SEPA
United States
Environmental Protection
Agency
Municipal Environmental Research EPA 600 2 78 088a
Laboratory iy 1978
Cincinnati OH 45268
Research and Development
Use of Dredgings
for Landfill;
Summary Technical
Report
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RESEARCH REPORTING SERIES
Research reports of the Office of Research and Development, U.S. Environmental
Protection Agency, have been grouped into nine series. These nine broad cate-
gories were established to facilitate further development and application of en-
vironmental technology. Elimination of traditional grouping was consciously
planned to foster technology transfer and a maximum interface in related fields.
The nine series are:
1. Environmental Health Effects Research
2 Environmental Protection Technology
3. Ecological Research
4. Environmental Monitoring
5. Socioeconomic Environmental Studies
6. Scientific and Technical Assessment Reports (STAR)
7. Interagency Energy-Environment Research and Development
8. "Special" Reports
9. Miscellaneous Reports
This report has been assigned to the ENVIRONMENTAL PROTECTION TECH-
NOLOGY series. This series describes research performed to develop and dem-
onstrate instrumentation, equipment, and methodology to repair or prevent en-
vironmental degradation from point and non-point sources of pollution. This work
provides the new or improved technology required for the control and treatment
of pollution sources to meet environmental quality standards.
This document is available to the public through the National Technical Informa-
tion Service, Springfield, Virginia 22161.
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EPA-600/2-78-088a
May 1978
USE OF DREDGINGS FOR LANDFILL
Summary Technical Report
by
Raymond J. Krizek
and
Max W. Giger
Department of Civil Engineering
The Technological Institute
Northwestern University
Evanston, Illinois 60201
Grant No. R-800948 (15070 GCK)
Project Officers
Clifford Risley
U.S. Environmental Protection Agency
Region V
Chicago, Illinois 60604
and
Richard P. Traver
Storm and Combined Sewer Section
Wastewater Research Division
Municipal Environmental Research Laboratory (Cincinnati)
Edison, New Jersey 08817
MUNICIPAL ENVIRONMENTAL RESEARCH LABORATORY
OFFICE OF RESEARCH AND DEVELOPMENT
U.S. ENVIRONMENTAL PROTECTION AGENCY
CINCINNATI, OHIO 45268
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DISCLAIMER
This report has been reviewed by the Municipal Environmental Research
Laboratory, U.S. Environmental Protection Agency, and approved for publication.
Approval does not signify that the contents necessarily reflect the views
and.policies of the U.S. Environmental Protection Agency, nor does mention
of trade names or commercial products constitute endorsement or recommendation
for use.
ii
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FOREWORD
The Environmental Protection Agency was created because of increasing
public and government 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 that environment and the interplay between its components
require a concentrated and integrated attack on the problem.
Research and development is that necessary first step in problem solu-
tion and it involves defining the problem, measuring its impact, and searching
for solutions. The Municipal Environmental Research Laboratory develops new
and improved technology and systems for the prevention, treatment, and manage-
ment of wastewater and solid and hazardous waste pollutant discharges from
municipal and community sources, for the preservation and treatment for 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 most vital communications link between the researcher and
the user community.
The need to protect the ecology of the Great Lakes and the other
waterways of the United States has led to a variety of problems concerned
with the dredging and disposal of increasing volumes of polluted dredge
spoil in areas of high population density and industrial development. One
commonly used alternative to open water disposal is to place these polluted
sediments in diked containment areas to form landfills of marginal value.
However, due to the high costs involved, the scarcity of land, and other
environmental and economic considerations, these landfills should desirably
serve some useful purpose. Accordingly, this study was directed toward
evaluating quantitatively the engineering characteristics of dredged
materials as they affect their potential usefulness in a landfill.
Francis T. Mayo
Director
Municipal Environmental Research
Laboratory
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ABSTRACT
This research program was initiated with the overall objective of
evaluating the usefulness of dredged sediments as landfill material. The
study is limited to the deposition of polluted fresh water dredgings from the
Great Lakes area, and the major effort was centered around four disposal
sites in the harbor serving Toledo, Ohio.
A comprehensive sampling and testing program was undertaken in the field
and in the laboratory to determine the engineering characteristics of hydrau-
lically placed maintenance dredgings and the water quality effects associated
with a typical dredging and disposal operation. Samples were taken from
seven Great Lakes harbors, but the vast majority of the laboratory tests and
virtually all of the field work were performed on dredged materials from the
Toledo area. However, these materials are considered to be representative of
maintenance dredgings that are found at a number of fresh water ports.
Several thousand chemical analyses were conducted to assess the
pollution potential of dredged materials under chemically treated and non-
treated conditions. Several series of flocculation-sedimentation,
sedimentation-leaching, repeated leaching, and evaporation tests were con-
ducted to study the possibility of stabilizing these materials with chemical
additives and to evaluate the effects, if any, of such chemicals on the
leachates. Numerous index property tests were performed for classificatory
purposes, and several correlations among different properties and the results
of the index tests were established. An extensive series of conventional and
unconventional consolidation tests was conducted, and a number.of permea-
bility and electro-osmosis tests were performed to complement the permea-
bility data backcalculated from the consolidation tests. Laboratory strength
determinations made by means of miniature vane, cone, and unconfined compres-
sion tests were compared directly with field strength data determined by
field vane tests.
An extensive field monitoring program was undertaken to evaluate the
effects of a typical dredging and disposal operation on the water quality
parameters of the environs. The major thrust was directed toward investigat-
ing the performance of one particular disposal area which was filled with
almost a million cubic yards of dredgings over a two-year period and three
other similar disposal areas which had been used during the preceding decade.
Periodic vane shear tests were conducted in two of the areas, and settlement
plates were installed at one site to determine the time-dependent variations
in the strength and settlement, respectively. Several in situ permeability
tests were conducted on the foundation soils and the dredged materials to
evaluate drainage conditions. Finally, a one-dimensional mathematical model
was developed to assess the relative importance of gravity drainage and
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evapotranspiration on the desiccation and consolidation of a landfill
composed of maintenance dredgings.
This report was submitted in fulfillment of Grant R-800948 by
Northwestern University under the partial sponsorship of the U. S. Environ-
mental Protection Agency. This report covers a period from September 1970 to
December 1974, and the work was completed as of September 1977.
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TABLE OF CONTENTS
Foreword iii
Abstract iv
List of Figures x
List of Tables xi
Acknowledgments xii
SECTION 1 PERSPECTIVE 1
PROBLEMS OF DISPOSAL 1
NATURE OF RESEARCH PROGRAM 3
SECTION 2 CONCLUSIONS , 5
SECTION 3 RECOMMENDATIONS 7
SECTION 4 EXPERIMENTAL PROGRAM 9
SAMPLING 12
SURVEYING AND LOGGING 12
FIELD STUDY 12
LABORATORY STUDY 14
SECTION 5 WATER QUALITY STUDY 15
WATER QUALITY EVALUATION 16
Sampling Program 16
Laboratory Analyses 17
Sample Variability 17
Comparison of Influent-Effluent Quality 18
Fate of Pollutants during Dredging and Disposal Cycle 18
Pesticides 21
Bacteriological Analyses 21
WATER BUDGET 23
Effluent 23
Seepage . . . • 23
Influent 23
Precipitation and Evaporation 24
Synthesis 24
SUMMARY 25
SECTION 6 MATERIAL CHARACTERIZATION 26
RESULTS 26
Natural Water Content and Dry Unit Weight 26
Variation of Liquid Limit and Plastic Limit with Clay Content . . 27
Variation of Plasticity Index with Percent Clay 29
Relationship between Plasticity Index and Liquid Limit 29
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Variation of Limits and Plasticity Index with Activity 29
Particle Size Characteristics 29
Organic Matter 30
Chemistry and Mineralogy 30
SUMMARY 31
SECTION 7 CONSOLIDATION AND COMPRESSIBILITY 32
TEST PROCEDURES 32
LABORATORY RESULTS AND ANALYSES 33
Compression Index ... 33
Coefficient of Consolidation 34
Secondary Compression 35
Coefficient of Secondary Compression 37
FIELD SETTLEMENTS 37
CONCLUSIONS 40
SECTION 8 PERMEABILITY AND DRAINAGE 42
TEST PROGRAM 42
RESULTS 43
Drainage 43
Direct Permeability 44
Conventional Consolidation 45
Slurry Consolidation 45
Electro-Osmosis 47
Field Tests 47
SUMMARY 47
SECTION 9 SHEAR STRENGTH 48
TEST PROGRAM 48
RESULTS 49
Correlation between Shear Strength and Index Properties 52
SUMMARY 57
SECTION 10 MATHEMATICAL MODEL 58
THEORETICAL DEVELOPMENT 58
EXPERIMENTAL CHARACTERIZATION OF ENGINEERING PROPERTIES 60
NUMERICAL SOLUTION OF FLOW PROCESS 61
RESULTS 62
SUMMARY 64
SECTION 11 STABILIZATION 65
TEST PROGRAM 65
RESULTS 68
Flocculation-Sedimentation 68
Sediment at ion-Leaching 69
Repeated Leaching 70
Evaporation 71
SUMMARY 72
SECTION 12 SYNTHESIS 73
NATIONAL PERSPECTIVE 73
Major Geographic Regions 74
viii
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Types of Dredging Equipment 76
Hopper Dredge 76
Tipeline Dredge 76
Sidecaster Dredge 76
Dipper, Clamshell, and Bucket Dredges 76
Grain Size Classification 77
Types of Disposal . 77
Pollution Status 77
Beneficial Uses 78
Environmental and Legal Constraints 78
Economics 80
GREAT LAKES STUDY 81
Water Quality Aspects of Confined Disposal 81
Characterization of Dredged Materials . . • 82
Compressibility and Consolidation 82
Shear Strength 83
Potential Usefulness of Landfills 83
Improvement Techniques 83
References 85
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LIST OF FIGURES
Figure 4-1. Aerial Views of Toledo Disposal Areas 10
Figure 4-2. Cumulative Volume of Dredgings Deposited in Toledo
Containment Areas 11
Figure 4-3. Locations of Field Tests 13
Figure 6-1. Plasticity Relationships 28
Figure 7-1. Average Coefficient of Consolidation versus
Consolidation Pressure 35
Figure 7-2. Coefficient of Secondary Compression versus
Compression Index 38
Figure 7-3. Measured Field Settlements and Piezometric Heads 39
Figure 8-1. Summary of Values for Coefficient of Permeability .... 44
Figure 8-2. Coefficient of Permeability versus Void Ratio for
Conventional Consolidation Tests 46
Figure 9-1. Typical Profiles at Riverside Site in 1973 50
Figure 9-2. Variation of Shear Strength with Natural Water Content . . 53
Figure 9-3. Variation of Shear Strength with Dry Density 54
Figure 9-4. Variation of Shear Strength with Liquidity Index 55
Figure 10-1. Settlement versus Time for No Transpiration and
Different Drainage Conditions 63
Figure 10-2. Settlement versus Time for Impeded Drainage and
Different Coefficients of Transpiration 63
Figure 11-1. General Outline of Chemical Stabilization Program .... 66
Figure 12-1. Major Regions of Dredging Activity in the United
States 74
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LIST OF TABLES
Table 5-1. Comparison of Average Influent-Effluent
Concentrations 19
Table 5-2. Guidelines for Limiting Concentrations of Various
Pollutants in Bottom Sediments 20
Table 5-3. Average Values of Chemical Parameters at Various Stages
of Dredging and Disposal Cycle 20
Table 5-4. Summary of Data from Bacteriological Analyses 22
Table 6-1. Summary of Grain Size Analyses 27
Table 9-1. Values of Coefficients for Strength Relationships .... 56
Table 12-1. Summary of Dredged Material Volumes by Category and
Region 75
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ACKNOWLEDGMENTS
An almost unlimited number of individuals have made significant
contributions to the successful accomplishment of this research effort. In
an attempt to appropriately acknowledge the major roles and with a sincere
apology for any omissions, grateful acknowledgments are extended to:
The Environmental Protection Agency for supporting the major portion of the
work under Grant R-800948 (15070 GCK)
Northwestern University for the many ways it has cost-shared in this effort
John Mulhern, EPA Office of Research and Monitoring in Washington, D.C., for
his administrative assistance and advice
Clifford Risley, Project Officer, and Stephen Poloncsik, Region V Office of
EPA, for their role in monitoring this project
Gabor M. Karadi for his constant advice and friendly assistance throughout
this investigation, but particularly in the water quality study and the
development of the mathematical model
Paul L. Hummel and Abdelsalam M. Salem for their very competent and tireless
efforts in organizing and supervising the many detailed tasks associated with
virtually all phases of this research program
Various offices and personnel of the Corps of Engineers, but particularly the
personnel of the Toledo Field Office, for their whole-hearted cooperation in
almost every request made of them
xii
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SECTION 1
PERSPECTIVE
The development and maintenance of the navigable waterways in the United
States have been assigned by Congress to the U. S. Army Corps of Engineers.
The extent of this task is manifested by the fact that approximately 19,000
miles of waterways and 1,000 harbors must be kept open in order to accommo-
date our nation's commercial water traffic. The single greatest problem in
dealing with this task is the continuous accumulation of bottom sediments
through the natural transport phenomena that occur in these waters. About
300,000,000 cubic yards of bottom sediments must be dredged annually to main-
tain these waterways and harbors, and an additional average of 80,000,000
cubic yards are dredged to develop new projects or to increase the capacity
of existing systems. Of this amount approximately 11,000,000 cubic yards are
dredged from 115 Great Lakes harbors. Current (1974) annual costs for these
operations are estimated to be about $200,000,000, and the average unit cost
of dredging is about 50 cents per cubic yard although the latter can vary
from about 20 cents to tens of dollars per cubic yard, depending on the
circumstances.
PROBLEMS OF DISPOSAL
Until recently, most of these materials were deposited in the open
waters at selected disposal areas located sufficiently near the harbors to
minimize dredging costs, but far enough away to avoid interference with water
intakes, beaches, and other facilities. However, as a consequence of popula-
tion growth and industrial development in certain regions, the sediments
dredged from nearby harbors and channels have become increasingly polluted,
and concern about the impact of these polluted dredgings on the environment
has been expressed publicly through appeals to halt the open water disposal
of such materials. For example, the Rivers and Harbors Act (Public Law
91-611, Section 123) of 1970 requires that all polluted sediments dredged
from the Great Lakes region be placed in diked containment areas. Accord-
ingly, the Environmental Protection Agency, which is charged with the respon-
sibility for safeguarding the environment through the imposition of appro-
priate controls on waste disposal, has developed criteria for determining the
acceptability of open water disposal. The enforcement of these criteria has
led to the increased use of land or offshore containment areas to deposit
these dredged materials.
Various criteria have been used from time to time to determine whether
or not dredged bottom sediments are acceptable for open water disposal; how-
ever, as with virtually all pollution control criteria, these have been sub-
jected to much controversy. Nevertheless, they have formed the basis for
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evaluating the pollution potential of dredged materials and have played a
major role in deciding which of the alternative disposal schemes is most
appropriate; as such, these criteria have had a substantial impact on the
economics and feasibility of dredging operations. Although most situations
are evaluated on a case-by-case basis with due consideration being given to
the volume of dredged material, time of year, method of disposal, etc., the
major factors that influence the decision pertain to the physical, chemical,
and biological characteristics of the dredged sediments; critical pollution
levels (generally in terms of percent concentration) are assigned to each of
these characteristics, and these values may not be exceeded. Such criteria
are usually different than the effluent quality requirements set by state or
regional water quality control boards.
The requirement to avoid open water disposal of polluted dredgings has
led to difficulties in many areas because of a lack of practical and economi-
cally feasible alternatives. Aware of this situation and realizing the
implications thereof, the U. S. Army Corps of Engineers has undertaken sev-
eral studies to address this problem and is currently involved in a more
extensive five-year, 30 million dollar research program that is being
directed and administered at the Waterways Experiment Station. As a result
of previous investigations, the currently used major alternative to open
water disposal is to deposit the dredged sediments within diked enclosures
that are located near the dredging operation. Such a procedure has been
found to satisfactorily prevent the polluted sediments from reaching the open
waters, and, although very costly, it appears generally more feasible than
any other method of disposal, except deposition in open waters. Although the
desirability of using diked disposal areas is reasonably well established,
there is still a need to study the details associated with such operations
and to evaluate the potential benefits that might emanate from confined dis-
posal practices.
While the Corps of Engineers acknowledges the need to restrict open
water disposal operations, there is simultaneous concern that proper balance
and perspective be retained. For example, it has been estimated that about
7,000 acres of new land are needed each year to contain the volume of mainte-
nance dredgings that are currently being confined; furthermore, because of
increasing needs and more stringent regulations, this land requirement will
probably increase in the future. Since most dredging projects are located in
areas where excessive and often conflicting land requirements exist, it is
doubtful that society can tolerate the continued use of diked containment
areas solely for waste disposal. On the other hand, if suitable disposal
facilities are not provided, dredging operations may be suspended with the
attendant adverse effects on shipping and commerce. The needs for judicious
trade-offs are obvious, and the problem cannot be approached with tunnel
vision.
With our increasing need for additional parks, recreational areas,
wildlife sanctuaries, etc., dredged materials, if properly handled, may be
construed as a resource rather than a waste. However, since the majority of
polluted maintenance dredgings are fine-grained materials with high organic
contents and high water contents, the effectiveness and economy of associated
landfill operations are often hampered by the time-consuming process of
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dewatering and consolidation. This aspect is very significant because the
costs and benefits associated with this method of disposal on a long-term
basis will eventually dictate the feasibility of using diked disposal areas.
Land in urban areas surrounding most harbors is usually expensive and diffi-
cult to locate. Therefore, landfills of sufficiently high quality will play
a positive role in forthcoming systems of urban and regional development, but
low quality landfills are virtually worthless and a liability to the commu-
nity. Since most maintenance dredgings are not ideal materials for building
landfills, methods must be sought to improve the settlement and strength
characteristics of such dredged materials. Although it is possible to iso-
late without much difficulty the individual problems involved, the solutions
are, unfortunately, not so readily available.
NATURE OF RESEARCH PROGRAM
Cognizant of the issues involved, an extensive four-year research
program was undertaken to establish a background of quantitative data and a
framework of engineering interpretation within which guidance and insight can
be provided regarding the use of dredgings for landfill. The engineering
characteristics and mechanical behavior of dredged materials from the Great
Lakes area in general, and from the Toledo, Ohio, area in particular, have
been studied in considerable detail, both in the laboratory and in the field,
and the results have been synthesized to yield information whereby the anti-
cipated response of a landfill composed of similar dredged materials can be
reasonably well predicted. The experimental program that was undertaken to
accomplish this goal is outlined in Section 4. In addition, a portion of
this research effort was devoted to a water quality and quantity study to
determine the effect of a typical confined area dredging and disposal opera-
tion on surrounding environment, and the results of this investigation are
summarized in Section 5.
The physical and chemical character of the polluted dredgings studied in
this program is reported in Section 6, and the results exert a significant
influence on the measuring and interpretations advanced. Sections 7, 8, and
9 summarize the results of field and laboratory test programs to examine the
consolidation and compressibility response, permeability and drainage charac-
teristics, and strength behavior, respectively, of dredged materials. In
order to assess the relative importance of gravity drainage and evapotranspi-
ration on the dewatering process of a landfill composed of maintenance dredg-
ings and to facilitate the prediction of their time-dependent water content
distribution and settlement response, the one-dimensional mathematical model
described in Section 10 was developed.
Section 11 presents the results of a study to evaluate the feasibility
of stabilizing dredged materials by means of various chemical additives;
while some attention was given to economic considerations, the principal
thrust of this work is technical. And finally, a synthesis of the most sig-
nificant conclusions emanating from this study is given in Section 12;
although these findings are developed primarily from tests on samples from
the Toledo area, it is expected that they will be applicable to describe the
response of reasonably similar dredged materials in diked containment areas.
Details of these various studies are reported in the following series of
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individual reports (available through the National Technical Information
Service, Springfield, Virginia 22151):
Technical Report No. 1, Engineering Characteristics of Polluted Dredgings, by
Raymond J. Krizek, Gabor M. Karadi, and Paul L. Hummel.
Technical Report No. 2, Stabilization of Dredged Materials, by Raymond J.
Krizek, Gilbert L. Roderick, and Jau S. Jin.
Technical Report No. 3, Mathematical Model for One-Dimensional Desiccation
and Consolidation of Dredged Materials, by Raymond J. Krizek and Manuel
Casteleiro.
Technical Report No. 4, Water Quality Study for a Dredgings Disposal Area, by
Raymond J. Krizek, Brian J. Gallagher, and Gabor M. Karadi.
Technical Report No. 5, Behavior of Dredged Materials in Diked Containment
Areas, by Raymond J. Krizek and Abdelsalam M. Salem.
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SECTION 2
CONCLUSIONS
One commonly used alternative to the open water disposal of polluted
maintenance dredgings is to place these sediments in diked containment areas
to form landfills of marginal value. This study was directed toward evaluat-
ing quantitatively the engineering characteristics of dredged materials as
they affect their potential usefulness in a landfill. The work was limited
to fresh water dredgings from Great Lakes harbors, and most of the effort was
centered around four disposal sites in the Toledo (Ohio) harbor; however, the
results are considered to be applicable to a wide range of fresh water main-
tenance dredgings.
The water quality study demonstrated very clearly that the use of a
diked containment area as a settling basin serves to effectively remove from
the waterways the contaminants associated with polluted maintenance dredgings
because these contaminants tend to associate with the solid particles that
are retained within the diked enclosure. Furthermore, the quality of the
effluent water discharged from the disposal area was similar to that of the
ambient river water and slightly better than that of the groundwater.
Although the spoil that is retained in the disposal area represents a concen-
trated source of various pollutants that might leach into the groundwater,
this pollution hazard will probably be small in most cases due to the low
permeability of the dredged materials, which consist largely of organic silts
and clays with medium to high plasticity or inorganic clays with high
plasticity.
Based on results from an extensive series of slurry and conventional
consolidation tests, the compression index of these dredgings was found to
lie between 0.3 and 0.7 and to increase linearly with both water content and
liquid limit, and, for all practical purposes, a value of 0.0006 cm /sec
can be assumed to represent their average coefficient of consolidation. How-
ever, experience suggests that the times needed to reach ultimate settlements
in the field may be much shorter than those predicted from conventional labo-
ratory consolidation tests.
