(5)
plastic flow (plastic deformation): The deformation of a plastic
material beyond the point of recovery, accompanied by
continuing deformation with no further increase in stress.
(5)
plastic limit: (a) The water content corresponding to an
arbitrary limit between the plastic and the semisolid states
of consistency of a soil. (b) Water content at which a soil
will just begin to crumble when rolled into a thread approxi-
mately 1/8 in. (3.2 mm) in diameter. (5)
plasticity: The property of a soil or rock which allows it to be
deformed beyond the point of recovery without cracking or
appreciable volume change. (5)
plasticity range: The range of moisture weight percentage within
which a small sample of soil exhibits plastic properties. (1)
pore-size distribution: The volume of the various sizes of pores
in a soil. Expressed as percentages of the bulk volume (soil
plus pore space). (1)
porosity: The ratio, usually expressed as a percentage, of: (a)
The volume of voids of a given soil or rock mass, to (b) The
total volume of the soil or rock mass. (5)
potential, soil water: See soil water.
preconsolidation pressure (prestress): The greatest effective
pressure to which a soil has been subjected. (5)
pressure surface: The level of the water surface in an
(imaginary) vertical well connecting with an aquifer. (5)
pressure-void ratio curve (compression curve): A curve repre-
senting the relationship between effective pressure and void
ratio of a soil as obtained from a consolidation test. The
curve has a characteristic shape when plotted on semilog paper
with pressure on the log scale. The various parts of the
curve and extensions to the parts have been designated as
recompression, compression, virgin compression, expansion,
rebound, and other descriptive names by various authorities.
(5)
primary state of stress: The stress in a geological formation
before it is disturbed by manmade works. (7)
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principal stress (strain): The stress (strain) normal to one of
three mutually perpendicular planes on which the shear
stresses (strains) at a point in a body are zero. (7)
profile, soil: A vertical section of the soil through all its
horizons and extending into the parent material. (1)
puddled soil: A soil in which structure has been mechanically
destroyed, which allows the soil to run together when
saturated with water. A soil that has been puddled occurs in
a massive nonstructural state. (2)
pyroclastic: Pertaining to fragmental materials produced by
usually explosive, aerial ejection of clastic particles from a
volcanic vent. (3)
reaction, soil: The degree of acidity or alkalinity of a soil,
usually expressed as a pH value. Descriptive terms commonly
associated with certain ranges in pH are: extremely acid,
less than 4.5; very strongly acid, 4.5 to 6.0; slightly cicid,
6.1 to 6.5; neutral, 6,6 to 7.3; slightly alkaline, 7.4 to
7.8; moderately alkaline, 7.9 to 8.4; strongly alkaline, 8.5
to 9.0; and very strongly alkaline, greater than 9.1. (1)
recharge: Natural or artificial replenishment of an aquifer.
(6)
regolith: All unconsolidated earth materials above the solid
bedrock. (3)
relative consistency: Ratio of: (a) The liquid minus the
natural water content, to (b) The plasticity index. (5)
relative density: The ratio of: (a) The difference between the
void ratio of a cohesionless soil in the loosest state and any
given void ratio, to (b) The difference between the void
ratios in the loosest and the densest states. (5)
remolded soil: Soil that has had its natural structure modified
by manipulation. (5)
residual shrinkage: The decrease in the bulk volume of soil in
addition to that caused by the loss of water. (1)
residual stress: Stress remaining in a solid under zero external
stress after some process that causes the dimensions of the
various parts of the solid to be incompatible under zero
stress; for example, (a) Deformation under the action of
external stress when some parts of the body suffer permanent
strain, or (b) Keating or cooling oi a boc'y in which the
thermal expcinuior coefficient ij, riot uniform throughout the
body. (S)
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retentivity profile, soil: A graph showing the retaining capa-
city of a soil as a function of depth. The retaining capacity
may be for water, for water at any given tension, for cations,
or for any other substances held by soils. (1)
rock: Natural solid mineral matter occurring in large masses or
fragments. (5)
sand: (a) A soil particle between 0.05 and 2.0 mm in diameter.
(b) Any one of five soil separates, namely: very coarse sand,
coarse sand, medium sand, fine sand, and very fine sand. See
soil separates. (c) A soil textural class. See soil texture.
