^ WATER POLLUTION CONTROL RESEARCH SERIES • 11022 DEI 05/72
Will 91^
SEWER BEDDING AND INFILTRATION
GULF COAST AREA
U.S. ENVIRONMENTAL PROTECTION AGENCY
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WATER POLLUTION CONTROL RESEARCH SERIES
The Water Pollution Control Research Series describes the
results and progress in the control and ^abatement of pollution
in our Nation's waters. They provide a central source of
information on the research, development, and demonstration
activities in the water research program of the Environmental
Protection Agency, through in-house research and grants and
contracts with Federal, state, and local agencies, research
institutions, and industrial organizations.
Inquiries pertaining to Water Pollution Control Research
Reports should be directed to the Chief, Publications Branch
CWaterJ r Research Information. Division, R&M, Environmental
Protection Agency, Washington, D. C. 20460
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SEWER BEDDING AND INFILTRATION
GULF COAST AREA
by
John K. Mayer, Frank W. Macdonald
and Stephen E. Steimle
Tulane University, New Orleans, Louisiana
for
OFFICE OF RESEARCH AND MONITORING
ENVIRONMENTAL PROTECTION AGENCY
Program Number 11022 DEI
Contract No. 80 - 04 - 68
May 1972
For sale by the Superintendent of Documents, U.S. Government Printing Office, Washington, D.C. 20402 - Price $1.50
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EPA Review Notice
This report has been reviewed by the Environmental Protection
Agency and approved for publication. Approval does not signify
that the contents necessarily reflect the views and policies
of the Environmental Protection Agency, nor does mention of
trade names or commercial products constitute endorsement or
recommendations for use.
ii
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ABSTRACT
Problems of excessive infiltration are found in the Gulf Coast area,
particularly those localities associated with high water table and deltaic
or alluvial soils. Infiltration and leaking sewers can cause problems of
water pollution and economics. Costs of sewerage systems can be
significantly increased from both a capital and an operating point of view.
Ground water infiltration studies were performed on several sewer systems
in 1962-63 and again in 1970 with the results being compared. Infiltration
measurements in the systems ranged from zero to 111,560 gallons per inch
of diameter per mile per day. The infiltration was slightly increased in
some lines and was greatly decreased in others. The decrease is attributed
to soil and grease clogging the breaks, as was observed in subsequent
television inspection. Infiltration has been found to vary with time. The
high infiltration rates were attributed to poor construction methods used by
contractors on the main sewer system and by plumbers on house connections.
A survey of 1600 manholes showed 3.5 percent to have infiltration at the
time of the inspection and others likely to develop infiltration during periods
of heavy rainfalls. Most of these could be easily repaired to prevent infil-
tration. Poor construction procedures are considered to be the most signifi-
cant contributor to infiltration and sewer failure. This situation can be
remedied through adequate inspection and testing.
Bedding and select cover (fill) should provide even distribution of load and
support for the pipe. A second function of this material should be to im-
pede the flow of water surrounding the sewer when the pipe is laid below
the water table. The material should completely surround the pipe. A coarse
granular material such as clam or oyster shells, gravel, crushed stone, etc.,
provides excellent support and load spreading but does not impede flow.
Mixtures of these with sand and other materials can provide flow impedance.
This report was submitted in fulfillment of Contract No. 80-04-68 under the
sponsorship of the U.S. Environmental Protection Agency.
iii
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CONTENTS Page
CONCLUSIONS
RECOMMENDATIONS
SECTION I INTRODUCTION
OBJECTIVES
SCOPE
THE GULF COAST AREA
SECTION II INFILTRATION
STORM WATER INFILTRATION
GROUND WATER INFILTRATION
EFFECTS OF INFILTRATION
COST OF INFILTRATION
INFILTRATION MEASUREMENT
FIELD STUDIES
SECTION III SEWER SETTLEMENT
COMPRESSION THEORY
MECHANISMS OF DOWNWARD MOVEMENT
SETTLEMENT MEASUREMENT
SECTION IV SEWER BEDDINGS
LABORATORY TESTING OF BEDDING MATERIALS
FIELD STUDIES
MATERIALS RECOMMENDATIONS
COST OF BEDDING MATERIALS
1
3
5
5
6
6
9
9
10
14
15
19
36
67
67
68
71
75
75
78
78
85
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Page
SECTION V SEWER TESTING 87
LABORATORY SIMULATION STUDIES 87
TEST SEWERS 87
SECTION VI GULF COAST AREA SANITARY SEWER SURVEY 107
SECTION VII SEWER CONSTRUCTION ' 111
INSPECTION 111
TRENCH WIDTH 112
TRENCH PREPARATION 114
BEDDING MATERIALS 115
LAYING OF PIPE 115
BACKFILLING 118
HOUSE SEWERS 119
MANHOLES- 122
INFILTRATION SPECIFICATION 123
SEWER ACCEPTANCE 123
GLOSSARY 129
ACKNOWLEDGEMENTS 133
KEY PERSONNEL 135
REFERENCES 137
OTHER REFERENCES 139
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APPENDIX A DEFLECTION AND JOINT RESISTANCE TESTS 141
APPENDIX B MANHOLE SURVEY 153
APPENDIX C MAYO ROAD SYSTEM 157-158
APPENDIX D LAKEWOOD SOUTH SUBDIVISION 159
APPENDIX E WEBER AVENUE SYSTEM 161-162
APPENDIX F BURKE STREET SYSTEM 163-164
APPENDIX G BERG ROAD SYSTEM 165-166
APPENDIX H MAINTENANCE RECORD AND 167
HOUSE CONNECTIONS
APPENDIX I WYOMING BENTONITE 171
TYPICAL PHYSICAL AND
CHEMICAL PROPERTIES
APPENDIX K BORING NC-1 IOTA STREET 173
APPENDIX L BORING NC-2 IOTA STREET 175
APPENDIX M BORING ND-1 HESSMER AVENUE 177
APPENDIX N BORING ND-2 HESSMER AVENUE 179
APPENDIX O BORING ND-3 HESSMER AVENUE 181
APPENDIX P MANHOLE SURVEY FORM 183
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FIGURES
No. Page
1. Typical Interconnection of Sanitary and Storm Sewers 11
2. Clay Sewer Cost (Installed) 16
3. Street Collapse 17
4. Capital Cost - Activated Sludge Treatment 18
5. Added Cost Due to Infiltration 20
Activated Sludge Treatment
6. Total Cost - Activated Sludge Treatment 21
7. Added Total Cost Due to Infiltration - 22
Activated Sludge
8. Capital Cost - Trickling Filter Treatment 23
9. Added Capital Cost - Trickling Filter Treatment 24
10. Total Cost - Trickling Filter Treatment 25
11. Added Total Cost - Trickling Filter Plants 26
12. Capital Cost Primary Treatment 27
13 . Added Capital Cost Due to Infiltration - 28
Primary Treatment
14. Total Cost - Primary Treatment 29
15. Added Total Cost - Primary Treatment 30
16. Sewer Leaks as Observed by Televising 32
17. Weir for Measuring Sewer Flow 34
18. Calibration Curve for A Triangular 90° Weir 35
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FIGURES
No. Page
19. Clay Dams in Manholes 37
20. Area of Flow in Partially Filled Clay Sewer 38
of Various Diameters
21. New Orleans, Louisiana Map of Sewer Systems 42
22. Photographs from Television Monitor 61
23. Leak Found in Hessmer Avenue Test Sewer 64
24. Photographs in Hessmer Avenue Test Sewer 65
25. Construction Conditions Causing Sewer Settlement 70
26. Sewer Settlement Measuring Devices 72
27. Pipe Loading and Support Conditions 76
28. Pipe Support by Coarse and Fine Materials 77
29. Average Long Term Permeability Sample "T" 80
30. Average Long Term Permeability Sample "U" 81
31. Testing Frame Cross-Section 88
32. Testing Frame in Operation 89
33. Sewer Foundations Iota Street 91
34. Sewer Foundations Hessmer Avenue 92
35. Cross-Section of Iota Street Site 95
36. Structural Damage to Street Pavement 104
Hessmer Avenue
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FIGURES
No.
37. Loads on Buried Pipes 113
38. Sewer Laid Through Stump 116
39. Unsupported Pipe Bell 117
40. Compaction of Select Backfill 120
41. Placing of General Backfill 121
42. Sewer Details - Clay Pipe - Gulf Coast Area 126-127
A-l Pipe Joint Test Assembly for Tests Performed at 142
Tulane University
A-2 Pipe Joint Test Assembly for Tests Performed at 147
Pittsburg, Kansas
A-3 Deflection Angle at Impending Leakage 148
VS. Shear Load
A-4 Pipe Joint Bending Resistance 149
A-5 Moment Resisting Capacity of the Pipe Joints 151
B-l Photographs of Manholes 154
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TABLES
No. Page
1. Inch Miles per 100 Feet of Pipe for Various Diameters 40
2. Length, Joints and Beddings of Sewer Systems 43
3. Physical Characteristics of The Mayo Road System 45
4. Infiltration Expressed in Gallons per Inch Mile per Day 46
Recorded in the Mayo Road System
5. Physical Characteristics of the Lakewood South System 47
6. Infiltration Expressed in Gallons per Inch Mile per Day 48
Recorded in the Lakewood South System
7. Physical Characteristics of the Weber Avenue System 49
8. Infiltration Expressed in Gallons per Inch Mile per Day 50
Recorded in the Weber Avenue System
9. Physical Characteristics of the Burke Street System 51
10. Infiltration Expressed in Gallons per Inch Mile per Day 52-53
Recorded in The Burke Street System
11. Physical Characteristics of The Berg Road System 54
12. Infiltration Expressed in Gallons per Inch Mile per Day 55
Recorded in the Berg Road System
13. Monthly Rainfall Record Record City of New Orleans 56
14. Comparison of Infiltration Tests of 1962-1963 to 1970 58
15. Infiltration- Test Sewers Jefferson Parish, Louisiana 63
16. Comparison of Weight of Pipe with Weight of Soil Removed 68
17. Indices of Permeability and Angles of Internal Friction 79
xiii
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TABLES
No. Page
18. Frequency of Bedding Material Use 82
19. Cost of Bedding Materials 86
20. Length and Depth of Lines 90
21. Settlements Iota Street Test Sewer 97-98
22. Manhole Elevations and Settlements 99
23. Settlements Hessmer Avenue Test Sewer 100-101
24. Manhole Elevations and Settlements Hessmer 103
Avenue Test Sewer
25. Types and Lengths of Sewer 107
26. Bedding Materials and Frequency of Use 108
27. Infiltration Specifications 109
28. Infiltration Specifications in Comparison with 124
Other Data
A-l Pipe Joint Deflection Test - No Load 144
A-2 Deflection per Foot of Pipe Length ASTM 144
A-3 Deflection Angle Summary 145
A-4 Pipe Joint Deflection Tests - Under Loading 146
A-5 Manhole Survey 155
xiv
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CONCLUSIONS
1. Sewer settlement alone is not a significant cause of infiltration in
clay sewers with factory moulded compression joints. The main cause
of infiltration rates in modern vitrified clay sewers is poor construction
procedures. Careless joining of factory moulded compression joints is
conducive to excessive infiltration. Dropping fill material directly onto
the pipes causes breaks and cracks, expecially in the pipe bells.
2. Observations made with a testing frame in the laboratory on vitri-
fied clay sewers showed little settlement with a range of from zero to 3.5
centimeters (1.38 inches). Sewer settlements observed in the field were
considerably larger ranging from zero to 1.50 feet. Although similar bed-
dings were used, no correlation could be observed between the laboratory
and field studies.
3. Sewer settlement appears to be caused by the drawdown of the water
table either during or after construction. In the drawdown phenomena, the
pressure on compressible strata beneath the sewer is increased.
4. In areas of high ground water table, extremely permeable materials
such as shells or gravel are undesirable for sewer foundations. These
materials serve as conduits along and surrounding the sewers, and readily
permit the flow of water along the bedding to leaking joints, cracks or
breaks, in the sewer.
5. Where high water tables exist, sewer beddings may be greatly im-
proved by the addition of expanding materials such as bentonite. Sand
and Portland cement mixed with coarse granular material such as shells
and gravel also provide excellent beddings for sewers. Mixtures of this
type also tend to reduce the flow of water along the trench bottom and to
reduce the effect of undermining of the sewer should a leak develop.
6. The moulded joint sewer pipe used in this research showed excellent
load bearing, deflection and infiltration resistance characteristics. In
joint deflection tests on this pipe, deflection angles as high as 10.9 de-
grees were observed with a head of 30 feet of water imposed on the joint
before leakage occurred.
7. The properties of pipe joints for brittle pipe are of considerable im-
port relative to infiltration.
&.. Garbage disposal units used in homes appear to have introduced a
detrimental factor in the hydraulics of sewers. Cold water introduced by
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infiltration causes the grease to coagulate and form masses at joints
and broken sections of sewers.
9. The manhole survey showed 3.5 percent of those inspected to
have infiltration. A higher percentage no doubt would be subject to
infiltration during periods of rainfalls. Manholes are easily repaired.
Periodic manhole inspection and maintenance would be advantageous
in reducing infiltration on sewer systems.
10. The establishment of infiltration specifications through the New
Orleans area was greatly influenced by this project.
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RECOMMENDATIONS
1. Standards for sewer construction and limits of infiltration should
be adopted for all new sewer systems. These should include all factors
to insure the proper laying of the pipe and filling the trench in a manner
to protect the sewer. Close supervision should be provided during the
construction of sewers to assure that the specifications are adhered to.
2. Infiltration tests for sewer acceptance should not be relied on as
the only means of sewer construction control, but should be utilized
along with effective inspection during construction.
3. When running infiltration tests on a sewer system, the practice of
testing the entire system at one time should be discontinued in favor of
testing the component parts. The length of line to be tested at one time
should be small enough so that areas of leakage will be isolated.
4. A good base has been established with the test sewers used in this
project. These sewers should be examined and studied periodically in
the future to determine the amounts of settlement and infiltration.
5. Where high water tables exist and soil conditions are unfavorable,
Portland cement or an expanding clay mineral like Bentonite should be
used with coarse granular materials for sewer beddings.
6. Manholes on sewer systems should be inspected periodically,and
the necessary repairs provided where infiltration is observed.
7. Adequate plumbing codes should be adopted for the construction of
house sewers with inspection required before connections are permitted
to sewer systems. Particular attention should be devoted to the connec-
tion of the house sewer to the main system. Breaking into the main sewer
system to make the connection should be prohibited.
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SECTION I
INTRODUCTION
THE GULF COAST AREA
UNITED STATES
Many locations in the southern coast of the United States along the Gulf
of Mexico, shown above, experience higher infiltration rates and greater
maintenance difficulties with sanitary sewers than other sections of the
nation. Infiltration related water pollution causes health hazards and
other intangible expense in the form of lost low cost recreation and the
degradation of our natural patrimony. In addition to pollution costs,
excessive infiltration places additional financial burdens on sewerage
authorities through capital outlay in the construction of transport and
treatment facilities, as well as additional operation expenses for sewer
maintenance. It is with the presentation, delineation, and possible
solutions of these problems that this manual deals.
OBJECTIVES
The objective of this manual is three-fold.
1. An attempt to obtain and delineate information that will be
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helpful to those persons engaged in the design, construction, mainte-
nance, and regulation of sewer systems.
2 . To present in a concise manner the results and findings of
research conducted during the past eight years.
3. To provide recommendations as to additions, deletions, and
changes in the planning, construction and acceptance of sanitary sewers
in the area of study.
SCOPE
The purpose of this manual is the presentation of information concerning
sanitary sewers. In so doing the following discussion topics are pre-
sented:
1. The nature, status and cost of infiltration.
2. Methods of measuring infiltration.
3. The causes, measurement and various aspects of sewer settle-
ment .
4. Sewer bedding materials.
5. Sewer construction in general and with respect to infiltration
control.
THE GULF COAST AREA
The Gulf Coast area includes the shore line of four states as well as the
delta of the Mississippi, largest river in the nation. It is comprised of
the southeastern part of Texas, the southern parts of Louisiana, Missis-
sippi and Alabama as well as the western half of the Florida peninsula.
The parts of the Gulf Coast area that are of primary concern in this
manual are those in which the in situ soils behave poorly as foundations
and in trenches accompanied by water tables located close to the ground
surface. These conditions predominate in the swamps and marshes of
the deltaic and alluvial plains as well as the coastal salt marshes. The
largest of these areas is the conjunction of the Mississippi River allu-
vium and deltaic plain joined with the Louisiana-Texas coastal marsh.
The topography is flat and near sea level with much of the area being
covered with tropical and semitropical vegetation. Only two rivers, the
Mississippi and the Apalachicola, form deltas into the Gulf of Mexico,
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but many other streams are concentrated along the coast providing the
area with a maze of surface waterways.
The climate is mild and subtropical with an average temperature of 67° F.
Rainfall is abundant throughout the area with as much as 66 inches per
year recorded in some localities. Prevailing winds are generally from
the south.
The low lying areas with their exceedingly fertile alluvial and deltaic
soils have attracted settlers since the first European colonization almost
three hundred years ago. Continued growth of the region; the develop-
ment of petroleum resources; and the influx of many varied and expanding
industries have over the years been conducive to metropolitan develop-
ment in large population centers such as New Orleans, Mobile, Houston,
Beaumont, Lake Charles and Lafayette.
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SECTION II
INFILTRATION
Infiltration is the entrance of water other than sewage into sanitary
sewers. It may be comprised of either one or both of the following:
1. Storm runoff entering through manhole covers or illicit con-
nections .
2. Ground water seepage influent through joints, cracks, breaks
and defective fittings or other appurtenances.
Infiltration adversely affects receiving water quality as well as the cost
of sewage transport and treatment.
STORM WATER INFILTRATION
The flow through openings in manhole covers that are inundated can
account for large amounts of water infiltrating a sanitary sewer system.
In studies by A. M. Rawn, the leakage through manhole covers with one
inch of submergence varied from 20 gallons per minute (gpm) to 70 gpm
and went as high as 127 gpm with a submergence of six inches.
In the coastal marsh and deltaic regions of the Gulf Coast area, street
flooding occurs frequently during heavy rains making this problem of
leakage into manholes a major one.
An illicit connection is any direct installed inlet into a sanitary sewer
which allows ingress of storm waters. The most common of these con-
nections involves roof gutter downspouts as well as yard, driveway,
and foundation drains.
Large quantities of water can usually be expected from downspouts
resulting in a runoff from roofs of 100 percent of the precipitation.
Excessive infiltration of this type may cause serious problems of over-
loading in sanitary sewers during and following heavy precipitation.
Illicit connections are usually prohibited by law, but they remain a
problem in areas not covered by or developed prior to adequate plumbing
inspection. Smoke tests run by sewer authorities in southern Louisiana
indicate that this mode of infiltration can be quite extensive in older
urban areas. Municipal sewer authorities are frequently reluctant to
release such findings because of the political implications of having to
condemn large numbers of illicit house connections.
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Interflow between the sanitary and storm sewers can occur when the
pipes are contiguous with adjacent leaks and when the intervening
material is amenable to flow. In a study conducted by the New Orleans
Sewerage and Water Board, this type of infiltration was found to be
widespread. It was determined in this study that this interflow
occurred at locations where the sanitary house connections crossed
beneath and close to the storm sewers as shown in Figure 1 . It is
believed that the breaking of the house connections was caused by the
settlement of the storm sewers. The flow was permitted through the
intervening clam shell bedding of the storm sewers. It was also found
in this study that the same interflow occurred at intersections where
the storm sewer crossed the sanitary main and the two pipes were in
close proximity.