A mathematical model was developed to simulate the one-dimensional
desiccation-consolidation process that takes place in the field, and theo-
retical predictions of settlements were found to be in good agreement with
measured values. The coefficient of permeability, as obtained from conven-
tional consolidation tests and from direct permeability tests, ranged from
about ID"? to 10~** cm/sec (0.1 to 0.01 ft/yr) fo* dredged materials with void
ratios on the order of 1 to 2; however; field infiltration tests on materials
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with comparable void ratios yielded permeability coefficients about three
orders of magnitude higher.
The shear strength of hydraulically deposited dredged materials is
generally very low due to the inherent nature of the materials and the high
water content that is associated with the placement process. As a conse-
quence of consolidation, which was found to progress at a rate of about 4%
per year, the shear strength increased at a rate of about 4 kN/m2 (0.6 psi)
per year for a period of one decade.
In summary, the disposal of dredged sediments in diked containment areas
does improve the overall quality of the surrounding surface waters, but it is
not clear whether the degree of improvement realized is sufficient to justify
the considerably higher costs involved. In addition, the low initial shear
strength of these high-water-content, organic materials under natural condi-
tions, along with their slow rate of strength increase with time and their
associated large volume changes, seriously limit the usefulness of landfills
composed of dredged materials. Unless special steps are taken to improve the
quality of these materials, their use will be restricted largely to wildlife
refuges, parks, recreational areas, parking lots, access roads, and the con-
struction of light buildings with flexible structural joints and flexible
floors which would allow several inches of total settlement and a few inches
of differential settlement.
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SECTION 3
RECOMMENDATIONS
Although this study contributes substantially to our knowledge regarding
the quantitative behavior of polluted maintenance dredgings in a landfill,
there are still a number of unanswered questions that need to be addressed;
many, but not all of these questions are a consequence of the limited nature
of this study. Comparable information must be accumulated for dredgings from
a salt water environment and from dredging and disposal operations involving
other than periodic deposition of materials in a containment area by use of a
hopper dredge. Longer-term effects must be investigated for both the
mechanical properties of the landfill and the pollution potential of the
leachates. Considerable effort is required to better quantify the pollution
status of bottom sediment candidates for dredging and the analytical methods
that should be employed.
More attention needs to be given to improvements in the internal
hydraulic design characteristics of confined disposal areas in order to
obtain a more homogeneous distribution of sediments, as well as greater stor-
age capacity and improved effluent quality. A methodology should be devel-
oped to allow the containment area to be designed as a solids-liquid separa-
tion facility, making optimum use of flocculating agents and effluent filters,
if appropriate and cost effective. Despite the traditional characterization
of maintenance dredgings as an undesirable waste product, the possibility of
beneficial uses (such as strip mine reclamation, creation of wildlife ref-
uges, beach nourishment, and bottom substrate enhancement) should be
examined.
There are a number of legal constraints and questions that demand
further attention. For example, water quality criteria often impose severe
restrictions on the disposal of dredgings, and turbidity standards for the
receiving waters are frequently difficult, if not impractical, to meet. A
number of federal and state laws concerned with water quality and land use
contain expressions of policy that restrict the disposal and potential use-
fulness of dredged materials, and these should be objectively evaluated.
There are a myriad of laws and regulations that describe the types of prop-
erty that can or cannot be sold or donated and the procedures that are to be
followed in either case; these need to be interpreted with regard to the
donation or sale of dredged materials.
A cost-benefit analysis usually provides the strongest argument
(notwithstanding public sentiment) for a given course of action, and further
effort must be directed toward assessing the economics associated with dredg-
ing and disposal operations on a broad scale. Although improved technology
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will undoubtedly enhance the economics and environmental acceptability of
dredging and disposal operations, the more significant economic factors will
probably arise from the nontechnical measures, such as national policy,
social acceptance, environmental compatibility, and nature of contractual
agreements; for example, a change in the method of payment (based on care and
accuracy, rather than primarily on quantity) may substantially affect current
practice on many projects.
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SECTION 4
EXPERIMENTAL PROGRAM
The engineering characteristics of hydraulically placed maintenance
dredgings and the water quality effects associated with a typical dredging
and disposal operation were investigated in a four-year field and laboratory
test program. Although samples were taken from seven Great Lakes harbors
(Chicago, Illinois; Cleveland, Ohio; Detroit, Michigan; Green Bay, Wisconsin;
Milwaukee, Wisconsin; Monroe, Michigan; and Toledo, Ohio), the vast majority
of the laboratory tests and virtually all of the field work were conducted on
dredged materials from Toledo, Ohio. The basic reasons for this choice were
(a) the availability of a new diked containment area (Penn 7) that would be
filled in two years and could therefore be studied from the very beginning of
its history and (b) the existence of three other similar disposal sites
(Riverside, Penn 8, and the Island) which had been filled during the past ten
years or so and could thus be synthesized with Penn 7 to obtain a meaningful
historical perspective of the time-dependent behavior of landfills composed
of dredged materials. A general layout of these sites is given in
Figure 4-1. All four areas are nearly rectangular in plan and enclosed by
dikes ranging from about 12 to 20 feet (4 to 6 meters) in height. The Island
Site is located at the mouth of the Maumee River at the entrance to the bay;
it has dimensions of approximately 3800 feet by 1800 feet (1140 by 540 meters)
and covers 150 acres (610,000 square meters). The other three sites are
located along the northwest bank of the Maumee River; Riverside, Penn 7, and
Penn 8 have respective dimensions of approximately 2200 feet by 700 feet (660
by 210 meters), 1750 feet by 900 feet (530 by 260 meters), and 1200 feet by
900 feet (370 by 280 meters) with areal extents of about 34 acres (140,000
square meters),.31 acres (130,000 square meters), and 25 acres (100,000
square meters), respectively. .
During the past ten years about 9 million cubic yards (7 million cubic
meters) of bottom sediments were deposited in these four containment areas.
As shown in Figure 4-2, approximately 5 million cubic yards (4 million cubic
meters) were placed in the Island Site during 1964, 1965, 1967, 1970, 1971,
and 1973; 2 million cubic yards (1.5 million cubic meters), in Riverside Site
during 1968, 1969, 1970, and 1972; 1 million cubic yards (0.75 million cubic
meters), in Penn 7 Site during 1972 and 1973; and 1 million cubic yards (0.75
million cubic meters), in Penn 8 Site during 1966 and 1972. In order to syn-
thesize the time-dependent data from each of these four sites, a time refer-
ence or "birthdate" had to be established in each case; for this purpose a
time datum for each individual site was selected as the year in which the
site was half filled. An examination of Figure 4-2 indicates that the time
bases for Penn 7, Penn 8, Riverside, and the Island were 1972, 1966, 1967,
and 1968, respectively.
-------
-
.
Island Site
Penn 7
Island Site
m.
Penn 8
Riverside Site
Figure 4-1. Aerial Views of Toledo Disposal Areas
10
-------
I.U
If)
1 0.5
o
o
•5 °'-
g '-0
0
I
' 0.5
R
en
o>
"^3 "
0
0 2.0
-0
"to
8- 10
0
0
0)
§ 1
1 5.0
o>
"o
3 2 5
O
0
::-:-Xv-'.:
.:•::.':.
•{^"•.•••••••.'•'•'•"••Iv-.1
.v. Penn 7 >|;
364 1966 1968 1970 1972 1974 1976
^5^::-:i:jjN;:;;^^^i:\^i^
Vff/:y/^;.}.V:';V.
':':'• Penn 8 '-.-
964 1966 1968 1970 1972 1974 1976
£v.v>V
*••".".*•• *. "V " " » •"•" *
!•"•"• *.'• ' *.'• '•"• " " i V."
{•vV.^-::;:-:'':.:>
'£§&$:'£/&
:£:i&:'-.y£%'-&$$ Riverside ;J>>v>S
964 1966 1968 1970 1972 1974 1976
•*•*."• * *•"*
* « t"B* J , •
rtllliiii
fAvV^V-y.V-;
Kv.- :•'.•'•
."•''•'••'"•
^®P'SI
• *,'•*•'*•*•*•*•• •"*"
"." "r ••••"• r • * *.• .*.*
and I-:''.;-":'-'-.-::;
964 1966 1968 1970 1972 1974 1976
Year
Figure 4-2. Cumulative Volume of Dredgings
Deposited in Toledo Containment Areas
11
-------
SAMPLING
The major objective of the sampling program undertaken in this study was
to obtain representative dredging samples that could be used to quantify the
time-dependent engineering characteristics (such as pollution potential,
strength, compressibility, permeability, susceptibility to stabilization,
rates of desiccation and consolidation, and evapotranspiration) of typical
dredged materials from the Great Lakes region. Accordingly, a sampling pro-
gram was devised to obtain samples of dredged material (a) before dredging
(ambient bottom sediments), (b) during dredging (hoppers of dredges), (c)
during placement (inlet pipes and overflow weirs), and (d) after placement
(fill area); the sampling techniques employed have been explained by Hummel
and Krizek (1974). Many disturbed samples were taken from locations near the
inlet pipe at Riverside Site to determine the particle size variation with
distance from the inlet pipe. A major effort was expended to obtain undis-
turbed piston tube samples from each of the four sites at the locations indi-
cated in Figure 4-3. In particular, samples were taken from three Island
locations in 1971 and one Island location (3) in 1973 and 1974, six Riverside
locations (1, 4, 5, 6, 7, and 8) in 1971 and three Riverside locations (1, 6,
and 8) in 1972, 1973, and 1974, two Penn 8 locations in 1973 and 1974, and
nine Penn 7 locations in 1974.
SURVEYING
Field surveys were performed to determine the areal extents of Riverside
Site and Penn 7, and periodic elevations were taken to monitor the time-
dependent changes in the surface topography of the landfills. In addition, a
traverse was run several times along the crest of the Penn 7 dike to ascer-
tain whether or not lateral movements had occurred due to the placement of
dredged material within the site. In the early phases of the study seismic
(Krizek, Franklin, and Soriano, 1974) and electrical (Giger, Franklin, and
Krizek, 1973) field logging techniques were used at Riverside and the Island
Site to estimate spatial variations in material characteristics, and varia-
tions determined therefrom were compared with subsequent boring logs.
FIELD STUDY
Field vane strengths were measured at all sampling locations shown in
Figure 4-3 at the time when samples were taken. At some locations in Penn 7,
additional field vane tests were conducted in the late summer of 1974, but no
samples were taken. In an effort to assess the possible effects of evapora-
tion on the dewatering and strength buildup of a landfill, several series of
small-scale (about 0.25 square meter) field evaporation tests under drained
and undrained conditions were performed in the vicinity of Penn 7 and the
Toledo Field Office of the Corps of Engineers. In view of the importance of
the permeability and drainage characteristics of dredged materials in a land-
fill, two field infiltration tests were conducted at Riverside Site to sup-
plement an extensive laboratory test program.
A major thrust of this study was to investigate in considerable detail
the performance of a typical disposal area, which was selected to be the
Penn 7 Site. As this containment area was being filled, an extensive field
12
-------
Weir
Island
Discharge Pipe
200 too o 200
Scale (meters)
4OO
N
•
a
•r *.
Discharge
Pipe
Riverside
N
Discharge
•!••*—••
Pipe
Weir
Discharge
Pipe
Penn 7
aoo 100
o zoo
Scale (meters)
4OO
Figure 4-3. Locations of Field Tests
13
-------
monitoring program was undertaken to evaluate the effects of such a dredging
and disposal operation on the water quality parameters of the environs; pri-
mary emphasis was given to the inflow and outflow materials from the contain-
ment area, and parameters obtained therefrom were compared with each other
and with similar parameters of ambient waters, groundwaters, and samples
taken at other stages of the dredging and disposal cycle. In the landfill
itself specially designed settlement plate-piezometer units were installed at
five locations (2/10, 5/8, 5/10, 5/13, and 15/10 in Figure 4-3) to monitor
the time-dependent variations in the settlements and the pore water pres-
sures. A series of field permeability tests was conducted on the foundation
soils of the Penn 7 disposal site in order to provide guidance for selecting
drainage conditions at the bottom boundary for use in the mathematical model.
As mentioned previously, Penn 7 was chosen for this work because it offered
an opportunity to study the history of a diked containment area from a time
prior to the deposition of any spoil until a time about one year after it was
filled. Slurry and groundwater sampling was required for this purpose.
Also, an attempt has been made to establish a water budget.
LABORATORY STUDY
Much supporting effort in this research program was directed towards a
rather comprehensive laboratory determination of the various engineering
characteristics of dredged materials. A large number (several thousand) of
chemical analyses were performed to assess the pollution potential of dredged
materials under chemically treated and nontreated conditions. Several series
of flocculation-sedimentation, sedimentation-leaching, repeated leaching, and
evaporation tests were conducted (a) to study the possibility of stabilizing
these materials with chemical additives and (b) to evaluate the effects, if
any, of such chemicals on the leachates. Numerous index property tests were
conducted for classificatory purposes, and several correlations among differ-
ent properties were established. An extensive series of conventional con-
solidation tests was performed on undisturbed samples to study both primary
and secondary consolidation characteristics, and this consolidation response
was supplemented by data from several slurry consolidation tests that were
conducted in specially designed slurry consolidometers (Sheeran and Krizek,
1971). A number of direct permeability, gravity drainage, and electro-
osmosis tests were performed to complement the permeability data that were
back-calculated from conventional consolidation tests. Laboratory shear
strength determinations made by means of miniature vane, cone, and unconfined
compression tests were compared directly with field strength data, and sev-
eral correlations with index properties were established.
14
-------
SECTION 5
WATER QUALITY STUDY
This water quality study was conducted at the Penn 7 disposal site in
Toledo, Ohio, and consists essentially of two parts. In the first part the
input slurry to a disposal site is characterized according to its pollution
loading, and the effectiveness of a diked containment area to retain the con-
taminants in the dredge spoil and to preserve the quality of the water
returning to the river is examined by means of an extensive sampling and
testing program of influent and effluent materials; also studied is the
change in the quality of the groundwater beneath a disposal site. The second
part of the study is directed toward evaluating, insofar as possible, the
quantitative aspects of the water budget for a typical disposal site.
The diked containment area is regarded as a closed system, and its
boundaries are considered to be the four earth sidewalls, the original ground
before deposition of any dredgings, and the surface of the water at any given
time. Accordingly, the water budget of the diked area can be described in
terms of the following variables:
I Influent of slurry pumped from hopper dredge (volume per unit time)
0 Outflow discharged over a control weir (volume per unit time)
P Precipitation (volume per unit time)
E Evaporation (volume per unit time)
D Drainage into the groundwater or through the dikes (volume per unit
time)
S Storage of water within the diked containment area at any given time
(volume)
Hence, at any point in the deposition process the time rate of water storage,
AS/AT, may be expressed as
AS/AT = (I + P) - (0 + E + D) (5-1)
However, only four of the six budget variables are known with any degree of
accuracy. The outflow quantity, 0, was measured and recorded by a flow mea-
suring system installed at the discharge weir. Precipitation and evapora-
tion, P and E, were monitored by a recording rain gauge and a recording
evaporimeter installed nearby at the Toledo Field Office of the Corps of
Engineers. The quantity of water stored, S, and time rate of change of water
stored, AS/AT, were obtained from measurements of the water level, which was
incrementally controlled by changing the height of the discharge weir. It
was planned to obtain the inflow quantity, I, from Corps of Engineers records
of pumping operations, but it turned out that these records do not reflect
15
-------
the quantities of flush water used to clean the hopper dredge and pipeline
before and after pumping operations; consequently, I is not known with any
degree of certainty. The sixth variable, D, was not measured. (This
variable was originally intended to play the role of the balance term in the
water budget.) Although it is possible that some slight runoff could enter
the diked containment area, surface runoff was assumed to be negligible.
This study spanned the period from August 20 to December 20, 1972,
during which time dredgings were pumped almost continuously (about 8 loads
per day, except on Sundays) into the Penn 7 area. However, it was not until
October 19, 1972, that the water level in the disposal site reached the point
where effluent began to flow over the weir; then, on November 13, 1972, the
flow meter malfunctioned. Although data for the water quality study were
accumulated over virtually the entire four-month period, the collection of
water quantity data to establish the water budget was limited to a 26-day
period for all practical purposes.
WATER QUALITY EVALUATION
A sampling program was undertaken to characterize, insofar as reasonably
possible, the quality of the dredged materials and associated waters at vari-
ous stages during the dredging and disposal cycle. Specifically included in
this characterization are samples of (a) bottom sediments, (b) water from the
overflow of the hopper dredge, (c) material from the bin of the hopper
dredge, (d) slurry from the inflow pipe to the disposal area, (e) water from
the overflow weir of the disposal area, (f) river water, and (g) groundwater,
but emphasis was given to the influent and effluent samples from the inflow
pipe and overflow weir. The details of this study have been presented by
Krizek, Gallagher, and Karadi (1974), and only a brief summary of the results
is included herein.
Sampling Program
Since dredgings were pumped into Penn 7 during 107 days over a 123-day
period at a rate of approximately 8 loads per day, there were about 850 indi-
vidual inputs of varying quality and quantity. Ideally, the influent and
effluent materials should have been sampled several times during each pumping
operation since the nature of the dredgings varied considerably. However,
this would have posed an impossible task of sampling and analysis, and a ran-
dom sampling approach was therefore pursued. One-gallon (3.8-liter) samples
were normally collected, packed in ice chests, and transported to the labora-
tory, where they were stored at approximately 4°C until tested. Special
handling was given to the samples to be subjected to bacteriological tests,
and such tests were conducted within 24 hours.
Special efforts were made to evaluate the adequacy of the sampling
procedures utilized and the statistical significance of the resulting data.
In certain cases samples were taken (a) simultaneously from different points
in the slurry jet emerging from the inflow pipe, (b) from the same load at
five-minute intervals, (c) from each load in any given day, and (d) from two
or three loads every day for four or five consecutive days. Variability
tests on these groups of samples were performed to assess the adequacy of a
16
-------
sampling, program wherein replicate samples of slurry inflow were collected
randomly once or twice a week; however, no samples were taken during the
extreme beginning or end of a pumping cycle since such periods would likely
be dominated by flush water and thereby yield grossly unrepresentative
samples. Variations in samples from the overflow weir were relatively small
compared to variations in slurry samples, and fewer samples were therefore
taken. Initial groundwater samples were taken prior to the deposition of any
dredgings in the area, and follow-up sets of samples were taken about one
year after dredging disposal had commence and after the site was filled. An
extremely limited number of samples were obtained during each of the other
stages of the dredging and disposal operation, so the results must be
assessed accordingly.
Laboratory Analyses
The influent into the diked disposal area was expected to have a high
solids content consisting of silt, clay, and organic matter. In addition,
high levels of phosphorus and nitrogen were expected since the sediments
originate in agricultural areas. Many trace metals and some heavy metals and
other toxic substances were anticipated, and, due to the industrial nature of
the local surroundings, it was likely that oil, grease, and other persistent
organics would be found. Although it was expected that most of the solids
and insoluble substances would be retained in the diked area, it is probable
that all of these contaminants would be found in trace quantities in the
effluent with the more soluble substances in higher concentrations. Accord-
ingly, the fairly comprehensive set of analyses outlined below was undertaken
to quantitatively evaluate these aspects of the problem. In addition, some
bacteriological tests were performed, and a gas chromatographic analysis was
conducted on the solids and water portions of one sample to determine the
presence of chlorinated organic compounds.
General Water Quality Parameters Organics
Total Solids
Dissolved Nonvolatile Solids
Suspended Nonvolatile Solids
Hydrogen Ion Concentration (pH)
Total Silica
Nutrients
Total Nitrogen
Ammonia Nitrogen
Nitrate Nitrogen
Nitrite Nitrogen
Total Phosphate
Soluble Phosphate
Sample Variability
Biochemical Oxygen Demand (BOD)
Chemical Oxygen Demand (COD)
Total Volatile Solids
Suspended Volatile Solids
Dissolved Volatile Solids
Oil and Grease
Metals
Cadmium Manganese
Calcium Potassium
Copper Sodium
Iron Zinc
Lead
During this sampling program, several variability tests were conducted
on the influent materials by sampling periodically during some particular
17
-------
phase of the disposal operation. In one series of tests samples were taken
at five-minute intervals after pumping started until it was almost completed,
and it was found that the concentrations of several constituents in the
sample varied considerably, but irregularly, with a slightly decreasing trend
as pumping continued. A similar series of variability tests was performed on
samples taken intermittently over a period of 14 hours, but again no clearly
predictable patterns were detected. Based on the results of these tests, it
was decided that replicate samples collected randomly (except to avoid the
extreme starting or ending periods of a pumpout cycle) once or twice a week
would yield representative samples for the determination of influent quality.
Comparison of Influent-Effluent Quality
Detailed data from the chemical analyses on the influent slurry samples
and effluent water samples were first averaged on a daily basis (that is, the
measured values for all samples taken in any given day were averaged); then,
these daily averages were averaged over the duration of the field test pro-
gram, and the overall results are summarized in Table 5-1. It can readily be
seen that the diked containment area serves effectively to retain a substan-
tial portion of virtually all pollutants. Of the sixteen parameters listed
in Table 5-J., the concentrations of ten were reduced by well over 95%, and
five were reduced by values ranging from 45% to 90%; nitrate nitrogen showed
a more than tenfold increase, but this was not unexpected. If viewed in
terms of the pollution criteria given in Table 5-2, the average values (when
converted to a dry weight basis) of volatile solids, COD, lead, and zinc
exceed the specified limiting concentrations, thereby ascertaining that these
dredgings are "polluted"; since no measurements of total Kjeldahl nitrogen,
oil and grease, or mercury were made, definite evaluations regarding their
role as "pollution parameters" cannot be advanced.
Fate of Pollutants during Dredging and Disposal Cycle
Table 5-3 places the influent-effluent comparisons described above in
the broader context of the overall dredging and disposal cycle. In addition
to the extensive sampling program undertaken for influent and effluent
samples, a limited number of samples were taken from the harbor bottom before
dredging, from the hopper of the dredge and from the hopper overflow during
the dredging operation, from the ambient river water away from the disposal
site, and from the groundwater in the vicinity of the disposal site. Within
the framework of these data (first averaged on a daily basis, and then an
average of the daily averages), the following conclusions may be advanced:
1. The concentrations of pollutants are very high in the bottom sediments,
the materials in the hopper bin, and the water that overflows the hopper
bins as they become filled.
2. Although still quite high, the concentrations of pollutants in the
slurry deposited in the containment area are reduced somewhat by the
addition of ambient river water, which acts as a carrier to pump the
dredgings into the diked enclosure; however, the contaminants appear to
reflect agricultural deposits rather than industrial or sewage wastes.