(1)
saturation: A condition reached by a material, whether it be in
solid, gaseous, or liquid state, that holds another material
within itself in a given state in an amount such that no more
of such material can be held within it in the same state. The
material is then said to be saturated on in a condition of
saturation. (2)
sedimentation: The process of subsidence and deposition of sus-
pended matter carried by water, wastewater, or other liquids,
by gravity. It is usually accomplished by reducing the
velocity of the liquid below the point at which it can
transport the suspended material. (2)
seepage (percolation): The slow movement of gravitational water
through the soil or rock. (5)
seepage force: The force transmitted to the soil or rock grains
by seepage. (5)
sensitivity: Ratio of disturbed to undisturbed shear strength of
a soil. (6)
shear failure (failure by rupture): Failure in which movement
cause by shearing stresses in a soil or rock mass is of
sufficient magnitude to destroy or seriously endanger a struc-
ture, (a) General shear failure: Failure in which the
ultimate strength of the soil or rock is mobilized along the
entire potential surface of sliding before the structure
supported by the soil or rock is impaired by excessive
movement. (b) Local shear failure: Failure in which the
ultimate shearing strength of the soil or rock is mobilized
only locally along the potential surface of sliding at the
time the structure supported by the soil or rock is impaired
by excessive movement. (5)
shear force: A force directed parallel to the surface element
across which it acts. (7)
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shear plane: A plane along which failure of material occurs by
shearing. (7)
shear strain: The change in shape, expressed by the relative
change of the right angles at the corner of what was in the
undeforraed state an infinitesimally small rectangle or cube.
(7)
shear strength: The maximum resistance of a soil or rock to
shearing stresses. (5)
shear stress: Stress directed parallel to the surface element
across which it acts. (7)
shrinkage limit: The maximum water content at which a reduction
in water content will not cause a decrease in volume of the
soil mass. (5)
silt: (a) A soil separate consisting of particles between 0.005
and 0.002 mm in equivalent diameter. See soil separates. (b)
A soil texture class. See soil texture. (1)
skeleton grains: The individual grains larger than colloidal
size (> 0.002 mm) of a soil material; they consist of mineral
grains originally present in the parent material and resistant
siliceous and organic bodies'. (4)
slickensides: Polished and grooved surfaces produced by one mass
sliding past another. (1)
S-matrix: The material (plasma and/or skeleton grains and
associated voids) within the simplest (primary) peds, or com-
posing apedal soil materials that does not occur as
pedalogical features other than plasma separations; it may be
absent in some soil materials, for example those that consist
entirely of pedological features. (4)
soil: (a) The unconsolidated mineral material on the immediate
surface of the Earth that serves as a natural medium for the
growth of land plants. (b) The unconsolidated mineral matter
on the surface of the Earth that has been subjected to and
influenced by genetic and environmental factors of: parent
material, climate (including moisture and temperature
effects), macro- and microorganisms, and topography, all
acting over a period of time and producing a product, soil,
that differs from the material from which it is derived in
many physical, chemical, biological, and morphological proper-
ties and characteristics. (1)
soil air: The soil atmosphere; the gaseous phase of the soil,
being that volume not occupied by solid or liquid. (1)
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soil auger: A tool for boring into the soil and withdrawing a
small sample for field or laboratory observation. Soil augers
may be classified into several types as follows: (a) Those
with worm-type bits, unenclosed; (b) Those with worm-type bits
enclosed in a hollow cylinder; and (c) Those with a hollow
cylinder with a cutting edge at the lower end. (1)
soil fabric: The physical constitution of a soil material as
expressed by the spatial arrangement of the solid particles
and associated voids. (4)
soil horizon: A layer of soil or soil material approximately
parallel to the land surface and differing from adjacent
genetically related layers in physical, chemical, and
biological properties or characteristics such as color, struc-
ture, texture, consistency, kinds and numbers of organisms
present, degree of acidity or alkalinity, etc. (1)
soil mechanics: The science dealing with all phenomena which
affect the action of soil in a capacity in any way associated
with engineering. (8)
soil mineral: (a) Any mineral that occurs as a part of or in the
soil. (b) A natural inorganic compound with definite
physical, chemical, and crystalline properties (within the
limits of isomorphism), that occurs in the soil. (1)
soil moisture: Water contained in the soil. (1)
soil-moisture tension: See moisture tension (or pressure).