GROUND WATER INFILTRATION
Of all the influencing factors relative to ground water infiltration, work-
manship is the most critical. It is also the parameter most subject to
variation. It is self-evident that a poorly constructed sewer system
will be one that will perform badly.
There are many variables which can affect the presence and extent of
ground water seepage into sanitary sewer systems. The following fac-
tors may also influence infiltration either individually or in combination
with one another.
Sewer Foundations
Through their failure to provide proper support and their ability to trans-
mit large quantities of water, inadequate sewer foundations can adverse-
ly affect the infiltration characteristics of sewers.
Pipe Joints
The properties of the pipe joint are of considerable influence on infil-
tration. All other measures for the control of infiltration are of secondary
importance unless the pipe joints are tight.
An ideal joint possesses the following properties:
1. It is water tight and will remain so with time.
2. It resists corrosion from both sewage and substances in the
soil.
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Storm Sewer (Joints Open)
Interchange of Liquid
15"
Small Clearance
6" House Connection
Sanitary Sewer
8"
TYPICAL INTERCONNECTION OF SANITARY AND STORM SEWERS
FIGURE 1
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3 . It is flexible.
4. Its material is resilient.
5 . It is durable.
6. It is easily assembled in the field.
7. It must be economical.
The relationship of infiltration to joint flexibility and resilience may
not be easily seen. In poor soils, particularly soft clays and peats,
there may be movement of the pipe due to settlement of the soil and
backfill long after the sewer has been installed. Joints should be
flexible enough to sustain a reasonable amount of this movement. The
joint material must be resilient in order to allow this flexibility.
Ease of installation is important in so far as it is reasonable to assume
that the number of improperly installed joints will increase with the
complexity of the joint used.
Appendix A is the report of a detailed study of joint deflection and
leakage for a particular joint (8 inch polyurethane factory moulded
joint as manufactured by the W. S. Dickey Clay Manufacturing
Company).
House Connections
A house connection is any branch from the main sewer that provides
service to a user. These are of major concern in infiltration control as
they may account for large portions of sewer systems. House sewers
should be installed with the same quality of workmanship and materials
as the main (municipal) sewer. This is often quite difficult to accom-
plish since the greatest length of house sewers is usually installed by
plumbers whose work is often improperly inspected.
Wyes, tees, and stacks can be extremely troublesome if considerable
care is not exercised in their installation. If these connections are not
properly closed or if they are broken during backfilling, a great deal of
ground water may gain entrance to the system. It has long been recog-
nized that wyes and tees are weak points in sewer systems, but with
the advent of monolithic fittings, part of this problem seems to have
been solved. House connections have been observed as accounting for
90% of the infiltration in a system. 3
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Manholes
Although extensive infiltration can take place in or near manholes, they
do not present as great a problem as other components of a sewer system.
This is mainly due to the ease with which they are inspected and re-
paired .
In a survey of 1600 manholes in the Greater New Orleans area a total of
402 or 25.1% were found to have interior cracks in the walls, around
the steps, around the inlet and outlet pipes, inverts, or bottoms, and
56 or 3.5% were actually leaking at the time of inspection. Observations
show that these leaks can be easily repaired. Appendix B summarizes
this study.
Infiltration problems have also been encountered due to differential
settlement between the sewer pipes and the manholes in a system.
Pipe Material
The material of which the pipe is made has no appreciable effect on
infiltration in modern sewers so long as this material possesses suffi-
cient strength to withstand the forces to which it is subjected and is
not susceptible to corrosive attack by the sewage or the soil.
Water Table
In order for significant ground water infiltration to take place the sewer
must be laid below the water table. In addition to the obvious proxi-
mity of water, sewers laid below the water table are usually constructed
with greater difficulty than those in drier soil. The seepage of water
into sewer trenches upon pumping may cause lateral and/or vertical
instability of the walls and bottom, thus adversely influencing work-
manship during construction.
When the water table is lowered after construction, subsidence can
cause sewer settlements which may result in cracking of the pipes.
Soils
There are two general characteristics of the soil which greatly influence
sewer infiltration. These are its water bearing capability and its pro-
perties as a foundation material.
The water bearing capability depends to some extent upon the volume of
water which may be held in the soil, but primarily upon the ease with
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which the water may flow through the interconnected voids in the soil
mass. Void ratio and permeability are both dependent upon grain size ,
distribution, grain shape, and the structural arrangement of the soil
grains. Clays have the ability to retain much water, but as a rule they
have low permeabilities and consequently small delivery capability-
The reverse is true of sands. Certain combinations and stratifications
of sands, clays, and intermediate materials can hold as well as provide
large amounts of water. Many organic soils, such as peats, have both
water holding and water delivery potential.
The amount and variety of movement that a sewer experiences is closely
related to the types, conditions, and stratifications of the surrounding
soil. In theory these factors, in conjunction with the seepage propen-
sity, water regimen, and shear strength of the soil, should form the
basis for the selection of a sewer bedding.
Ground Surface Characteristics
The disposition of the ground surface can exert some effect on the
infiltration properties of a sewer. The availability of precipitation to
the mass of ground water is a function of the runoff coefficient which in
turn depends on the topography as well as the local vegetation. The
type of vegetation will also influence the tendency toward root pene-
tration into joints and cracks in sewers.
Climate
Rainfall and temperature are the two climatic variables which enter
directly into the infiltration problem. It is evident that rainfall is an
influential parameter in the replenishment of ground water. In warmer
climates, water percolates through the soil more readily because vis-
cosity varies inversely with temperature.
EFFECTS OF INFILTRATION
Extent of the Problem
Infiltration creates problems of health, aesthetic, sociological and
economic impact. The overflowing of sewers and the pollution of
receiving waters are health problems of significant importance when
the public bathing areas of our natural water courses are polluted.
Children from low income families are often deprived of the only swim-
ming facilities economically available to them. Infiltration increases
the capital and operating cost of sewage transport and treatment.
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Ground water infiltration is widespread, but only in localities where the
water table is high is the ground water seepage a significant problem.
Many sewer systems throughout the nation possess significant storm
water infiltration. In a national inventory of sanitary sewers and com-
bined sewer flows, it was found that 14% of the respondents indicated
a problem with excessive dry-weather flows and 53% indicated problems
with increased wet-weather flows. It was also found that 36% reported
the flows did not exceed design or code limitations, 25% stated that
they did, and 35% were unaware whether or not their flows were exces-
sive. It may be concluded from this survey that one-third of the nation's
sewer authorities are not fully aware of the extent of their infiltration
problems.
In a survey of 39 sewer authorities in the Gulf Coast area, replies
indicated that dry-weather flow accounted for an average of 14% of the
total flow. Thirteen, or 53%, of those answering reported that they had
no information on dry-weather flow.^
Water Pollution
Receiving waters are degraded through infiltration with regard to pol-
lution control,plant bypassing, combined sewers, and interflow between
sanitary and storm sewers. From a survey in 1967, it was found that
the average annual time in which water pollution control plants were
bypassed was 350 hours.4 In combined sewers, infiltrated water makes
hydraulic demands on much needed sewer and sewage treatment capa-
city, thus increasing the total time of bypass. It has been shown that
the interflow of sewage between sanitary and storm sewers is responsible
for a significant part of the pollution of the southern shore of Lake
Pontchartrain at New Orleans. 2
COST OF INFILTRATION
The tangible cost of infiltration is reflected in the construction and
operation of sewage collection systems and pollution abatement facili-
ties as well as the enormous expense of pollution.
Collection Systems
Infiltration causes a need for larger sewers as well as greater pumping
capacity. An indication of the cost of sewers with respect to increased
capacity is shown in Figure 2 . 5
Infiltration can cause the collapse of streets and other structures in the
15
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20
o
o
(0
0)
c
(X
4J
W
O
u
10
9
8
7
6
8' to 10' Cut
8 10 12 15
Nominal Sewer Diameters (in.)
Note: Curves For National Averages.
1967 Values
Note: Diameters Shown are those Available.
CLAY SEWER COST (INSTALLED)
FIGURE 2
18
21
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vicinity of the sewer. When the surrounding soil and/or the backfill is
a fine non-cohesive material in a loose state, it can be washed into the
sewer and carried through the system, thus undermining surface struc-
tures and even the sewer itself. Figure 3 shows a street collapse due
to infiltration undermining.
STREET COLIAPSE DUE TO INFILTRATION
FIGURE 3
Sewage Treatment
The greatest tangible cost of infiltration is incurred in the added cost of
construction and operation of water pollution control plants.
Figure 4 is a family of curves showing the capital cost of activated
sludge treatment at various percentages of infiltration allowance. For
example, at a design flow of 20 M.G.D. (million gallons per day) with
no infiltration, the capital cost of treatment would be 55 million dollars;
however, with an added infiltration flow of 12 MGD (60% increase) the
cost would be 83 million dollars. 5
17
-------
12 16 20
Design Flow MGD
24
100
- 90
*- 80
70
— 60
— 50
— 40
30
- 20
— 10
28
w
O
U
"(0
fO
U
(0
«—I
"o
Q
UH
O
in
O
CAPITAL COST-ACTIVATED SLUDGE TREATMENT
FIGURE 4
18
-------
Information for all sewage treatment cost curves was obtained from one
data source, and was given in June 1967 dollars. "
Figure 5 shows the added capital cost incurred as a result of infiltration
for activated sludge treatment. Figures 6 and 7 are families of curves
showing the total and added total cost, respectively, due to infiltration,
and thus reflecting operational expenditures as well as capital debt ser-
vice.
Figures 8,9 ,10 and 11 provide infiltration costs for trickling filter
treatment, and Figures 12 , 13 , 14 and 15, for primary treatment.
It can be seen from these curves that the cost of treating infiltrated
water is only slightly less than that for sewage.
INFILTRATION MEASUREMENT
Infiltration measurement can be either qualitative or quantitative. The
qualitative measurements are made to determine the presence and source
of infiltrated water, whether of storm or ground water origin. The quan-
titative tests are made to ascertain the amount of non-sewage water
flowing in a sewer at a given time.
Qualitative Observations
The following methods can be used for detecting and locating infiltration.
Smoke Testing
This method is used for the detection of illicit connections. It consists
of isolating a section of sewer and either placing a smoke bomb in a
manhole or pumping in smoke produced with a generating ma/chine. The
neighborhood served by the isolated section is then visually inspected
for smoke escaping from roof downspouts, yard drains, driveway drains,
etc. The escaping of smoke from any of these fixtures is considered
proof of an illicit connection.
Dye, of a fluorescent variety, can be poured into appurtenances sus-
pected of being illicitly connected. The dye will be observed at the
closest downstream manhole if there is an illicit connection.
Dye may also be used to detect infiltration in foundation drains and
house connections. The dye is poured on the ground near the foundation
19
-------
60% Infiltration
50%
40%
30%
20%
10%
0%
12 16 20
Design Flow MGD
24
28
ADDED CAPITAL COST DUE TO INFILTRATION
ACTIVATED SLUDGE TREATMENT
FIGURE 5
20
-------
3600
-7 3200
2800
2400
— 2000
— 1600
— 1200
— 800
— 400
C/)
O
U
"ro
4->
O
H
>,
fO
Q
I-,
CD
CL,
C/3
i_
JO
"o
Q
12 16 20
Design Flow MGD
24
TOTAL COST-ACTIVATED SLUDGE TREATMENT
FIGURE 6
21
-------
60% Infiltration
50%
40%
30%
20%
10%
0%
— 1000
— 800
— 600
— 400
— 200
8 12 16 20
Design Flow MGD
24
28
W
O
U
"(0
T3
0)
•a
T3
to
Q
u
0)
D-
o
P
ADDED TOTAL COST DUE TO IN FILTRATION-ACTIVATED SLUDGE
FIGURE 7
22
-------
60% Infiltration
50%
40%
30%
20%
10%
0%
100
90
- 80
— 70
— 60
— 50
_ 40
- 30
— 20
- 10
tn
O
(0
+->
•rH
a
(0
O
en
u
(0
>— H
•-H
O
Q
en
C
O
8 12 16 20
Design Flow MGD
24
CAPITAL COST-TRICKLING FILTER TREATMENT
FIGURE 8
23
-------
en
O
U
(0
"a,
(0
C
-------
Infiltration
3200
2800
2400
2000
1600
1200
800
400
w
O
u
I—I
(0
-M
O
H
S
(0
Q
i_
0)
cu
en
i_
(0
i—i
i—i
O
Q
8 12 16 20
Design Flow MGD
24
28
TOTAL COST-TRICKLING FILTER TREATMENT
FIGURE 1.0
25
-------
60% Infiltration
900
800
700
600
500
400
w
o
U
•—I
fO
«
H
T»
0)
T3
T3
<
tx
(0
Q
ii
Q)
Cu
to
In
(0
300 a
o
P
200
100
12 -16 20
Design Flow MGD
24
28
ADDED TOTAL COST-TRICKLING FILTER PLANTS
FIGURE 11
26
-------
50
*- 45
40
<- 35
— 25
12 16 20
Design Flow MGD
— 15
— 10
~~~ 5
28
OT
O
U
a
(0
w
U
fO
w
20 §
CAPITAL COST-PRIMARY TREATMENT
FIGURE 12
27
-------
-I 18
16
14
-J 12
H 10
12 16 20
Design Flow MGD
24
- 6
-I 4
28
en
O
U
i— i
(0
ro
U
T3
0
T5
T3
-------
60%
50%-
40%
30%
20%
Infiltration
1800
1600
1400
8 12 16 20
Design Flow MGD
24
28
CO
O
O
1200
-------
— 900
— 800
— 700
<- 600
500
400
300
— 200
— 100
V)
O
u
i— H
(0
+->
O
EH
T3
0)
T5
T3
JO
. — i
O
Q
C
O
12 16 20
Design Flow MGD
ADDED TOTAL COST-PRIMARY TREATMENT
FIGURE 15
30
-------
or above the house sewer. The ground is then wet with a lawn sprinkler.
The presence of this dye at the nearest downstream manhole is proof of
infiltration. There are dyes available for this purpose that are detectable
at very low concentrations. Other tracers such as radioactive material
and soluble chemicals that are readily detected can also be used.
Mirror Inspection
The simplest method for the detection of ground water infiltration is
visual inspection with the use of a mirror. This is done by reflecting
light into the sewer line. This method is best suited for detecting large
leaks that are near manholes.
Photography
Photography has, in the past few years, come into wide use for sewer
inspection. There are two methods employed, television and still photo-
graphy. With television inspection, the camera is pulled through the
sewer with a rope or a cable marked in feet. The observations are made
on a television screen. Figure 16 shows photographs taken from a tele-
vision monitor of leaks and breaks in a sewer line. The photographs
were taken from the television monitor. Using the same methods, a
special camera may be pulled through the sewer to take still pictures.
Still shots have a disadvantage in that time is required for developing,
but their cost is considerably lower than that of television. Both of
these methods are excellent for locating small and large leaks. Also,
with these methods, the size of the leaks can be more accurately deter-
mined .
Sounding
Sounding is a relatively new innovation in infiltration detection. The
New Orleans Sewerage and Water Board has recently used an instrument
called a "Dripaphone" for the detection of leaks in sewers. This instru-
ment consists of a sound detection device inside of a bottle. The opera-
tor listens on earphones for the sound of water dripping on the bottle as
it is pulled through the sewer. An experienced operator is able to deter-
mine the approximate size of leaks as well as the location. The advan-
tages of this equipment lie in its ease of operation and low cost.
Air Pressure
Two other methods for determining infiltration employ air pressure. In
the first, a sewer is plugged and a pressure is maintained with the use
31
-------
SEWER LEAKS AS OBSERVED BY TELEVISING
FIGURE 16
32
-------
of a blower. A correlation is then made between the air needed to main-
tain the pressure and the possibility of leakage. This method is not
very exact since the correlation is difficult to make. A more exact
method, using air, consists of maintaining a pressure in a sewer before
the trench is backfilled. The leaks are then observed from the outside
of the pipe. This second procedure can also be carried out using water
instead of air.
Quantitative Measurement
In quantifying the infiltration flow into a sanitary sewer there are several
procedures that can be used. Each can be utilized during two general
periods in the life of a sewer. Infiltration can be easily determined
prior to the connection of house or building sewers as the entire flow at
this time is attributable to ground water infiltration. After the sewer is
put into service, some means of segregation of sewage and infiltration
must be employed. This can be accomplished by plugging the house
sewers and measuring flow or measuring the flow during a period of
natural or requested non-use. At best, it is difficult to measure infil-
tration after a sewer is put into service.
It is important in measuring infiltration that the lines be unobstructed
and that the flow be allowed to stabilize prior to measurement in order
to obtain accurate readings. In making flow measurements, several
readings should be taken at sufficient time intervals to insure that a
reasonably constant discharge has been achieved.
Weirs
Weirs have long been used for the measurement of various kinds of flow.
The same principle and methods are involved in their use for infiltration
measurements. The section of sewer is plugged on the upstream end, and
the weir is placed at the lower end. By knowing the characteristics of
the weir and the head of the water, the flow may be calculated.
A typical 90° "V" notch weir is shown in Figure 17. The hydrostatic
head at the notch is observed in the piezometer glass. Figure 18 is a
calibration curve for such a weir. Plastic or metal weirs of this type
are commercially available and are calibrated to read flow directly.
It is not advisable to use weirs for small discharges because the con-
tinuity of flow is hot uniform at low flows due to the surface tension
effects. This method finds its greatest application in the range of
moderate discharges. If the discharge is too high, the water rises above
the top of the weir. If too low, the weir cannot be read.
33
-------
1. Clamping Device
2. Observation Glass
3. Weir Notch
4. Rubber Seal
WEIR FOR MEASURING SEWER FLOW
FIGURE 17
-------
(0
0)
Cu
13,000
12,000
11,000
10,000
9,000
8,000
7,000
6,000
5,000
o 4,000
PL,
3,000
2,000
1,000
0
I
1.4 cm at no flow
O
I
I
14 20 30 40
Height Above Bottom of "V" in cm
CALIBRATION CURVE FOR A TRIANGULAR 90° WEIR
FIGURE 18
50
35
-------
Catchment
This method involves the volume or weight measurement of all flow in a
given time. The procedure consists of damning the downstream end of
the sewer section that has been isolated for study. A small pipe must
protrude through the dam. A device with the pipe protruding can be sho
fabricated from metal with the appropriate seals or it can be made in th(
field with clay and a short length of thin wall tubing. Figure 14 shows
several arrangements of clay dams in manholes.
Two factors relative to the dam and pipe must be considered. No leakac
must be allowed around the edges of the dam and the tubing must be of
sufficient size to allow the maintenance of non-pressure flow. The
measurements are made by catching the water in a container and measur:
the time with a stop watch. The water can then be weighed or its volum
can be determined with a graduated cylinder. It is quite common to use
a calibrated container of a convenient size. This method is quite accu-
rate over a wide range of discharge, but is particularly useful for low
flows where weirs are inaccurate.
Area Velocity Method
This prodedure consists of measuring the velocity and the area of flow
and then calculating the discharge from the continuity equation, Q = AV,
with Q being discharge, A equalling the cross-sectional area of flow,
and V being the velocity of flow.
An estimate of the velocity can be made by timing the traverse of a
float or a dye between two manholes. The area of flow can be deter-
mined from one or more depth measurements. Figure 20 gives the
relationship of depth to area of flow for circular pipes up to 18 inches
in diameter.