18
-------
Table 5-1. Comparison of Average Influent-Effluent Concentrations
Parameter
Total Solids
Total Silica
Chemical Oxygen Demand
Biological Oxygen Demand
Total Phosphate
Nitrite Nitrogen
Nitrate Nitrogen
Cadmium
Calcium
Copper
Iron
Lead
Manganese
Potassium
Sodium
Zinc
Units
-%
7.
mg/X
mg/X
ppm
ppm
"pprn
ppm
ppm
ppm
ppm
ppm
ppm
ppm
ppm
ppm
Concentration
Influent
Penn 7
14.9
11.5
15,000
334
344
0.045
0.7
0.66
4000
7.1
3000
10.3
63
525
120
17
Effluent
Penn 7
0.043
0.014
135
5.3
4.5
0.010
8.0
0.24
100
3.9
.5.6
5.7
2.1
6.5
15
0.7
Percent
Increase (+)
or
Decrease (-)
-99.7
-99.9
-99.1
-98.4
-98.7
-77.8
+1145
-63.5
-97.5
-45.0
-99.8
-45.0
-96.7
-98.8
-87.5
-95.9
19
-------
Table 5-2. Guidelines for Limiting Concentrations of
Various Pollutants in Bottom Sediments
Perm 7
Parameter
Percent Concentration
(Dry Weight Basis)
Volatile Solids
Chemical Oxygen Demand (COD)
Total Kjeldahl Nitrogen
Oil and Grease
Mercury
Lead
Zinc
6
•5
0
0
0.10
0.15
0.0001
0.005
0.005
Table 5-3. Average Values of Chemical Parameters at
Various Stages of Dredging and Disposal Cycle
Perm 7
QmSal Til Bat lei
Teui Solid!
Tool Nonvolatile Solid!
Total Volatile Sol Us
Komolatlle Suspended Solids
Volatile Suspended Solids
femmlatlle Diitolnd Solid!
Volatile Dissolved SolUi
Ton! SI lira
Onicat fertea Dsaonl
llodnicil Ocrtm Hound
Total Mtnfni
Aaaonia Kltrocra
Nitrite Utrefcn
nitrate Kitrotcn
Total Phosphate
Soluble PhosphaU
ChMaa
Calehu
&TT"
Iron
lead
IhnfafleM
Potasstal
Sodiui
Zinc
niuitnat
P«
tkiitt
«*/! '
•S/i
Pf
PP*
PI*1
PP*
PP*
PP»
PF*
PP*
PI"
PI"
PP"
PP"
PP"
PP"
PI»>
t
lOttfli
Sedtaenu
53.031
11. «a
1.17J
U.IIZ
1.1S»
0.026
0.014
Z6.203
51. 100
0.051
O.«02
Ui
0.112
1.S7
7.400
1.4
4.400
14.2
us. 4
29S
IZ1.I
33.9
t.l
Hefner
0»«TflO»
19.1M .
1I.4S9 '
O.H7
11.411
0.6S1
0.021
0.016
14.294
MO
e.n«
0.176
1.15
t.MO
9.2
J.roo
11. S
12.1
155
117.5
29.4
<•>
Avcrsfc »
•isr
43. 5M
42.072
1.417
42.044
1.425
0.021
0.012
55.171
0.015
0.142
47«
0.065
1.J9
6.600
l.«
3,600
1S.6
157.1
240
164. S
59. t
7.9
line
Slurry
Inflov
14.190
13.909
1.116
11.IU
1.099
O.OS1
0.017
11. SO
IS, 000
334
155
17
0.04S
0.694
J44
0.146
0.66
4,000
7.1
3.000
10.2
62. »
S2S
121.2
17.1
0.19
6.9
Dikr
dm-nov
0.046
. 0.03*
0.012
0.014
US
5.5
0.01
1.05
4.S
0.34
101
5.<
S.S
S.7
2.1
6.5
1S.1
0.7
6.7
Htm
Miter
0.025
0.019
0.004
0.019
0.004
0.012
m
2
0.01
7.1
5.9
t.50
7$
.5
.5
.0
.0
.9
10.2
O.I
6.1
Ciuuul
Hater
0.221
0.179
0.075
0.122
0.052
O.OS7
0.041
0.079
117
4.1
15. S
13.S
0.026
11.1
7.4
0.5!
m
6.2
65.5
6.7
3.2
26.4
31.1
1.12
6.7
20
-------
3. With the exception of nitrate nitrogen, a marked reduction in pollutant
concentrations occurs before the effluent water is discharged over the
weir back into the river, and the quality of the effluent water is simi-
lar to that of the river water.
4. The quality of the groundwater is slightly worse than that of either the
river water or the effluent water.
Pesticides
Gas chromatograph analyses were conducted on the solid and supernatant
phases of one slurry sample to check for the presence of pesticide materials.
Based on this very limited amount of data, it appears that significant
amounts of chlorinated organic compounds are present in dredged sediments or
suspended solids, but, due to their insolubility, only a trace of these com-
pounds was detected in the supernatant water. A similar conclusion was
obtained from a much more comprehensive investigation reported by Krizek,
Karadi, and Hummel (1973).
Bacteriological Analyses
Samples taken from the slurry influent, dike overflow, underlying
groundwater, and a few other sources were tested before, during, and after
the disposal of dredgings in the Penn 7 area to determine the presence of
bacteriological organisms, and the detailed results are summarized in
Table 5-4. The total and fecal coliform tests have been used traditionally
as indicators of polluted water which could be a health hazard; the presence
of fecal coliforms in significant numbers suggests that fecal matter from
animals or human beings has contaminated the water and that other pathogenic
bacteria may be present.
Although the interpretation of such tests is very difficult due to the
many variables that can affect the results, the limited data given in
Table 5-4 suggest that the slurry influent is extremely polluted from a bac-
teriological point of view; fecal coliforms are in the tens of thousands of
organisms per 100 m&, and total coliforms typically range from tens of thou-
sands to hundreds of thousands of organisms per 100 m£. The effluent water
from the diked enclosure, as well as the water from the. Maumee River, is
quite polluted at some times but relatively unpolluted at other times. To
place the test data in perspective, the standards for most states require
zero coliforms for drinking water "quality, but they allow as high as 1000
organisms per 100 m& for contact sports (such as swimming) and up to 5000
organisms per 100 m& for noncontact sports (such as boating). The State of
Ohio standards for lakes and streams require that the average of at least
five samples taken within 30 days does not exceed 200 fecal coliforms per
100 m& and that not more than 10% of the samples exceed 400 organisms per
100 m&. Although many more samples would have to be taken and tested before
any final judgment could be made (as the numbers of bacteriological organisms
can change rapidly due to varying environmental conditions), it appears that
the effluent water from the Penn 7 containment area resembles the general
quality of the water in the Maumee River.
21
-------
Table 5-4. Summary of Data from Bacteriological Analyses
9»BpIo Location rad Tlam
CrouodMUr fro. Utlli (0 Co 10 f««t)
Autiiot J. 1972
Crauoawur (TOM IfclU (10 to 20 (tic)
AufuM 2. 1*72
Crooadintor fro. UilU (0 to 10 fwt)
Atifuic 1, 197}
eramdwcor fro. U.L1. (10 Co JO f««c)
toliut 1, 1973
etouadwur fro. Hilli (0 to 10 fe.t)
Aupuc 22, 1974
GrauadMCor fro. utlli (0 to 10 ftct)
F.bruMT 6, 197S
XaflaraC Slurry
tetut 25, 1972
laflaant Slurry
ABfuoc 1, 1973
SUfuat Hid fro. Dl>oa«*l An*
Jufuic 1, !»>}
St«(MU Itaur fro. Dl«po»«l Aru
Auia>t I. 197}
««t«r fro. ovirf la* Hiti
Aaruc 1, 1973
>U«T fro. ontflov ttiir
*u(u«c 22, 1974
tbttr (rax MIII.II Slor
Aufiut 1, 1973
VMir fro. NUBM tlwr
Aatu»C 21. 1974
Itaur fro. IU >B>U with * Tlluo of 120,000
on« iopl< irtch •
-------
The situation regarding the groundwater is very difficult to assess due
to the wide variation of test results. Although some localized areas appear
reasonably unpolluted, others appear quite highly polluted. The data indi-
cate that some degree of pollution existed before any dredged spoil was
placed in the diked enclosure; this was probably caused by the presence of
stagnant surface waters. It was observed that many wild animals, such as
pheasants, ducks, rabbits, and rats, used the partially water-filled dike
enclosure as a habitat, and this could account for the presence of coliforms
in relatively high numbers. However, these data do not suggest that the dis-
posal of dredgings in the Penn 7 area has adversely affected the quality of
the groundwater from a bacteriological point of view during the time period
of this study. The stagnant mud and water within the diked area are
extremely polluted, and the goundwater may become polluted with time due to
leaching of the deposited dredged materials.
WATER BUDGET
Included in this section are brief descriptions of the techniques used
to establish quantitative values for the various components of the water bud-
get. Detailed data have been presented by Krizek, Gallagher, and Karadi
(1974), and only summaries of the results are given here.
Effluent
A recording flow meter was installed at the overflow weir to record the
quantity of effluent that exited the system over the weir. The outflow quan-
tity was calculated from the recorded crest height in conjunction with a
rectangular weir arrangement. The system was installed on October 3, 1972,
before the dike had filled to the overflow level, and it began recording on
October 19, 1972. The recording system operated satisfactorily for the first
24 days, but it malfunctioned during the last 30 days while the disposal area
was being filled. However, usable data obtained during the period of opera-
tion provided considerable insight into the water quantity budget. The quan-
tity of water that left the disposal area via the calibrated overflow weir
between October 19 (at which time the water first began to flow over the
weir) and November 13 (about which time the probe became inoperable due to
vandalism) was recorded. An average of these data taken over the 26-day test
period indicates that about 425,000 cubic feet (12,000 cubic meters) of water
exited the disposal area each day via the overflow weir.
Seepage
Undetermined amounts of water may have seeped into the underlying
foundation soils or through the earthen dikes during the course of this test
program. Although there was no reasonable way to measure this quantity, it
is believed to be small due to the low permeability of the dredged materials
(Krizek and Casteleiro, 1974).
Influent
As stated previously, it was intended to obtain the quantity of influent
water and slurry pumped into the disposal area from Corps of Engineers
23
-------
records, but available data render impossible the task of determining this
quantity with any degree of accuracy. Nevertheless, inflow quantities
deduced from the information available are reasonably consistent with mea-
sured outflow quantities and the nature of the pumping operation,
Precipitation and Evaporation
A recording rain gauge and a recording evaporimeter were installed at
the Toledo Field Office of the Corps of Engineers, and daily records of the
precipitation, evaporation, net input, and accumulative input between
August 20 and December 20, 1972, were obtained. The net accumulative input
over the entire test period was recorded as 8.64 inches (22.0 centimeters)
which, when distributed over an area of 1.34 million square feet (0.125 mil-
lion square meters), represents a total volume input to the disposal area of
about 970,000 cubic feet (27,000 cubic meters) or almost 8,000 cubic feet
(220 cubic meters) per day on the average. Of particular concern to this
study is the 26-day period from October 19 to November 13, 1972, during which
time the major part of the usable data was accumulated. Since there was a
net accumulative input of 2.60 inches (6.6 centimeters) during this period,
the total volume input would amount to about 290,000 cubic feet (8,000 cubic
meters) and the daily input was almost 11,000 cubic feet (300 cubic meters).
These daily volumes represent about 2% of the daily quantity of water that
exited the disposal area via the overflow weir; consequently, its role in
modifying the quality of the waters comprising the water budget can be rea-
sonably neglected.
Synthesis
Although the water budget cannot be balanced with any degree of accuracy
due to a combination of incomplete and inadequate data, the proper orders of
magnitude can be reasonably well established from an overall evaluation of
the available data. The quantity of effluent from the area was determined
with a fair degree of confidence to average about 425,000 cubic feet (12,000
cubic meters) per day for the first 26 days during which water overflowed the
weir, and the quantity of influent substantiates this measurement in a gen-
eral way. Since the measured net volume of precipitation and evaporation
represents less than 2% of the effluent quantity, it can be neglected, espe-
cially in the water quality analyses. The undetermined quantity of seepage
into the underlying foundation soils is probably small due to the low permea-
bility of both the dredgings and the upper strata of the original ground.
Runoff into the containment area is almost certainly negligible due to the
presence of a surrounding dike.
The total amounts of dredged material placed in Perm 7 during the 1972
and 1973 dredging seasons were about 570,000 and 350,000 cubic yards (440,000
and 270,000 cubic meters), respectively, in terms of bin-measure volume.
When multiplied by 0.65 to convert bin-measure volumes to disposal-site vol-
umes (Krizek and Giger, 1974), these materials occupy about 370,000 and
230,001 cubic yards (280,000 and 180,000 cubic meters), respectively.
Assuming an in-place dry density of 50 pounds per cubic foot (8 kN/m^) and a
value of 2.70 for the specific gravity of solids, the actual solids may be
determined to occupy only about 30% of the bulk volume. Hence, when viewed
24
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in context of the overall volumes of solids and water pumped into a disposal
area, the net volume of the solid particles represents only a small portion
of the total volume.
SUMMARY
A four-month water quality study was conducted at the Penn 7 disposal
site in Toledo, Ohio, and an assessment of the fate of pollutants during the
dredging disposal cycle was made. In general, it was found that (a) the con-
cept of using a diked containment area as a settling basin to retain the sol-
ids in dredged materials does effectively improve the water quality of the
mixtures that pass through it; many of the contaminants apparently associate
with the solid particles, thereby settling out of suspension with the solids
and reducing significantly the concentrations of polluting materials; (b) the
quality of the effluent that was discharged from the disposal area is similar
to that of the ambient river water and slightly better than that of the
groundwater; and (c) the retained spoil in the diked enclosure represents a
concentrated source of various pollutants that may leach into the groundwater
as time passes, thereby reducing to some extent the advantage gained by plac-
ing polluted dredged materials in confined disposal areas. Although consid-
erable efforts were expended to monitor the various components of the water
budget, limited success was achieved because it was impossible to obtain
accurate information on the quantity of influent materials and the seepage
losses could not be measured.
25
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SECTION 6
MATERIAL CHARACTERIZATION
The characterization, of dredged materials constitutes an essential part
of this study because (a) it provides the background for subsequent correla-
tions among index properties and engineering properties and (b) it estab-
lishes the feasibility of combining the data from all four Toledo disposal
sites to form one hypothetical site with a deposition history of about ten
years. Therefore, a number of conventional criteria employed in the field of
soil mechanics have been used to characterize many dredging samples, most of
which were taken from the four Toledo sites. In particular, the Atterberg
Limits, water content, dry density, grain size parameters, organic content,
mineralogy, and chemical composition were found although all parameters were
not determined for all samples. Index properties were determined according
to standard procedures (Lambe, 1951) except for a minor modification in some
of the hydrometer analyses (where the dispersing agent was omitted to more
realistically reflect the actual conditions of sedimentation in a disposal
area). The methods of testing for organic content, chemical constituents,
and mineralogical composition have been explained by Krizek, Karadi, and
Hummel (1973). Index property tests were conducted on materials sampled at
three different consistencies; these were 6 samples of a high-water-content
slurry (solids content of about 15% by weight), 8 samples with a mud-like
consistency (solids content larger than 25% by weight), and 120 samples (23
from the Island, 49 from Riverside, 31 from Penn 7, and 17 from Penn 8) of
solid material that was capable of maintaining a given shape. In addition,
over 3000 chemical analyses were performed to determine the chemical con-
stituents of many of these samples, as well as a large number of water
samples.
RESULTS
The general results of these characterization tests are presented in the
following paragraphs and in Table 6-1 and Figure 6-1, which summarize grain
size characteristics and Atterberg Limit relationships, respectively.
Natural Water Content and Dry Unit Weight
Water contents ranged from 45% to 70%, 47% to 73%, and 42% to 68% for
samples obtained from Riverside in the summers of 1972, 1973, and 1974,
respectively; from 51% to 74% and 52% to 70% for Penn 8 samples and from 54%
to 55% and 43% to 78% for Island samples taken in the summers of 1973 and
1974, respectively; and from 67% to 98% for Penn 7 samples taken in the sum-
mer of 1974. Dry unit weights ranged from 910 kg/m3 to 1090 kg/m3, 860 kg/m3
to 1140 kg/m3, and 880 kg/m3 to 1125 kg/m3 for samples obtained from
26
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Riverside Site in 1972, 1973, and 1974, respectively; from 890 kg/m3 to
1070 kg/m3 and 850 kg/m3 to 1110 kg/m3 for Perm 8 samples and from 980 kg/m3
to 1120 kg/m3 and 840 kg/m3 to 1240 kg/m3 for Island samples taken in 1973
and 1974, respectively; and from 740 kg/m3 to 980 kg/m3 for Penn 7 samples
taken in 1974. These values provide an appreciation for the water contents
and dry unit weights of dredgings that are left dormant in diked areas for
different periods of time. Some of the variations in the water contents and
dry unit weights of samples from different sites can be explained by varia-
tions in drainage conditions, thickness of layer, relative surface levels of
the different sites compared to that of Lake Erie, and the partial flooding
that occurred in some sites due to certain abnormally high water levels of
Lake Erie and the Maumee River.
Table 6-1. Summary of Grain Size Analyses
Site
Island
Penn 8
Riverside
Perm 7
Overall
Average
Percent
Clay
31
37
40
36
37
Percent
Silt
SO
48
46
47
47
Percent
Sand
19
15
14
17
16
Mean
Size
D50
- (mm)
0.0098
0.0073
0.0082
0.0075
0.0079
Effective
Size
D10
(mm)
0.0026
0.0022
0.0019
0.0020
0.0021
Uniformity
Coefficient
U-D60/D10
6.1
5.5
5.9
7.0
6.2
Number
of
Samples
5
12
26
23
66
Variation of Liquid Limit and Plastic Limit with Clay Content
The liquid and plastic limits are plotted in Figure 6-1 versus percent
clay for 65 dredging samples. Four different symbols are used in these plots
to distinguish the four different field sites, but the years during which the
samples were obtained are not identified.. In general, no patterns can be
identified to distinguish one site from another, and the data from the dif-
ferent sites appear to be randomly interspersed, thereby suggesting that the
limits can be treated as representative of samples from one source. The
liquid limit, WL, varies between about 50% and 100% whereas the clay content
ranges from about 20% to 50%, and, as shown in Figure 6-1, the relationship
between the two can be expressed as
wT - 1.3 (% clay + 20)
(6-1)
in which the variables are expressed in percent. The scatter around the line
represented by Equation (6-1) is about ±15% and is attributed to the varia-
tions in the materials. The plastic limit, wp, for the same samples is
plotted in Figure 6-1 versus percent clay, but no definite trend can be
discerned.
27
-------
120
E
1 80
_]
•a
| 60
_l
40 c
£ 60
>
-- 40
e
*-
•
e oc
a island
wL = l,3
o Riverside v Perm 7
(% Clay • 20)
L^^
^
r .*>
^l
ij&^r
^IFV °1
&
(a)
a.
X
a>
•3
20 4O 60 >, ""
Percent Clay
* *
J7
A oo 4%
^^T"
(b)
20 4O 6
Percent Clay
u>
£L
°c
-PI =
.40
'o Cla^
^ Penn 8
-10)
V
/
17 $ JV •«
~*l*Y]
/••'• * -
°/l
/a
y
i
|(c)
20 4O 6
Percent Clay
80
60
. 40
•o
u
In
Q
0.
20
CL
OH and MH
PI =l.l(wL-40)
(d)
20
40 SO 80
Liquid Limit, WL (%)
100
120
Figure 6-1. Plasticity Relationships
28
-------
Variation of Plasticity Index with Percent Clay
Of interest in any soil classification system is the relationship
between plasticity index, PI, and clay content; the ratio of the plasticity
index to the percent clay has been used as the basis for defining the
activity of clays (Skempton, 1953). Based on the plot in Figure 6-1 for 65
dredging samples, a straight line relationship showing an increase in plas-
ticity index with an increase in percent clay was found, but the most repre-
sentative line did not pass through the origin. The empirical equation best
representing this relationship can be written as
PI = 1.4 (% clay - 10) , (6-2)
where the variables are expressed in percent. Hence, the average value of
the activity for these dredged materials is found to be about 1.4.
Relationship between Plasticity Index and Liquid Limit
The plasticity index, PI, is plotted in Figure 6-1 versus the liquid
limit, WL, on the Casagrande (1948) plasticity chart for 83 samples of dredg-
ings (6 from the Island, 16 from Penn 8, 30 from Riverside, and 31 from
Perm 7). All data points lie essentially within a PI range from about 20% to
slightly more than 50%, and according to the plasticity chart, these dredg-
ings can be classified as a mixture of organic clays of medium to high com-
pressibility and inorganic clays of high plasticity, with slightly more than
one half of the samples falling into the former category. The relationship
between plasticity index and liquid limit can be expressed as
PI = 1.1 (WL - 40) (6-3)
Variation of Limits and Plasticity Index with Activity
Since the nature of the clay fraction may vary considerably in dredged
materials, variations in the Atterberg Limits and plasticity index with
changes in activity were investigated. The liquid limit was found to
increase linearly with an increase in the activity, A, and the relationship
can be written as
WL =25 (A + 1.6) (6-4)
The plastic limit was observed to have no definite correlation with the
activity, and a nonlinear increase of plasticity index was found to occur
with an increase in activity. The rate of increase of the plasticity index
is high at low values of activity and decreases gradually as the latter
increases.
Particle Size Characteristics
The results of particle size distribution curves for 66 samples from the
four different sites are summarized in Table 6-1. The average percentages of
sand, silt, and clay fractions for the materials in each of the four sites
are essentially the same, with the individual components being proportioned
on approximately a 1:3:2 basis. The average values of the mean particle
29
-------
size, D^Q, and the effective particle size, D-^Q, are practically the same for
the materials in each of the different sites, with overall averages of 0.0079
mm and 0.0021 mm, respectively. The individual average values for the coef-
ficient of uniformity, Dgo/D10» vary between 5.5 and 7.0 with an overall
average of 6.2.
Organic Matter
Wet combustion (organic carbon) and dry combustion (ignition loss)
techniques were used to determine the organic content of these dr edgings .