soil morphology: (a) The physical constitution, particularly the
structural properties, of the soil profile as exhibited by the
kinds, thickness, and arrangement of the horizons in the
profile, and by the texture, structure, consistency, and the
porosity of each horizon. (b) The structural characteristics
of the soil or any of its parts. (1)
soil physics: The organized body of knowledge concerned with the
physical characteristics of soil and with the methods employed
in their determinations. (5)
soil piping or tunneling: Accelerated erosion which results in
subterranean voids and tunnels. (1)
soil science: That science dealing with soils as a natural
resource on the surface of the Earth including soil formation,
classification, and mapping, and physical, chemical,
biological, and fertility properties of soil per se; and these
properties in relation to their management. (1)
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soil separates: Mineral particles, < 2.0 mm in equivalent
diameter, ranging between specified size limits. The names
and size limits of separates recognized in the U.S.D.A. system
are: very coarse sand, 2.0 to 1.0 mm; coarse sand, 1.0 to 0.5
mm; medium sand, 0.5 to 0.25 mm; fine sand, 0.25 to 0.10 mm;
very fine sand, 0.10 to 0.05 mm; silt, 0.05 to 0.002 mm; and
clay, < 0.002 mm. The U.S.C.S. particle and size range are as
follows: coarse sand, 2.0 to 4.76 mm; medium sand, 0.42 to
2.0 mm; fine sand, 0.074 to 0.42 mm; fines (silt and clay), <
0.074 mm. (Note: U.S.C.S. silt and clay designations are
determined by response of the soil to manipulation at various
water contents rather than by measurement of size.)
soil series: The basic unit of U.S.D.A. soil classification
being a subdivision of a family and consisting of soils which
are essentially alike in all major profile characteristics
except the texture of the A horizon. (1)
soil solution: The aqueous liquid phase of the soil and its
solutes. (1)
soil structure: The combination or arrangement of primary soil
particles into secondary particles, units, or peds. These
secondary units may be, but usually are not, arranged in the
profile in such a manner as to give a distinctive, charac-
teristic pattern. The secondary units are characterized and
classified on the basis of size, shape, arid degree of dis-
tinctness into classes, types, and grades, respectively. (1)
soil suction: A measure of the force of water retention in
unsaturated soil. Soil suction is equal to a force per unit
area that must be exceeded by an externally cipplied suction to
initiate water flow from the soil. Soil suction is expressed
in standard pressure terms. (2)
soil texture: The relative proportion of the various soil
separates in a soil as described by the classes of soil tex-
ture. (1)
soil water: A general term emphasizing the physical rather than
the chemical properties and behavior of the soil solution-
A. TERMS RELATING TO THE STATE OF WATER IN SOIL:
Water in soil is subject to several force fields originating
from: the presence of the soil solid phase; the dissolved salts;
the action of external gas pressure; and, the gravitational
field. These effects may be quantitatively expressed by
assigning an individual component potential to each. The sum of
these potentials is designated the total potential of soil water
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and may be identified with the partial specific Gibb's free
energy of the soil water relative to free pure water at the same
temperature. It should be noted that soil water is understood to
be the equilibrium solution in the soil; pure water refers to the
chemically pure compound HOH. (1)
capillary potential: The amount of work that must be done per
unit of pure water in order to transport reversibly and
isothermally an iitfinitesimal quantity of water, identical in
composition to the soil water, from a pool at the elevation
and the external gas pressure of the point under considera-
tion, to the soil water.
differential water capacity: The absolute value of the rate of
change of water content with soil water pressure. The water
capacity at a given water content will depend on the particu-
lar desorption or adsorption curve employed. Distinction
should be made between volumetric and specific water capacity.
gas pressure potential: This potential component is to be
considered only when external gas pressure differs from
atmospheric pressure as, e.g., in a pressure membrane
apparatus. A specific term and definition is not given.
gravitational potential: The amount of work that must be done
per unit quantity of pure water in order to transport
reversibly and isothermally an infinitesimal quantity of
water, identical in composition to the soil water, from a pool
at a specified elevation and at atmospheric pressure, to a
similar pool at the elevation of the point under considera-
tion.
hydraulic head: The elevation with respect to a specified
reference level at which water stands in a piezometer con-
nected to the point in question in the soil. Its definition
can be extended to soil above the water table if the
piezometer is replaced by a tensiometer. The hydraulic head
in systems under atmospheric pressure may be identified with a
potential expressed in terms of the height of a water column.
More specifically it can be identified with the sum of gravi-
tational and capillary potentials, and may be termed the
hydraulic potential.
osmotic potential: The amount of work that must be done per unit
quantity of pure water in order to transport reversibly and
isothermally an infinitesimal quantity of water from a pool of
pure water, at a specified elevation and at atmospheric pres-
sure, to a pool of water identical in composition to the soil
water (at the point under consideration), but in all other
respects being identical to the reference pool.