FIELD STUDIES
Two infiltration studies were performed in the Greater New Orleans Area
between 1962 and 1970. In one study, performed on sewers laid in 1962
and 1962, infiltration was measured shortly after construction and moni-
tored again in 1970. In the second study infiltration was measured on
two test sewers which were laid in 1967-68.
Long Term Infiltration Measurements
The project was initiated in 1962 through infiltration studies that were
made on five separate systems in the City of New Orleans, accounting
36
-------
Drop Manhole
Standard Manhole
Note: Dams in Drop Manholes Can Be Built Either in
the Line or in the Bottom of the Drop.
CLAY DAMS IN MANHOLES
FIGURE 19
37
-------
1.8
1.7
1.6
1.5
1.4
1.3
1.2
1.1
1.0
5 °'9
CT n fi
J2 '
2 0.7
0.6
0.5
0.4
0.3
0.2
0.1
0
(0
Q)
18"
68 10 12 14 16
Flow Depth (inches)
18
AREA OF FLOW IN PARTIALLY FILLED
CLAY SEWER OF VARIOUS DIAMETERS
FIGURE 20
38
-------
for 69,020 linear feet of sewer. The sewers had just been installed in
sections of the City being developed for subdivisions and house con-
nections had not yet been made to the system. At that time the City of
New Orleans did not require infiltration test procedures on new sewer
installations. The objectives of these initial studies were to develop
infiltration tests procedures and infiltration limits to be included in
the New Orleans specifications for sewer construction. This initial
study served as the basis for the continuation of the work through the
financial support received by Federal Demonstration Grants and the
Dickey Clay Products Co., Inc. 6
These first infiltration measurements were made in 1962 and 1963 with
four to five readings generally being taken on each system. In the
current project, sections of the five separate sewer systems were
selected for re-study with measurements being made during the summer
of 1970. These latest measurements provide a long term - eight year
period comparison, for infiltration with sewers laid with the conven-
tional beddings used in the Gulf Coast Area. All lines used in this
study were vitrified clay. Records of the City of New Orleans are no
longer available on the specific type of joint used on each sewer line
tested. All were either "O" ring or moulded bead compression joints.
Materials and Methods
When construction was completed on new sewers the lines were usually
filled with water. The procedure used in performing the infiltration
test under these conditions is as follows:
a) The sewer was pumped dry.
b) The sewer was cleaned by flushing.
c) The clay dam arrangement was constructed.
d) When the water built up behind the dam and the flow became
stable through the pipe, a flow measurement was made utilizing
the catchment method.
Readings were taken in five minute intervals until the flow became
stabilized. When several constant readings were obtained the test was
considered complete.
On sewers that have been in use, the testing procedures were somewhat
similar but arrangements were made to eliminate sewage flow. This was
accomplished in the study by informing the residents along the test
section of the nature of the study and requesting that no water be used
for the test period. Experience showed that the residents were very
39
-------
cooperative in this respect and many were quite interested in the project.
After the residents along the sewer were requested to discontinue using
water, the test procedures described above were used. In older lines
the experience usually was that the flow took longer to stabilize.
Initial readings were high with the flow gradually diminishing to a con-
stant low level. The lowest series of constant readings were taken as
the amount of infiltration in the line.
In computing the infiltration into the sewers in gallons per inch mile of
line, the average outside diameter was used. As extra strength clay
pipe was used in all installations tested, the average of the minimum
and maximum values indicated for barrels in the dimension tables of
the ASTM specifications was taken. Table 1 is a tabulation of the
values used in computing the infiltration.
TABLE 1
INCH MILES PER 100 FEET OF PIPE FOR VARIOUS DIAMETERS
Diameter-Inches
6
8
10
12
15
18
Inch Miles per 100 Ft. of Pipe
0.137
0.18
0.223
0.265
0.331
0.395
When the infiltration was measured in gallons and a period of time in
seconds, the infiltration was computed as indicated in the following
example.
Given: Diameter = 10 inches
Length of Line = 380 feet
Solution:
Flow
Time
From Table 1
Inch Miles =
Time
Flow
= 2.8 gallons
= 102 seconds
.223 x 3.80 = 0.847
102 = 1.7 minutes
60
2.8
1.7
= 1. 65 gpm
40
-------
Solution (cont):
Flow = 1.65 x 60 x 24 = 2380 GPD
Infiltration = 2380 =2810 gallons/inch mile/day
0.847
All sewers studied in 1962 and 1963 were made of vitrified clay. Records
are not available on the specific type of bedding or joints on each of the
lines tested. It was reported that some were "O" ring and other con-
sisted of moulded bead compression joints. Some of those used were
polyvinyl-chloride joints and others were polyurethane joints. The
first joint immediately adjacent to each manhole on the systems studied
was a hot poured joint. Infiltration measurements included the flow con-
tributed by the 6 inch house connections and manholes as well as the
sewer being tested.
Five separate systems were tested in this part of the project. All were
located in the City of New Orleans. These are shown as Systems 1 to
5 on Figure 21. Table 2 shows the length of sewers in each system,
the type of joint and describes the beddings used.
It may be noted from Figure 21 that the systems were in different parts
of the City of New Orleans. Four extended along a four mile section
known as New Orleans East which is adjacent to Lake Pontchartrain and
the other is in the western side of the city. Apendices C,D,E,F and G
show the sewers in each system. The following observations are made
concerning the systems;
a) There were different contractors on the jobs and because of
this there were various methods of construction used.
b) Each system had different types of joints.
c) The depths of the lines varied.
d) The soil conditions in the systems ranged from coarse sand to
soft clay.
e) The systems tested were in two different areas of the city.
This made a difference in the amount of rainfall on each system. In
turn the variation in rainfall may have caused a possible difference in the
heights of the water tables and in the hydrostatic heads on the pipes.
41
-------
LAKE PONTCHARTRAIN
TEST AREAS
NEW ORLEANS. LOUISIANA
I. LAKE WOOD SOUTH SYSTEM
2. MAYO ROAD SYSTEM
3. 8URKE STREET SYSTEM
4. WEBER AVENUE SYSTEM
5. BERG ROAD SYSTEM
6. HESSMER AVENUE SYSTEM
7. IOTA STREET SYSTEM
TEST AREAS
NEW ORLEANS, LOUISIANA
MAP OF SEWER SYSTEM
FIGURE 21
-------
TABLE 2
LENGTH, JOINTS AND BEDDINGS OF SEWER SYSTEMS
Length of Lines
System Feet
Mayo Road 13,390
Lakewood South 6,290
Weber Avenue 15 , 840
Burke Street 17,400
Berg Road 16,100
Type of
Joint
P.V.C
Beaded
P.V.C
Beaded
"O"
Ring
"O"
Ring
"O"
Ring
Description of
Bedding
Clam shell 8"
below pipe and
to top of pipe
Clam shell 6"
below pipe and
to spring line
Clam shell 6"
below pipe and
to top of pipe
Clam shell 6"
below pipe and
to top of pipe
Clam shell 6"
below pipe and
to spring line
43
-------
Results - 1962-1963 Tests
Ninety-six flow readings were taken on sewer lines in the five separate
systems. As these systems had just been installed there was no sewage
flow in the systems. As house connections were made to the system,
the tests were discontinued. This is the reason why only one set of
readings was taken on the Weber Avenue, Berg Road and Mayo Road
systems. Tables 3,4,5,6 and 7 show the physical characteristics
of the systems studied and Tables 8,9,10, 11 and 12 show the infil-
tration in gallons per inch mile per day that was recorded on the lines.
The amount of rainfall in the vicinity of the systems was recorded during
the test period. The rainfall observations are shown in Table 13. The
Metairie Gauge is located in the vicinity of the Lakewood South System
and the Citrus Gauge is located near the Mayo Road, Burke Street, Weber
Avenue and Berg Road Systems.
A review of the infiltration records of the system shows considerable
variations with single line readings and wide range between individual
lines. Of the 48 lines tested eight were found to have no infiltration
and one of the lines of the Weber System (Line 2-12) recorded the maxi-
mum infiltration of 111,560 gallons per inch mile per day.
Significant variations occurred within the same lines where several
observations were made. Line 7-8 of the Lakewood South System, for
example, where seven observations were made showed a 400 percent
difference with a minimum of 909 and a maximum of 3610 gallons per
inch mile per day. No correlation appears to exist between rainfall and
infiltration. Similarly the depth of the sewer appears to have no effect
on infiltration. This is probably due to the fact that in the areas studied,
the ground surface was at or near Mean Gulf Level and the ground water
table is within a few feet of the ground surface. As a consequence,
sewers are consistently under a hydraulic head of considerable magnitude.
The following observations were made concerning the systems tested:
Mayo Road System
In the Mayo Road System, the infiltration in Line 7-8 was found to be
16,050 gallons per inch mile per day. The line was shined with mirrors
from both ends and no leaks could be seen. A closed circuit television
camera was run through the line and a leak was found in one joint
The line was dug up and it was discovered that the bell was cracked.
After the pipe was repaired the line was televised again and found to be
almost dry.
44
-------
Number
2-3
1-3
3-4
Length of Line
8"-
6"-
8"-
6"-
8"-
6"-
720.0'
48.0'
660.5'
132.0'
1675.0'
372.0'
Inch Miles
1.361
1.370
3.519
•TABLE 3
PHYSICAL CHARACTERISTICS OF THE MAYO ROAD SYSTEM
Average Depth
8.1'
7.1'
10.11
4-5 12"- 608.2' 2.320 10.4'
10"- 318.3'
5-6 15"-1770.3' 5.866 11.4'
4-10 15"-2139.3' 9.410 11.6'
12"- 608.2'
10"- 318.3
7-8 15"- 381.6' 1.265 10.3'
8-9 18"- 1589.5' 6.284 11.5'
8-10 18"-2051.5' 8.112 11.7'
45
-------
TABLE 4
INFILTRATION EXPRESSED IN GALLONS PER INCH MILE PER DAY RECORDED
IN THE MAYO ROAD SYSTEM
Number
Date
Infiltration
gal/in/mile/day
2-3
1-3
3-4
4-5
5-6
4-10
7-8
8-9
8-10
8/17/62
8/17/62
8/17/62
8/17/62
8/17/62
5/ 8/63
7/21/62
7/21/62
5/ 8/63
0
1,313
539
541
248
10,712
16,050
0
828
Current Allowable
Infiltration
Specification
ga 1/in/mile/day
250 -*
250 +
250 +
250 +
250
250 +
250 +
250
250 +
*Minus sign indicates value measured is within the current infiltration
specification and a positive sign indicates that the measured value is
not within the current infiltration specification.
46
-------
TABLE 5
PHYSICAL CHARACTERISTICS OF THE IAKEWOQD SOUTH SYSTEM
Number Length of Line Inch Miles Average Depth
10-12 8"-744.0' 1.918 8.0'
6"-424.0'
11-12 8"-375.4' 0.961 8.5'
6"-224.0'
7-9 8"-681.4' 1.916 8.5'
6"-500.0'
5-6 8"-418.8' 1.126 8.01
6"-271.0'
3-4 8"-741.8' 2.135 8.5'
6"-524.5'
1-2 8"-417.9' 1.119 8.1'
6"-268.5'
12-13 18"-145.7' 0.661 12.5'
6"- 60.0'
7-8 8"-269.5' 0.794 8.9'
6"-225.0'
47
-------
TABLE 6
INFILTRATION EXPRESSED IN GALLONS PER INCH MILE PER DAY RECORDED
IN THE LAKEWOOD SOUTH SYSTEM
Number
10-12
11-12
7-9
5-6
3-4
1-2
12-13
7-8
Date
8/10/62
9/ 7/62
10/ 9/62
ll/ 6/62
12/ 4/62
I/ 8/63
4/23/63
8/10/62
8/10/62
9/ 7/62
8/10/62
9/ 7/62
8/10/62
8/10/62
9/ 7/62
10/ 9/62
10/23/62
ll/ 6/62
12/ 4/62
I/ 8/63
4/23/63
8/10/62
9/ 7/62
10/ 9/62
10/23/62
ll/ 6/62
12/ 4/62
I/ 8/63
Infiltration
gal/in/mile/day
3870
3840
4230
1875
1715
1873
1713
3320
0
0
0
0
1970
2780
2472
2540
4650
2370
1530
2511
2440
925
1508
3610
1220
2850
925
909
Current Allowable
Infiltration
Specification
gal/in/mile/day
250 +*
250 +
250 +
250 +
250 +
250 +
250 +
250 +
250
250
250
250
250 +
250 +
250 +
250 +
250 +
250 +
250 +
250 +
250 +
250 +
250 +
250 +
250 +
250 +
250 +
250 +
*Minus sign indicates value measured is within the current infiltration
specification and a positive sign indicates that the measured value is
not within the current infiltration specification.
48
-------
TABLE 7
PHYSICAL CHARACTERISTICS OF THE WEBER AVENUE SYSTEM
Number
1-2
3-4
5-6
7-9
8-9
2-12
2-10
10-11
11-12
13-14
15-16
17-18
Length of
8
6
8
6
8
6
8
6
8
6
12
12
12
12
8
6
8
6
8
6
"-1298
"- 425
"-1566
"- 623
"-1286
"- 406
"-1494
"- 551
"-1509
"- 429
"-1216
"- 410
"- 408
"- 398
"-1128
"- 150
"-1124
"- 100
"-1143
"- 175
Line
.1'
.0'
.3'
.0'
.4'
.0'
.6'
.0'
.2'
.8'
.8'
.2'
.1'
.5'
.8'
.0'
.1'
.0'
.8'
.0'
Inch Miles
2
3
2
3
3
3
1
1
1
2
2
2
.919
.773
.871
.446
.305
.227
.088
.082
.056
.237
.159
.298
Average
9
7
•
8
7
7
12
11
12
12
9
9
9
De
.1'
.5'
.1'
.6'
.6'
.0'
.3'
.1'
.7'
.5'
.5'
.5'
49
-------
TABLE 8
INFILTRATION EXPRESSED IN GALLONS PER INCH MILE PER DAY RECORDED
IN THE WEBER AVENUE SYSTEM
Number
Date
Infiltration
gal/in/mile/day
1-2
3-4
5-6
7-9
8-9
2-12
2-10
10-11
11-12
13-14
15-16
17-18
3/20/63
3/20/63
3/20/63
3/20/63
3/20/63
3/28/63
4/ 4/63
4/ 4/63
4/ 4/63
3/28/63
3/28/63
3/28/63
3,364
2,673
1,508
1,256
2,178
111,560
42,613
0
0
2,413
3,580
2,136
Current Allowable
Infiltration
Specification
gal/in/mile/day
250 +*
250 +
250 +
250 +
250 +
250 +
250 +
250
250
250 +
250 +
250 +
*Minus sign indicates value measured is within the current infiltration
specification and a positive sign indicates that the measured value is
not within the current infiltration specification.
50
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TABLE 9
PHYSICAL CHARACTERISTICS OF THE BURKE STREET SYSTEM
Number Length of Line -Inch Miles Average Depth
1-3-4 12"- 620.1' 8.184 8.6'
8"-3227.T
6"- 516.5'
1-2
5-6
7-8
9-10
11-14
12-13-14
15-4 10"- 351.9' 2.016 8.1'
8"- 623.3'
6"- 81.0'
16-17 18"-1156.6' 4.898 11.5'
6"- 235.0'
8
6
8
6
8
6
8
6
8
6
8
6
"-2124.
"- 298.
"-1212.
"- 104.
"-1199.
"- 68.
"-1197.
"- 105.
"-1578.
"- 122.
"-2265.
"- 314.
6'
5'
9'
O1
8'
0'
8'
0'
5'
O1
5'
O1
4
2
2
2
2
4
.234
.325
.250
.299
.937
.502
9
7
7
7
6
7
.9'
.7'
.7'
.7'
.7'
.2'
51
-------
TABLE 10
INFILTRATION EXPRESSED IN GALLONS PER INCH MILE PER DAY RECORDED
IN THE BURKE STREET SYSTEM
Current Allowable
Infiltration
Infiltration Specification
gal/in/mile/day gal/in/mile/day
Number
1-3-4
1-2
5-6
7-8
9-10
Date
8/24/62
10/ 1/62
10/30/62
11/20/62
12/11/62
8/24/62
8/24/62
10/ 1/62
10/30/62
11/20/62
12/11/62
8/24/62
10/ 1/62
10/30/62
11/20/62
12/11/62
8/24/62
10/ 1/62
10/30/62
11/20/62
12/11/62
1319
4505
3700
3360
2950
1821
316
426
328
0
0
552
1044
385
568
592
587
957
448
442
564
250
250
250
250
250
250
250
250
250
250
250
250
250
250
250
250
250
250
250
250
250
+*
+
+
+
+
*Minus sign indicates value measured is within the current infiltration
specification and a positive sign indicates that the measured value is
not within the current infiltration specification.
52
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TABLE 10 (continued)
INFILTRATION EXPRESSED IN GALLONS PER INCH MILE PER DAY RECORDED
IN THE BURKE STREET SYSTEM
Number
11-14
12-13-14
15-4
16-17
Date
8/24/62
10/ 1/62
10/30/62
11/20/62
12/11/62
8/24/62
10/ 1/62
10/30/62
11/20/62
12/11/62
8/24/62
10/ 1/62
10/30/62
11/20/62
12/11/62
8/24/62
Infiltration
gal/in/mile/day
197
732
335
768
800
2525
2664
1867
1370
1145
1165
1448
2190
1070
2240
4500
Current Allowable
Infiltration
Specification
gal/in/mile/day
250 -*
250 +
250 +
250 +
250 +
250 +
250 +
250 +
250 +
250 +
250 +
250 +
250 +
250 +
250 +
250 +
*Minus sign indicates value measured is within the current infiltration
specification and a positive sign indicates that the measured value is
not within the current infiltration specification.
53
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TABLE 11
PHYSICAL CHARACTERISTICS OF THE BERG ROAD SYSTEM
Number Length of Line Inch Miles Average Depth
1-2-3 8"-1691.4' 3.805 5.8'
6"- 556.1'
4-5 8"-l200.2' 2.640 5.3'
6"- 350.0'
6-7-8 8"-1747.5' 3.779 5.8'
6"- 462.4'
9-10 8"-2013.r 4.547 7.6'
6"- 674.5'
11-14 8"- 953.0' 1.749 5.4'
6"- 26.0'
12-13-14 8"-l409.8' 2.908 4.9'
6"- 271.5'
15-16 8"-1132.8' 2.210 6.9'
6"- 125.0'
17-18 8"- 691.2' 1.338 7.5'
6"- 69.0'
19-20 8"-1125.4' 2.333 6.9'
6"- 225.O1
21-22 8"-1126.2' 2.368 6.9'
6"- 250.0
54
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TABLE 12
INFILTRATION EXPRESSED IN GALLONS PER INCH MILE PER DAY RECORDED
IN THE BERG ROAD SYSTEM
Number
Date
Infiltration
gal/in/mile/day
1-2-3
4-5
6-7-8
9-10
11-14
12-13-14
15-16
17-18
19-20
21-22
2/7/63
2/7/63
2/7/63
2/7/63
2/7/63
2/7/63
2/7/63
2/7/63
2/7/63
2/7/63
4055
2045
2508
2639
0
1062
4889
1494
5143
9199
Current Allowable
Infiltration
Specification
gal/in/mile/day
250 +*
250 +
250 +
250 +
250
250 +
250 +
250 +
250 +
250 +
*Minus sign indicates value measured is within the current infiltration
specification and a positive sign indicates that the measured value is
not within the current infiltration specification.