Except for a few instances, the organic carbon of the samples tested was
found to be on the order of 2% to 4%. If it is accepted that organic matter
consists of about 50% organic carbon, the organic matter content for most of
the samples will vary from 4% to 8%. It was noticed that the samples with
high organic contents exhibited a strong oily odor, and the presence of
hydrocarbons may account for such high organic carbon contents. An attempt
was made to correlate limit test data with the organic carbon content and the
ignition loss, but no success was attained. Although the limit values gener-
ally increase with increasing values of organic carbon content or ignition
loss, the indicated relationships were not well defined; this is probably due
in large part to the effects of other variables, such as gradation, precent-
age of fines, clay mineralogy, and type of organic material. Furthermore,
since the degree of decomposition of the organic matter in the dredgings is
generally very high, the existing organic compounds have probably reached a
chemically stable condition and do not impart to the dredged materials the
same type of behavior as organic matter with a low degree of humification,
such as that often found in organic soils.
and Mineralogy
The results of an extensive experimental program to analyze the chemical
composition of dredged materials has been reported by Krizek, Karadi, and
Hummel (1973) and Krizek, Gallagher, and Karadi (1974). In general, virtu-
ally all of the dredgings tested would be classified as polluted. The degree
of pollution varied considerably from harbor to harbor, from sample to sample
within a harbor, and in the intensity of the various pollutants for a par-
ticular sample. The chemical composition of the water was very consistent
with that expected at particular locations. For example, where sewage was
emitted, the dissolved oxygen was low and the biological oxygen demand and
nitrogen content were high; this was also true for bottom sediments. How-
ever, the chemical oxygen demand depended not only on organic compounds, but
also on other materials (such as the nitrite and sulfide anions and the mer-
curous, cuprous, and ferrous cations) that are found in high concentrations
in these dredgings. No definitive relationships could be established between
the chemical composition of a sample and its engineering behavior, nor can
any general conclusions be advanced regarding the chemical nature of mainte-
nance dredgings since the chemical components of a sample are so highly
dependent on the localized environment from which it was taken. Mineralogi-
cal analyses on seven different dredgings indicated the presence of substan-
tial amounts of common clay minerals, such as illite and kaolinite. This
finding is consistent with findings reported by other agencies (for example,
Philadelphia District Corps of Engineers, 1969).
30
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SUMMARY
Samples of dredged .materials taken from the four sites at Toledo, Ohio,
were found to be essentially the same, thereby allowing data from all four
sites to be synthesized and treated as representative of one large site span-
ning a time period of nearly a decade. The liquid limit and plasticity index
were found to exhibit approximately linear relationships with the clay con-
tent, but no correlation could be found between the plastic limit and the
percent clay. Particle size analyses indicated that sand, silt, and clay
fractions exist in approximate proportions of 1:3:2. Virtually all of these
dredged materials can be classified as a mixture of organic silts and clays
of medium to high plasticity (OH) and inorganic clays of high plasticity
(CH), with approximately 60% of the materials tested lying in the first cate-
gory and 40% in the second. The organic contents of most of these materials
were between 4% and 8%, thus suggesting that they are basically intermediate
organic soils.
31
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SECTION 7
CONSOLIDATION AND COMPRESSIBILITY
The consolidation characteristics and compressibility of dredgings are
two important properties that must be determined in order to assess the
quality and potential usefulness of landfills composed of these materials.
In general, maintenance dredgings have a high water content and contain sub-
stantial amounts of clay-like and/or organic materials, as well as various
concentrations of pollutants; hence, their compressibility is usually large
and the process of consolidation is quite time-consuming. Accordingly, this
part of the overall study is directed toward evaluating the consolidation and
compressibility characteristics of various dredgings from the vicinity of
Toledo, Ohio. Fourteen slurry consolidation tests were conducted on slurry
samples obtained during various stages of the dredging and deposition pro-
cess, and an extensive series of 64 conventional consolidation tests was per-
formed on "undisturbed" samples taken by piston sampler from different land-
fills. In addition, the secondary compression characteristics of eight
undisturbed samples and two slurry samples were investigated, and time-
dependent field settlements at several elevations are given for five loca-
tions in the Penn 7 Site.
TEST PROCEDURES
Fourteen slurry samples with an initial water content of about 150% to
200% were tested in specially designed slurry consolidometers (Sheeran and
Krizek, 1971; Salem and Krizek, 1973). The loading scheme for these tests
was similar to that normally used for a conventional consolidation test; a
load increment ratio of unity was employed, and the load increments were 14,
28, 55, 110, and 220 kN/m2. The first four load increments were applied for
a period between 10 and 45 days to insure that primary consolidation was com-
plete, and when primary consolidation due to the final load was essentially
complete, the load was removed and the block of consolidated dredgings was
extracted from the bottom of the test chamber. In two cases the final load
increment was allowed to remain on the sample for 150 days to investigate the
secondary compression, and in two other cases conventional consolidation
tests were conducted on samples trimmed from the consolidated blocks.
Sixty-four undisturbed tube samples of dredged materials from three
different landfills were tested by means of conventional consolidation tests.
Sixteen of these samples were obtained from Riverside Site during the summer
of 1972, and the other 48 samples were taken during the summers of 1973 and
1974 from Riverside Site, the Island Site, and Penn 8 Site. A 3-inch diam-
eter, lightweight, manually operated piston sampler (Hummel and Krizek, 1974)
was used to obtain all samples. For the first 16 specimens the initial load
32
-------
was 31 kN/m2 and the maximum load was 248 kN/m2; eight specimens were
rebounded incrementally to the initial load, at which point the test was ter-
minated, while the load of 248 kN/m2 was maintained constant for over seven
months on six samples and for ten months on two samples to investigate their
secondary compression characteristics. The maximum load for the rest of the
specimens reached 496 kN/m , after which all specimens were rebounded incre-
mentally to 31 kN/m2.
LABORATORY RESULTS AND ANALYSES
Presented in the following sections is a series of empirical
relationships which may be used to estimate the magnitude and rate of settle-
ment that might be anticipated in landfills composed of hydraulically placed
maintenance dredgings. Relationships for the compression index and the coef-
ficient of secondary compression are established as functions of the liquid
limit, natural water content, dry unit weight, percent clay, and consolida-
tion pressure, and the coefficient of consolidation is correlated with the
consolidation pressure.
Compression Index
A study of the void ratio versus consolidation pressure curves for
dredging slurries revealed a nearly linear plot in most cases for the last
few load increments (Salem and Krizek, 1973). The compression index, Cc, was
computed for each sample by taking the slope of a "best fit" straight line
through the last two or three points; values for Cc would probably be lower
if additional load increments (beyond 220 kN/m2) were applied. The Cc values
for virtually all of the dredging slurries tested were found to lie within a
fairly narrow range of about 0.94 ± 0.17; Cc as a function of the liquid
limit, Wj, may be described by the empirical equation
Cc = 0.02 WL - 0.44 , (7-1)
where WT is expressed as a percentage. Most observed values for Cc lie
within 10% of the value predicted by Equation (7-1), but the range of liquid
limit values is relatively small (60% to 76%).
The compression indices for the 64 samples tested in conventional
consolidation tests varied between about 0.3 and 0.7, which lie in the lower
portion of the 0.4 to 1.4 range reported by the Corps of Engineers (1969).
When Cc is plotted versus the natural water content, wn, and the liquid
limit, WL, respectively, the observed trend in both cases justifies the use
of a first-order linear model, and the associated equations are
Cc = 0.01 (wn - 7) ± 0.04 (7-2)
and
Cc - 0.008 (WL - 5) ± 0.06 , (7-3)
where wn and WL are expressed as percentages; these equations are similar to
those reported by Terzaghi and Peck (1948), Van Zelst (1948), and Cozzolino
(1961). For the work reported herein, the respective ranges of validity of
Equations (7-2) and (7-3) are approximately 40 £ wn £ 80 and 45 £ WL £ 90,
33
-------
and the corresponding dimensionless correlation coefficients are 0.89 and
0.80. The simultaneous effect of both >r and w, on C! may be expressed as
n LI c
Cc = 0.04 (WL + 2 wn - 50) , (7-4)
for which the computed multiple correlation coefficient is 0.88.
In two cases conventional consolidation tests were conducted on
specimens trimmed from slurry consolidated blocks; these specimens were con-
solidated to a maximum consolidation stress of 1984 kN/m , and the resulting
compression indices were 0.51 and 0.55, as compared with values of 0.80 and
0.90 obtained from the associated slurry consolidation tests, which attained
a maximum consolidation stress of only 220 kN/m2. The observed reductions in
the values of Cc may be attributed to the fact that the virgin compression
curves were not adequately defined in the slurry consolidation tests.
Coefficient of Consolidation
The coefficient of consolidation, o^, corresponding to each load
increment for slurry and conventionally consolidated samples was calculated
from the relation
^ = Th2/t , (7-5)
where t is time, h is the length of the shortest drainage path at the appli-
cation of each load increment, and T is the time factor, which is a function
of the degree of consolidation, U (taken to be 50% for the analyses conducted
herein); in this study h equals one half of the specimen thickness because
drainage took place in both tests from both the top and bottom. For the
slurry samples the c^ values corresponding to consolidation pressures up to
220 kN/m2 vary between a high of 0.00021 ± 0.00004 cm2/sec and a low of
0.000025 ± 0.000011 cm2/sec with an average value of 0.00011 ± 0.00002
cm2/sec. The variation of the average coefficient of consolidation, cv, with
consolidation pressure, p, is given in Figure 7-1 together with the average
values and ranges of the 70 percentile (70% of the values lying within this
range) and may be described within very broad limits by the empirical
equation
Cy = (18-3.3 log p) 10~5 , (7-6)
where p must be expressed in kN/m2 and cv is determined in units of cm2/sec.
The observed variations in Cy for a given dredging sample are consistent with
previous experience on a variety of clayey soils. For all practical purposes
the coefficient of consolidation obtained from slurry consolidation tests can
be taken as 10 cm^/sec.
For conventionally consolidated tube samples the ranges and means of the
c-y values corresponding to the various consolidation pressures are shown in
Figure 7-1. Although this relationship exhibits a minimum for cv at a con-
solidation pressure of about 125 kN/m2, a reasonably constant value of about
0.0006 cm2/sec can be used to characterize the time dependency of the con-
solidation response of these dredgings (except for the somewhat higher cv
values at the lowest consolidation pressure, 31 kN/m2). The manifested
variation of cv with p is similar to those reported by Taylor (1948) for
34
-------
&
1C?
•s
Average value-
-Range of 70 percentile
— Range of values
0.0020
o 0.0015
§
~- 0.0010
c
.2
o
0.0005
o>
o
I
Slurry Consolidation
Conventional Consolidation
50 100 200
500 1000
Consolidation Pressure, p(kN/m2)
Figure 7-1. Average Coefficient of Consolidation
versus Consolidation Pressure
Boston blue clay, Chicago clay, Newfoundland silt, and Newfoundland'peat.
The average value of Cy obtained from conventional consolidation tests is
about six times that obtained from slurry consolidation tests; this may be
attributed in part to the variation in the thickness of the samples whereby
higher gradients were developed in the samples with the smaller thickness.
(The thicknesses of the samples at the end of the slurry and conventional
tests were about 15 cm and 2 cm, respectively.) This same explanation can be
offered as the reason for the increase in cv with consolidation pressure for
values of the latter greater than 125 kN/m^ in the case of conventional
tests. However, it is probable that much of the observed difference in
behavior was caused by the different ways in which the samples were prepared
and consolidated.
Secondary Compression
The long-term compression-time curves (Krizek and Salem, 1974) of the
slurry consolidated samples and the undisturbed tube samples both manifested
a double-S pattern. Upon completion of primary consolidation, the secondary
35
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compression of all samples increased in essentially a linear manner with the
logarithm of time for a considerable period of time, after which the rate of
secondary compression became significantly greater, reaching a maximum and
then decreasing to zero at large times; this type of behavior suggests that a
structural breakdown of interparticle bonds occurs at some value of strain
for each particular load increment. Although the unusual behavior pattern
which starts at the beginning of the second S-shaped portion of the response
curves for the conventional consolidation tests resembles that obtained from
the slurry consolidation tests, there are different proportions of secondary
to primary compressions and the times required to reach the end of primary
consolidation and ultimate settlements are different. In the case of the
slurry consolidation tests the proportion of secondary compression to total
compression is about 0.25 whereas it is on the order of 0.60 for the conven-
tional consolidation tests for essentially the same increment of applied
stress; both ratios were evaluated at long times when the rates of settlement
were essentially zero. This phenomenon may be a consequence of the different
thicknesses of the specimens in the two types of test; such behavior is con-
sistent with the findings of Barden (1965).
The time required to reach ultimate settlements is shorter for the
slurry consolidation tests than for the conventional consolidation tests even
though the specimen thickness in the former is about five or six times that
in the latter. Alternatively, the time required to complete primary consoli-
dation (as determined by the conventional Casagrande method) in the slurry
consolidation tests is about 30 times that for the conventional consolidation
tests; these times are approximately proportional to the square of the speci-
men thicknesses, as predicted by the classical theory of consolidation
(Terzaghi, 1923). These observations suggest that (a) the time required to
reach ultimate settlements (including secondary compression) does not neces-
sarily have to be longer for greater thicknesses of material and (b) the
relative amount of secondary compression that occurs in the field, where the
thickness of material is normally much larger than that in the laboratory,
may be considerably less than the value predicted from laboratory tests. The
average ultimate settlement for the specimens in the slurry consolidation
tests was about 10% under the final load increment (110 to 220 kN/m2) whereas
it was about 14% for the specimens in the conventional tests for essentially
the same load increment (124 to 248 kN/m2). A comparison of final settle-
ments and the corresponding stresses indicates that the rates of settlement
are approximately the same despite the variation in the time needed to attain
such settlements and the proportions of secondary to total settlements.
Average underestimations in the values of secondary compressions due to
a linear extrapolation of the straight line portions of the compression-log
time plots were about 45% and 60% for slurry and conventional consolidation
tests, respectively, whereas average underestimations in secondary compres-
sion with respect to total compressions were about 10% and 35% for the two
types of tests. These results suggest that data from the slurry consolida-
tion tests on the thicker specimens may be sufficient to predict ultimate
settlements, once the slope of the straight line portion of the consolidation
curve is defined and the ratio between the secondary and total settlement is
known, but the use of similar data from conventional consolidation tests
should be made with considerably more caution.
36
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Coefficient of Secondary Compression
The coefficient of secondary compression, Ca, can be expressed as
Ca = (Ah/h)/(A log t) , (7-7)
where Ah is the reduction in specimen thickness for a given change in time
(represented by A log t) and h is the thickness of the specimen at the time
the load increment under consideration is applied. Despite variations in the
proportions of secondary to primary settlements and underestimations of set-
tlements due to a linear extrapolation of the settlement-log time curves
after primary consolidation, the values of the coefficient of secondary com-
pression, Ca, from both slurry consolidation and conventional consolidation
tests are practically the same, varying from 0.0072 to 0.0085 and from 0.0073
to 0.0128, respectively, for the last load increment. Accordingly, a knowl-
edge of the relationships between this coefficient and certain other proper-
ties of dredgings, together with information concerning the relative propor-
tions of secondary and total settlements and the settlement-time behavior of
the primary portion of consolidation, will enable the engineer to estimate
the extent of the expected settlements due to secondary compression. Ca was
found to increase in a reasonably linear manner with the logarithm of p for
the eight dredging samples tested by use of conventional consolidation tests;
in general, a different relationship was obtained for each specimen, but all
straight lines were approximately parallel with a change of about 0.006 in
the value of Ca for a change in pressure from 31 kN/m^ to 248 kN/m^. A rea-
sonably good straight line relationship was obtained between the logarithm of
Ca and the logarithm of wn for a given load increment; values of Ca ranged
from about 0.002 to 0.013 for a natural water content range from 45% to 65%.
Values of the compression index, Cc, determined from the e-log p curves,
varied between 0.32 and 0.55, and, as shown in Figure 7-2, Ca showed a gener-
ally linear increase with an increase in Cc for a given load increment.
FIELD SETTLEMENTS
The field measurement of settlements and pore water pressures is usually
accomplished by means of settlement plates and piezometers, and the accessi-
bility of this instrumentation is as important as its performance. For land-
fills composed of dredged materials the conditions that exist during the pro-
cess of deposition pose a particularly difficult access and installation
problem because most of the units must be placed while the fill material is
in a slurry form.
Original plans included the placement of settlement plate-piezometer
units at four different elevations (original ground and about 1-meter inter-
vals during the deposition of dredged materials) at each of ten locations in
the Penn 7 Site, as shown in Figure 4-3. Due to various factors (weather
conditions, vandalism, inaccessibility, etc.), five of these units were lost
or destroyed before installing others at higher levels, and they could not be
replaced; subsequently, it was decided to omit all units at these locations
because the settlement at the bottom boundary could not be monitored. All
other units were placed at the remaining locations (2/10, 5/8, 5/10, 5/13,
37
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and 15/10) at appropriate times during the dredging and disposal process, but
a few of these units were lost or destroyed subsequently due to vandalism.
0.015
Compression Index, Cc
Figure 7-2. Coefficient of Secondary Compression
versus Compression Index
Figure 7-3 shows the measured settlements and piezometric heads for two
units at location 2/10 and three units at each of locations 5/8, 5/10, 5/13,
and 15/10. (No water heads were measured at location 2/10.) The latest
installed units near the surface of the fill were dry throughout the period
of observation; hence, records of piezometric heads are given only for the
deeper units. The monitoring of settlements started about 280 days after
placing the set of bottom settlement plates and continued thereafter for
about 440 days. Some of the units were destroyed at intermediate times, and
therefore complete sets of data are not available for all locations.
Observed settlements varied between about 0.2 to 0.5 meter for bottom units
and about 0.2 to 0.8 meter for plates near the surface of the fill. Piezo-
metric heads above the midheight of the porous tips indicated values near the
elevation of the fill surface for a long time, but a considerable drop was
measured in August of 1974.
In addition to the settlements measured at the Penn 7 Site, surface
settlements were monitored at various locations at Riverside Site for several
years. The measured settlements at both sites are compared (Krizek and
Salem, 1974) with those computed from a simple model based on the classical
38
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i
a
-
Settlement of First Layer Total Settlement
o Uncorrected • Corrected Q Uncorrected • Corrected
R • Ratio of observed thickness, of layer to assumed average thickness of layer
O.I
0.2
Q3
0.4
50
250
100
150
200
250
I • 1.17 { \ V
^, *
'
IOO 150 200
Time (days)
250
Figure 7-3. Measured Field Settlements and Piezometric Heads
39
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theory of consolidation, and a more sophisticated model (Krizek and
Casteleiro, 1974) that accounts for both consolidation and desiccation, as
well as a nonhomogeneous distribution of mechanical properties in the verti-
cal direction, is used to compute comparative settlements for the Perm 7 data
only. In each case the input information was determined, insofar as pos-
sible, by laboratory and field tests; when appropriate test data were
unavailable or inconclusive, engineering judgment was used to select the
input parameters.
CONCLUSIONS
Although the samples investigated herein were all obtained from the
Toledo area, these materials are typical of many maintenance dredgings, and
it is felt that the empirical relationships established in this study will be
reasonably applicable for all dredged materials that possess similar classi-
ficatory indices. Based on the analysis and interpretation of the data
obtained from the field and laboratory testing programs, the following con-
clusions can be advanced:
1. The compression index obtained from conventional tests lies between 0.3
and 0.7 and increases linearly with-both water content and liquid limit;
its value obtained from slurry consolidation tests is about 1. For all
practical purposes values of 0.0006 cmr/sec and 0.0001 cm^/sec can be
assumed to represent the average coefficient of consolidation obtained
from conventional consolidation tests and slurry consolidation tests,
respectively. The difference in the values of Cc and cv from both tests
is attributed primarily to the variation in the nature of deposition of
the tested materials.
2. After primary consolidation was complete, the secondary compression of
all samples tended to increase in essentially a linear manner with the
logarithm of time for a considerable period of time, after which the
rate of secondary compression increased significantly, reaching a maxi-
mum and then decreasing to zero at large times. This type of behavior
suggests that a structural breakdown of interparticle bonds occurs at
some value of strain for each particular load increment.
3. Despite the significant difference in the proportions of secondary and
primary compressions obtained from slurry and conventional consolidation
tests, the total settlement per unit height associated with correspond-
ing stress levels is about the same for both tests; the times necessary
to reach ultimate settlements are shorter for slurry consolidation tests
than for conventional tests, and this suggests that the times needed to
reach ultimate settlements in the field may be much shorter than those
predicted from conventional consolidation tests.
4. The coefficients of secondary compression from both slurry and
conventional consolidation tests are practically the same for corre-
sponding ranges of load, irrespective of the method of testing and the
ratios of secondary to total settlements from each test, and values
ranged between 0.002 and 0.013 for a natural water content range from
45% to 65%, increasing as a power function for a given load increment.
40
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In addition, the coefficient of secondary compression increased
exponentially with the consolidation stress for a given natural water
content and linearly with the compression index for a given load
increment.
41
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SECTION 8
PERMEABILITY AND DRAINAGE
The potential usefulness of fine-grained maintenance dredgings for
landfill depends to a large extent on the ease with which these sediments can
be dewatered from a slurry to a solid state. Accordingly, several series of
field and laboratory tests were conducted to examine the permeability and
drainage characteristics of a number of typical dredgings from various har-
bors around the Great Lakes, but the majority of the tests were performed on
materials from the vicinity of Toledo, Ohio. Slurry samples were taken
either from the fill area or directly from the inlet pipes through which the
materials were pumped, and undisturbed samples of existing landfills were
obtained by means of a manually operated, specially designed, piston sampler
(Hummel and Krizek, 1974).
TEST PROGRAM
Three series of drainage tests were conducted to study the rate of water
loss from several different dredged materials due to (a) gravity only, (b)
gravity plus vacuum with the air pressure being applied directly to the sur-
face of the dredgings, and (c) gravity plus vacuum with a membrane between
the surface of the dredgings and the atmosphere. The test equipment con-
sisted of a series of Plexiglas cylinders (7% or 15 cm in diameter and 50 or
60 cm high) with porous stones fitted into the bottom of each cylinder; the
effluent was collected in bottles, and the bottle was either vented to the
atmosphere for gravity drainage or connected to a vacuum line for vacuum
drainage. Two variations of vacuum drainage were used; in the first the air
pressure due to the atmosphere was applied directly to the surface of the
dredgings whereas in the second a membrane was placed between the dredgings
and the atmosphere. Although all tests were conducted in a humid room to
minimize incidental water losses, it was found during the first test series
that significant moisture was still being lost through the top surfaces;
hence, one improvement in the second and third series was to use a smooth
fitting Plexiglas disk for the top plate (Krizek, Karadi, and Hummel, 1973).