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osmotic pressure: The pressure to which a pool of water,
identical in composition to the soil water, must be subjected
in order to be in equilibrium, through a semipermeable mem-
brane, with a pool of pure water (semipermeable means
permeable only to water) . May be identified with the osmotic
potential defined above.
soil water pressure: The pressure (positive or negative),
relative to the external gas pressure Qn the soil water, to
which a solution identical in composition to the soil water
must be subjected in order to be in equilibrium through a
porous permeable wall with the soil water. May be identified
with the capillary potential defined above.
total potential (of soil water): The amount of work that must be
done per unit quantity of pure water in order to transport
reversibly and isothermally an infinitesimal, quantity of water
from a pool of pure water, at a specified elevation and at
atmospheric pressure, to the soil water (at the point under
consideration). The total potential (of soil water) consists
of the following:
total pressure: The pressure (positive or negative), relative to
the external gas pressure on the soil water, to which a pool
of pure water must be subjected in order to be in equilibrium
through a semipermeable membrane with the soil water. Total
pressure is thus equal to the sum of soil water pressure and
osmotic pressure. Total pressure may also be derived from the
measurement of the partial pressure of the water vapor in
equilibrium with the soil water. May be identified with the
total potential defined above when gravitational and external
gas pressure potentials can be neglected.
water content: The amount of water lost from the soil upon
drying to constant weight at 105 degrees Centigrade; expressed
either as the weight of water per unit weight of dry soil or
as the volume of water per unit bulk volume of soil. The
relationships between water content and soil water pressure
can be referred to as the soil moisture characteristic curve.
Depending upon whether the curve is determined with decreasing
or increasing water content one may designate it as a desorp-
tion or adsorption curve, respectively.
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B. TERMS RELATING TO THE MOVEMENT OF WATER IN SOIL
Experimentally it has been established that generally the
flow of a fluid in a porous medium can be described by Darcy's
law which states that the flux of fluid is proportional to the
driving force. In viscous flow of water in soils, the driving
force equals the negative gradient of the hydraulic potential.
(1)
hydraulic conductivity: The proportionality factor in Darcy's
law as applied to the viscous flow of water in soil, i.e., the
flux of water per unit gradient of hydraulic potential. For
the purpose of solving the partial differential equation of
the non-steady-state flow in unsaturated soil it is often
convenient to introduce a variable termed the soil water
diffusivity.
soil water diffusivity: The hydraulic conductivity divided by
the differential water capacity (care being taken to be con-
sistent with units), or the flux of water per unit gradient of
moisture content in the absence of other force fields.
specific gravity (of solids): Ratio of: (a) The weight in air
of a given volume of solids at a stated temperature, to (b)
The weight in air of an equal volume of distilled water at a
stated temperature. (1)
specific retention: Ratio of volume of suspended water to volume
of associated voids. (6)
specific surface: The surface area per unit of volume of soil
particles. (5)
specific yield: Ratio of voids not occupied by suspended water
to the total volume of the associated area. (6)
stability: The condition of a structure or a mass of material
when it is able to support the applied stress for a long time
without suffering any significant deformation or movement that
is not reversed by the release of stress. (7)
Standard Penetration Test (SPT): The most commonly used in situ
test to measure in relative terms the resistance of soil to
deformation by shearing. (6)
strain (linear or normal): The change in length per unit of
length in a given direction. (5)
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stratified: Arranged in strata, or layers. The term refers to
geologic material. Layers in soils that'result from the
processes of soil formation are called horizons; those
inherited from the parent material are called strata. (3)
strength: Maximum stress which a material can resist without
failing* for any given type of loading. (7)
stress: The force per unit area acting within the soil mass.
(5)
structure: One of the larger features of a rock mass, like
bedding, foliation, jointing, cleavage, or brecciation; also
the sum total of such features as contrasted with texture.
Also, in a broader sense, it refers to the structural features
of an area such as anticlines or synclines. (7) See also
soil structure.
susbsidence: The downward displacement of the overburden (rock
or soil, or both) lying above an underground excavation or
adjoining a surface excavation. Also the sinking of a part of
the earth's crust. (7)
subsoil: In general concept, that part of the soil below the
depth of plowing. (2)
/•
summation curve, particle size: A curve showing the accumulative
percentage by weight of particles within increasing (or de-
creasing) size limits as a function of diameter; the percent
by weight of each size fraction is plotted accumulatively on
the ordinate as a function of the total range of diameter
represented in the sample plotted on the abscissa. (1)
surface sealing: The orientation and packing of dispersed soil
particles in the immediate surface layer of the soil,
rendering it relatively impermeable to water. (1)
swelling pressure: Pressure exerted by confined swelling clays
when moisture content is increased. (6)
tensile strength (unconfined or uniaxial tensile strength): The
load per unit area at wjaich an unconfined cylindrical specimen
will fail in a simple tension (pull) test. (5)
tensiometer: A device for measuring the negative pressure (or
tension) of water in soil in situ; a porous, permeable ceramic
cup connected through a tube to a manometer or vacuum gauge.