55
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TABLE 13
MONTHLY RAINFALL RECORD
CITY OF NEW ORLEANS
Month
1962 'July
August
September
October
November
December
1963 January
February
March
April
May
Rainfall-Inches
Metairie Gauge
2.36
3.30
4.25
2.44
2.45
3.10
3.65
5.90
1.76
2.11
1.46
per Month
Citrus Gauge
3.03
3.95
5.78
1.71
3.53
3.90
5.71
6.45
1.17
3.72
4.34
-------
Lakewood South System
In the Lakewood South System several sources of infiltration were found
in line 10-12. One major leak was adjacent to a manhole where there
was a poor seal between the pipe and the manhole. This leak was
measured and approximated at 500 gallons per day. In another joint on
an 18" line adjacent to a manhole, a leakage amounting to one thousand
gallons per day was found. This was a hot poured bituminous joint
used for the last pipe section adjacent to the manhole.
Weber Avenue System
In line 2-12 of the Weber Avenue System it may be noted from Table
that the infiltration was 111,560 gallons per inch mile per day. The
major portion of this was found to be coming from a hot poured joint
adjacent to a manhole. The joint was open at the top and the hot poured
material used to make the joint had been squeezed out of the bottom.
Burke Street System
In the Burke Street System, line 1-2 had the greatest infiltration with a
value of 2664 gallons per inch mile per day. A television inspection
of this line showed several cracked bells that were causing the infiltration.
Results of 1970 Tests
As a part of the current project some of the lines used in the 1962-1963
tests were selected for infiltration measurements. These tests were
made during the summer of 1970. The purpose of this portion of the
study was to determine the changes that may have occurred in the five
systems during the period between the measurements. In selecting the
lines to be tested, consideration was given to the magnitude of infiltra-
tion in the initial study, type of beddings and number of house connec-
tions. It was recognized that the fewer houses along the lines selected,
the easier it would be to eliminate residential flow. A cross section of
lines was selected where both maximum and minimum infiltration flows
were recorded on the initial survey. Materials and methods used in the
1970 study were identical to those used in the 1962-1963 tests.
A comparison of the results of the two infiltration tests are shown in
Table 14. A tabulation of repairs performed on the system during the
interval between the two tests and the number of house connections in
1970 is presented in Appendix H.
At the time that the infiltration studies were made on the sewers in the
57
-------
en
oo
TABLE 14
COMEA.RISON OF INFILTRATION TESTS OF 1962-1963 to 1970
System
&
Line
Numbers
Weber
2-12
11-12
2-10
Lakewood
7-9
5-6
1-2
Burke
15-4
Mayo
4-5
4-10
7-8
Berg
17-18
19-20
Infiltration Tests Run
1962-1963
Date of
Infilt. Test
4-63
4-63
4-63
South
8-62
S&9-62
8-62
8 to 12-62
8-62
5-63
7-62
2-6i
2-f 3
Infiltration*
111,560
0
42,613
3,320
0
1,970
1,622
541
10,712
16,050
1,494
5,143
Infiltration Tests Run
1970
Date of
Infilt. Test
6-70
6-70
6-70
5-70
5-70
5-70
6-70
8-70
6-70
7-70
6-70
6-70
Infiltration*
6,660
1,535
8,110
2,100
1,710
1,630
2,480
12,600
3,350
1,170
1,830
1,545
Interval
Between
Tests
Yrs.-Mo.
7
7
7
7
7
7
8
8
7
8
8
8
2
2
2
9
9
9
0
10
1
0
4
4
Infiltration*
+ Increase
- Decrease
*
-104,900
+ 1,535
- 34,503
- 1,220
+ 1,710
340
+ 858
+ 12,069
- 7,362
- 14,880
+ 336
- 3,598
*Gallons per inch of diameter per mile per day.
-------
City of New Orleans in 1962-1963, there were not requirements included
in the city's specifications on infiltration. As a result of the 1962-1963
infiltration studies the City of New Orleans adopted specifications for
sewer construction limiting the infiltration to 1000 gallons per inch mile
per day. In March of 1966 the infiltration limitation in the specifications
for new sanitary sewer construction was reduced to 250 gallons per inch
mile per day. These are the standards currently used by the City of New
Orleans.
A review of Table 14 indicates that substantial reductions have occurred
in the infiltration of some of the lines. For example, this is particularly
true in line 2-12 of the Weber Avenue System where the infiltration dropped
from 111,560 to 6,660 gallons per inch mile per day. No doubt some of
the decrease in this line and others was due to repairs provided during
the interim. In the case of line 2-12, after the major leak in the joint
adjacent to a manhole was repaired, a substantial decrease in the infil-
tration followed. Other repairs made to the lines studied are shown in
Appendix H.
In each of the lines measured in the 1970 study the infiltration exceeded
the present allowable limit set in the New Orleans specifications of
250 gallons per inch mile per day. The highest recorded was line 4-5
of the Mayo Road System of 12,600 gallons per inch mile per day. It is
interesting to note also that lines 11-12 of Weber and 5-6 of Lakewood
where no infiltration was recorded in 1962-1963, now show infiltration
rates exceeding 1500 gallons per inch mile per day.
1970 Television Inspection
To determine the cause of the infiltration in the system the following
lines were selected for televising.
Diam. Length Amount of Infiltration
System Line Inches Feet Gal/Inch Mile/Day
Weber Ave 2-12 8 1216 6600
Mayo Road 7-8 15 381 1170
Considerable difficulty was experienced in televising these sections
because of blockages in the lines. The blockages experienced included
breaks in sewers, roots of trees and large accumulations of grease. The
sections of sewers studied were all serving new subdivisions. It is the
common practice in residential construction in this area to equip the new
homes with garbage disposals on the kitchen sinks. It is believed that
the cold water entering the sewers through infiltration was causing the
59
-------
grease to coagulate and in some cases mix or adhere to mud entering the
sewers through cracks or other openings. Large quantities of grease
were observed on the television camera when it was removed from the
sewer. In some cases a mixture of grease and clay at joints was ob-
served with no infiltration. Apparently the mixture had succeeded in
sealing off joint leakages.
The following comments are submitted concerning some of the conditions
found in the lines:
Weber Avenue
Between manholes 2 and 10 a break was found through which soil and
roots had entered. Large quantities of grease were observed in the mass
of roots and mud. The sewer appeared to have partially collapsed and
the camera could not pass the blockage. In another section of this line
a leaking joint was found near a house connection. The house connec-
tion appeared to have been made by breaking through the sewer and
inserting a smaller (probably 6" diameter) pipe into the main conduit. A
considerable accumulation of grease was noticed in the area of the leak-
ing joint. In the 1216 feet of this line that were televised approximately
twelve leaks appeared to be present that were caused by breaks, improper
house connections or open joints. Figure 22 shows television photo-
graphs of some of the conditions found.
Mayo Road
i
Conditions observed along this line were generally similar to those found
in the Weber Avenue System. This line was 381 feet in length. Three
house connections made by breaking the sewer were observed and in
each case infiltration appeared to be occurring. Considerable accumu-
lation of grease was noticed around each connection. Photographs of
the conditions found in this line are shown in Figure 22 .
The results of the studies made in 1962-1963 and 1970 clearly indicate
that large quantities of infiltration are entering the system. The amounts
found in every line studied in 1970 are far in excess of the City of New
Orleans' limit of 250 gallons per inch mile per day. Observations made
during the laying of these systems in 1962 and 1963 indicated that poor
construction methods were used. A new factor appears to have been
introduced in the hydraulics of sewage flow with the inception of the
garbage disposal units used in homes. The use of these units is esti-
mated to increase the organic content of domestic sewage by 50 per
cent. This material with the grease that is included, will undoubtedly
add to sewer maintenance problems. This condition was strikingly
60
-------
0>
Leaking Joint - Weber Ave.
Tree Root - Weber Ave.
House Connection Broken into Top of Jpewer
Mayo Road
Grease Accumulations at House Connection
Weber Ave.
FIGURE 22 - PHOTOGRAPHS FROM TELEVISION MONITOR
-------
emphasized through conditions observed in the lines that were televised.
Closer supervision over plumbers making connections to main sewer lines
appears to be warranted. It was very apparent from the televising of the
lines that in almost every case where the non-conventional connection
was made by breaking into the main sewer line, a leak developed.
Where leaks occur in breaks or defective joints some sealing appears to
occur through backfill soil entering the opening. Grease also has a
tendency to adhere or mix with soil entering these openings.
Test Sewer Studies 1968-1970
During the period from 1967 to 1970, the two test sewers located in
Jefferson Parish, Louisiana, were observed during and after construction.
One was located on Iota Street (constructed in November and December
1967) and the other, on Hessmer Avenue (constructed in May and June
1968). Section V provides a description of these studies. Each con-
sisted of three sections between manholes. Table 15 shows the infil-
tration records of each section of each test sewer. On 9-14-70 Sections
I and II were not measured because the bottom of the manholes were
constantly flooded with infiltrated water.
The construction practices used on the Iota Street sewer were generally
good with the single exception that backfill was dropped onto the pipe.
Although continuous pumping was required in order to maintain a dry
trench, the conditions of soil and water could be considered good and
no sheeting was required. An average trench width of two feet was
maintained throughout the construction.
In contrast,the sewer on Hessmer Avenue was laid under adverse condi-
tions of soil and water and the construction practices were extremely
bad. The soil at the bottom of the trench throughout the job was in a
constant semi-liquid state, and the slight upward movement of particles
indicated an impending quick condition. The side flow of particles and
water through the sheeting existed throughout the work. Poor construc-
tion practices were common and are listed as follows:
1. The trench was maintained with a bottom width of from 4 1/2
to 5 feet.
2. Bedding material was dropped directly on the pipe with a front
end loader.
3. Backfill was pushed onto the bedded pipe from the upper edge
of the trench. At times the impact from this procedure could be strongly
felt by observers alongside of the trench.
62
-------
4. The method of adjusting the grade downward was for two or
three laborers to jump on the pipe in unison. This practice was so
common that any other would be considered an oddity.
TABLE 15
INFILTRATION TEST SEWERS
JEFFERSON PARISH, LOUISIANA
Iota Street Infiltration*
Date Section I Section II Section III
1-19-69 425 752 1090
2-23-68 0 0 473
3-2-68 00 0
6-1-68 00 0
8-27-68 00 0
1-2-69 00 0
8-9-69 00 0
1-17-70 00 0
4-30-70 00 0
8-12-70 00 0
Hessmer Avenue Infiltration*
Date Section I Section II Section III
7-19-68 662 1140 584
8-7-68 31 236 650
8-27-68 0 595 177
9-14-70 - - 31000
*Gallons per inch of diameter per mile per day.
In April of 1968 both test sewers were televised. No leaks, breaks or
cracks were found in the Iota Street installation. One leak caused by a
cracked bell was found in Section III on Hessmer Avenue, and is shown
in Figure 23.
During April of 1970 the Hessmer Avenue test sewer was televised again
to determine the cause of the high infiltration. The line was found to be
so badly damaged and had so many obstructions caused by breaks that
it was impossible to run the camera through the entire system. Only
portions of Section II and III could be televised. Numerous small leaks
were observed along Section III until a collapsed section was reached.
In Section II several small leaks were observed, and an obstruction con-
sisting of bedding material (clam shell) and pieces of broken pipe pre-
vented the passage of the camera. Figure 24 shows pictures taken in
this line.
63
-------
LEAK FOUND IN HESSMER AVENUE 1968
FIGURE 23
CONCLUSIONS
It appears from these studies that the predominant factors influencing
infiltration are construction procedures. It is thought that soil condi-
tions effect their greatest influence in the degree to which they influence
construction. The practice of breaking the trunk sewer to form a house
connection should be prevented by closer supervision of plumbers making
these connections.
As a result of the 1962-63 infiltration studies,the City of New Orleans
established its first infiltration specification for new sewer construction.
64
-------
0)
en
PHOTOGRAPHS IN HESSMER AVENUE TEST SEWER 1970
FIGURE 24
-------
SECTION III
SEWER SETTLEMENT
COMPRESSION THEORY
According to the Terzaghi theory of consolidation, the compression
settlement of a structure is composed of the sum of the compressions of
the underlying clay strata within the zone of influence of the applied
load. 7
The settlement is dependent upon:
1. The vertical permeability of the compressible underlying strata.
2. The drainage of the compressible underlying strata.
3. The thickness of the underlying strata.
4. The applied load (pressure to each stratum).
5. The pre-loading history of each stratum.
In order for settlement to take place a load must be applied to compres-
sible strata beneath the structure. This load is usually generated by the
net weight of the structure. Table 16 shows a comparison between the
weight of soil displaced by clay sewer pipe and the pipe itself. For
example, with 8 inch sewer pipe laid in a soil with a unit weight of 80
pounds per cubic foot, the weight of the soil, previously occupying the
location of the pipe, is 37 pounds per linear foot and the weight of the
sewer is 26 pounds per linear foot. This leaves a net difference of 11
pounds per linear foot after construction, and with the sewage at design
flow, there is no net positive load. It can be seen that for the range of
unit weights given, all the weights after construction are lighter than
those before, and at design flow the only positive pressures are seen in
the lightest soil and are very small. This table excludes any net change
in load due to the bedding or the disturbed or replaced backfill. Most
granular bedding causes very little net change in weight, and this change
is a reduction where clam or oyster shells are used. If select backfill
is used, it may be heavier than the material which occupied that space
before construction. More commonly the original soil is used as back-
fill, and in this disturbed state is less dense than prior to excavation,
causing a decrease in the net load if there is any. It can be seen,
therefore, that the net load produced by a sewer on an underlying com-
pressible strata is usually negative or zero, and some means of load
imposition other than net weight must exist for sewers to settle.
67
-------
TABLE 16
COMPARISON OF WEIGHT OF PIPE WITH
WEIGHT OF SOIL REMOVED
Nominal Pipe
Size, Inches
Weights in Pounds per
Linear Foot of Soil
Replaced by Pipe
Exclusive of Bedding
Approximate Weight
Clay Pipe, Pounds per
Linear Foot
6
8
10
12
15
18
21
24
Soil
62
17
29
45
64
99
144
193
255
Unit
80
22
37
58
83
128
186
248
329
Weights
100
27
46
72
104
160
232
311
412
(pcf)*
125
34
58
90
130
200
290
389
515
Dry
17
26
35
49
78
115
150
200
Flowing
1/2 Full
23
37
52
74
116
170
225
298
* Pounds per Cubic Foot
MECHANISMS OF DOWNWARD MOVEMENT
There are three mechanisms that enable sewers to settle: undermining,
soil remoulding, and drawdown, of which there are several types. These
phenomena can be classified as general subsidence, localized subsi-
dence, construction settlement, and undermining.
General Subsidence
In localities where water tables are high and soils are compressible,
general subsidence is a function of urbanization as it produces drainage
of an area. The cause of this generalized settlement is the lowering of
the water table. For every foot the water table is lowered, a load of
62.4 psf is added to underlying strata because of the corresponding loss
of buoyant pressure. It follows, therefore, that a significant increase in
load and subsequent settlement of structures can be caused by lowering
the water table only a few feet if the underlying soils are highly com-
pressible. This generalized settlement over a large area usually causes
no serious problems with sewers unless the downstream end of the sys-
tem is not within the area of subsidence, in which case sewage will be
backed up in the system. This may then result in the sewage arriving
at the point of disposal in a septic condition.
68
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Localized Subsidence
The subsidence mechanism discussed above can affect sewers and other
structures under extremely localized conditions. In this case the water
table is drawn down by one of the following:
1. A canal or stream in the vicinity.
2. A leaking storm or sanitary sewer.
3. A shallow well or dewatered excavation.
This type of subsidence can cause local sewer settlement sufficient to
result in flattening and even reversal of the sewer grade. It is highly
unlikely that this differential settlement can produce structural damage
or joint opening in clay sewers. In a study of clay sewers (8 inch
beaded polyurethane joint) a deflection in excess of 10 degrees (1.65
inches per foot) was observed while the joint maintained its integrity.
The deflections produced in a length of clay pipe as a result of all
subsidence will, in all probability, not exceed the ASTM specification
for deflection.
Construction Settlement
This condition is probably responsible for a great portion of sewer
settlement. It is the special case of localized subsidence in which the
sewer construction itself lowers the water table causing subsequent
settlement. In areas of high water table, dewatering by well points or
trench pumping is usually required in sewer construction.
In order for appreciable settlement to occur, the water table drawdown
must be maintained for a sufficient time to effect consolidation of under-
lying compressible strata. Two factors aid in the maintenance of the
drawdown even though only a small section of trench may be open at one
time. The use of extremely permeable granular bedding material will
cause the transmission of water for great distances along the trench.
The backfill, because of its disturbed condition, will usually transmit
large amounts of water, except when backfill is composed predominantly
of soft clay. Figure 25 shows the drawdown condition for a sewer trench.
The movement produced by this mechanism occurs during or immediately
after construction since a shearing and not a compression phenomenon is
taking place.
Undermining
The undermining of sewers can cause not only settlement but complete
failure of a sewer and surrounding structures. In'order for this to exist,
69
-------
y/j®y/#$w§Ff2
I
i0pw/$w3$
Original Water Table
Drawdown Curve
Drawdown of Water Table Due to
Sewer Construction
Note:
Arrows Indicate
Direction of Soil
Movement. Dashed
Lines Indicate New
Position of Displaced
Soil.
Shear Planes
Downward Movement of Pipe Due to Failure
of Remoulded Adjacent Underlying Strata
CONSTRUCTION CONDITIONS CAUSING SEWER SETTLEMENT
FIGURE 25
70
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the following four conditions must be simultaneously present:
1. A sand or silt must underlie and/or surround the sewer structure.
2. The sewer must be located below the water table.
3. There must be a sewer leak of sufficient magnitude to cause the
transport of the sand or silt.
4. The bedding material interposed between the leak and the soil
must be permeable enough to a How the passage of soil.
Undermining should be avoided at all cost since it can cause a great
deal of damage and even loss of life in the case of sudden failure of
overlying structures.
SETTLEMENT MEASUREMENT
1
Two methods of measurement have been used.for measuring sewer ele-
vations. One was fixed to the sewer, and it was intended as a permanent
gage. The other was a jetting device used to locate the sewer and serve
as a temporary form of level rod to the pipe.
Fixed Settlement Gages
These gages consisted of a casing made of P.V.C. pipe going from the
surface down to the sewer. All gages were provided with two slip joints
to avoid damage to the sewer. A level rod could be placed on the sewer
through the casing and the elevation determined with an engineer's level.
Figure 26 contains two photographs of one of these gages.
Several problems arise with the use of this gage. It is difficult to install
and the materials are relatively expensive. It is susceptible to destruc-
tion by construction equipment working in the area. It has also been found
that people occasionally fill the casing with soil.
Jetting Device
This device consisted mainly of a small diameter pipe connected to a
garden hose to supply water from a fire hydrant. Figure 26 contains a
photograph of this jet in use. Level readings were taken on the top of
the jet. Very accurate results can be obtained by this method. It is also
inexpensive to fabricate and operate and it requires no protection since
it is not left in the ground. This method was found to be superior to the
use of casings for settlement determinations. The destruction of many
of the permanent gages necessitated the development .of this device. In
these studies sewer settlements as large as 1.5 feet and manhole settle-
ments in excess of 0.7 feet were observed. This is an extremely large
-------
fo
Sanitary Settlement Devices
Jetting Device for Measuring Settlement
SEWER SETTLEMENT MEASURING DEVICES
FIGURE 26
-------
settlement in light of the three-tenths of one percent grade to which these
sewers were laid. Complete settlement records are presented in Section V.