The average flow rate was determined from the total amount of water drained
in a given period of time; then, with a knowledge of the sample height and
the height of the water, the gradient was calculated and the permeability was
computed by use of Darcy's law. In the case of the vacuum tests, the vacuum
was converted to an equivalent head.
The Anteus consolidation device (Lowe, Jonas, and Obrician, 1969) was
used to conduct several direct permeability tests. Undisturbed samples were
trimmed to fit the consolidometer ring, placed in the device, and subjected
to 80 psi (550 kN/m2) backpressure to achieve a high degree of saturation.
42
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After being consolidated under a 10 psi (70 kN/m2) stress for at least 12
hours, the samples were unloaded and tested to determine their permeability
while still under the backpressure. The permeability values were calculated
by use of the standard expression for a falling head permeability test. The
coefficient of permeability was also backcalculated from conventional con-
solidation test data (Krizek and Salem, 1974) on undisturbed specimens and
from slurry consolidation test data on slurry samples. A series of electro-
osmosis tests with average electrical gradients of 0, %, and 1 volt per cen-
timeter and a pressure gradient of approximately 0.5 Ib/in2/in (1.4 kN/m2/cm)
was conducted on four dredging samples (Krizek, Karadi, and Hummel, 1973).
In an effort to shed some light on the in situ field permeability of a land-
fill composed of dredged materials, two infiltration tests were conducted at
Riverside Site in Toledo, Ohio; the majority of the dredgings in this dis-
posal area were placed in the late 1960's and 1970, and the deposit is about
4 meters (13 feet) deep. The water table is about 0.4 to 0.8 meter (1.3 to
2.6 feet) below the surface, and wells with a perforated tip surrounded by a
sand filter were placed approximately 2 meters (6.5 feet) deep. The wells
were pumped dry and the time rate of recovery was measured; data were inter-
preted according to the procedure outlined by Lambe and Whitman (1969;
pp. 284-285, Case G) with the assumption that the coefficient of permeability
is isotropic.
RESULTS
Data from seven different types of permeability tests are summarized in
Figure 8-1; the different testing techniques include conventional consolida-
tion, single-load consolidation, slurry consolidation, direct permeability,
gravity drainage, vacuum drainage, and field infiltration. In general, these
test data fall into three groups; the results from the gravity drainage tests
span a permeability range between 10~4 and 10~6 cm/sec (100 and 1 ft/yr) and
a corresponding void ratio range between 2 and 10; ranges of permeability and
void ratio of 10~6 to 10~7 cm/sec (1 to 0.1 ft/yr) and 1 to 5, respectively,
are associated with vacuum drainage; the consolidation and direct permea-
bility test data lie within a permeability range between 10~° and 10~y cm/sec
(1 and 0.001 ft/yr) and a void ratio range between 1.0 and 1.5; although the
void ratio range for the field infiltration tests is between 1.0 and 1.5, the
permeability values are generally between 10~^ and 10~5 cm/sec (100 to 10
ft/yr), or about three orders of magnitude higher than those measured in the
laboratory tests. Despite the relatively wide scatter in the data plotted in
Figure 8-1, a distinguishable trend is evident in the relationships between
permeability and void ratio; the solid and dashed curves represent suggested
average values and ranges, respectively, for the coefficient of permeability
as a function of void ratio.
Drainage
Based on data from five typical dredged materials tested under three
different drainage conditions, it was found that (a) the use of a vacuum
extracted significantly larger quantities of water from the dredgings than
did gravity alone and (b) the major effect of the vacuum occurs during the
initial time period. For example, the drainage quantities after one day with
vacuum were from one and a half to five times the quantities obtained for
43
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gravity alone; viewed differently, the quantity of drainage with vacuum
during the first five hours was about the same as by gravity alone for the
first day or two while the drainage by vacuum for one day was comparable to
that by gravity alone for about a week. After three weeks, the quantities of
drainage by gravity alone were about one half of those achieved by vacuum for
all samples. Although extracting greater quantities of water in a given
time, the vacuum tests employed a greater applied head and thus generated a
greater flow resistance; the head for the vacuum test was about twenty times
that for the gravity test, and the flow resistance was increased by a factor
of about ten, as reflected in the lower values of permeability for the vacuum
tests.
-------
Conventional Consolidation
Two series of conventional consolidation tests were conducted on
undisturbed tube samples of typical dredged materials from two disposal sites
near Toledo, Ohio. In the first series, the data from which are plotted in
Figure 8-1, the range of consolidation stress was relatively low (up to
36 psi or 248 kN/m2) and permeability values lay between 2 x 10~^ and
4 x 10~8 cm/sec (0.02 and 0.04 ft/yr) with no apparent correlation with the
effective particle size (0.0004 mm < D10 < 0.0005 mm), percent clay
(30 < % clay < 50), coefficient of uniformity (15 < Cu < 40), or liquid limit
(45 < w^ < 85). These values are comparable to those obtained from the
slurry consolidation tests for the same range' of consolidation stresses. In
the second series, the results of which are given in Figure 8-2, permeability
values were determined over a much wider range of consolidation stress
(namely, double the range investigated in the first series). A typical plot
of the permeability versus the void ratio for a given sample subjected to a
given load increment is shown in Figure 8-2a, and similar plots for all
samples subjected to five different load increments are given in Figures 8-2b
to 8-2f. All data plotted in Figures 8-2b through 8-2f are replotted on the
general correlation graph in Figure 8-2g, and the resulting empirical rela-
tionship can be described by
k = log~J (1.35 e - 9) , (8-1)
where k is expressed in cm/sec. Most of these permeability values lie
between 10~° and 10"^ cm/sec (1 and 0.01 ft/yr) and coincide with those found
from the direct permeability tests.
Slurry Consolidation
The coefficient of permeability was evaluated from 12 slurry
consolidation tests at stresses up to 224 kN/m2 (32 psi), and average values
can be reasonably well described by the empirical expression
k = log'J (1.35 e - 10) , (8-2)
where k is expressed in cm/sec. A comparison of Equations (8-1) and (8-2)
indicates a similar rate of change of permeability with respect to void
ratio, but there is a difference of one order of magnitude between the two
empirical expressions. Since both equations cover approximately the same
lower range of void ratio (0.8 < e < 2.0 for the conventional consolidation
tests whereas 0.9 < e < 5.0 for the slurry consolidation tests), the lower
permeability values backcalculated from slurry consolidation tests must be
attributed to the testing technique; apparently the particle arrangements of
slurry consolidated dredgings in the laboratory are different than those of
hydraulically placed dredged materials that consolidate in the field under
their own weight. Data from a limited number of conventional consolidation
tests on samples trimmed front slurry consolidated blocks suggest that the
rate of change of permeability with respect to void ratio will increase as
the consolidation stress increases (to 256 psi or 1800 kN/m2) and the void
ratio decreases (to e of 0.5).
45
-------
o
_Q
C
-------
Electro-Osmosis
The electro-osmotic coefficient of permeability ranged from about
1.5 x 10~~5 to 4.5 x 10~5 cm2/volt-sec. These values are approximately one
half of the values associated with a large variety of soils. However, the
problems associated with extrapolating these limited laboratory data on small
samples to field cases involving substantially larger dimensions must be
approached with caution.
Field Tests
The results from two field infiltration tests reveal permeability values
of approximately 10 cm/sec (100 ft/yr) for the well located in about the
middle of the disposal area and approximately 10~^ cm/sec (10 ft/yr) for the
well near the outflow weir. These values are both consistent with engineer-
ing reasoning. First, both values are significantly higher (three orders of
magnitude) than those obtained from laboratory tests on samples from essen-
tially the same locations; the observed discrepancies are likely due in large
part to the seasonal stratifications associated with dormant periods between
dredging seasons. And second, the permeability value determined from the
well near the outflow weir is about one order of magnitude smaller than that
obtained from the well in the middle of the disposal area; this may be
readily explained by the fact that the finer materials tend to accumulate
near the overflow weir.
SUMMARY
The drainage characteristics of a given material were found to depend on
the nature of the solids and the fluids, as well as the water content at the
time of drainage. Different dredgings drain at different rates and are
affected to different degrees by the application of a partial vacuum. In
general, vacuum drainage was found to remove water from dredgings much faster
than gravity drainage alone, and it allowed greater amounts of water to be
extracted in a given period of time. However, the maximum effect of vacuum
on the drainage response was achieved during the initial time period, and
less significant effects were observed over longer periods of time.
The coefficient of'permeability is strongly dependent on the void ratio
and decreases from about 10~^ to 10~9 cm/sec (100 to 0.001 ft/yr) as the void
ratio decreases from approximately 10 to 1. Most permeability values for the
firmer materials, which had void ratios on the order of 1 to 2, were in the
range of 10~7 to 10~8 cm/sec (0.1 to 0.01 ft/yr). Field.infiltration tests
yielded permeability coefficients approximately three orders of magnitude
higher than those obtained from laboratory tests on undisturbed and remolded
samples with comparable void ratios. The electro-osmotic coefficient of per-
meability was found to be about 3 x 10~5 cm2/volt-sec, which is approximately
one half the value determined for a large variety of soils.
47
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SECTION 9
SHEAR STRENGTH
An extensive field and laboratory test program was conducted to obtain
information on the shear strength characteristics of dredged materials.
Field tests were performed at the four Toledo disposal sites (Island, River-
side, Penn 7, and Penn 8) at the locations indicated in Figure 4-3.
TEST PROGRAM
Thirty-one strength profiles were obtained during the years from 1971 to
1974, and 90 undisturbed piston samples were taken at the same times and
locations that field vane tests were performed in order to compare field vane
strength values with those determined in the laboratory by means of miniature
vane tests, cone penetration tests, and unconfined compression tests. In
addition, correlations were established between shear strength and various
other index properties.
The Swedish vane borer (Cadling and Odenstad, 1950) with a vane 6.5 cm
in diameter and 13 cm in height and a vane rotation of six degrees per minute
was used for the in situ shear strength determinations reported herein.
After the peak torque was reached and recorded, the vane shaft was rotated
rapidly through 20 revolutions to remold the soil in the zone where the shear
strength was determined, and the test was repeated in the usual manner to
measure the remolded strength. The miniature vane apparatus used for these
tests was designed and manufactured in England by Leonard Farnell and Com-
pany, Limited; the diameter and height of the vane were both 0.5 inch
(1.25 cm), and the rotation rate was six degrees per minute. Although the
cone penetration test employed in this study is widely used in the laboratory
to evaluate the consistency or shear strength of soft cohesive soils
(Skempton and Bishop, 1950), the empirically determined cone factor was found
in previous studies to be strongly dependent on the type of clay and to vary
with water content for a given clay; accordingly, the cone test can be con-
sidered only as a rough approximation to the undrained shear strength of a
clay. Even as a measure of the sensitivity of one particular clay, the cone
test can be misleading because the cone factor (which depends on the ratio of
the soil modulus to the shear strength) will generally be different for
undisturbed and remolded soils. Standard unconfined compression tests were
conducted on specimens with a length-to-diameter ratio of about 2 to 2.5; the
height of these specimens varied between 7.5 cm and 10 cm and the diameter
varied between 3.5 cm and 4 cm. A constant strain rate of approximately 1%
per minute was used for all tests.
48
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RESULTS
Three typical plots of shear strength versus depth, together with the
associated values of water content, Atterberg Limits, percent clay, and dry
density, are shown in Figure 9-1. Although the shear strength values are
quite low, they are generally comparable to those of ordinary fine-grained
soils with similar water contents and dry densities. Similar trends were
found at all four sites except at locations close to the inlet pipe where the
material becomes more granular.
Physical reasoning suggests that the shear strength of a layer of
dredged material should be highest at the top (where desiccation and evapo-
transpiration have lowered the water content considerably) and bottom (where
some consolidation has taken place due to the overburden of dredged material
and drainage into the underlying foundation soil) and lowest in the middle
(where less consolidation and no desiccation have occurred); such profiles
are illustrated typically in Figure 9-1. Although this anticipated profile
was found at many locations, there were some variations due to the existence
of preconsolidated layers at intermediate depths (caused by desiccation
between dredging seasons).
In general, the shear strength at a given site in a given year was found
to increase with horizontal distance from the overflow weir. For example,
Figure 9-1 shows that the 1973 field vane strengths at a depth of 0.6 meter
at locations 1, 6, and 8 of Riverside Site are 7, 17, and 24 kN/m , respec-
tively, and laboratory vane strengths at the same locations at a depth of
slightly more than 1 meter are 15, 27, and 60 kN/m^. This variation is
probably due in large part to the grain size distribution in a typical site
since the coarse particles tend to settle near the inlet pipe and the fine
particles settle closer to the overflow weir; in addition to strength varia-
tions that are related directly to variations in particle sizes, the coarse
material drains and consolidates faster, thereby developing greater strength
in a given period of time. At all four sites field vane tests could not be
conducted over more than about two thirds of the distance from the overflow
weir to the inlet pipe because the fill material near the inlet pipe was too
granular and dense to allow the vane to be advanced manually.
Since field vane tests were conducted at all four sites during the early
summer of each year from 1971 to 1974 and since the sites each had a differ-
ent time history beginning about a decade ago, the variation of strength with
time could be studied. In general, the strengths measured in any given year
are somewhat greater than those measured in a preceding year, but the evi-
dence is not entirely consistent. The reasons for the manifested inconsis-
tencies are varied, but they seem to frequently relate to the water content
of the dredged material as affected by the immediate past history of the
site. For example, one inconsistency was observed near the overflow weir at
the Island Site where the 1971 strength values were higher than those of
1973; however, field records indicate that there had been an unusual rise in
the water level of Lake Erie for several days during the month of April 1973,
and this caused part of the Island Site close to the overflow weir to be
flooded. The effect of this flooding was noticed a few months later when the
field tests were conducted; the surface of the fill was very wet compared to
49
-------
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Figure 9-1. Typical Profiles at Riverside Site in 1973
50
-------
that in 1971, and several pools of water were found. As a consequence, the
water content of the dredged material increased from 1971 to 1973. Another
condition which may have contributed to the higher water content and asso-
ciated loss of strength is the fact that dredged spoil was pumped into the
area for four months Immediately after the 1971 field program was completed.
(Field tests were conducted in June of 1971, and pumping was done from August
to November of the same year.) The amount of dredgings placed during these
four months was 16% of the total material deposited in the years before 1971.
Since an extensive series of characterization tests indicated that the
dredged materials deposited in all four sites were generally similar, the
time-dependent strength response at each of these sites can be combined and
treated as one representative site which has a history covering the life
spans of the four individual sites. The thickness of the fill in each site
is nearly equal, and this tends to justify the elimination of this parameter
(which reflects the drainage effectiveness) from the analysis. However,
because the placement of dredgings into a given site took place discontinu-
ously during several dredging seasons, the synthesis of the strength response
from these four sites necessitates that an "equivalent zero time" or "birth-
date" be established for each site. For this purpose the time corresponding
to the placement of one half of the final volume of dredgings in a site is
arbitrarily assumed to be the equivalent zero time for that site; accord-
ingly, as illustrated in Figure 4-2, 1967, 1968, 1972, and 1966 were taken to
be the birthdates of the Island Site, Riverside Site, Penn 7, and Penn 8,
respectively. Within the framework of this assumption, the average shear
strength, savg, defined as the integral of the shear strength profile over a
given depth divided by the corresponding depth, was found to be given by
savg = [2.9 + 2(x/A)][t - 1.0] , (9-1)
subject to the constraints that x/& < 0.7 and 1 < t < 10, where x is the dis-
tance of the test location from the overflow weir, i is the distance between
the overflow weir and the inlet pipe, t is expressed in years, and savg is
expressed in kN/m .
Many normally or lightly overconsolidated clays and silts manifest a
reduction in strength upon remolding, and in some problems the fact that a
soil may be sensitive is as important as its undisturbed strength. The
undrained strength and sensitivity can be obtained from vane tests, and these
two parameters have been found to give a very characteristic description of a
clay (Andresen and Bjerrum, 1958). Values of sensitivity ranged from about 2
to 10 for the field vane tests and from about 3 to 7 for the laboratory vane
tests although considerable scatter was observed. In general, for lower val-
ues of natural water content and liquidity index and higher values of dry
density, the sensitivity measured by the field vane is higher than that mea-
sured by the laboratory vane, and it is relatively unaffected by the indepen-
dent variable in the case of high values of natural water content and
liquidity index and low values of dry density. The measured sensitivity
values place many of these dredgings in the category of "sensitive" soils
according to the classification given by Terzaghi and Peck (1968).
51
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Correlation between Shear Strength and Index Properties
The measured field and laboratory strengths (designated as Sfv for the
field vane, s^v for the laboratory vane, Sfc for the fall cone, and suc for
the unconfined compression tests) are correlated in Figures 9-2, 9-3, and 9-4
with the natural water content, wn, dry density, Yd» and liquidity index, LI,
respectively. Figure 9-2 shows the correlations between the various shear
strengths and the natural water content. All of these relationships can be
reasonably well described by an equation in the form
-bw(wn - 40)
log s - a^ , (9-2)
where aw and bw are empirical constants that depend on the type of test. To
select the "best" estimate for these two constants, Equation (9-2) was trans-
formed to a linear equation, and the stepwise regression method tempered with
engineering judgment was used to determine the aw and bw values listed in
Table 9-1. The measured strengths are plotted in Figure 9-3 and 9-4 as func-
tions of the dry density and the liquidity index, respectively, and the data
in each case manifest a linear variation between the logarithm of strength
and both variables; these relationships can be represented in general form by
log s = aY[(Yd/Yw) - by] (9-3)
for the dependence of s on Yd» an
-------
Laboratory Vane
— Field Vane
100
100
60 80 100 40 60 80
Natural Water Content, wn (%;
100
Figure 9-2. Variation of Shear Strength
with Natural Water Content
:
-------
-------
IUU
DU
- -
-
3
lo
x»°
o ~>^
0°
c
Fie
9sfv *
*^8<
o^WF
0 0 &*
o f
.5
d Va
1.7 -L
0
|V 0
.• N,
3 O
0
ne
I
^-°
jy;
0 0
-0
•„
' "X
IUU
DU
-y\
i n
c
5 '(
i
Laboratory Vane
so ° Ootogsj, = 1.03(1 7-LI)
o 7*^6 ^
ttSjjJ cPo o
: ^W^
o «T^F«
0 ; ° ^iv
i ° ' o o SCS
1
0.5 1.0 I
lOOr
•
c/> 20
CP
C
.1
i
'
Fall Cone-
. Laboratory Vane
Field Vane
Unconfined Compression
0.5
50
20
:
E
Fall Cone
5-LI)
50
20
10
5
0.5
1.0
15 0
Unconfined
Compression
log suc = l.ll'(l.5-
0.5
l.O
Liquidity Index, LI
1.5
Figure 9-4. Variation of Shear Strength with Liquidity Index
55
-------
Table 9-1. Values of Coefficients for Strength Relationships
Independent
Variables
Water
Content
Type of Test
Field Vane
Laboratory Vane
Fall Cone
Unconfined
Compression
w
2.1
2.3
2.4
1.8
b
w
0.035
0.035
0.035
0.035
Independent
Variables
Dry
Density
Type of Test
Field Vane
Laboratory Vane
Fall Cone
Unconfined
Compression
a
Y
2.6
2.7
3.1
1.9
b
Y
0.58
0.57
0.60
0.50
Independent
Variables
Liquidity
Index
Type of Test
Field Vane
Laboratory Vane
Fall Cone
Unconfined
Compression
\
1.00
1.03
1.23
1,11
bL
1.7
1.7
1.6
1.5
56
-------
trimming disturbances, which pose particularly difficult problems for soft
soils, as was the case for most of the samples tested in this program. As a
matter of fact, a detailed study of the individual profiles previously
described (and shown typically in Figure 9-1) indicated that in most cases
the greatest reductions in unconfined compressive strengths relative to, for
example, field vane strengths occurred in the middle (or softest) portion of
the dredging layer; in such cases the unconfined compressive strengths were
generally about midway between the undisturbed and remolded field vane
strengths.
Although the probability of some disturbance of the material during the
process of sampling would suggest that the laboratory vane and fall cone
strengths should be lower than the field vane strength, the contrary observa-
tion may be explained to some extent by (a) the confinement of the samples in
the tubes during the laboratory test compared with the relatively free
lateral movement of the soil around the blades of the vane during a field
test and (b) the difference in the basic nature of the testing procedures
(for example, size and height-to-diameter ratio of the two vanes and vane
geometry versus cone geometry). Remolded strengths measured by both field
vane and laboratory vane are generally found to be in agreement; values
obtained by the field vane are usually somewhat lower for the top crust and
somewhat higher in the soft zone at depths between 1 and 2 meters. In
general, the shear strength values obtained in this experimental program com-
pare well with those reported by the Philadelphia District Corps of Engineers
(1969) for samples from four sites along the Delaware River, where shear
strengths varied from about 100 psf (5 kN/m^) to 1000 psf (50 kN/m^) with an
average of approximately 500 psf (25 kN/m^).
SUMMARY
The strength characteristics of the dredgings studied in the Toledo
harbor area are comparable to those associated with fine-grained organic
soils with similar water contents and dry densities. Although the shear
strength of these materials is generally low shortly after deposition, it
increases rather consistently with time. Dredged materials of this nature
can be categorized as sensitive, where the sensitivity decreases with
increasing dry density. The logarithm of shear strength varied exponen-
tially with the natural water content and linearly with the dry density and
liquidity index. In most cases the strength values determined in the field
and in the laboratory were found to agree reasonably well, but values mea-
sured by means of the unconfined compression test were considerably lower
than those measured by all other tests and values measured by the fall cone
test were the highest.
57
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SECTION 10
MATHEMATICAL MODEL
As mentioned previously, a major factor that controls the usefulness of
landfills composed of dredged sediments is their high water content, which
affects both the strength and compressibility of these materials and thereby
renders any landfill effectively unusable for long periods of time. In order
to better understand the nature of the time-dependent water content changes
that take place in the dredged materials after deposition, a one-dimentional
(vertical) mathematical model was developed (Krizek and Casteleiro, 1974) (a)
to describe the water content distribution in the fill at any time after
deposition, (b) to predict the desiccation and consolidation behavior of the
dredged materials as a function of time, and (c) to aid in evaluating the
different techniques that are available to accelerate the dewatering of the
landfill. This model is capable of handling the flow of water through a ver-
tically heterogeneous soil at any degree of saturation, together with the
associated desiccation and consolidation processes that may occur
simultaneously.