(1)
tension, soil water: The expression, in positive terms, of the
negative hydraulic pressure of soil water. (2)
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transmissivity: Rate of transmission of water through unit width
of an aquifer under unit hydraulic gradient. (6)
transpiration: Water loss from leaves and other plant organs to
the atmosphere. (6)
triaxial compression: Compression caused by the application of
normal stresses in three perpendicular directions. (7)
triaxial shear test (triaxial compression test): A test in which
a cylndrical specimen of soil or rock encased in an impervious
membrane is subjected to a confining pressure and then loaded
axially to failure. (5)
triaxial state of stress: State of stress in which none of the
three principal stresses is zero. (5)
tuff: Volcanic ash usually more or less stratified and in
various states of consolidation. (1)
ultimate bearing capacity: The average load per unit of area
required to produce failure by rupture of a supporting soil or
rock mass. (5)
unconsolidated-undrained test (quick test): A soil test in which
the water content of the test specimen remains practically
unchanged during the application of the confining pressure and
the additional axial (or shearing) force. (5)
undisturbed sample: A soil sample that has been obtained by
methods in which every precaution has been taken to minimize
disturbance to the sample. (5)
uniaxial (unconfined) compression: Compression caused by the
application of normal stress in a single direction. (7)
uplift: The hydrostatic force of water exerted on or underneath
a structure, tending to cause a displacement of the structure.
(7)
unsaturated flow: The movement of water in a soil which is not
filled to capacity with water. (1)
vane shear test: An in-place shear test in which a rod with thin
radial vanes at the end is forced into the soil and the re-
sistance to rotation of the rod is determined. (5)
vapor pressure: (a) The pressure exerted by a vapor in a con-
fined space. It is a function of the temperature. (b) The
partial pressure of water vapor in the atmosphere. (c)
Partial pressure of any liquid. (2)
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viscosity: The cohesive force existing between particles of a
fluid which causes the fluid to offer resistance to a relative
sliding motion between particles. (2)
voids: Entities which are interconnected with each other either
through voids of dissimilar size and shape, through narrow
necks, or through intersection with voids of similar size and
shape. (4)
void ratio: The ratio of: (a) The volume of void space, to (b)
The volume of solid particles in a given soil mass. (5)
volumetric shrinkage (volumetric change): The decrease in
volume, expressed as a percentage of the soil mass when dried,
of a soil mass when the water content is reduced from a given
percentage to the shrinkage limit. (5)
water-holding capacity: The smallest value to which the water
content of a soil or rock can be reduced by gravity drainage.
(5)
water-retention curve: See moisture-retention curve.
water table: The upper surface of ground water or that level
below which the soil is saturated with water; locus of points
in soil water at which the hydraulic pressure is equal to
atmospheric pressure. (1)
weathering: All physical and chemical changes produced in rocks,
at or near the earth's surface, by atmospheric agents. (1)
yield stress; The stress beyond which the induced deformation is
not fully annulled after complete destressing. (7)
zero air voids curve (saturation curve): The curve showing the
zero air voids unit weight as a function of water content.
(1)
zone of aeration: That part of the ground in which the voids are
not continuously saturated. (1)
zone of saturation: That part of the ground in which the voids
are continuously saturated. (1)
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SOURCES
(1) Soil Science Society of America. 1975. Glossary of Soil
Science Terms. Madison, Wisconsin. 35 pp.
(2) Small Scale Waste Management Project (SSWMP). 1978.
Management of Small Waste Flows. EPA 600/2-78-173, U.S.
Environmental Protection Agency, Cincinnati, Ohio. 764 pp.
(3) Soil Conservation Service. 1977. Glossary of Selected
Geologic and Geomorphic Terms. Western Technical Service
Center, Portland, Oregon. 24 pp.
(4) Brewer, R. 1976. Fabric and Mineral Analysis of Soils.
R.E. Krieger Publishing Co., Huntington, New York. 482 pp.
(5) ASTM Committee D-18. 1979. Tentative Definitions of Terms
and Symbols Relating to Soil Mechanics, ASTM D 653-42T.
Annual Book of ASTM Standards, Part 19, Amer. Soc. for
Testing and Materials, Philadelphia, Pennsylvania.
(6) Institution of Civil Engineers. 1976. Manual of Applied
Geology for Engineers. Institution of Civil Engineers,
London. 378 pp.
(7) International Society for Rock Mechanics. 1972. Final
Document on Terminology, English Version. Comm. on Term-
inology, Symbols and Graphic Representation. 19 pp.
(8) Taylor, Donald W. 1948. Soil Mechanics. John Wiley and
Sons, Inc. 700 pp.
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