73
-------
SECTION IV
SEWER BEDDINGS
Sewer beddings are generally composed of either coarse granular
materials, concrete, lumber or combinations of the three. Their primary
purpose is to provide even support and load distribution to the pipe.
Figure 27 illustrates desirable and undesirable conditions of loading
and support. The part of the bedding that underlies the pipe should pro-
vide evenly distributed support thus preventing stress concentrations.
The overlying bedding material will perform the same function of distri-
bution with respect to the backfill load.
It has been found that the coarsest possible angular shaped material
that will not produce point load problems is the most desirable from the
point of view of pipe support. This is due to the fact that the column
of support beneath the pipe covers a much wider area when coarse ma-
terial is used as shown in Figure 28. It is for this reason that sand
alone is less desirable as a bedding material.
The bedding (following the joint and the pipe) should provide a second
line of defense against infiltration. In this respect, the extensive use
of coarse granular materials presents an outstanding drawback since
these beddings serve as "French Drains" permitting water to travel long
distances along the sewer to pipe openings. They also allow the trans-
port of soil fines into the pipe which can cause shoaling in the lines,
grit problems in sewage treatment facilities, and undermining of the
sewer and/or surrounding structures.
LABORATORY TESTING OF BEDDING MATERIALS
Permeability
The permeability of a bedding material is a measure of its water carrying
capacity. It is defined in Darcy's Law for laminar flow through a per-
meable media: „
Q = KT A
Q = Flow Rate, volume/time
H = Head Loss for the Length in Question
L = Length of Travel
A = Cross-sectional Area of Soil Mass
K = Permeability, length/time
75
-------
rnTTTTTrn
Concentrated Load
6
1 LI 1 1 1 1 1 L
r
1
1
<<
Cross-Sectional
Load Support
Concentration
Concentrated Support
Undesirable
i LI t it i mi
Evenly Distributed Load and Support
Desirable
PIPE LOADING AND SUPPORT CONDITIONS
FIGURE 27
76
-------
Broad Column of Support
Coarse Granular Material
Small Column of Support
Fine Granular Material
PIPE SUPPORT BY COARSE AND FINE
GRANULAR MATERIALS
FIGURE 28
77
-------
A study was performed in order to compare the permeability of several
bedding mixtures made from common materials. The mixtures and their
indices of permeability are given in Table 17 . The term Index of Permea-
bility is used instead of Permeability because it could not be determined
if flow was truly laminar throughout the sample during testing. For prac-
tical purposes the index and the true permeability can be used interchange-
ably. These permeability tests were run on eight inch diameter samples
using a constant head permeameter constructed during the project.
Samples "T" and "U" as shown in Table 17 were selected for long term
permeability testing. Sample "T" was soaked in water and tested for
479 hours and sample "U" was soaked and tested for 1381 hours. Figures
29 and 30 illustrate the results of these tests and show that the index of
permeability decreased approximately 45 percent for both samples.
Shear Tests
Table 17 also shows the results of shear tests run on the same materials
for which permeability was studied. It can be seen that the shear
(reported as angle of internal friction) varied approximately between 42°
and 50° which is not considered to be a great fluctuation.
FIELD STUDIES
Field studies were initiated in 1968 on two test sewers located in
Jefferson Parish, Louisiana. In these studies, bedding performance was
completely overshadowed by construction procedures as the prime influ-
ences in sewer behavior relative to infiltration, and efficacy of one
bedding relative to another could not be ascertained. The beddings used
are described in Section V. These materials were readily prepared and
placed during construction with those containing Portland cement, demon-
strating an ability to stabilize the trench bottom where impending quick
conditions were encountered.
MATERIALS RECOMMENDATIONS
Many different materials and combinations of materials are used with
varying success throughout the Gulf Coast Area. Table 18 shows the
frequency of use of various materials as bedding by 40 sewer authorities
in the area. Some authorities indicated that more than one of these
materials was used or that combinations of two or more were utilized for
a standard bedding.
78
-------
TABLE 17
INDICES OF PERMEABILITY AND
ANGLES OF INTERNAL FRICTION
MIXED MATERIALS
0
i — i
a
S
(0
CO
A
B
C
D
E
F
G
H
I
I
K
L
M
N
0
P
Q
R
S
T+
U+
CH O
(0 ^
CO
59.1
58.6
57.7
59.0
49.6
38.5
29.1
19.2
38.8
40.2
29.5
50.0
37.4
36.8
39.2
43.5
38.5
39.8
43.2
45.0
42.7
CD dS -C "c £
m 7! 0) ° Zl c §5
"y CD r-» TI ^-*
° -c -5 o Q^
0 co £ (So
40.9
41.4
42.3
41.0
50.4
61.5
70.9
80.8
61.2
59.8
70.5
Bentonite
50.0
54.4
57.7
54.5
57.1
55.1
45.0
46.1
48.4
46.5
5.2
5.5
5.3
6.0
8.7
6.4
6.6
6.4
1.0
1.2
3.2
6.5
4.3
4.4
*Too permeable to measure.
+Representative of the two mixtures used in the field.
**Permeability adjusted to 20°C.
(0
Q)
S5
CU
•ft
C
c -^ S?
m +J °
« 0
1.0
1.2 Lime 1.2
3 . 2 Lime 3 . 2
6.5
4.3
4.4
*
*
-r-H
•rH ^-^
^ .0 0
° ro Q)
^
1 oil
*
*
0.6xlO"2
0.54xlO~2
1.12x10-2
2.37xlO"2
3.73x10-2
*
3.35xlO"2
2.91xlO~2
*
l.lxlO'2
1.07x10
3.8xlO-2
3.5xlO"2
2.99xlO"2
6.68xlO"2
_9
0.9x10 L
0.4xlO"2
g£
o> 6
•£ °
C 1-1
HH pi.
^ C
0 0
CO -lH
•S. o ^
D> y M
c; d cu
< PH EH
48°30'
45°40'
45°25'
46°25'
42°40'
50°10'
45°00'
45°00'
42°50'
45°20'
48°00'
44°30'
46°10'
44°50'
48°00'
44°50'
79
-------
10X10
-3
u
Q)
OT
6
o
00
o
fO
g 5X10~3
Q)
PL,
M-l
O
X
TJ
c
1X1
S0
100
I I I
150
200 250 300 350 400
Elapsed Time in Oiours)
Note: Sample Mixture "T" - Sand - Shell - Portland Cement
Curve - Average from Eight Samples
450
AVERAGE LONG TERM PERMEABILITY SAMPLE "T"
FIGURE 29
-------
CD
4X10-3
o
o>
w
j 3X10-3
(0
CD
X
CD
T3
C
1X10
-3
-0
200
400
600 800 1000
Elapsed Time in (hours)
1200
1400
Note: Sample Mixture "U" - Sand - Shell - Portland Cement - Bentonite
Curve - Average from Eight Samples
AVERAGE LONG TERM PERMEABILITY SAMPLE "U"
FIGURE 30
-------
TABLE 18
FREQUENCY OF BEDDING MATERIAL USE*
Clam and/or Oyster Shell 16
Gravel 8
Crushed Stone 7
Sand 4
Cement Stabilized Sand 3
Board Bottom 5
Piles 5
Concrete Encasement 3
Slag 1
Sand and Shell Mixed 1
No Bedding Used 7
*From survey
82
-------
Coarse Aggregates
As can be seen from Table 18 clam or oyster shells find wide usage as a
bedding material. An analysis of clam shell is shown in Appendix I.
Both of these materials provide good pipe support; however, oyster shells
are more difficult to shape, so that care should be taken to insure uni-
form contact between the pipe and the bed. Masses of these shells
possess angles of internal friction in excess of 45° and with available
moisture and time a cementing phenomenon takes place. Oyster (reef)
and clam shells are available throughout the Gulf Coast area. Coarse
gravel is also readily available in most localities and also provides
excellent support. On the other hand crushed stone is almost unknown
in many areas along the Gulf Coast.
The materials, as previously mentioned, provide extensive channels for
water transmission when they are used alone. Even though coarse aggre-
gates provide good support, they should be used only in conjunction with
some system for retarding flow where the sewer is located below the
water table. Where the subsoil is very soft, graded materials should be
used to prevent the soil from penetrating the bedding or the bedding from
penetrating the soil.
Sand
Sand is the only fine aggregate that is used alone as a bedding material
to any great extent. This is undesirable in light of the small column of
support provided (with its associated cross-sectional point load) beneath
the pipe. Sand is, however, an excellent constituent of bedding mixtures.
Mixtures
Combinations of materials in mixtures provide an excellent means of
retarding the flow of water in the bedding. Sand and shell serve as
excellent base constituents for such mixtures, and they are both avail-
able through most of the Gulf Coast area.
Whenever a mixture of fine and coarse aggregates is used in constructing
a bedding, an ideal combination would contain enough fines sufficient
to fill the voids between the coarse material. This yields a bedding that
has the support properties of the coarse aggregate and the water trans-
mission characteristics of the fines. In practice it is more efficacious
to provide less fine material than the optimum and rely on migration in
place to provide the optimum in the field (provided that no binding or
cohesive effects have occurred at the time of placement). Slight vibration
by hand compaction will usually cause this migration.
83
-------
Sand and Shell Mixtures
If leakage occurs with a bedding of this type, the sand may be trans-
ported into the pipe. This can be prevented by using sand of a larger
effective size, but this makes the bedding more permeable. A better
solution is to provide a binder that will prevent the transport of sand.
Another problem associated with unbound sand is the possibility of
floatation under quick trench conditions .
Portland Cement
In the field study, it was found that with an impending quick condition
in a 5 foot width trench of shell bedding, stabilization was accomplished
by spreading from one half to one sack of Portland Cement on the shell
surface. Concrete beddings should be avoided where soils are soft and
appreciable settlement is likely to occur. The additional weight of con-
crete will aggravate the settlement, and because of its rigidity, cracking
of bedding and pipe is probable.
Bentonite
Bentonite is a clay mineral with an expanding lattice structure that enables
it to swell with the addition of water. An analysis of a particular type
of bentonite is shown in Appendix J. The idea of its use is to provide
a barrier to water flow by expanding into and filling the voids in a sand-
coarse aggregate mixture. Undoubtedly there are other materials that
would have the same effect and could be tried or developed for this
purpose.
In using material such as this it is important that the amount used is less
than that which would cause a serious reduction in strength due to sepa-
ration of the granular component. The bedding combinations used in the
field studies indicated that four percent or less bentonite will not cause
separation in a sand and clam shell mixture.
Lumber
Planking in the trench bottom can be beneficial by providing uniform
longitudinal support. The following factors should be considered in
the use of planking:
1. Cross-Sectional Support - Where lumber is used below the
bedding in alignment with the pipe, it should be several inches wider
than the horizontal projection of the pipe. Without this there will be
84
-------
a difference of supporting ability across the pipe due to the changing
of the column of support.
. 2. Point and Line Loadings - It is sometimes the practice to place
the pipe barrels on short spans with no planking beneath the bells. This
should of course be avoided since it provides only line support for the
pipe (column of support as narrow as possible).
Pilings are used successfully throughout the Gulf Coast Area and usually
consist of 2x timbers that also serve as sheeting or 2x timber bents.
When using piles to support sanitary sewers the following factors should
be considered:
1. Sufficient trench flooring and bedding should be used to insure
the even distribution of support.
2. If the soil possesses a sensitive structure, pile driving may
decrease soil shear strength by liquifaction or seriously increase settle-
ments due to loss of preconsolidation. This phenomenon will only occur
near the pile; however, the extent of its effect should be considered.
COST OF BEDDING MATERIALS
The cost of bedding materials is shown in Table 19. These data are for
purchase in New Orleans in December of 1970 on a delivered basis.
The information for Portland Cement and bentonite in various percentages
is given as their fractions of cost as portions of mixtures. Bentonite
could probably be purchased in bulk at some saving especially if its
demand was raised above the current level.
For the purpose of estimation the weights of materials are given as
follows:
Clam Shell 1750 #/cy
Reef Shell 1400 #/cy
River Sand 2400 #/cy
65% Reef Shell & 35% Sand 3200 #/cy
65% Clam Shell & 35% Sand 3000 #/cy
85
-------
TABLE 19
COST OF BEDDING MATERIALS
Cost per Cost per foot of
Material Cubic Yard Trench, 8" pipe*
Clam Shell $ 3.25 $ 0.48
Reef Shell 3.45 0.51
River Sand 1.85 0.27
Clam & Sand (65%-35%) 4.05 0.60
Reef & Sand (65%-35%) 4.25 0.63
Portland Cement
($1.50/94* Sack)
4 1/2% 1.69 0.25
5% 1.86 0.28
6% 2.25 0.33
Bentonite
($2.71/100* Sack)
4 1/2% 3.06 0.45
5% 3.36 0.50
6% 4.07 0.60
Clam & Sand (65%-35%)+Portland Cement
4 1/2% Cement 5.74 0.85
5% Cement 5.91 0.88
6% Cement 6.30 0.93
Reef & Sand (65%-35%)+ Portland Cement
4 1/2% Cement 5.94 0.88
5% Cement 6.11 0.91
6% Cement 6.50 0.96
Clam & Sand (65%-35%) + Bentonite
4 1/2% Bentonite 7.11 1.05
5% Bentonite 7.41 1.10
6% Bentonite 8.12 1.20
Clam & Sand (65%-35%) + Bentonite
4 1/2% Bentonite 7.31 1.08
5% Bentonite 7.61 1.13
6% Bentonite 8.32 1.23
*Average Trench Width of 36"
86
-------
SECTION V
SEWER TESTING
LABORATORY SIMULATION STUDIES
These studies were conducted in the laboratory with a testing frame
designed to simulate loadings and beddings that may be used on sewers
installed in the field. It was anticipated that this testing frame would
provide a means of observing the tightness of joints, compaction of
soils, settlement and movements of sewer pipes with various soils and
bedding combinations.
The testing frame was equipped with an overhead loading system that
permitted the development of a backfill equivalent of a trench of 17 feet
depth. Three types of soils commonly found in the Gulf Coast area were
used in the study. Figure 31 is a cross-section of the 23 foot long test-
ing frame, and Figure 32 is a picture of the apparatus in operation. Three
different types of soil (sand, clay and organic soil) were used with 8
inch clay sewer laid with several beddings.
In using the loading frame it was very difficult to simulate the true condi-
tion of laying sewers with beddings used under field conditions. The
results of the loading frame tests were therefore at best of marginal
value. For this reason similar testing for sewer and bedding behavior is
not recommended.
TEST SEWERS
This portion of the project dealt with a study of sewers in the field that
were laid under controlled conditions. Two separate systems were used,
both located in Jefferson Parish which is adjacent to the City of New
Orleans.
Each installation consisted of three sections of sewers located between
four manholes. Combinations of different materials were used for each
bedding. Measurements were made on infiltration and settlement of
these lines over a two year period. The two systems used in this portion
of the study were located on Iota Street and Hessmer Avenue. These are
shown as Systems 6 and 7 on Figure 21.
Materials and Methods
Both sewers were constructed by the same firm under contract with the
Parish of Jefferson and with a subsidy from this research project. Eight
87
-------
14WF34
I I
10WF25
CO
OQ
1/4" Plate
4'-9"
12B14
14WF34
CD
I
3'
_ 3/l6"Checkered
Decking
Notes: Tank 23' Long
Observation Deck on Each Side. One Shown.
TESTING FRAME CROSS SECTION
FIGURE 31
88
-------
CO
CO
TESTING FRAME IN OPERATION
FIGURE 32
-------
inch extra strength vitrified sewers with polyurethane factory moulded
joints manufactured by W. S. Dickey Clay Mfg. Co. were used in the
systems. Each system was laid in three sections with different beddings
used in each section. Table 20 shows the length of the lines and the
average depth in each section.
TABLE 20
LENGTH AND DEPTH OF LINES
Length of Line Iota Street Hessmer Avenue
Section 1 229' 195'
Section 2 240' 225'
Sections 245' 263'
Average Depth of Line
Section 1 7.8 10.0
Section 2 6.9 9.2
Sections 6.2 7.9
The Iota Street system was constructed in three days. Section I was
constructed on November 3, 1967 and Sections II and III on December 5
and 6, 1967. No sheeting was required in the construction and the
trench was maintained in a dry condition with moderate pumping. Good
care was taken in laying the sewer but this backfilling was accomplished
by pushing the fill into the trench and onto the bedded pipe. The average
trench width was two feet. Three different beddings were used, one in
each section. The materials and bedding arrangements are shown in
Figure 33.
Infiltration measurements were made in accordance with the procedures
previously described under the section, Long Term Infiltration Measure-
ments .
The Hessmer Avenue system was under construction from May 16, 1968,
to June 11, 1968. Its location was about 2 miles from the Iota Street
sewer. A concrete roadway had already been provided on Hessmer Ave.
and about 25% of the lots were fully developed with apartment buildings
and residences. Septic tanks and package treatment units were used in
the area. Sheeting with wale and strut supports at the third points were
used for the entire sewer trench. Constant dewatering with several
pumps was required during the entire construction period. On many occa-
sions the pumps could not completely dewater the trench and the water
elevation was above the sewer invert. The beddings used in the three
sections of this installation are shown in Figure 34.
90
-------
2X12 Oak
Section I. Coarse Clam Shells Only
Section II. Sand 47%
Portland Cement 6%
Coarse Shells 47%
Section III. Sand 45%
Coarse Shells 45%
Portland Cement 6%
Bentonite 4%
SEWER FOUNDATIONS IOTA STREET
FIGURE 33:
91
-------
to
j
Section I
^L
E
Backfill
~-X' Mixture '•/-.
"•V'.'r
Lumber
i
1/2' to 5' |jf
Mixture
Sand 45%
Shell 45%
Portland
Cement 6%
Bentonite 4%
Tight
Sheeting
6"
I Tight
Sheeting
Portland Cement
1 Sack Per
10 Lin. Ft of
Trench
Section III
Backfill
2" Lumber
4 1/21 to 5'
I
IE6"
SEWER FOUNDATIONS HESSMER AVENUE
FIGURE 34.
-------
Construction Procedures
The method of construction was typical of that used in the coastal marsh
areas of the Gulf Coast. A back-hoe was used for excavation and de-
watering was accomplished from within the trench by continuous pumping
with diaphragm and/or centrifugal pumps. Where sheeting was required,
it was driven prior to excavation with bracing being placed as the trench
was deepened. The sheeting was not pulled after construction, but was
cut off two feet below the ground surface.
Construction steps following excavation were as follows:
a) The trench bottom was finished by laborers with shovels.
b) Two inch timber was laid in the trench bottom.
c) The bedding material was deposited and spread to grade on
the timber.
d) The pipe was laid to grade.
e) Additional bedding material was deposited on top of the pipe.
f) The trench was backfilled.
The sewer laying was advanced using this procedure while maintaining
only as much open trench as necessary.
Settlement Gages
Gages were designed to be used in determining the settlement of the test
.sewers. Two types were used. One was fixed to the pipe intended to
provide a permanent type of gage. The other was a jetting device used
to locate the sewer and serve as a temporary form of level rod to the line,
Both are described in Section III.