The consolidation of a partially saturated medium leads to a variety of
conflicting hypotheses. For example, classical consolidation theory, which
deals with time-dependent volume change characteristics, is based on the
assumption of a fully saturated soil, and the definition of concepts and
coefficients for partially saturated media poses a problem for which only
incomplete answers exist. On the other hand, soil scientists have directed
much effort to studying flow through partially saturated porous media, but
they usually assume that such media have a rigid structure and undergo no
volume change during flow. The combination of these two approaches consti-
tutes the essential basis for the mathematical model developed herein.
THEORETICAL DEVELOPMENT
Since the deposition of dredged material in a given containment area
usually takes place over a period of several years, each year during which
spoil is deposited is termed a cycle and the thickness of the sediment layer
at the end of each cycle is assumed to be proportional to the amount of
slurry placed in the site during that cycle. Furthermore, upon completion of
the first cycle, it is assumed that there exists within the site (a) a fully
saturated layer of dredged sediments with the same spatial distribution of
void ratio and (b) a free water layer with its lower boundary at the sediment
surface and its upper boundary at the same elevation as that of the overflow
weir. After a certain period of time, the overlying free water evaporates
and the top of the layer begins to desiccate. Due to this desiccation and
the possible drainage of water into the underlying soil, the position of the
58
-------
groundwater table will lower and the weight of the sediments comprising the
layer will increase due to the loss of buoyancy by the material situated
above the phreatic surface, thereby causing the thickness of the layer to
decrease. This process of desiccation, drainage, and consolidation continues
until the beginning of the next cycle, at which time the site is again inun-
dated and the same steps are repeated.
During this second cycle, an additional sediment layer of some finite
thickness is deposited in the disposal area. If the rate of deposition is
relatively continuous, it can be assumed that the thickness of this layer
will increase linearly, and thus the rate of stress increase on the first
layer will be constant. This sequence of activities will be repeated as many
times as necessary to fill the site. Hence, the basic phenomenon involved in
this process is one of water flowing through a consolidating medium in which
the location of the interface between the saturated and the partially satu-
rated zones is unknown and dependent on the properties of the dredged mate-
rial, weather conditions, the nature of the foundation soils, and the par-
ticular stage of the cycle.
The above-described flow of water through a heterogeneous porous medium,
regardless of its degree of saturation, was modeled one-dimensionally by a
general nonlinear partial differential equation. Then, simplifying assump-
tions were employed to deduce two nonlinear parabolic differential equations,
one for the fully saturated zone and the other for the partially saturated
zone. The simplifying assumptions are that (a) the velocity of the solids
can be neglected with respect to the velocity of the fluid and (b) the gener-
alized form of Darcy's law holds throughout the process.
The boundary conditions incorporated in the model include those natural
conditions which are usually found in the field and certain artificial condi-
tions that can be implemented to accelerate the dewatering process. However,
due to a general lack of knowledge about the volume change characteristics of
partially saturated soils, this boundary value problem cannot be solved
directly; therefore, a step-by-step technique was developed to adjust for the
effects of the simplifying assumptions, including the differential pressure
increase due to the lowering of the water table during desiccation or due to
the deposition of a new layer of sediments during dredging periods.
The step-by-step technique involves a multistage correction procedure
and is based on the assumptions that, during a small time increment, the non-
saturated zone of the dredgings is incompressible (i.e. 9e/3t = 0) and the
total stress acting on the underlying dredgings does not change (i.e.
9a/3t = 0); after this time increment, the errors introduced in the results
by these two assumptions are corrected. The field equations for the satu-
rated and unsaturated zones of this boundary value problem can be represented
0.4343 Cc Yw f ^u 30 ] _ J_ f 9u ]
(1 + e)(a0 + o - u) I 3t 3t J " 3z [ * 9z j UU L)
and
(1 + e]
59
-------
respectively, where z is the vertical coordinate, t is time, e is void ratio,
u is the excess pore water pressure, C is the specific water capacity of the
dredgings, Cc is the compression index, 6 is the volumetric water content, Q0
is the initial effective stress, a is the total stress, Yw is the unit weight
of water, k is the coefficient of permeability, and il> is the soil -water
potential (or capillary potential). With the assumptions that 9e/3t = 0 and
3o/3t = 0, Equations (10-1) and (10-2) can be reduced to two single-variable
nonlinear parabolic differential equations that may be solved numerically in
the specified time interval. The differential equation governing the satu-
rated phase has the form
0.4343 Cc Yw 8u _ 9 [ k Bu
(1 + e)(50 + o - u) 3t 3z [ k 3z
and the equation governing the unsaturated domain is
EXPERIMENTAL CHARACTERIZATION OF ENGINEERING PROPERTIES
The results of an extensive experimental program allow the development
of empirical relationships for various functions occurring in Equations
(10-3) and (10-4). In particular, it was found that the saturated permea-
bility, k (in cm/sec), over a void ratio range from 1 to 10 can be reasonably
well approximated by
log k = - [ (0.8 e2 - 10.2 e + 62)^ ] . (10-5)
Based on previous experience with nonsaturated soils, the permeability, k, of
these dredged materials in the nonsaturated state can be written in terms of
their permeability, ks, in the saturated condition, the void ratio, e, and
the volumetric water content, 6, as
k = ks [ ^-=-e ] • (10~6)
From the available test data it was impossible to find a unique
relationship between the volumetric water content and the soil-water poten-
tial, which, for partially saturated soils, is probably the single most
important factor describing their physical behavior. If the volumetric water
content, 0, is written as a function of the weight water content, w, as
0 = YT~Z w ' (10~7)
a maximum value for 0 can be obtained by setting e equal to the final void
ratio whereas a minimum is obtained by setting e equal to the initial void
ratio. After considerable background work, it was found that the general
water retention characteristics of the dredged materials under consideration
can be reasonably well represented by
60
-------
where i|j is the soil-water potential, 6S is the volumetric water content at
saturation, 0cr is the limiting or air-dry volumetric water content, ^Jcr is
the limiting or air-dry soil-water potential, and u and v are two empirical
material-dependent parameters. There were three principal reasons for choos-
ing this particular relationship. First, it complies directly with the spe-
cific water capacity requirement that C •* 0 as IJJ •*• °°; second, it was conve-
nient to program; and third, it applies reasonably well to many other soils.
The specific water capacity, C, can be derived from Equation (10-8) and has
the form
It has been found that the relationship between 6S and 6cr for most of the
dredged materials considered herein is approximately linear; this means that
the air-dry water content of a given dredged material can be determined from
a knowledge of its minimum void ratio at saturation.
The relationship between the compression index, Cc, and the void ratio,
e, in this model has the form
Cc - 0.01 (37 e - 7) . (10-10)
However, because e is a function of time, the partial derivative of Cc with
respect to time is generally not zero. The spatial distribution of the com-
pression index was assumed to be constant during any given time increment,
and an appropriate adjustment was made after each time step. Since no data
were available to describe the compressibility of the unsaturated dredged
materials, it was assumed that the only volume change in the partially satu-
rated zone resulted from the increase in the total stress at the end of the
step; this implies that any reduction in void ratio due to an increase in the
soil-water potential is neglected.
The heterogeneity of the deposit in the vertical direction is considered
by incorporating the concept of scale heterogeneity in the model. Although
this concept is widely employed by soil scientists, the difficulties in char-
acterizing the heterogeneity of these dredged materials precluded its practi-
cal application, and only initially homogeneous deposits are considered in
this work. Of course, the deposit becomes heterogeneous as the processes of
desiccation and consolidation take place.
NUMERICAL SOLUTION OF FLOW PROCESS
The solutions to the nonlinear boundary value problem characterized by
Equations (10-3) and (10-4) were determined by means of a finite difference
technique. The Crank-Nicolson scheme was employed in conjunction with mixed
boundary conditions in such a way that both the governing equation and the
surface condition are applied at points on the boundary. The governing dif-
ferential equations and the boundary conditions were expressed in terms of
dimensionless parameters. Moreover, a reduced time factor was introduced in
61
-------
the definition of the dimensionless time variable in order to allow the real
time increment to be modified without changing the dimensionless time incre-
ment; accordingly, the program could be written to allow for an automatic
change of the reduced time factor, if necessary, to enhance convergence. The
continuity condition at the interface between individual layers was treated
in essentially the same manner.
A noniterative Gaussian elimination method was used to solve the banded
coefficient matrix associated with the system of linear algebraic equations
that results from the technique applied to discretize the boundary condi-
tions. Test equations were incorporated to guarantee stability of the compu-
tational process, which is performed on a digital computer. The time and
expense required to obtain the desired information from this mathematical
model on the computer were found to be very large (on the order of an hour or
more on a CDC 6400), particularly if several cycles are considered.
RESULTS
This mathematical model was used to make settlement predictions at
various points in the Penn 7 Site where several measurements have been made
since 1972, when the deposition of dredged sediments in this area began. At
the time when these computations were performed, the dredging history of this
site covered two seasons (September 1972 to December 1972, and June 1973 to
August 1973). An average layer thickness for each of these two dredging
cycles was calculated by converting the bin-measure volumes actually pumped
into the site (Boresch, Personal Communication, 1974) to disposal-site vol-
umes; the latter was accomplished by using the conversion factor of 0.65
determined by Krizek and Giger (1974). Furthermore, it was assumed that 5 cm
of water overlaid the surface of the sediments at the end of each cycle; this
value corresponds to an estimated average that was observed in the field on
several occasions. The soil characteristics used in the model were described
previously. Since no consistent data were available to characterize the ver-
tical variation of the fill, the dredged material at a given location within
the site was assumed homogeneous, which implies that the scale heterogeneity
functions are unity.
A number of different boundary conditions were studied in order to
evaluate the effect of different boundary conditions on the settlement
response, and the results for three such locations (shown in Figure 4-3) in
the Penn 7 area are given, together with field measurements, in Figures 10-1
and 10-2. For this purpose the weather conditions, as expressed in terms of
a statistical year, were held constant to guarantee a constant evaporation
rate for the initially overlying water and thereby allow for a proper rela-
tive comparison. Although a variation in the drainage boundary conditions
(where kf and H£ are the permeability and thickness, respectively, of the
foundation soil) can lead to noticeable differences in computed settlements
when the second or subsequent layers are being deposited and the situation
resembles somewhat a conventional consolidation process, the effect of such a
variation was found to be small during the stages when evapotranspiration is
taking place. Thus, if an improvement in the bottom drainage characteristics
is anticipated to enhance the settlement rate of the landfill, such benefit
will take place almost exclusively during periods of no evapotranspiration
62
-------
Timt Idcys)
200 300
• Locoior 5/8
A Locales ;/iC
p Location 5/13
Time looy«)
100 a»
500
• Locator 5/6
A LDCOtlon 5/10
• Location 5/13
— Motncniaticoi Mod«:
Figure 10-1.
Settlement versus Time for No Transpiration
and Different Drainage Conditions
Time Ifloys]
200
300
• Locator 5/8
* Locoion 5/C
• Location 5/13
— Moirwmoticei Motfti
(bl 18-02
Time lOoys)
20O
500
• Locator! 5/8
A LOCOtDn 5/C
• Locolor 5/13
— Mathcmoticcl M
uiB'ia
Time (doyf)
ZOO
• Locator. 5/8
A Locoton 5/10
• LDCOIKM 5/13
" '
V
Figure 10-2.
Settlement versus Time for Impeded Drainage
and Different Coefficients of Transpiration
63
-------
and, unless these periods are sufficiently long, a careful study should be
performed before costly modifications to improve drainage at the bottom boun-
dary are undertaken.
The effect of transpiration on the settlement response of landfills
composed of dredged materials was investigated for different coefficients of
transpiration, 3, with an impeded drainage condition at the bottom boundary.
In this study it was assumed that vegetation starts to grow as soon as the
top layer becomes slightly unsaturated; although this condition may not nec-
essarily exist in all cases, it can be enhanced by seeding. Based on these
assumptions, it was found that the use of vegetation with high rates of
transpiration appears to offer a relatively effective and inexpensive way to
dewater dredge spoil and increase the settlement rate. The results produced
by proper vegetation will likely be as good as or better than those obtained
by improving drainage conditions at the bottom, and the costs will usually be
significantly lower. In general, the greater the percentage of last-stage
desiccation with respect to the total time of deposition, the larger will be
the consolidation due to evapotranspiration.
SUMMARY
A one-dimensional mathematical model has been developed to describe the
desiccation-consolidation response of a landfill composed of maintenance
dredgings. This model has the capability of predicting the water content
distribution and the settlement response of a landfill at any given time
after deposition of the dredged materials, and it can serve to evaluate the
various techniques that may be used to accelerate dewatering of the fill.
Any type of soil at any degree of saturation can be analyzed, provided the
material properties are reasonably well known.
The flow of water through a heterogeneous medium is described by a
nonlinear partial differential equation based on the simplifying assumptions
that (a) the generalized form of Darcy's law holds throughout the process and
(b) the velocity of the solids can be neglected with respect to the velocity
of the fluid. Scale heterogeneity functions are incorporated into the model
to account for spatially variable soil characteristics, and the combined
effects of evaporation and transpiration at the top boundary, as well .as
drainage conditions at the bottom boundary, are handled in a general way.
The solution to this boundary value problem was obtained by means of a step-
by-step finite difference procedure. However, due to the nonlinear character
of the governing equation, the time required to solve a practical problem was
very large.
The settlement predictions calculated by means of this mathematical
model were in reasonably good agreement with those actually measured at the
Penn 7 disposal site in the Toledo harbor area. Based on the results of a
parameter study with varying boundary conditions, it was found that the
effects of evapotranspiration on the dewatering process are quite substan-
tial, and the benefits gained by using vegetation with high transpiration
rates may be as good as or better than those obtained by improving drainage
conditions at the bottom boundary.
64
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SECTION 11
STABILIZATION
The effective stabilization of dredged materials that are placed in
diked containment areas poses challenging problems to the engineer, and many
different stabilization techniques (such as dewatering by ditching, sand
drains, preloading, and evaporation) have been investigated (Garbe and Jeno,
1968; Corps of Engineers, Philadelphia District, 1969; Greeley and Hansen,
1969; Waterways Experiment Station, U. S. Army Corps of Engineers, 1972;
Office of Dredged Material Research, 1974).' Included herein is a summary of
a more detailed study that has been reported by Krizek, Roderick, and Jin,
(1974) on the stabilization of dredged materials by use of chemical additives
and by evaporation.
TEST PROGRAM
In the chemical stabilization program outlined in Figure 11-1, three
main series were conducted; these included flocculation-sedimentation tests,
sedimentation-leaching tests, and repeated leaching tests. These three types
of test were developed in successive stages wherein the findings of the
flocculation-sedimentation tests formed background for the sedimentation-
leaching tests, the findings of which, in turn, constituted the basis for the
repeated leaching tests.
The addition of a flocculating agent to a soil suspension causes a
flocculation or joining together of fine-grained soil particles, thereby
increasing the effective particle sizes of the material; these larger floes
then settle more rapidly from the suspension to form a relatively large sedi-
ment volume. The admixture of flocculating agents to dredged materials dur-
ing the process of disposal into a diked containment area can effectively
increase the sedimentation rate and consequently decrease the amount of sus-
pended solids in the effluent water. In addition, the flocculation of sus-
pended solids may cause increased retention of pollutants in the disposal
area and further improvement in the quality of the effluent water.
A total of 114 individual flocculation-sedimentation tests were
conducted with 22 different chemical additives that were selected on the
basis of test results from previous nonrelated studies. Grain size distribu-
tion curves and sediment volume data were used to evaluate the effectiveness
of the various chemical additives on the degree of flocculation and the sedi-
mentation rate of suspended solids. The criteria for evaluating the floccu-
lation effectiveness of these chemicals were (a) percentage of fines that
flocculated, (b) initial sediment volume, and (c) color and clarity of the
supernatant. Once a slurry has settled in a diked containment area and the
65
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Licaracura SL«Tl«w
Sanaling Program
Twanty-two Dtffaranc
Chemical Addltivaa
Ftv» Typical Sradgad MacariaU
Datrolc. Michigan Clavaland, Ohio
Monroa. Michigan Toledo, Ohio
flocculaeloa-SadlMacacloa T««c Sariai
Sunbar o{ taica: 114
Twancy-cwo addlclvaa u*ad iflcb oat Tolado
oacarlal; fourcaan addltivai uMd with oclwr
ucarlala; varlau* blank laapUi ctftad for
eoaparKea
t>
P«rform*nc» Cricaria
1. Ptrciatag* flocculacioa of (inai
2. Inlclal sadiaaac voluna
3.- Color and clarlcy of suparnacaac
Effacciv* Flocculaacs
Lint «M affacctva vtch all oacariali
Calclua cblorid*, calcium cnbonaca, and sodium
ehlerida «•» afftcclva with ToUdo and
Hoaroa aacariaU
Lcii ?tonroa ipaccrjal
Sadlaaucacloa-Laachlng Ta*c Sarlai
Nwibar of T**c*: ZS
Oaa Tolado matarial t««tad with Caraa p«rc*a-
ta(aa of aach of thraa floccuLaoCs; Mooroa
aacarial caacad with fiva floeeulaaCi, chra*
with chraa parcaacafaa and two with ooa par-
cantage: varloua blank »aagla» also eascad.
Parfomanca Cricaria
1. Sacclaaanc
2. Ftrnaabilicy
3. Wacar coocaac
Dry daruity
Shaar •eranjch
Follucloa (Wtaatlal
Mete Provlaiog Addtctva
Sapaacad Laachlag Ta»e Sarlai
ir of latci: 22
Savan matarlal* froai flva harbors cat cad wleh
and without lisa addlciva; ehamlcal aaalyaaa
war* eoaduecad aa four to taa laaehata laaqila*
frog aaeh taat
Farforaanea Criteria
I. Long-can pollucloa pocaacial
2. Loog-tarm variation In paraaabllity
Inproremant Obtainad by Llaa Addltiva
Scabla soil jcruccura
Incraaiad panaablllty
Sacreasad pollution pocaacial
Figure 11-1. General Outline of Chemical Stabilization Program
66
-------
dewatering-consolidation process begins, several forces (such as seepage
forces, overburden stresses, physicochemical forces, capillary forces, and
forces caused by vegetation) act on the sediment. For sediments that are
subjected to only their self-weight, the latter two forces are probably domi-
nant in enhancing consolidation, particularly in the top few feet of the
fill.
Twenty-six sedimentation-leaching tests were performed with two typical
dredged materials to study the effectiveness of chemical additives in stabi-
lizing such materials. The shear strength and the corresponding water con-
tent were measured, the coefficient of permeability was calculated, and the
water quality of the leachate was analyzed. In addition, an associated sedi-
mentation test without drainage was conducted in order to observe the sedi-
ment behavior with time and the effect of the seepage force. All of these
parameters were used as criteria to judge the effectiveness of various chemi-
cal stabilization methods. These tests were performed in cylindrical sedi-
mentation chambers 18 inches (45 cm) high and 3 inches (7.5 cm) in diameter
with a porous stone at the bottom for drainage and an outlet to collect the
leachate.
Twenty-two repeated leaching tests were conducted on various typical
dredged materials with and without chemical additives to study the long-term
pollution potential of the leachates; these tests were performed in chambers
similar to those described above, except they were 24 inches (60 cm) high and
6 inches (15 cm) in diameter. In addition, the hydraulic gradient was varied
to assess its effect on the pollution potential of the leachates. Under some
conditions a substantial volume of water might pass through the deposited
sediments and enter the foundation soils underlying a diked containment area,
and the possible pollution of the groundwater by these leachates could pose a
problem. The contaminants carried by a leachate depend on the composition of
the dredged material and the chemical additive, as well as on the physical,
chemical, and biological activities that take place within the landfill.
Since the repeated leaching tests conducted in this experimental program fre-
quently lasted several months due to the low filtration capacity of the
dredged materials, biochemical reactions might have taken place during the
tests; however, only chemical analyses were conducted on the leachates.
Evaporation is known to be a promising technique for the economical
dewatering of dredged sediments within diked containment areas, and an inves-
tigation was therefore conducted to evaluate laboratory and field evaporation
from dredged materials and the associated strength gains and water retention
curves. A knowledge of the soil-water potential of dredged materials pro-
vides the background for a better understanding of the material behavior dur-
ing the evaporation process.
Three different series of laboratory evaporation tests were conducted.
The purposes of the first series were (a) to study the rate of water loss
from dredged materials from several different areas and (b) to determine the
effect of mixing on the rate of water loss; seven different materials were
tested under the same conditions of temperature and relative humidity. The
second series of laboratory evaporation tests was directed toward (a) evalu-
ating the influence of sample thickness and surface area on the rate of water
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loss, (b) observing crack sizes and crack patterns, and (c) determining shear
strength gains in the drying soils. The objectives of the third series of
tests were (a) to study the effect of lime (CaO) on the water losses, shear
strength, deformation, and cracking patterns of the sediments, (b) to obtain
additional data to help in interpreting the results of the previous labora-
tory evaporation tests, and (c) to serve as a guideline for the interpreta-
tion of the field evaporation test data. All tests were performed either in
glass containers 6 inches (15 cm) high and 6 inches (15 cm) in diameter or in
plastic pans 18 inches (45 cm) by 13 inches (33 cm) in areal extent and 4
inches (10 cm) high; the average temperature and relative humidity were about
78°F and 35%, respectively.
Two series of field evaporation tests were conducted in the Toledo area.
Both of these test programs were designed to study the strength and deforma-
tion behavior of dredged materials subjected to the climatic conditions at
Fenn 7 (average temperature about 73°F; average relative humidity about 65%,
and total precipitation about 9 inches (23 cm) during both testing periods).
Relatively small-scale tests were used to obtain better control of sediment
thickness, drainage conditions, and lime. (CaO) treatment. In the first
series 12 drums (22 inches (56 cm) in diameter and 35 inches (88 cm) in
height) were used; five of these had perforated bottoms and sand filters to
allow drainage during the test period, which began on August 1, 1973, and
continued for 14 days. The second series of ten field evaporation tests was
conducted at the same site and with the same drums, but greater sample depths
were used and a longer test period of 113 days (August 15 through December 5,
1973) was allowed.
RESULTS
Described briefly in the following paragraphs are the major results that
were obtained from these various series of tests. As mentioned previously,
the parameters involved in each successive test sequence were selectively
chosen from the results of the preceding series.