Results
The two test sewers were studied for settlement and infiltration over a
period extending from 1967 to 1970. The results of the two systems lo-
cated on Iota Street and Hessmer Avenue are summarized as follows.
Iota Street
This system was part of a new subdivision and street construction had
not yet been completed. A sand fill of from two to three feet had been
provided at the street location. Where the sewer trench was dug the
93
-------
ground surface was at the original elevation. Figure 35 shows the cross-
sectional relationship between the test sewer and the street fill. The
sewer was located outside of the street area about 9 feet from the curbing.
As mentioned above, 26 gages were located along the Iota Street line.
The location of these gages was established by stations beginning at the
downstream end of the line. Two soil borings were taken, one at each
end of the line. The analyses and the soil samples are shown as Appendix
K and L. The soil at this site consisted of an organic material from the
ground surface to a depth of 2 to 3 feet. Beneath this to the depth of the
boring was a finely layered system of clay silt and sand. The soil sur-
rounding the pipe consisted of a very soft silty clay of the "CL" (Lean
Clay; Sandy Clay; Silty Clay of low to medium plasticity) and "MH" (silt,
fine sandy or silty soil with high plasticity) varieties with alternating
layers of sand and silt.
When the Iota Street line was constructed no apartment buildings or
residences had been constructed along the line. Over the period of study
of the line extending from 1967 to 1970, no construction has been made
along this location and there are still no connections to the line. The
sewer has been measured or checked ten times for infiltration. The infil-
tration tabulated in gallons/inch of diameter/mile/day is shown as follows:
Date Section I Section II Section III
1-19-69 425 752 1090
2-23-68 0 0 473
3-2-68 00 0
6-1-68 00 0
8-27-68 00 0
1-2-69 00 0
8-9-69 00 0
1-17-70 00 0
4-30-70 00 0
8-12-70 00 0
It may be noted from the above tabulation that readings taken on January 19
and February 23, 1968 showed evidence of infiltration. An observation
made on March 2, 1968 showed no infiltration. The line was televised
on April 2, 1968 and no leaks, cracks or breaks were observed in the sewer.
No repairs were made on the line after the completion of the construction.
Apparently heavy soils such as clays, had sealed the opening initially
causing the infiltration to the line.
Table 21 shows the settlement observations taken on the Iota Street sewer.
94
-------
Approximate Future Street Level
to
en
Sand Fill
45
2'
Natural Ground Level
I
| Sewer Trench
I
CROSS-SECTION OF IOTA STREET SITE
FIGURE 35
-------
Station 0+00 is at the downstream end of the system at Section I. All
elevations were read with an engineer's level from a bench mark in the
area. Readings from November 3, 1967, to April 22, 1968, were taken
by means of the permanent gages installed on the sewers. Shortly
after April 22, 1968, Iota Street was paved and the property adjacent
to the street filled and graded. This construction workdestroyed most
of the gages along the line. Accordingly, the readings shown for
December 20, 1969, were obtained by means of the jet device already
described.
It may be noted from Table 21 that most of the settlement took place
immediately after the construction. It is believed that a significant
part of the settlements was caused by the drawing down of the water
table in the location of the sewer during and shortly after construction
thereby increasing the effective load on the compressible clay strata
below the pipe. This drawdown is thought to be caused by construction
pumping and water transmission through the permeable beddings or dis-
turbed backfill.
The speed at which settlement takes place is proportional to the number
of drainage faces. The type of soil at both study sites is subject to
relatively fast settlements under applied load due to the very large
number of drainage faces presented to the clay by the intermingling sand
and silt layers. In order for settlement to take place, a long time is not
required; however, the period of settlement can not be precisely deter-
mined because the number and relationship of drainage faces are unknown.
On the Iota Street sewer, the drawdown was probably a result of the con-
struction, and this drawdown could have been responsible for the greatest
portion of the settlement. The remainder of this sewer's downward motion
can be attributed to the dropping of backfill on the sewer. Most of the
settlement in this sewer occurred between the construction and the first
reading date. The minimum settlement recorded is 0.22 feet and the maxi-
mum is 0.52 feet. No correlation exists between settlement and types of
beddings used on this test sewer. As no severe settlement occurred on
this line and no damage was observed during construction or the tele-
vising, the sewer appears to be in good condition. This condition is
confirmed through numerous recent observations of the line when no infil-
tration was reported.
Table 22 shows the elevation of the manholes over the period of the study.
It is interesting to note that two of the manholes were also subjected to
damage through the construction of the streets following the elevation
taken on April 22, 1968. The settlement of the manholes was very slight
ranging from 0.02 feet for MH 913 to 0.14 for MH 898.
96
-------
TABLE 21
SETTLEMENTS
IOTA STREET TEST SEWER
Settlements (Feet)
Date
Station li-3-67 12-14-67 12-21-67 1-6-68 4-22-68 12-20-69
0+00 MH879 Section I (Constructed 11-3-67)
0+13
0+26
0+33
0+41
0+53
0+76
0+78
1+01
0+98
1+18
1+43
1+45
1+72
1+90
1+94
2+16
2+19
2+29
2+40
2+51
2+72
2+80
2+99
3+20
3+21
3+45
3+51
3+65
3+80
3+93
4+07
4+13
4+27
4+32
4+54
0.03
0.12
0.14
0.14
0.00
0.17
0.15
0.13
0.04
MH898
0.14
0.17
0.17
0.17
0.01
0.17
0.19
0.17
0.10
0.14
Section II
0.29
0.31
0.29
0.22
0.27
0.22
0.32
0.39
0.25
0.12
0.14
0.15
0.15
0.01
0.16
0.18
0.17
0.11
0.15
(Constructed
0.29
0.32
0.31
0.26
0.31
0.24
0.35
0.42
0.25
0.12
0.16
0.17
0.17
0.03
0.21
0.20
0.21
0.13
0.16
12-5-67)
0.32
0.36
0.32
0.25
0.30
0.23
0.35
0.40
0.26
0.20
0.23
0.24
0.24
+0.02
0.21
0.27
0.26
0.20
0.39
0.39
0.32
0.37
0.36
0.40
0.47
0.22
0.27
0.21
0.16
0.23
0.26
0.32
0.38
0.29
0.39
0.39
0.52
0.35
0.42
0.35
0.26
0.45
0.42
0.50
0.43
0.49
97
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TABLE 21 (continued)
SETTLEMENTS
IOTA STREET TEST SEWER
Settlements (Feet)
Date
Station 11-3-67 12-14-67 12-21-67 1-6-68 4-22-68 12-20-69
4+69 MH913 Section III (Constructed 12-6-67)
4+80 0.44
4+89 0.32 0.32 0.32 0.33
5+00 0.49
5+16 0.53 0.51 0.53 0.55
5+20 0.41
5+46 0.32 0.31 0.33 0.32
5+60 0.40
5+73 0.29 0.28 0.30 0.31
5+80 0.40
6+12 0.28 0.26 0.30 0.31
6+19 0.37
6+37 0.24 0.21 0.25 0.25
6+39 0.38
6+61 0.24 0.21 0.24 0.24
6+80 0.41
7+14 MH914
Hessmer Avenue
The conditions experienced during the construction of this system were
exceptionally bad. The soil at the bottom of the trench was constantly
in a semi-liquid state and the upward movements of particles in several
locations indicated a quick condition. Side flow of water and particles
occurred during the entire construction. The sewer was constructed
adjacent to a paved street at a distance of 9 feet from the curbing. Al-
though the line was only 8 inches in diameter a trench width of 4 1/2
to 5 feet was maintained during the construction. Three soil borings were
taken along this installation. The results of the soil analyses are shown
in Appendices M, N and O. The organic top soil layer extended to a
distance of about 4 feet from the ground surface. All the soil below this
level consisted of a very soft silty clay of the "MH" type, in a fine
layered system, with sands and silts.
Because of the poor soil conditions experienced at this location, con-
struction practices were below standard. Shells and combinations of
98
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TABLE 22
MANHOLE ELEVATIONS AND SETTLEMENTS
to
CD
IOTA STREET TEST SEWER
Station Datum: As Established in Study
Elevations (feet)
Date Read
11-3-67 12-14-67 12-21-67 1-16-68 4-22-68 12-27-59
MH879 98.11 98.11 98.12 98.12 98.05 *
MH898 — 98.22 98.21 98.18 98.16 98.08
MH913 — 98.46 98.45 98.45 98.45 98.44
MH914 — 97.73 97.73 97.73 97.71 *
Total
Settlement
0.06
0.14
0.02
0.02
-------
mixed materials prepared for the beddings were dropped into the trench
and on top of the pipe after it was placed in position. During the laying
of the pipe it was the common practice to have several laborers jump on
the pipe to adjust the grade downward. Backfill was pushed onto the
bedded pipe from the ground surface creating a severe impact on the pipe.
Table 23 shows the settlement observation on Hessmer Avenue. Station
0+00 is the beginning of the system at the downstream end of the line at
Section I. These elevations were also read with an engineer's level from
a benchmark in the area. The readings from July 9, 1968, to November 16,
1968, were taken on the 23 permanent gages installed on the sewers. As
the construction of residences and apartments developed following this
period, many of the gages were destroyed or covered with automobile
driveways and parking areas. The readings shown in Table 23 for Janu-
ary 10, 1970, were all taken with the jet. It may be noted that only ten
observations could be obtained along the line because of the large paved
areas that had been provided.
TABLE 23
SETTLEMENTS
HESSMER AVENUE TEST SEWER
Station
0+00
0+07
0+09
0+29
0+49
0+51
0+76
0+83
1+00
1+06
1+27
1+62
1+98
2+20
2+60
2+82
7-9-68
Settlements (Feet)
Date
8-1-68 8-22-68 11-16-68
1-10-70
MH362 Section I (Construction 5-16 to 5-22-68)
0.19
0.26
0.23
0.38
0.18
0.18
0.01
0.38
0.44
0.44
0.56
0.52
0.40
0.20
0.34
0.41
0.38
0.47
0.45
0.35
0.51
0.58
0.62
0.8
0.9
0.9
0.9
0.8
1+95 MH363 Section II (Construction 5-23 to 6-3-68)
1.0
0.56
0.33
0.43
0.48
0.53
0.59
0.52
0.55
0.64
100
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TABLE 2 3 (continued)
SETTLEMENTS
HESSMER AVENUE TEST SEWER
Station 7-9-68
3+17
3+34
3+54
3+89
0.42
Settlements (Feet)
Date
8-1-68 8-22-68
Destroyed
Destroyed
Destroyed
0.57 0.67
11-16-68 1-10-70
4+20
4+40
4+72
4+92
5+24
5+44
5+64
5+89
5+91
5+93
6+16
6+36
6+60
6+53
6+83
0.42
0.56
.
0.50
0.50
0.49
0.51
0.39
0.32
MH365
MH364 Section III (Construction 6-4 to 6-.11-68)
1.08
0.59
0.74
0.71
0.80
0.65
0.66
0.64
0.81
0.89
0.84
1.14
1.09
0.67
0.57 .
0.46
0.98
0.76
1
0.72
1.45
1.5
1.45
1.2
A significant amount of settlement occurred within the first few months
following construction. As in the case of Iota Street, this is believed to
be due to drawing down the water table and also dropping backfill on the
top of the pipe. This latter condition may also account for some of the
damage to the pipe. The last settlement readings on the sewer showed
values as high as 1.5 feet. No correlation exists between settlement
and types of beddings used on this test sewer.
Table 24 shows the five manhole elevation readings from July 9, 1968,
to September 26, 1970. A maximum of 0.74 feet was recorded on one of
the manholes. These high values also reflect settlements due to the bad
soil conditions in the area and difficult construction conditions experi-
enced.
I
Infiltration measurements were made on the Hessmer Avenue line on four
occasions. The infiltration measured in gallons/inch of diameter/mile/
101
-------
day was as follows:
Date Section I Section II Section III
7-19-68 662 1140 584
8-7-68 31 236 650
8-27-68 0 595 177
9-14-70 - - 31,000
In the tabulation shown above it should be noted that the upper end of the
line begins at Section III with flow towards Section II and I. Sections
I and II could not be measured for infiltration because the bottoms of the
manholes were flooded with water from infiltration. A review of the
infiltration observation indicates excessively high rates. The amounts
are far in excess of the 250 gallons per inch of diameter per mile per
day that are now required in the construction specifications of Jefferson
Parish. These specifications were adopted after the line was constructed
in 1968.
In order to determine the cause of the high infiltration in this line, it was
televised on April 16 and 17, 1970. The line was found to be so badly
damaged and had so many obstructions that it was impossible to run the
camera through the entire system. Only a portion of Sections II and III
could be televised. Numerous small leaks were observed along Section
III. At station 4+77 the sewer was crushed and the shells and other debris
at the location prevented the passage of the camera. In Section II several
small leakages were observed and at Station 1+47 an obstruction consist-
ing of shell and broken pipe prevented the passage of the camera.
The high infiltration rates and damage to the Hessmer Avenue line were
probably due to the poor soil conditions experienced and the difficulties
encountered with the construction. This is evidenced by the large set-
tlement values experienced with this sewer, some as great as 1.5 feet.
The laying of the sewer was followed by construction of apartment build-
ings, concrete parking areas and automobile driveways. As noted above,
a trench width of 5 feet was used with the center line of Ithe trench 9
feet from the street curbing. During the construction of the sewer, struc-
tural cracks developed which are now present in the street are illustrated
in Figure 36. The weight of the over burden and vehicular traffic may have
contributed to the settlement and failure of this sewer.
The studies on the two test sewers indicate that settlement within the
beddings is small in comparison to the soil below. The soil settlement
is believed to be caused by the water table being lowered at the location
during and shortly after construction. The water table drawdown is
102
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o
co
TABLE 24
MANHOLE ELEVATIONS AND SETTIEMENTS
HESSMER AVENUE TEST SEWER
Station Datum: Utility Survey — M S L
Elevations (feet)
Date Read
7-9-68
MH362 16.86
MH363 16.59
MH364 16.38
MH365 16.76
8-1-68 8-22-68 11-16-68 9-26-70
16.67 16.70 16.48 16.17
16.40 16.41 16.58 16.48
16.19 16.08 15.77 15.56
16.58 16.33 16.15 16.02
Settlement From First
To Last Reading Date
0.69
0.11
0.72
0.74
-------
-,f "VWUJ'I
STRUCTURAL DAMAGE TO STREET PAVEMENT - HESSMER AVE
FIGURE 36
J04
-------
believed to be due to trench dewatering construction and water transmission
through the permeable beddings or disturbed backfill.
No correlations existed between the settlements observed in the field
tests and the laboratory studies. This was due to the difficulties experi-
enced in simulating, in the testing frame, the true conditions experienced
with the field studies. An example of this is the settlement that occurs
in the soil below the field test sewers, believed to be due to the lowering
of the water table.
105
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SECTION VI
GULF COAST AREA SANITARY SEWER SURVEY
This study was performed in the latter part of 1967 and the beginning of
1968. The survey was designed to obtain background information on
sewers in the Gulf Coast area. The survey was sent to the responsible
officials of 71 cities and sewer districts located in the Gulf Coast area.
The survey form is shown in Appendix P. Thirty-nine replies were re-
ceived for an effective return of 55%. The estimated population of the
area considered was 7,250,000. The sample reporting represented a pop-
ulation of 4,582,000 for a return of 63%. The study showed that 13,568
miles of sanitary sewers were in use in the reporting areas. Approxi-
mately 6 miles of combined sewers were reported to be in use. Table 25
gives the results of the types and lengths of sewers in use:
TABLE 25
TYPE AND LENGTHS OF SEWERS
Type of Sewer Length Percent
(miles) of Total
Clay - Factory Joint 2754 20.3
Clay - Other Joints 5989 44.1
Concrete 4479 33.0
Cement Asbestos 216 1.6
Plastic 14 0.1
Other 116 0.9
It may be noted that clay pipe is more commonly used in the area. The
factory joint has generally replaced the cement-mortar and bituminous
joints used in the older sewers.
Several communities reported that more than one type of bedding material
was used. Table 26 shows the materials used for sewer beddings and the
frequency of use.
The table indicates a preference for clam and oyster shell for sewer bed-
dings. These shells are readily available in coastal waters and in many
sections have an economic advantage over other materials. Seven com-
munities reported that no special beddings were used.
Information was requested on specification requirements for infiltration.
Of those reporting, 74% provided information on infiltration and 26% did
107
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TABLE 26
BEDDING MATERIALS AND FREQUENCY OF USE
Material Frequency of Use
Clam and Oyster Shell 16
Gravel 8
Crushed Stone 7
Sand 4
Cement Stabilized Sand 3
Board Bottom 5
Piles 5
Concrete Encasement 3
Slag 1
Sand and Shell Mixed 1
None Used or Only Seldom 7
not. Table 27 gives the results on infiltration requirements. The weighted
average according to the length of sewer was 571 gal/inch of diam/mile/
day. The weighted average according to sewage flow was 486 gal/inch of
diam/mile/day.
108
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o
CO
TABLE 27
INFILTRATION SPECIFICATIONS
No. of Political
Divisions
1
3
14
2
3
4
1
1
10
Population
15,000
1,464, 000
516,000
61, 000
787,000
1, 153, 000
71,000
42,000
473,000
Length of Sewer
(miles)
44
4,433
2,017
82
2, 166
2, 547
250
160
1, 869
Length of Sewer
(Percent)
0.3
32.7
14.8
0.6
16.0
18.8
1.8
1.2
13.8
Infiltration
Specifications
g/in/mi/dy
1500
1000
500
400
300
250
200
100
None
Total
39
4,582,000
13,568
100.0
-------
SECTION VII
SEWER CONSTRUCTION
The manner in which a sewer is constructed is the most important factor
governing its behavior throughout the duration of its use. Only with good
construction practices can an adequate design be transformed into a ser-
viceable sewer requiring a minimum of maintenance. This can only be
accomplished by the enforcement of good performance and procedural spec-
ifications .
INSPECTION
In recent years there had been a tendency to supplant on site inspection
with post construction observation and testing of sewers. The argument
for this type of control is that "performance specifications are always
superior to procedural specifications." Unfortunately this type of mea-
sure is not presently available since infiltration, settlement, and sewer
failure may manifest themselves at various time intervals after construc-
tion. IN LIGHT OF THE ABOVE IT CAN BE SEEN THAT COMPETENT AND
THOROUGH INSPECTION SHOULD FORM THE BASIS FOR ANY PROGRAM
OF CONSTRUCTION CONTROL AND SHOULD BE CONSIDERED THE FIRST
LINE OF DEFENSE IN THE EFFORT TO OBTAIN QUALITY SEWERS.
Inspectors should be skilled in the methods of construction and knowledge-
able of the specifications to which sewers are built. They should also
be well trained in the procedures of measurement and observation that
will enable them to apply sound judgment in questions of construction
procedures and quality. Salaries should be adequate to attract competent
personnel and training provided to enable them to execute their jobs
properly.
It is common practice to assign the responsibility for multiple sewer jobs
in different areas to one inspector. This makes adequate inspection dif-
ficult. Where only a small section of trench is kept open at a time, the
inspector may see only a small fraction of the sewer prior to backfilling.
This practice should be discontinued in favor of continuous inspection
throughout construction.
As a part of an inspector's duties, he should keep a detailed set of con-
struction notes in a field book. In addition normal reports should be kept
as a permanent record by the sewer authority.