Flocculation-Sediment at ion
Calcium oxide and calcium chloride were found to be effective
flocculants for most of the dredged materials; the supernatants were color-
less and clear for all of the samples tested. The chemicals o-nitrophenol,
p-nitrophenol, and tri-nitrophenol were effective flocculants and the super-
natants were clear, but they exhibited yellow and pink coloration; this
visual pollution of the effluent and the toxicity of the chemicals make them
undesirable as practical flocculating agents. Similarly, acetic acid, phos-
phoric acid, sulfuric acid, nitric acid, hydrochloric acid, and aluminum sul-
fate were all found to be effective flocculants, but the supernatants became
cloudy and had a brownish-yellow coloration after a day of settling. Calcium
carbonate was also quite effective as a flocculant for three of the five
materials tested, and sodium chloride was effective with two, but the super-
natants remained cloudy with both chemicals. The organic chemicals
p-benzoquinone, pyrogallol, polyvinyl alcohol, and krilium were not effective
flocculants. Resorcinol was effective with only one of the dredged materials
and the supernatant remained cloudy.
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Sodium hydroxide, potassium hydroxide, and sodium hexametaphosphate
(Calgon) were found to be good dispersing agents. Considering the initial
sediment volume data and general observations, the higher percentages of
organic substituted benzene ring compounds (7 millimole/m.e. or about 10% by
weight of the solids) had a better flocculating effect than did the lower
percentages of the same organic compounds. According to reports by the Dow
Chemical Company, their polymers Purifloc C-31 and Separon 273 are effective
flocculants for dredging slurries at 0.4 to 20 grains per liter concentration;
hence, these chemicals are promising flocculants for dredge overflow and weir
outflow treatments. After studying the test results of this program and com-
paring the engineering characteristics of the five dredged materials tested,
it was found that the coarser dredged materials are less affected by chemical
additives.
Sedimentation-Leaching
A comparison of the observed sediment volume versus time relationships
for the 26 samples tested suggests the following conclusions. For both of
the lime (CaO) treated samples it was found that the sedimentation process
was shorter than that of the nontreated samples and a more stable and larger
sediment was formed. This is probably due to the flocculation and cementa-
tion effects of the lime. The sodium chloride (NaCl) treatment, on the other
hand, led to inconsistent results; in one case there was no improvement at
all whereas in the other cases some improvement was observed. Calcium chlo-
ride (CaCJ^) and resorcinol (CglfyCOH^) gave virtually no improvement in any
case; this may be due to the fact that the chosen concentrations were larger
than 50 grams per liter used in the flocculation-sedimentation tests. In
general, all chemicals appeared to be more effective when used with finer-
grained materials.
Downward seepage forces would logically tend to densify dredged
materials as leaching takes place, and the densities of the samples in
sedimentation-leaching tests were indeed found to be higher than those of the
corresponding samples in sedimentation tests only. In addition, even though
the treated samples exhibited lower densities than the untreated samples in
the sedimentation tests alone, they ultimately achieved higher densities when
subjected to leaching; this suggests that the effects of seepage forces are
greater than those of physicochemical forces. The permeabilities of the
lime, calcium carbonate, and sodium chloride treated samples were substan-
tially higher (at least by an order of magnitude) than those of the untreated
materials; this is evidently due to flocculating effects which were insig-
nificant for the other chemicals.
Shear strength and dry density were expected to increase as leaching
approached completion and capillary tension became more effective. However,
this was not the case for lime treated materials, which in all cases exhib-
ited lower densities than untreated materials. At a water content of about
150%, it was found that the cementation effect of the lime was too small to
affect the shear strength, but at water contents of about 30%, cementation
does substantially increase the strength of the same material approximately
proportionally to the amount of lime used. Calcium carbonate treatment
resulted in a slight increase in strength whereas sodium chloride had a
69
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decreasing effect on strength when compared with the results of untreated
materials; this is perhaps due to the deflocculating effect at higher per-
centages of sodium chloride.
The frequent scatter in the results of the chemical analyses of the
leachates is due in large part to the heterogeneous nature of the dredged
materials; although this scatter makes it somewhat difficult to draw specific
conclusions, it is possible to infer general trends. For example, for chemi-
cally treated materials a larger sediment volume is formed at the beginning
due to the flocculating effect of the additive. Thus, the fine solids in
suspension pass more readily through the pores, thereby resulting in higher
suspended and total solids contents for treated than for untreated total and
suspended solids contents.
For those flocculants that completely dissolve in the sample (for
example, sodium chloride or calcium chloride) the associated leachate usually
contained higher amounts of dissolved solids. Moreover, the concentrations
of volatile solids and suspended volatile solids in the leachates of the
treated materials increase approximately proportionally to the increases in
the total solids and suspended solids contents of the treated materials. No
general trend can be associated with the pH values; this could be due to the
biochemical reactions that took place during testing. The silica content
related essentially to the total solids content for each material tested, and
no significant variation was observed. The leachates of the lime, calcium
carbonate, calcium chloride, and sodium chloride treated samples were found
to exhibit increases in calcium and sodium ion concentrations, and these
increases were directly related to their respective additives. On the other
hand, the ion concentrations on a wet weight basis increase sometimes for
total iron and potassium but no significant variation was manifested on a dry
weight basis; this may imply that these ions are associated with the passage
of solid particles during the process of leaching. The opposite phenomenon
was observed for the concentrations of copper, cadmium, lead, and mercury
ions; this suggests that these ions may be dissolved in the solution. Based
on chemical analyses of the leachates, it appears that none of these addi-
tives causes any significant changes in the water quality of the leachates,
except for an increase in the solids content due to flocculation and an
increase in the specific ion concentration that is directly related to the
additive used in the treatment.
Repeated Leaching
Based on 22 individual repeated leaching tests that were conducted on
seven different materials with and without lime treatment under different
hydraulic gradients, it was found that the leachates from the well-graded
coarser dredged materials had lower total solids contents than those of the
finer more cohesive materials; this may be due to the presence of fewer fines
and more nonactive particles in the coarser samples. An increase in the
hydraulic gradient was observed to be associated with an increase in the
final percentages of solids, and, in general, the leachates of lime treated
samples had a slightly greater solids content. For untreated, undisturbed
samples, the solids content of the leachates seemed to decrease with an
increase in the volume of water drained; a similar trend was observed with
70
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the turbidities of the leachates. The slightly basic pH values did not
change significantly during leaching; this could be due to the effect of the
slightly basic deionized filling water. The concentrations of metals, such
as calcium, copper, total iron, potassium, sodium, and lead, are comparable
to those of field samples of water from the wells in Penn 7. The permea-
bility of these sediments decreased slightly with time as leaching pro-
gressed, probably due to seepage effects.
For the lime treated, undisturbed sediments, the volatile solids
contents of the leachates were higher than in the case of the untreated
samples because of the greater removal of organics from the sediments by cal-
cium ions. Moreover, the total iron, potassium, and sodium ion concentra-
tions of the leachates were lower than those of untreated materials; this may
be due to the removal of organics by the calcium ions or to ion fixation.
Since lime treatment introduced a larger amount of calcium ions in the leach-
ate, the pH was increased to about 12 at the beginning of the test and the
permeability increased by a factor of about ten relative to the permeability
of untreated materials.
In summary, the leachates of dredged materials placed with or without
chemical additives in diked containment areas do not appear to cause any
serious pollution problems; this is due in large part to the fact that the
permeability of most silty-clay dredged materials is very low, as compared
with that of sanitary sludge, and the groundwater is able to adequately
dilute the relatively small amounts of contaminants that are leached from the
solids.
Evaporation
In the first series of laboratory evaporation tests, the initial rate of
water loss increased with increasing initial water content and decreased with
increasing clay content, and there was no significant difference in the rate
of water loss for mixed and unmixed samples. This may be due to the infre-
quent mixing and the high initial water content of the samples. Despite this
observation for a limited series of tests, there is considerable evidence
(Garbe and Jeno, 1968; Greeley and Hansen, 1969; Office of Dredged Material
Research, 1974) to suggest that mixing substantially increases the rate of
water loss due to evaporation. For any given sample in the second series,
the rate of water loss was essentially constant at the beginning of the test
period, and higher initial rates of water loss occurred with the thinner
samples. Shear strengths increased rapidly with drying; after about 40 days,
strengths were greater than the measuring capacity of the equipment used
(4000 psf or 192 kN/m2). The results of the third series of laboratory tests
indicated that, in general, the addition of lime (CaO) to the materials does
not change the initial rate of water loss, but it does reduce the final rate.
The addition of lime greatly increases the gain in shear strength with time.
From the results of the first series of field experiments it was found
that the drained samples manifested greater final shear strengths with the
greatest shear strengths being found in the samples with the smallest initial
heights; this was undoubtedly due to the higher degree of consolidation
caused by seepage forces and capillary stresses. The strengths of undrained
71
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samples were essentially the same and insignificant, regardless of the
initial depth of material and the degree of lime treatment. In the case of
the drained samples, lime treatment resulted in lower shear strengths; this
was apparently caused by a reduction in the degree of consolidation during
the test period.
Results from the second series of field evaporation tests indicated that
the thinner samples developed wider and deeper cracks during drying; this may
be due to a higher thermal gradient causing a higher rate of water loss.
Lime treatment resulted in fewer, but larger, cracks in the drained samples.
Except for the sample with the lowest water content, no cracks formed in the
undrained sediments. Under undrained conditions, lime treatment resulted in
low strengths in the upper portions of the samples.
SUMMARY
Among the many effective flocculants, calcium oxide and calcium chloride
are the most suitable from the viewpoint of coloration and clearness of the
supernatant. Upon studying the test results of this program and comparing
the engineering characteristics of the five dredged materials tested, it was
found that the coarser dredged materials were less affected by chemical addi-
tives. Based on an overall comparison of all additives tested, lime appears
to be the most effective; it has the ability to decrease the long-term rate
of volume change, increase the permeability, and retain some of the pollut-
ants. Although the addition of lime causes a reduction in strength and an
increase in the calcium ion concentration, it can alter the sediments
favorably for further stabilization, such as compaction. The results of
repeated leaching tests indicate that the leachates of chemically stabilized
dredged materials do not constitute a very serious potential pollution
hazard; in particular, if additives such as lime are used, the pollution
potential will likely be reduced. Previous experience suggests that the rate
of water loss due to evaporation can be increased substantially by mixing the
sediments and destroying the crust that forms at the surface. If the sedi-
ments are not mixed, the exposed surface area per unit volume of dredged
material for evaporative purposes will be dictated largely by the formation
of shrinkage cracks and the depth of the layer.
72
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SECTION 12
SYNTHESIS
Synthesized In this section are the major results of an extensive study
of the dredging and disposal problem in the United States; of particular con-
cern in this work is the potential usefulness of dredged materials as land-
fill. The overall dredging and disposal problem is first placed into
national perspective by a concise review of the magnitudes and types of
dredged materials that are encountered throughout the country, the types of
equipment that are employed, the types of disposal that prevail in various
regions, the environmental and legal constraints that exist, the beneficial
uses that can be made of dredge spoil, and the general economics of the dif-
ferent alternatives. Then, the detailed findings of a concentrated research
effort in the Great Lakes area are described; this latter part of the study
comprised the thrust of the research program, and it was directed toward a
quantitative assessment of the engineering characteristics (strength, permea-
bility, compressibility, consolidation, etc.) of typical Great Lakes sedi-
ments as they pertain to the construction of landfills.
NATIONAL PERSPECTIVE
The importance of navigable waterways and harbors to the economic growth
of the United States is manifested by the fact that waterborne commerce now
exceeds 1.5 billion tons per year; this represents more than an 80% increase
in total tonnage during the 20-year period from 1950 to 1970, and future pro-
jections indicate that this important role will persist in the years to come.
In order to maintain the almost 32,000 kilometers (20,000 miles) of waterways
and 1,000 harbors, approximately 230,000,000 cubic meters (300,000,000 cubic
yards) of bottom sediments are dredged annually, and an additional 60,000,000
cubic meters (80,000,000 cubic yards) are removed to develop new projects
(Boyd et al, 1972). Although some of this work is performed by private con-
tractors, the development and maintenance of the navigable waterways in the
United States rest with the U. S. Army Corps of Engineers. Current annual
costs for these operations amount to about $200,000,000 with the unit cost
ranging from about 20C to more than $10 per cubic meter. Presented herein is
a brief overview of the current dredging and disposal problem in the United
States; addressed in a very general way are the various types of materials
that are encountered, the techniques used to dredge and dispose of these
materials, the environmental and legal constraints that must be satisfied,
and the economic considerations that are involved.
73
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500
Scale (miles)
1000
800
Scale (kilometers)
1600
Figure 12-1. Major Regions of Dredging Activity in the United States
Major Geographic Regions
As illustrated in Figure 12-1, the major regions of dredging operations
throughout the continental United States can be arbitrarily grouped into the
East Coast, Great Lakes, Southeast and Central, Gulf Coast, and West Coast.
The East Coast region includes primarily the New England area and the harbors
of New York, Philadelphia, Baltimore, Norfolk, Wilmington, Charleston, Savan-
nah, and Jacksonville. The main harbors in the Great Lakes region are Buf-
falo, Huntington, Detroit, Chicago, and St. Paul. The Southeast and Central
region includes Nashville, Mobile, Vicksburg, Memphis, St. Louis, Rock
Island, Kansas City, and Tulsa. The Gulf Coast region consists essentially
of the harbors and waterways serving New Orleans and Galveston. And the West
Coast region includes Seattle, Portland, Sacramento, San Francisco, San
Diego, and Los Angeles. Table 12-1 gives a breakdown of the approximate
quantities and percentages of dredged materials that are handled in each
region.
-
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Table 12-1. Summary of Dredged Material
Volumes by Category and Region
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75
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Types of Dredging Equipment
The types of dredging equipment used by both the Corps of Engineers and
private contractors are discussed briefly in the context of the average
annual quantity of maintenance dredging associated with each type, and the
results are summarized in Table 12-1. Although this table shows only that
equipment used in maintenance dredging operations, it is a fairly accurate
reflection of the types and relative usage of each type for all dredging
activities.
Hopper Dredge
All hopper dredges are owned and operated by the Corps of Engineers, and
their use is confined primarily to maintenance operations in the coastal
regions (45,000,000 cubic meters or 60,000,000 cubic yards per year) and the
Great Lakes region (5,700,000 cubic meters or 7,500,000 cubic yards per
year). Although hopper dredges have traditionally disposed of their materi-
als in open water, the situation is changing somewhat; due primarily to envi-
ronmental concerns over open water disposal, several hopper dredges (espe-
cially those operating in the Great Lakes) have been modified to allow direct
pumpout for land disposal, and other hopper dredges have been modified for
sidecasting to allow such disposal procedures as beach nourishment.
Pipeline Dredge
Hydraulic pipeline dredging by dustpans and cutterheads accounts for
approximately 70% (157,000,000 cubic meters or 205,000,000 cubic yards) of
the average annual maintenance dredging. Dustpan dredges are all owned by
the Corps of Engineers and are used almost exclusively for channel mainte-
nance in the Mississippi and Missouri Rivers; they account for a dredging
volume of less than 40,000,000 cubic meters (50,000,000 cubic yards), most of
which is deposited in open water. Since cutterhead dredges, which are used
for both maintenance and new work, are not all owned by the Corps of Engi-
neers, the remaining volume of about 115,000,000 cubic meters (150,000,000
cubic yards) does not necessarily represent the total quantities dredged by
all cutterheads (but rather that volume dredged by those cutterheads owned
and operated by the Corps of Engineers).
Sidecaster Dredge
Sidecaster hydraulic dredges are all Corps-owned and are used primarily
for maintenance dredging in the- East Coast region. Although they operate in
somewhat the same way as hopper dredges, they differ in that the dredging and
disposal operations are carried on simultaneously with the dredged materials
discharged to the side of the navigation channel. Sidecaster dredging aver-
ages less than 750,000 cubic meters (1,000,000 cubic yards) per year, and, as
far as can be determined, all disposal operations fall into the open water
disposal category.
Dipper, Clamshell, and Bucket Dredges
Dipper, clamshell, and bucket dredges collectively account for an annual
average of approximately 3,000,000 cubic meters (4,000,000 cubic yards) of
maintenance dredging. Unlike the dredges described above, these dredges
operate on mechanical, rather than hydraulic, principles. Most mechanical
dredging is done for the Corps of Engineers by private contractors. Although
76
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the rate at which the materials are removed by these dredges is small
compared to that of hydraulic dredges, they are ideally suited for working in
small areas such as harbors and slips; the dredged materials are usually
placed in barges or scows and transported to the disposal site, which may be
on land or in the water.
Grain Size Classification
As shown in Table 12-1, the types of dredged materials may be classified
into five broad categories. By far the largest category (approximately)
118,000,000 cubic meters or 154,000,000 cubic yards per year) is that termed
mixed sand and silt; about 60% of these materials come from the coastal areas
and 40% are from the inland rivers and the Great Lakes. . Approximately
23,000,000 cubic meters (30,000,000 cubic yards) per year of sand, gravel,
and shell are dredged from the coastal regions while about 16,000,000 cubic
meters (21,000,000 cubic yards) are dredged from the inland waterways and the
Great Lakes; indeed, the moving sand bottoms of many navigable rivers have
been a long-exploited supply of sand and gravel for construction purposes.
Mud, clay, silt, topsoil, and shale account for 60,000,000 cubic meters
(80,000,000 cubic yards) per year, about 46,000,000 cubic meters (60,000,000
cubic yards) of which are dredged from the coastal areas and the rest from
the inland rivers and Great Lakes. Although organic muck, sludge, peat, and
municipal-industrial wastes account for only 1,200,000 cubic meters
(1,500,000 cubic yards) per year, some of the more pressing environmental
problems are associated with these materials.
Types of Disposal
In the past dredged materials were deposited at selected disposal sites
near enough to the dredging site to minimize disposal cost, but sufficiently
far from beaches, water intakes, etc., to negate any adverse effects on these
facilities; within these constraints the decisions regarding the means of
disposal (open water, confined, unconfined upland, and undifferentiated) were
based primarily on economic considerations. In recent years, however, con-
fined disposal has increased in importance because environmental factors have
introduced additional constraints. Approximately 200 active Corps of Engi-
neers dredging projects rely in whole or in part on the confined disposal of
dredged materials, and almost 3000 hectacres of new land are acquired each
year to contain the volume of material generated solely by maintenance opera-
tions (Kirby, Keeley, and Harrison, 1973). Notwithstanding this trend, the
data in Table 12-1 show that open water disposal is still used for over 60%
of the materials.
Pollution Status
When the concentration of one or more of seven selected chemical
parameters exceed prescribed limits, dredged sediments are considered to be
polluted according to current standards. Table 12-1 indicates the approxi-
mate quantities of dredgings that are considered polluted and unpolluted in
each region. Almost 30% (66,000,000 cubic meters or 87,000,000 cubic yards)
of all maintenance dredgings are considered to be polluted, but the percent-
age in the Great Lakes region is more than double this average percentage.
77
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Of the 140,000,000 cubic meters (182,000,000 cubic yards) per year of
maintenance dredglngs reported as being placed in open water, approximately
20% (27,000,000 cubic meters or 36,000,000 cubic yards) are classified as
polluted. Confined disposal accounts for almost one fourth of the total
amount of maintenance dredgings with the largest percentages being handled in
the East Coast and Great Lakes regions.
Beneficial Uses
In contrast to the traditional characterization of maintenance dredgings
as an undesirable waste product, there are many beneficial uses that can be
made of dredged materials. Perhaps the most obvious of these is their use as
a fill material to form islands or waterfront developments. Although most
maintenance dredgings cannot be classified as ideal fill materials, history
has witnessed the development, either intentional or unintentional, of a num-
ber of man-made landfills which have been used to great advantage; in this
regard virtually every major harbor in the United States includes terminals
and piers that are built on landfills of dredged materials, and many airports
and highways, as well as recreational areas, are founded at least in part on
dredge spoil. There is also a significant potential for the use of dredged
materials in beach nourishment, creation of wildlife refuges, bottom sub-
strate enhancement, and strip mine reclamation. Very possibly nutrient
enriched dredged materials could be used to improve the sterile wastes that
will evolve from the processing of oil shale. As mentioned earlier, dredged
sands and gravels have been used as construction materials for many years,
and there is every indication that this trend will continue.
Environmental and Legal Constraints
Some of the early concerns over possible adverse effects of dredged
materials on aquatic environment appear to have arisen in the Great Lakes
area, where in 1966 the Corps of Engineers started to investigate feasible
alternatives to open water disposal at a few selected harbors. The increas-
ing awareness of this problem by environmental groups and the reaction of
various public organizations eventually led to a jointly sponsored pilot
study by the Corps of Engineers and the Environmental Protection Agency in
1969 to assess the impact of open water disposal on the lake environment. As
a consequence of this pilot study, it was recognized that the problem is
extremely complex and in need of a large-scale research effort over a period
of several years; in the interim it was concluded that contained storage for
a period of a few years would greatly enhance water quality in the Great
Lakes.
This work led to the enactment of the River and Harbor Act of 1970
(Public Law 91-611), wherein the Congress authorized the Secretary of the
Army to construct, operate, and maintain contained disposal facilities with a
ten-year absorption capacity in the Great Lakes area. At that time, the
Great Lakes area was apparently the only region in the United States where,
in the interest of pollution abatement, specific legislation was enacted to
provide for confined disposal of polluted dredge spoil regardless of the
local cooperation requirements of existing federal navigation projects or the
resulting increase in dredging and disposal costs. In the last few years,
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however, the disposal of dredged spoil has become a problem of national
concern, and there have been several instances where harbors and channels
have not been dredged because no suitable spoil disposal scheme could be
devised to satisfy the constraints imposed by various groups and individuals
concerned with the ecologic and aesthetic aspects of the environment and by
the variety of new legislation at the federal, state, and local levels.
Three groups of laws involving mandatory, discretionary, and other
environmental conditions pertaining to regulations and policies that repre-
sent constraints on the disposal of dredged materials are well described in a
report by Wakeford and MacDonald (1974). Most of these laws deal in one way
or another with policy statements of the U. S. Congress and the various state
legislatures; some outline general policies whereas others contain specific
prohibitions. In particular, a number of these federal and state laws are
concerned with water quality, land use, and the protection of wetlands and
coastal areas, and they contain expressions of policy that restrict the dis-
posal and potential usefulness of dredged materials. Water quality criteria
often impose severe restrictions on the disposal of dredgings, and turbidity
standards for the receiving waters are frequently difficult, if not impracti-
cal, to meet.