By maintaining adequate inspection the cost of proper construction prac-
tices will be included in the bid price. It is much cheaper to pay for
111
-------
proper construction practices and good inspection than to assume the
burden of improper sewer performance and additional maintenance. Too
often a low bid price may be predicated on short cuts and the practice
of poor workmanship on the job.
It should be carefully noted that good inspection coupled with adequate
and accurate post construction testing provides the surest means of
obtaining quality sewer construction in the Gulf Coast area.
TRENCH WIDTH
The design trench width should be determined by consideration of the
load on the pipe and the supporting strength of the pipe.
Load on Pipe
The load on a sewer pipe is a function of trench width and the weight of
the material. The wider the trench the greater is the load. The accepted
method for determining loads on sewer pipe is with the Marston Formula. "•
Wc = Cd w B*
where:
Wc = Load on the pipe in pounds per linear foot
Cfj = A dimensionless coefficient which is a function of the
ratio of height of fill to width of trench, internal soil
friction, and friction between the trench walls and the
fill
w = The unit weight of the backfill in pounds per cubic foot
Bfj = The width of the trench at the top of the pipe in feet
It can be seen that the load on the pipe is a function of the square of the
trench width, and a small increase in trench width results in a large in-
crease in load. Accordingly, trench widths should be kept as narrow as
possible while still allowing working room.
There have been a number of tables, nomographs and curves for the
solution of the Marston Formula, the complexity of which hinges about
the determination of the coefficient. One such nomograph which was
recently developed by Mouser and Clark is presented in Figure 37 . 12
112
-------
CO
o
o.
I
0>
10 12
14
I
.c
o
c
CD
H
I
DQ
-120
-100
- 90
- 7.0
_ 5.0
- 4.0
- 3.0
2.0
1.5
L 1.0
ro
o;
X!
i 1
I
CD
o,
-i—t
cu
c
o
h-1
I
- 40,000
- 10,000
- 5,000
. 2,000
- 1,000
500
200
100
30
ro
O
CO
4.0
3.0
2.0
•S 1.6
0
-iH
O
? 1.2
o
U
T3
ro
3 0.8
U
0.6
0.4
A
^-Saturated Clay
B-Damp Clay
C-Saturated Topsoil
D-Sand and Damp Topsoil
W = load on pipe, Ib/linear ft
C = load coefficient; a function
of pipe depth, trench width,
and type of soil
w = weight of backfill, Ib/ft
B = width of trench at top of
pipe, ft
24 6 8 10 12 14
Ratio of Pipe Depth to Trench Width
LOADS ON BURIED PIPES
FIGURE 37
-------
The following example illustrates the use of this nomograph:
8 inch clay sewer
Depth to top of pipe =10 feet width of trench at top of pipes
2.5 feet
Saturated topsoil fill, 115 pounds per cubic foot
Pipe depth to trench width ratio = ~r~~r = 4.0
Z • o
Solution: Load =1700 Pounds per Linear Foot
Another method which is commonly used is found in the tables located in
the Clay Pipe Engineering Manual. ^
Supporting Strength of Pipe
The laboratory supporting strength of pipe is normally determined by the
three-edge test. 2 The field supporting strength is related to the labo-
ratory supporting strength by the load factor which is a function of the
bedding according to,
Field Supporting Strength = Load Factor x Laboratory
Supporting Strength.
The beddings discussed in this manual should be assigned a load factor
of at least 2, provided that they are compacted in lifts.
TRENCH PREPARATION
The preparation of the trench is an extremely important part of construc-
tion as it greatly affects the conditions under which the pipe is laid and
therefore the subsequent behavior of the sewer.
Dewatering
Under normal conditions a sewer should not be laid in a flooded trench
because of the inability to insure good joining and the proper formation
of the pipe bedding. The methods used for dewatering are interior trench
pumping and well pointing. Where quick or impending quick conditions
are anticipated, well pointing can be used as a method of stabilization
in addition to dewatering if the soil conditions permit this type of opera-
tion. Where quick conditions develop in conjunction with interior trench
pumping, additional pumping capacity will not alleviate but only aggra-
vate the problem.
114
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Sheeting and Bracing
Sheeting and bracing should, where necessary, provide sufficient lateral
support to prevent the collapse of the trench walls. This is its primary
purpose. It can also be used as friction piling for support of the pipe.
This requires the attachment of a trench flooring system by nailing it to
the sheeting.
Trench Flooring
When flooring is used it should be relatively even, with reasonably
straight lumber and no overlapping of planks. Uneven flooring can cause
conditions of point support.
Stumps
In many localities of the Gulf Coast area large cypress and other stumps
are encountered in sewer construction. When these are found it is occa-
sionally the procedure to cut (with axes and chainsaws) a portion of the
stump to permit passage of the sewer. An illustration of this is shown
in Figure 38. If possible this procedure should be avoided since stumps
beneath the pipe can cause conditions of uneven support.
BEDDING MATERIALS
As has been previously mentioned, the bedding material should have the
ability to provide support and load spreading as well as retard the trans-
mission of water. Materials or combinations of materials with these
properties should be specified.
Care should be taken to insure that the specified thicknesses of bedding
material both above and below the pipe are adhered to. In addition to
the thicknesses shown on the design drawings, a provision should be
added to the specifications stating that the bedding material below the
pipe should be sufficiently thick to stabilize the trench bottom.
Where timber is used below the bedding material the pipe bells should
not rest on the timber and should be unsupported as shown in Figure 39 .
Bell holes should be provided whether timber is used or not used.
LAYING OF FIFE
The laying of the pipe should be done with great care and under the close
supervision of the inspector. Cracked or broken pipe should not be used.
115
-------
Bedding
CT)
Stump
SEWER LAID THROUGH STUMP
FIGURE 38
-------
Pipe
Bedding Material
*s^-v4J—|p?
y^^
Bell Holes
Flooring or Plank if Used
UNSUPPORTED PIPE BELLS
FIGURE 39
-------
Line and Grade
The alignment or horizontal location of a new sewer usually presents very
little problem as compared to the difficulties associated with setting
grade (slope). It is advisable to bring the underlying bedding to approxi-
mate grade prior to laying each length of pipe. All adjustments in grade
should be made prior to laying each length of pipe, and should be accom-
plished by working the underlying bedding material. There should be no
blocking of the pipe with bricks, tiles, etc. to obtain grade. The prac-
tice of adjusting the grade by having laborers jump on the pipe should be
strictly prohibited.
In light of the range of settlements that can occur, careful consideration
should be given to specifying steeper grades on sanitary sewers to pre-
vent septic conditions from developing in the sewage. In the flat terrain
of the Gulf Coast area such a specification would necessitate a greater
amount of pumping and therefore greater expenditure in sewer construction.
Joining
The pipe manufacturer's construction instructions should be followed in
connecting lengths of pipe together. Care must be taken to see that the
joint is clear when the coupling is effected and that no foreign materials
such as shells or gravel get wedged in the joint. Soil and foreign ma-
terials in the joints can cause cracked or broken pipe with resulting large
leaks. In the case of compression joint bell and spigot pipe, joining
pressure should not be applied with a pry bar in a manner that would dam-
age the bell.
Sealants
It has become common practice in some localities to use sealing materials
on the outside of "O" ring and compression bead joints as a means of
meeting the infiltration specifications. This practice should be forbidden
since it provides only a procedure by which cracked or broken joints can
be made temporarily water tight.
BACKFILLING
Backfilling includes the use of select material placed alongside (sidefill)
and directly above the pipe as well as the general material with which
the remainder of the trench above che pipe is filled.
118
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Select Fill
It is recommended that the pipe always be covered and side filled with
select and compacted material. This will insure even distribution of the
backfill load to the pipe. The select material should preferably be the
same as the bedding material. This material should be compacted in at
least three lifts as shown in Figure 40. The select backfill should never
be dropped onto the pipe but should be carefully poured along the trench
wall.
General Fill
This material should have any large stumps, logs and other debris re-
moved before it is used as backfill. It should never be dropped into the
trench but should be carefully placed as shown in Figure 41.
HOUSE SEWERS
House sewers can be considered in two separate parts, municipal and
private.
Municipal Connections
A municipal connection is that part of the house connection that is made
at the time that the municipal sewer is constructed. These connections
should be made with care, and the use of monolithic fittings (Tees and
Wyes) is strongly recommended.
In light of recent findings in New Orleans concerning the interflow be-
tween storm and sanitary sewers involving house connections, the fol-
lowing recommendations are made.
1. Sanitary and storm sewers should be planned at the same
time so that grades and locations can be worked out to the benefit of
both systems.
2. Wherever storm and sanitary sewers (especially house sewers)
cross one another, sufficient cushion should be provided to insure the
integrity of both pipes. This cushion material should be of a flow retar-
dant nature.
3. Wherever house sewers cross one another the house sewer
should pass over the storm sewer if possible.
H9
-------
Lift* 3
Lift* 2
Spring Line
Lift* 1
COMPACTION OF SELECT BACKFILL
FIGURE 40
120
-------
Direction of Backfill Placement
L
Previously Placed Fill
Plan
Direction of Backfill Placement
, Previously
Placed
Fill
\
„
V
7,
Bedding Pipe —A Select Fill
Elevation
PLACING OF GENERAL BACKFILL
FIGURE 41
121
-------
4. Siphons in house sewers should be avoided.
5. Where a large number of house sewers will be in spatial
conflict with the storm drains, it may be desirable to provide one sani-
tary sewer on each side of the street.
Private Connections
A private connection is that portion of a house connection that is made by
the plumber. The most important factor concerning the private portion of
a house sewer is inspection. The work of plumbers in laying these pipes
should be properly inspected. If no municipal connection is available,
the connection should not be made by merely breaking the municipal sewer
and inserting a pipe. Any connections of this type should be made by the
sewer authority using proper fittings.
MANHOLES
Based on construction observations and a survey of 1600 manholes in the
Greater New Orleans area, the following recommendations are made.
1. The practice of raising the manhole frame by wedging several
bricks between it and the wall should be discontinued. This practice
affords ready entry of water from the surrounding soil during rainy weather
especially if the water table is near the ground surface. In raising a frame
the wall should be brought to the proper level and a mortar seal should be
placed between it and the frame.
2. Great care should be taken to insure that the point of con-
nection between the sewer and the manhole is water tight. The practice
of building a manhole over the top of a pipe and then breaking the pipe
should be avoided. Breaking the pipe inside a manhole will cause breaks
extending outward into the sewer. This breaking of the sewer can also
disturb the seal between the pipe and the manhole wall.
3. A joint should be provided in the sewer just outside of the
manhole to allow for any differential in settlement.
4. Where the sewer is supported on piles the manholes should
also be pile supported.
5. Heavy loads should be kept off of manholes until the mortar
has reached its design strength.
122
-------
6. The use of manhole covers with ventilation holes should be
avoided in areas where street flooding is common.
INFILTRATION S PECIFICATION
Specifications for infiltration have in the past twenty years found wide
use. In a survey study in the Gulf Coast area 74% of the sewer authori-
ties answering indicated that they had an infiltration specification.
Table 28 is a comparison of the infiltration specification together with
other data collected during the survey. There seems to be no relationship
between the various parameters and the value of the infiltration specifi-
cation reported. The weighted average of these infiltration specifications
according to length of sewer sampled was 571 gallons per inch of dia-
meter per mile per day, and weighted according to sewage flow was 486
gallons per inch of diameter per mile per day.
It is recommended that a specification of not more than 200 gallons per
inch of diameter per mile per day be adopted in areas with high water
tables. This value can be accomplished in conjunction with a good sys-
tem of "on the job" inspection. It is believed that much less than 200
gallons per inch of diameter per mile per day can be achieved with good
inspection and factory made joints.
SEWER ACCEPTANCE
Ideally the measure used for sewer acceptance would be one or a group
that would delineate the behavior of a sewer over its entire lifetime.
Unfortunately, no such measure exists. Instead, tests and observations
are made which are hoped will be indicative of lifetime sewer behavior.
If good inspection is available then the following inspection procedure
will provide a good review for acceptance following sewer construction.
1. Infiltration tests should be run on the entire system and se-
lected small segments. If a test is run only on the entire system, bad
conditions in any one component will not be detected because of the com-
pensating effect of the non-leaking parts of the system. The size and
number of segments should be based on the engineer's knowledge of the
system and the inspector's construction log.
2. All manholes should be inspected.
3. All lines should be lamped for straightness. Lines can be
checked for straightness by jetting as previously discussed.
123
-------
TABLE 28
INFILTRATION SPECIFICATIONS
to
IN COMPARISON WITH OTHER DATA
Inf. Spec.
g/in/mi/dy
1500
1000
500
400
300
250
200
100
None
Sampled Length
of Sewer Miles
44
4,433
2,017
82
2, 166
2, 547
250
160
1,869
13,568
Sampled
Population
15,000
1, 464, 000
516,000
61,000
787,000
1, 153,000
71,000
42,000
473,000
4, 582,000
No. of Political
Divisions
1
3
14
2
3
4
1
1
10
39
% Length of Sewer
0.3
32.7
14.8
0.6
16.0
18.8
1.8
1.2
13.8
100.0
% Populat
0.3
31.9
11.3
1.3
17.2
25.2
1.6
0.9
10.3
100.0
-------
4. Any lines not meeting the infiltration specification can be
televised and repaired based on these findings. The televising of entire
systems on a routine basis would probably be justified, in known problem
areas.
The practice of accepting sewers only on the basis of one infiltration test
at the terminus of the system should be discontinued.
SEWER CONSTRUCTION DETAILS
Figure 42 presents a typical sewer construction detail for the Gulf Coast
area.
125
-------
DO NOT CUT SHEETING BELOW
W
FLOORING
TRANSVERSE
= TRENCH WIDTH
FLOW RETARDANT
BEDDING a SELECT
FILL MATERIAL
BEDDING AND
SELECT FILL
MATERIAL
PLANKS
SPIKED
TO SILLS
CD
SPIKE TO SHEETING
FILL THIS SPACE WITH
BEDDING MATERIAL PRIOR
TO FLOORING
NOTE' IF PILE SUPPORT IS NOT DESIRED,
DO NOT SPIKE FLOOR SYSTEM.
SHEETED TRENCH */ FLOORING
BELOW WATER TABLE
BEDDING ft COVER
MINIMUM THICKNESSES
PILE
2" X 12"
SILL-6"X6"
LOCATE PILE 8
SILL EVERY 5'
NOMINAL
PIPE SIZE
6"
8"
10"
12"
15"
IB"
D
4"
6"
8"
10"
13"
16"
C
6"
8"
10"
12"
15"
18"
ALTERNATE PILE DETAIL
SCALE' NONE
SCALE' NONE
FLOW RETARDANT
BEDDING a SELECT
FILL MATERIAL
-PLANKS
SELECT/
FILL \
NOTE' SPIKE
PLANKS TO SILLS
6 X 6 SILL
I LOCATE
'EVERY 5'
NON-SHEETED TRENCH BELOW WATER TABLE
SCALE' NONE
NOTE: HAND TAMP
PLACEMENT 8
COMPACTION OF
BEDDING 8 SELECT
FILL MATERIAL
SCALE' NONE
INVERT
MANHOLE
CONNECTION
DETAIL
SCALE: NONE
SEWER DETAILS
CLAY PIPE
GULF COAST AREA
FIGURE 42
Sheet 1 of 2
-------
to
NOTE' NO PIPE BELL SHALL REST ON BEDDING
MATERIAL OR SUB-PIPE LUMBER.
BELL HOLES
-TRENCH BOTTOM OR FLOOR
BELL HOLE DETAIL
NO SCALE
DRAIN
-PLANKING
0 SANITARY [JSEWER
.^?*™^!^'^~~
^-PLANKING
SEWER-DRAIN CROSSING
NO SCALE
CLAY
CUSHION
2 MIN.
! SEWER [JHOUSE CONNECTION"
HOUSE CONNECTION-DRAIN CROSSING
NO SCALE
GENERAL NOTES
I. ALL DETAILS ABOVE WATER TABLE SAME AS THOSE BELOW
EXCEPT FOR BEDDING AND SELECT FILL MATERIAL.
2. BEDDING AND SELECT FILL ARE SAME MATERIAL.
3. BEDDING AND SELECT FILL MATERIAL ABOVE WATER
TABLE NEED NOT BE FLOW RETARDANT.
4. BEDDING AND SELECT FILL MATERIAL BELOW WATER
TABLE MUST BE FLOW RETARDANT MATERIAL.
5. TRENCH WIDTH SHOULD BE AS NARROW AS POSSIBLE AND
NOT TO EXCEED THAT WHICH WOULD PRODUCE A PIPE
SAFETY FACTOR OF LESS THAN 1.5.
6. CUT ALL SHEETING OFF AT LEAST 2 Ife" BELOW GROUND
SURFACE.
7. DO NOT PULL SHEETING.
8. SHEETING MAY BE USED IF NECESSARY FOR ANY TRENCH.
9. IF TRENCH IS OVERDUG, FILL TO GRADE WITH SELECT
FILL MATERIAL.
10. ALL PLANKING BELOW PIPE SHOULD BE AT LEAST 2"
LUMBER.
SEWER DETAILS
CLAY PIPE
PULF COAST AREA
FIGURE 42
Sheet 2 of 2
-------
GLOSSARY
1. BACKFILL: That material that is used to cover a sewer in a trench
extending from the sewer or select fill to the ground surface.
2 . BENTONITE; A clay with a high content of montmorillonite. It has
an expanding lattice structure which enables it to absorb large
amounts of water. Bentonite deposits are normally formed by
chemical alteration of volcanic ash.
3. COHESION; The capacity of a soil to resist shearing stress, ex-
clusive of functional resistance.
4. DRAWDOWN: The change in elevation of water table due to pump-
ing or other drainage.
5. FRICTION ANGLE: The angle of internal friction in a granular
material. The angle increases with density, and for loose mate-
rials is approximately equal to the angle of repose.
6. GROUND WATER INFILTRATIONS; The seepage of ground water into
an opening in a sewer.
7. HOUSE CONNECTION: That portion of a sewer extending from the
trunk sewer to the plumbing in a residence or apartment.
8. ILLICIT CONNECTION: A connection from a residence, apartment,
etc. which introduces liquid other than sewage (usually stormwater)
into the sanitary sewer.
9. INFILTRATION: Any water other than sewage entering a sanitary
sewer.
10. INFILTRATION SPECIFICATION: A condition for acceptance of a
sanitary sewer from a contractor by a sewer authority. This
specification limits the amount of infiltration acceptable in a
sewer system.
11. INFILTRATION UNITS; Those units used in reporting infiltration.
They are as follows:
a) Gallons per inch of diameter of pipe per mile of line per day.
129
-------
b) Gallons per day - The system characteristics and size must
also be given if the reporting is to be effective.
c) Gallons per mile of pipe per day - The pipe sizes and their
respective lengths must also be given for the reporting to be
effective.
d) Gallons per acre per day - The system characteristics and
size as well as scale maps must also be provided for this
reporting to be effective.
12. JOINTS (PIPE):
a) COMPRESSION: A joint made utilizing a compression bead in
the bell end and a bearing pad on the spigot. This joint is
made of resilient material.
b) FACTORY MOULDED: A joint that is manufactured and not
constructed in the field.
c) HOT POURED; A joint constructed in the field by the appli-
cation in a hot liquid state of bituminous material.
d) MORTAR; A joint constructed in the field of port land cement
mortar.
e) "O" RING: A manufactured joint that consists of one or more
rubber compression rings confined in seatings on both the bell
and spigot ends of the pipe.