Once the states have a plan approved by the Secretary of Commerce under
the Coastal Zone Management Act of 1972, land enhancement and proposed mar-
ketable uses for dredged materials are subject to the legal requirements that
(a) major land or water fill operations require a detailed Environmental
Impact Statement, (b) the placement of even unpolluted materials in water to
make marshes or islands requires prior coordination with various fish and
wildlife agencies, and (c) the proposed action must be consistent with the
state program for coastal management. However, the Marine Protection
Research and Sanctuaries Act of 1972 does not apply to marshes and islands
constructed pursuant to an unauthorized state or federal project.
The balance of the federal and state laws dealing with the end use of
dredged materials may be characterized as "permit" laws; these laws, all of
which require some form of state approval, have been enacted to protect the
coastal and wetland areas, to oversee general land use requirements, and to
guarantee the preservation of minimum water quality standards. Almost with-
out exception, however, these laws allow the undertaking of justifiable
affirmative action programs that are, on the whole, environmentally sound and
in accord with the public interest. The temporary storage of dredged materi-
als for several years will, in general, require the protection of wetlands.
In such cases county or municipal ordinances usually control the height to
which materials may be stored and the restrictions that must be satisfied if
the materials exhibit offensive odors. On the other hand, clean materials
intended for use in construction are subject to codes of a technical nature
only.
With regard to the donation or sale of dredged material, there are a
myriad of laws, federal regulations, Army regulations, and Corps of Engineers
regulations that describe the types of property that can or cannot be sold or
donated and the procedures that are to be followed in either case. In
essence, the Corps of Engineers owns that material which is regularly placed
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on federal lands, but that portion which is surplus to the requirements of
the government can be sold or donated. Depending on the statutory authority
selected, there are different hierarchies of preferred donees, but the only
firm prohibitions contained in these laws are that the material must be sold
at its fair market price and that it must not be injurious to the public.
Aside from the various legal constraints, there are many other social
and political constraints that influence the potential uses of dredged mate-
rials. For example, since maintenance dredgings have an established (though
not necessarily justified) reputation of being environmentally detrimental,
public reaction is often negative to their disposal near recreational or liv-
ing areas due to a fear of pollution effects, offensive odors, attraction of
undesired insects, and potential diseases that might emanate from such depos-
its. Further constraints may be imposed by local business interests, such as
the possible effect of dredged sand and gravel on the prices of similar mate-
rials from commercial pits.
Economics
An assessment of the economics associated with dredging and disposal
operations on a broad scale is virtually an impossible task because of the
many factors, both technical and nontechnical, that are involved. Although
several technical measures (such as automation, improved equipment, better
training of personnel, more accurate positioning, use of chemicals, and modi-
fication of dredging operations) may improve the economy and environmental
acceptability of dredging and disposal operations, the more significant eco-
nomic factors arise from the nontechnical measures (such as national policy,
social acceptance, environmental compatibility, and nature of contractual
agreements). For example, a change in the method of payment (based on care
and accuracy, rather than primarily on quantity) for dredging may substan-
tially affect current practice on many projects. Since factors such as
social acceptance and environmental compatibility are rather subjective,
their inclusion in any quantitative economic analysis is invariably based on
somewhat arbitrary and often controversial hypotheses, and a change in these
basic assumptions may completely alter the economics of the situation.
If the disposal of dredged materials in a given situation presents the
alternatives of a containment area and open water deposition at a large dis-
tance from the source of the dredgings, the tangible economics revolve around
comparing the costs of constructing and maintaining a containment facility
(less any benefits realized) and the transportation costs associated with
hauling the dredgings to a satisfactory open water disposal point. While it
is difficult to generalize the economics of disposal for the above reasons,
many projects yield unit costs between $1 and $3 per cubic yard for dredging
and disposal either in a containment area or in open water; for example, the
recent cost of dredging and disposal in the Toledo harbor has been about $1
per cubic yard for either confined or open water disposal whereas in the Nor-
folk area ocean dumping costs several dollars per cubic yard and confined
disposal costs less than $1. However, many unit costs for confined disposal
exceed $10 or $15 per cubic yard; typical examples include some proposals in
Baltimore for the disposal of dredgings in abandoned quarries many miles
inland and a new ten-year disposal site that will ultimately become usable
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lakefront land in Milwaukee. Notwithstanding any potential economic
advantage of open water disposal, there are many cases where open water dis-
posal is specifically prohibited and no feasible alternative other than con-
fined disposal exists.
GREAT LAKES STUDY
Within the context of the foregoing national perspective, almost
10,500,000 cubic meters (14,000,000 cubic yards) of spoil are dredged
annually from more than 100 Great Lakes harbors. Of this volume about one
third is considered to be polluted, and virtually all of this polluted spoil
is placed in confined disposal areas. Summarized in this section are the
salient features of a four-year study directed toward evaluating the poten-
tial usefulness of dredged materials as landfill in the Great Lakes region.
Although test data on bottom sediments from seven Great Lakes harbors are
contained in this study, most of the work, including the instrumented field
site, was undertaken in the Toledo harbor area, and the conclusions, although
believed to be reasonably applicable to any sediments of a similar nature,
are strongly weighted in favor of the conditions experienced in the Toledo
area.
Water Quality Aspects of Confined Disposal
The water quality study conducted at the Penn 7 disposal site in Toledo,
Ohio, has led to several important conclusions. First, the majority of the
pollutants in dredge spoil tend to associate with the solid particles, and
the concept of using a diked containment area as a settling basin to retain
the polluted solids does effectively improve the quality of the surface
waters on the surrounding region. Second, the quality of the effluent that
was discharged from the disposal area is similar to that of the ambient river
water and slightly better than that of the groundwater. And, third, the
spoil retained within the diked enclosure represents a highly concentrated
source of pollutants which might leach into the groundwater, thereby reducing
to some extent the advantage gained by placing the polluted materials in a
confined disposal area in the first place. However, for the particular
dredgings investigated, the coefficient of permeability obtained from labora-
tory tests was found to range from about 10"? to 10~8 cm/sec for void ratios
between 1 and 2. (Such void ratios are commonly found in hydraulically
placed deposits of dredged materials.) For a 10-foot (3-meter) layer of
dredged material subjected to a hydraulic gradient of unity, one throughput
of leachate would require more than 50 years. On the other hand, field
infiltration tests on materials with comparable void ratios yielded permea-
bility coefficients about three orders of magnitude higher; use of these
field-measured values would indicate that one throughput of leachate may
require as little as one month. The true coefficient of permeability obvi-
ously exerts a very strong influence of the groundwater pollution from the
disposal area leachates. If the higher permeability should actually prevail,
it can be argued that the pollutants might not leach readily from the solids
and that the dispersion in the groundwater might be sufficient to reduce the
concentrations of pollutants to acceptable levels over a long period of time,
whereas if the lower permeability actually exists, the quantity of pollutants
entering the groundwater would be so small that effects would certainly be
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negligible. One advantage demonstrated by the results of the stabilization
study is that the addition of lime reduces the amount of pollutants that is
leached.
Characterization of Dredged Materials
The characterization tests on the dredged materials obtained from four
different disposal sites in the Toledo harbor area indicated that all materi-
als are essentially similar in nature and can be classified as a mixture of
organic silts and clays of medium to high plasticity (OH) and inorganic clays
of high plasticity (CH), with approximately 60% of the materials tested lying
in the first category and 40% in the second. Most of the, materials were
found to contain about 4% to 8% organic constituents, placing them in the
category of intermediate organic soils. Sand, silt, and clay components were
present in the approximate proportions of 1:3:2, respectively. The liquid
limit of these materials ranged between about 50% and 90% for respective clay
contents of 20% and 50% with an approximately linear relationship for inter-
mediate values. The plastic limit ranged between 30% and 50% and was found
to be independent of clay content within this range. Since the characteris-
tics of the materials deposited in each of the four Toledo sites were found
to be essentially the same, data from all four sites were synthesized and
treated as representative of one large site spanning a time, period of almost
a decade.
Compressibility and Consolidation
Data from an extensive series of conventional consolidation tests on
undisturbed samples indicated that the compression index lies between 0.3 and
0.7 and increases linearly with both water content and liquid limit. The
secondary compression characteristics were studied by means of long-term
slurry and conventional tests, and the deflection-log time response was found
to exhibit a consistent, but unusual, pattern wherein the rate of secondary
compression, after being constant with log time for a considerable length of
time, started to increase and form a second S-shaped curve similar to that
associated with the classical response for primary consolidation. The coef-
ficient of secondary compression was correlated with index properties and
consolidation stress in order to facilitate a rapid estimate of the magnitude
of the secondary settlement. Despite the significant difference in the pro-
portions of secondary and primary compression obtained from slurry and con-
ventional tests, the total settlement per unit height associated with corre-
sponding stress levels is about the same for both tests. However, the times
necessary to reach ultimate settlements are shorter in the case of slurry
consolidation tests than in the conventional tests. The coefficient of con-
solidation for these materials was about 0.0006 ± 0.0003 cm2/sec for all con-
solidation stresses except possibly the very low values. A comparison of the
actual settlement-time response measured in the field with that predicted by
the use of classical consolidation theory showed that measured field settle-
ments were considerably higher than those calculated, even for the so-called
settlement conditions. However, measured field settlements agreed
reasonably well with those calculated by use of an improved mathematical
model that accounted more realistically for the actual physical phenomena
that occur during the desiccation and one-dimensional consolidation of
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successive layers of dredged materials as they are deposited periodically in
a diked containment area.
Shear Strength
As with virtually all soils, the water content of these fine-grained
dredged materials was found to bear a major influence on their shear
strength, which is generally very low, and, unless landfills consisting of
these materials are adequately drained, they will likely remain soft and weak
for many years. The field strengths of these materials increased rather con-
sistently with time for a period as long as ten years, but the rate was
rather low (about 4 kN/m2 or 0.6 psi per year). The logarithm of the shear
strength of these dredgings varied exponentially with water content and lin-
early with dry density or liquid limit, and their strength characteristics
are similar to those associated with fine-grained organic soils. Based on
measured sensitivity values, these dredged materials can be classified as
"sensitive soils." The results of the chemical stabilization study indicated
that lime, although generally the most favorable stabilizing agent from an
overall point of view, actually reduced the sheaf strength of these materials
somewhat through alteration of the soil structure.
Potential Usefulness of Landfills
Within the context of this four-year study to evaluate the usefulness of
fine-grained, polluted, dredged materials for landfill, certain broad conclu-
sions can be advanced. In a relative sense, the disposal of dredged sedi-
ments in diked containment areas does improve the overall quality of the sur-
rounding surface waters, but it is not clear whether the degree of improve-
ment realized is sufficient to justify the considerably higher costs
involved. In addition, the low initial shear strength of these high-water-
content, organic materials under natural conditions, along with their slow
rate of strength increase with time and their associated large volume
changes, seriously limit the usefulness of landfills composed of dredged
materials. Unless special steps are taken to improve the quality of these
materials, their use will be restricted largely to wildlife refuges, parks,
recreational areas, parking lots, access roads, and the construction of light
buildings with flexible structural joints and flexible floors which would
allow several inches of total settlement and a few inches of differential
settlement.
Improvement Techniques
The improvement of such landfills can be accomplished by use of chemical
additives or mechanical methods, such as preloading, sand drains, sand blan-
kets, vacuum drainage, electro-osmosis, or combinations thereof, or by evapo-
ration in conjunction with continuous mechanical conditioning. Another tech-
nique for improving the natural soil conditions (that is, the homogeneity of
the landfill) within a diked containment area consists of systematically
changing the positions of the inflow and outflow points, thereby enhancing
the homogeneity of the grain size distribution throughout the site (because
larger particles would settle near the inflow point and combine with the
finer particles resulting from a previous positioning of inflow and outflow
83
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points) and increasing the uniformity of both strength and volume change
characteristics.
In general, however, these methods are expensive and a proper
cost-benefit analysis will be required to decide whether or not any of them
are justified in a given set of circumstances. From a purely technical point
of view, the efficient dewatering of dredged materials probably imposes the
greatest engineering constraint on their use as landfill materials, and novel
techniques for accomplishing this goal at lower costs are highly desirable.
84
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REFERENCES
Andresen, A. and Bjerrum, L. (1958), "Vane Testing in Norway," Contributions
from Scandinavia, Discussion, Norwegian Geotechnical Institute, Publica-
tion Number 28.
Barden, L. (1965), "Consolidation of Clay with Nonlinear Viscosity,"
Geotechnique, Volume 15, Number 4, pp. 345-362.
Boyd, M. B., Saucier, R. T., Keeley, J. W., Montgomery, R. L., Brown, R. D.,
Mathis, D. B., and Guice, C. J. (1972), Disposal of Dredge Spoil, Tech-
nical Report H-72-8, U. S. Army Engineer Waterways Experiment Station,
Vicksburg, Mississippi.
Cadling, L. and Odenstad, S. (1950), "The Vane Borer: An Apparatus for
Determining the Shear Strength of Clay Soils Directly in the Ground,"
Proceedings of the Royal Swedish Geotechnical Institute, Number 2,
Sweden.
Casagrande, A. (1948), "Classification and Identification of Soils,"
Transactions of the American Society of Civil Engineers, Volume 113,
pp. 901-930.
Corps of Engineers, Philadelphia District (1969), Long Range Disposal Study,
Six-Volume Technical Report, Pennsylvania.
Cozzolino, V. M. (1961), "Statistical Forecasting of Compression Index,"
Proceedings of the Fifth International Conference on Soil Mechanics and
Foundation Engineering, Paris, France, Volume 1, pp. 51-53.
Garbe, C. W. and Jeno, J. J. (1968), Reclamation of Hydraulic Dredge Spoil,
Dames and Moore Technical Topics, San Francisco, California.
Giger, M. W., Franklin, A. G., and Krizek, R. J. (1973), "Electrical
Resistivity Survey of Two Dredging Disposal Sites," Bulletin of the
Association of Engineering Geologists, Volume 10, Number 12, pp. 107-119.
Greeley and Hansen, Engineers (1969), Report on the Feasibility of Drying
Dredged Material for the Ace Scavenger Company, Chicago, Illinois.
Hummel, P. L. and Krizek, R. J. (1974), "Sampling of Maintenance Dredgings,"
Journal of Testing and Evaluation, American Society for Testing and
Materials, Volume 2, Number 3, pp. 139-145.
85
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Kirby, C. J., Keeley, J. W., and Harrison, J. (1973), An Overview of the
Technical Aspects of the Corps of Engineers National Dredged Material
Research Program, Miscellaneous Paper D-73-9, U. S. Army Waterways
Experiment Station, Vicksburg, Mississippi.
Krizek, R. J., Franklin, A. G., and Soriano, A. (1974), "Seismic Survey of a
Hydraulic Landfill Composed of Maintenance Dredgings," Bulletin of the
Association of Engineering Geologists, Volume 11, Number 3, pp. 173-202.
Krizek, R. J. and Giger, M. W. (1974), "Storage Capacity of Diked Containment
Areas for Polluted Dredgings," Proceedings of the World Conference on
Dredgings (WODCON), Taipei, Taiwan, pp. 353-364.
Krizek, R. J., Karadi, G. M., and Hummel, P. L. (1973), Engineering
Characteristics of Polluted Dredgings, Technical Report Number 1, by
Northwestern University to the Environmental Protection Agency, EPA
Grants 15070-GCK and R-800948, Evanston, Illinois.
Krizek, R. J., Roderick, G. L., and Jin, J. S. (1974), Stabilization of
Dredged Materials, Technical Report Number 2, by Northwestern University
to the Environmental Protection Agency, EPA Grants 15070-GCK and
R-800948, Evanston, Illinois.
Krizek, R. J. and Casteleiro, M. (1974), Mathematical Model for One- .
Dimensional Desiccation and Consolidation of Dredged Materials, Tech-
nical Report Number 3, by Northwestern University to the Environmental
Protection Agency, EPA Grants 15070-GCK and R-800948, Evanston, Illinois.
Krizek, R. J., Gallagher, B. J., and Karadi, G. M. (1974), Water Quality
Study for a Dredging Disposal Area, Technical Report Number 4, by North-
western University to the Environmental Protection Agency, EPA Grants
15070-GCK and R-800948, Evanston, Illinois.
Krizek, R. J. and Salem, A. M. (1974), Behavior of Dredged Materials in Diked
Containment Areas, Technical Report Number 5, by Northwestern University
to the Environmental Protection Agency, EPA Grants 15070-GCK and
R-800948, Evanston, Illinois.
Lambe, T. W. (1951), Soil Testing for Engineers, John Wiley & Sons, Inc., New
York.
Lambe, T. W. and Whitman, R. V. (1969), Soil Mechanics, John Wiley & Sons,
Inc., New York.
Lowe, J., Jonas, E., and Obrician, V. (1969), "Controlled Gradient
Consolidation Test," Journal of the Soil Mechanics and Foundations Divi-
sion, American Society of Civil Engineers, Volume 95, Number SMI, pp.
77-97.
Office of Dredged Material Research (1974), Spoil Compaction Method Tested,
World Dredging and Marine Construction, Volume 10, Number 6, pp. 57-58.
86
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Salem, A. M. and Krizek, R. J. (1973), "Consolidation Characteristics of
Dredging Slurries," Journal of the Waterways, Harbors, and Coastal Engi-
neering Division, American Society of Civil Engineers, Volume 99, Number
WW4, pp. 439-457.
Sheeran, D. E. and Krizek, R. J. (1971), "Preparation of Homogeneous Soils
Samples by Slurry Consolidation," Journal of Materials, Volume 6, Number
2, pp. 356-373.
Skempton, A. W. (1953), "The Colloidal Activities of Clays," Proceedings of
the Third International Conference on Soil Mechanics and Foundation
Engineering, Zurich, Switzerland, Volume 1, pp. 57-61
Skempton, A. W. and Bishop, A. W. (1950), "The Measurement of Shear Strength
of Soils," Geotechnique, Volume 2, Number 2, pp. 90-108.
Taylor, D. W. (1948), Fundamentals of Soil Mechanics, John Wiley & Sons, Inc.,
New York.
Terzaghi, K. (1923), "Die Berechnung der Durchlassigkeit des Tones aus dem
Verlauf der hydrodynamischen Spannungsercheinungen," Akadamie der Wissen-
schaften in Wien, Mathematischnaturwissenschaftliche Klasse, Sitzungsbe-
richte, Abteilung Ha, Volume 132, Number 3/4, pp. 125-138.
Terzaghi, K. and Peck, R. B. (1948), Soil Mechanics in Engineering Practice,
First Edition, John Wiley & Sons, Inc., New York (second edition pub-
lished in 1968).
Van Zelst, T. W. (1948), "An Investigation of the Factors Affecting Laboratory
Consolidation of Clay," Proceedings of the Second International Confer-
ence on Soil Mechanics and Foundation Engineering, Rotterdam, Holland,
Volume 7, pp. 52-61.
Wakeford, R. C. and Macdonald, D. (1974), Legal, Policy, and Institutional
Constraints Associated with Dredged Material Marketing and Land Enhance-
ment, Contract Report D-74-7, by American Technical Assistance Corpora-
tion to the U. S. Army Engineering Waterways Experiment Station, Vicks-
burg, Mississippi.
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TECHNICAL REPORT DATA
(Please read Instructions on the reverse before completing)
1. REPORT NO.
EPA-600/2-78-088a
3. RECIPIENT'S ACCESSION-NO.
4. TITLE AND SUBTITLE
USE OF DREDGINGS FOR LANDFILL
Summary Technical Report
5. REPORT DATE
May 1978 (Issuing Date)
6. PERFORMING ORGANIZATION CODE
7. AUTHOR(S)
Raymond J. Krizek and Max W. Giger
8. PERFORMING ORGANIZATION REPORT NO.
9. PERFORMING ORG -\NIZATION NAME AND ADDRESS
Northwestern University
Department of Civil Engineering
Evanston, Illinois 60201
1O. PROGRAM ELEMENT NO.
1BC611
11. MMWUfcCr/GRANT NO.
Grant No. R-800948
12. SPONSORING AGENCY NAME AND ADDRESS
Municipal Environmental Research Laboratory—Cin.,OH
Office of Research and Development
U.S. Environmental Protection Agency
Cincinnati, Ohio 45268
13. TYPE OF REPORT AND PERIOD COVERED
Final
14. SPONSORING AGENCY CODE
EPA/600/14
15. SUPPLEMENTARY NOTES Project Officers: Clifford Risley, Phone (312) 353-2200, and
Richard P. Traver, Phone (201) 321-6677 8-340-6677. See also Technical Reports No. 1,
2, 3, 4, & 5, EPA-600/2-78-088b, c, d, e, & f, available from the National Technical
Information Service, Springfield, VA.
16. ABSTRACT Q^ commoniy used alternative to the open water disposal of polluted main-
tenance dredgings is to place these sediments in diked containment areas to form land-
fills of marginal value. This study was directed toward evaluating quantitatively the
engineering characteristics of dredged materials as they affect their potential use-
fulness in a landfill. The work was limited to fresh water dredgings from Great Lakes
harbors, and most of the effort was centered around four disposal sites in the Toledo
(OH) harbor; however, the results are considered to be applicable to a wide range of
fresh water maintenance dredgings.
The disposal of dredged sediments in diked containment areas does improve the
overall quality of the surrounding surface waters, but it is not clear whether the
degree of improvement realized is sufficient to justify the considerably higher costs
involved. In addition, the low initial shear strength of these high-water-content,
organic materials under natural conditions, along with their slow rate of strength
increase with time and their associated large volume changes, seriously limit the
usefulness of landfills composed of dredged materials. Unless special steps are taken
to improve the quality of these materials, their use will be restricted largely to
wildlife refuges, parks, recreational areas, parking lots, access roads, and the con-
struction of light buildings with flexible structural joints and flexible floors which
would allow several inches of total settlement and a few inches of differential
17.
KEY WORDS AND DOCUMENT ANALYSIS
DESCRIPTORS
b.lDENTIFIERS/OPEN ENDED TERMS C. COSATI Field/Group
Dredging, Dredges, Sediments, Harbors,
Dikes, Channels (waterways), Excavation,
Spoil, Waterways (watercourses),
Channel stabilization
Landfills
13B
68C
18. DISTRIBUTION STATEMENT
RELEASE TO PUBLIC
19. SECURITY CLASS (ThisReport)
UNCLASSIFIED
21. NO. OF PAGES
100
20. SECURITY CLASS (Thispage)
UNCLASSIFIED
22. PRICE
EPA Form 2220-1 (9-73)
88
•St U.S. GOVERNMENT PRINTING OFFICE: 1978-757-140/1303
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