13. LIQUID LIMIT: The water content in percent of dry weight at the
point where the consistency of a cohesive soil changes from the
plastic to liquid state. This parameter is based on an operation-
ally defined test.
14. MONOLITHIC FITTINGS; Clay pipe fittings (wyes and tees) that
are formed in one operation.
15. PERFORMANCE SPECIFICATION; A specification that is gauged
based on the behavior of the finished product or some behavioral
characteristic. A performance specification does not provide
directions as to how to obtain a satisfactory end product.
16. PERMEABILITY: The characteristic of a soil or granular material
130
-------
to transmit water through its interstitial spaces.
17. PIASTIC LIMIT: The water content in percent of dry weight at the
point where the consistency of a cohesive soil changes from the
solid to the plastic state. This parameter is based on an operation-
ally defined test.
18. PRIVATE CONNECTION: That portion of a house connection that is
constructed by a private plumber working for the sewer user.
19- PROCEDURAL SPECIFICATION: A specification based on providing
detailed instructions for the construction of a product.
20. SELECT FILL: A high quality material used for the backfilling directly
above and in contact with a sewer pipe.
21. SEPTIC SEWAGE: Wastewater which is in the process of anaerobic
decomposition.
22. SEWAGE - SANITARY: The wastewater from homes, apartments, etc.
which enters a sewer system through plumbing fixtures.
23. SEWAGE - STORM; Precipitation runoff which is normally carried in
drainage systems.
24. SEWER BEDDING: That material placed beneath a sewer pipe that
forms the foundation for the pipe.
25. SOIL REMOULDING: The process whereby a cohesive soil is kneaded
or worked. This process normally creates a softening in a virgin
soil which is considered as being caused by destruction of the order-
ly arrangement of the molecules and the destruction of the structure
produced during original deposition.
2 6. STORM WATER INFILTRATION: The entrance of stormwater into a
sanitary sewer.
27. SUBSIDENCE: The decrease in elevation of the ground surface or a
particular stratum of soil due to the lowering of the water table.
28. UNDERMINING - SEWER: The process whereby the material support-
ing and surrounding a sewer is removed by hydraulic forces, thus
denying support to the sewer.
29. VOID RATIO: The ratio of the volume of the voids to the volume of
the solid material in a soil mass.
131
-------
ACKNOWLEDGEMENTS
The support of the W. S. Dickey Clay Manufacturing Company for the
technical assistance and financial aid is acknowledged with sincere
thanks. Gratitude is particularly expressed to Messrs. Ernest H.
Newman, Jr. , Elmer R. Ligon, Ted Kalencki, Oliver Newton, Fred
Me Donald and Charles Locke.
Special acknowledgement is extended to Mr. Ben J. Haneyjr. of the
New Orleans Sewerage and Water Board and Mr. Walter Frey of the
Jefferson Parish Department of Sanitation for their assistance in develop-
ing a system for the field study and for their valuable technical advice
on the project.
The technical assistance of the special committee of the Louisiana
Section of the American Society of Civil Engineers is acknowledged with
great appreciation.
For the support and contribution to the project, sincere appreciation is
expressed to the following organizations:
New Orleans Sewerage and Water Board
Louisiana State Board of Health
Louisiana Materials Company
Jefferson Parish East Bank Consolidation Sewer District
R. J. L'Hoste Company
Albert Switzer Engineering Company
Dr. Ann M. Anderson's, Mrs. Nathalie Caragliano's, Mrs. Cynthia
Lindlof's and Mrs. Janet Winkler's contribution in editing and assem-
bling the report is recognized by all members associated with the
project.
Mr. Joshua L. Brener is commended for performing the initial infiltration
study in 1962 and for his guidance in the development of the project.
The support of the project by the Federal Water Quality Control Adminis-
tration of the U.S. Department of Interior is acknowledged with sincere
thanks. The assistance in particular of Mr. Francis J. Condon, Project
Engineer, Federal Water Quality Control Administration is recognized
with great appreciation.
133
-------
KEY PERSONNEL
Prof. Tohn K. Mayer - Professor of Civil Engineering, Tulane University
6823 St. Charles Avenue, New Orleans, Louisiana 70118.
Dr. Frank W. Macdonald - Professor of Civil Engineering and Chairman
of the Department of Environmental Health, School of Public Health
and Tropical Medicine, Tulane University 6823 St. Charles Avenue
New Orleans, Louisiana 70118.
Dr. Stephen E. Steimle - Assistant Professor of Civil Engineering and
Environmental Health, Tulane University 6823 St. Charles Avenue
New Orleans, Louisiana 70118.
Mr. Francis J. Condon - Project Engineer
U.S. Department of the Interior, Federal Water Quality Adminis-
tration, Washington, D.C. 20242.
135
-------
REFERENCES
1. Rawn, A.M., "What Cost Leaking Manholes ?" Water & Sewage
Works. 84, 12, 549 (Dec. 1937).
2. Sewerage and Water Board of New Orleans, Sources of Storm
Water Pollution by Sewage from Sanitary Sewers, Community
Renewal Extension Project No. La.-R-6 CR (June 1970).
3. American Society of Civil Engineers, Design and Construction
of Sanitary Sewers. Manual of Engineering Practice No. 37 (1969).
4. Federal Water Pollution Control Administration, Problems of
Combined Sewer Facilities and Overflows. WP-20-11, (Dec. 1967).
5. Pelmoter, A.L., Chief Analysis Branch, Division of Construction
Grants, Federal Water Pollution Control Administration, Personal
Correspondence, Washington, D.C. (July 24, 1968).
6. Brener, J. L., "An Infiltration Study in the New Gravity Sewers of
New Orleans (Unpublished Thesis, Tulane University, Civil
Engineering Dept.) 1963).
7. Taylor, Fundamentals of Soil Mechanics, John Wiley & Sons,
Inc., London 1948.
8. American Society for Testing Materials, "Standard Specification
for Vitrified Clay Pipe Joints Using Materials Having Resilient
Properties: C425-64 or Tentative Specification C425-66T.
9. Griffith and Keeney. "Load Bearing Characteristics of Bedding
Materials for Sewer Pipe, "Journal Water Pollution Control
Federation, Vol. 39, No. 4, April 1968, Page 571.
10. Uniform Soil Classification, Adopted to New Orleans Soils,
Soil Laboratory, U.S. Army Engineer District, New Orleans,
Corps of Engineers, May 1949.
11. Marston, A., "The Theory of External Loads in Closed Conduits
in Light of the Latest Experiments", Iowa Engr. Experiment
Station, Bull. No. 96 (1930).
12. Mouser, G., and Clark, R., Loads on Buried Pipes, Water.and
Sewage Works, Vol. 117, No. 7 (July 1970).
13. National Clay Pipe Institute, Clay Pipe Engineering Manual, 1968.
137
-------
OTHER REFERENCES
1. American Society for Testing Materials Designation C-301 (Clay
Pipe).
2. Correspondence with R.J. White, National Lead Company,
Houston, Texas, 1967.
3. Design and Construction of Sanitary and Storm Sewers, American
Society of Civil Engineers, Manual of Engineering Practice No.
37 (1967).
4. Rice, Dornblatt, and Ernst, Engineering & Financial Feasibility
Report for Sewage Treatment Facilities, Prepared for the Sewerage
and Water Board of New Orleans (1965).
5. Santry, I.W., "Infiltration in Sanitary Sewers" Journal Water
Pollution Control Federation, 36, 10, 1256 (October 1954).
6. Shipley, Ben F., Shell Concrete, Thirty-First Annual Short Course
in Highway Engineering, College Station, Texas, Page 1, 1957.
7. Standard Rate & Data Service, Inc., Skokie, 111. 1968.
8. Steimle, S. E., "An Investigation of Beddings and Infiltration,
and the Development of Improved Foundations for Sewers in the
Gulf Coast Area", (Unpublished Dissertation, Tulane University,
Civil Engineering Dept.) 1969).
139
-------
APPENDIX A
DEFLECTION AND JOINT RESISTANCE TESTS
The purpose of this study was the acquisition of information concerning
the behavior of the joint of the pipe to be used throughout this project.
Two types of tests were conducted. The first consisted of deflection
tests designed to determine the interrelationships at impending leakage,
of deflection angle, hydrostatic head and external load. The second
consisted of loading tests in which the moment resistance and flexibility
of the joint were determined.
All pipe tested was 8 inch diameter vitrified clay extra strength with a
polyurethane factory moulded joint, as manufactured by the W. S. Dickey
Clay Manufacturing Company. Each section of the pipe was 5 feet in
length. Prior to performing all the tests described in this section, the
pipes and joints were carefully inspected for defects. Only good speci-
mens conforming to applicable specifications were used.
DEFLECTION TESTS - NO LOAD
This study was made with two sealed sections of pipe submerged in water.
The pipe was subjected to a vacuum and deflected until leakage occurred
in the joint.
Materials and Methods
The test was performed in a flume in a hydraulic laboratory. Two sections
of pipe were placed in a wooden cradle which confined the pipe allowing
movement only in the horizontal plane. Figure A 1 is a diagram of the
testing equipment. The cradle, along with the pipe, was lowered into the
pit prior to starting each test. After positioning this assembly in the bot-
tom of the pit, it was secured horizontally by means of wedges bearing
on the pit walls and vertically with sufficient lead weights to overcome
floatation.
The unjointed ends of the pipes used were sealed so that they were air
and water tight. The spigot ends were covered with plywood caps, and
the seal was made using liquid rubber cement. The belled ends were
capped with 8 inch clay stoppers, and the seal was reinforced with liquid
rubber. Liquid rubber was also used at openings for wires and vacuum
tubes. This was done prior to the beginning of each series of tests.
The deflection was set in the joint using a small hydraulic ram, and was
measured by determining the distance traversed by moving a plumb line
141
-------
GO
Ohm meter
Vacuum Pump
OffiO
Vacuum Tube
^S=s=» ,_ pit Wall
,/////, X ,/////;
jA
n
Hand Operated
jc^r^* Hydra n lie Pump
if — 1 ^ 1 ,-j-f, i/Sj
'r
_^- Hydraulic Ram
I I
Pit Wall
Note: Both Ends of Pipe Sealed
Mercury
Manometer
Plastic
Cemented to
Pipe at
Joint
A - Water Sensor
PIPE JOINT TESTS ASSEMBLY FOR TESTS PERFORMED
AT TULANE UNIVERSITY
FIGURE A 1
-------
from the initial position of the joint to the final position at which leakage
occurred.
The pipe joint, in the testing position, was covered by two inches of
water. The desired differential head between the outside of the joint
and the inside of the pipe was obtained by creating a vacuum in the pipe.
This vacuum was read with a mercury manometer.
Leakage of the joint was determined by the presence of water in the pipe
as detected by a simple water sensor. When the sensor became immersed,
the reading on the ohm meter changed from that of the resistance between
the contacts in air to that of the resistance in the water which acted as
an electrolyte. The observance of this change signaled the leaking of
the joint. Pipe sections were changed after each series of variation of
hydraulic head.
The sequence of testing was as follows:
a) Polish sensor contacts.
b) Assemble pipe section in cradle.
c) Lower cradle and pipe into pit.
d) Secure cradle.
e) Set desired differential head by evacuating the pipe.
f) Deflect joint until leakage occurs.
g) Measure deflection.
Results
The results of the deflection tests under no loading are shown in Table Al.
It may be noted that the hydrostatic head which varied between 6 and 30
feet of water, had little effect on joint leakage under pipe deflection.
The range of deflection where leakage occurred was from 6.95 to 10.92
degrees. The median of the test was 9.75 degrees and the average of
9.72 indicates a good sewer joint which should allow normal pipe move-
ments experienced in construction without failure occurring.
The ASTM standard specifications for permissible joint deflection of
vitrified clay pipe using materials having resilient properties are shown
in Table A2.
The deflections in terms of inch per linear foot of pipe were computed for
the minimum, median and maximum values shown in Table A3. These values
for the 8 inch diameter and five foot linear sections used in the test are
tabulated in Table A4.
143
-------
TABLE A 1
PIPE JOINT DEFLECTION TESTS-NO LOAD
Head
Ft. of Water
10
10
10
10
10
10
10
10
6
8
12
14
16
18
22
30
Deflection Angle
Degrees
6.95
7.68
8.68
8.98
8.98
8.98
8.98
9.12
9.75
9.75
9.75
9.75
9.75
9.75
9.75
9.75
Head
Ft. of Water
6
10
14
18
24
30
14
14
4
8
18
24
30
Deflection Angle
Degrees
9.87
9.87
9.87
9.87
9.87
9.87
10.81
10.85
10.92
10.92
10.92
10.92
10.92
TABLE A 2
DEFLECTION PER FOOT OF PIPE LENGTH*
Nominal Diameter
(inch)
4 to 12 inclusive
15 to 24 inclusive
27 to 36 inclusive
Deflection per Foot
of Pipe Length
(inch)
1/2
3/8
1/4
*Standard Specifications for Vitrified Clay Pipe Joints Using
Materials Having Resilient 'Properties - ASTM: Designation:
C 425-64
144
-------
TABLE A 3
DEFLECTION ANGLE SUMMARY
Deflection per Foot
Angle of Pipe Length
(degrees) (inch)
6.95 (minimum) 1.46
9.75 (median) 2.07
10.92 (maximum) 2.32
It may be noted that the deflections obtained in the test compare very
favorably with the limits provided by the ASTM specifications. The joint
of the 8 inch pipe used in the test deflected nearly three times the ASTM
limiting amount of 1/2 inches per foot before leakage occurred. This
comparison further indicates the good resilient qualities of the joint of
the sewer used in the project.
DEFLECTION TESTS-UNDER LOADING
These tests were performed by project personnel at the research laboratory
of the W. S. Dickey Clay Products Co. at Pittsburg, Kansas. The test
consisted of applying a predetermined load to the joint and deflecting the
pipe until leakage occurs.
Materials and Methods
FigureA2 shows the method used in the test. The shear load was applied
across the joint by means of a lever system and was measured with a
dynamometer. The deflection was obtained by means of a screw jack.
Hydrostatic heads of 10 and 20 feet were used in the test. Pipe sections
were changed after each series of variation of loadings.
Results
The results of the joint deflection tests under the loadings used are shown
in TableA4 . No significant differences were noted in the joint leakage
in the 10 and 20 foot heads used in the test.
Figure A3 is a plot of the deflection angle where leakage occurred with
respect to the load applied on the joint. This curve provides a means of
determining the limiting deflection angle at the joint for applied loads.
As the depth of a sewer trench increases and the load of the backfill ma-
terial on the sewer increases, the limit of the deflection angle of the joint
decreases.
145
-------
TABLE A 4
PIPE JOINT DEFLECTION TESTS - UNDER LOADING
Head Ft.
of Water
10
10
10
10
10
10
10
10
10
10
10
10
10
10
10
10
10
10
10
10
10
10
10
10
10
10
10
10
10
10
10
10
10
Load
Lbs.
895
1289
1748
436
895
1289
1748
2208
2670
436
895
1289
1748
2208
3126
3386
2336
1024
563
3386
3649
2993
2008
433
2993
3321
2599
1925
499
2927
2993
2468
761
Def. Angle
Degrees
4.98
5.65
5.13
6.13
6.35
6.75
5.96
5.13
4.03
7.35
6.83
4.91
4.76
3.71
0
2.38
3.58
4.78
7.13
0
2.38
3.58
4.78
7.13
0
2.38
3.58
4.78
7.13
0
2.38
3.58
4.78
Head Ft.
of Water
10
10
10
10
10
10
10
10
10
10
10
10
10
10
10
10
10
10
10
10
20
20
20
20
20
20
20
20
20
20
20
20
20
Load
Lbs.
3386
3780
3714
3124
1050
3518
3714
3058
2533
827
3386
3649
3518
2861
761
3649
3518
2993
2273
761
436
895
1289
1748
2208
436
1895
1289
1748
2208
2667
3061
3520
Def. Angle
Degrees
0
2.38
3.58
4.78
7.13
0
2.38 .
3.58
4.78
7.13
0
2.38
3.58
4.78
7.13
0
2.38
3.58
4.78
7.13
6.75
6.38
5.79
4.25
3.35
8.22
7.71
6.98
6.38
6.25
5.79
5.50
5.28
146
-------
Point of
Rotation ,
End
Restraint
Attached
Movable
Supports
Load
48"
Load Width
Support Width
Applied
Load
Fixed Pipe Length.
48"
Piezometer
End Restraint
Support
Notes
1.Deflection measured in inches at point "D".
2. 6 = Deflection angle.
3.Heads of 10' & 20' were used.
4.End restraint only large enough to prevent jointpullout.
5.Pipe - 8" V.C.P. - W.S. Dickey Clay Mfg. Co.
6.Pipe selected at random.
7.Free pipe ends sealed with diaphragm plugs.
Support
Bearings
PIPE JOINT TESTS ASSEMBLY FOR TESTS PERFORMED AT
PITTSBURG,KANSAS
FIGURE A 2
-------
3500
3000
2500
2000
(0
o
1-1
(0
Q)
£
CO
1500
1000
500
Estimated
Smooth Curve
012 34567 89 10
Deflection Angle (degrees)
DEFLECTION ANGLE AT IMPENDING LEAKAGE VS. SHEAR LOAD
FIGURE A 3
148
-------
,Load
Dlal J§)
Indicator V
CG |
^ *r/\
•Y3» ^.-""77, ,,.,.,. ,,,... J,....
\
s]
••s
I/
CG^
/
1
'
\
"n
Note: The load was applied in increments and the dial indicator was
read at each increment.
CG = Center of gravity of a particular length of pipe.
Load was applied by placing lead weights in a 30 gallon drum
and filling the drum with water.
PIPE JOINT BENDING RESISTANCE
FIGURE A 4
-------
JOINT RESISTANCE TEST
The purpose of this study was to determine through deflection tests the
resistance moment of joints.
Materials and Methods
Two four foot lengths of pipe were assembled in this study. Figure A 4
shows the arrangement that was used, firior to testing all lengths of
pipe were balanced to determine their centers of gravity. Before each
test, the two lengths of pipe to be used were joined and placed across
the two fulcrums located beneath their centers of gravity. By supporting
the pipes in this manner, no moment was imparted to the joint due to the
weight or location of the pipe lengths. The joined pipes were allowed to
remain undisturbed for 24 hours before the test was run. The load was
applied directly to the pipe joints. The deflection was measured by means
of a dial indicator gage which was read for each increment of load applied.
Five series of tests were performed with the pipe sections being changed
for each run.
Results
The moment in terms of inch-pounds was determined for each load applied
in this study. Figure A5shows the moment deflection curves that were
developed from the five tests. The results showed that the joint used did
not offer much resistance to moment. The variations in the curves were
due to the difficulty experienced in applying loads of the desired amounts
to the joints, and also to differences in joining stress relaxation. Dis-
turbances occurred even though loads were applied as softly as possible.
The results of this test indicated that the joint used in this study was
flexible and when deflected does not transfer excessive loads to the bell
or spigot of vitrified clay sewers.
150
-------
300( —
2500 -
en
XI
_c
c
iH
0)
I
2000
1500-
10.00 -
500
0.4 0.8 1.2
Deflection A in (in.)
1.6
MOMENT RESISTING CAPACITY OF THE PIPE JOINTS
FIGURE A 5
151
-------
APPENDIX B
MANHOLE SURVEY
Observations of sewer construction methods and inspection of manholes
during infiltration studies indicated that manholes contribute greatly to
infiltration in sewer systems. In order to evaluate the significance of
this source of infiltration further, a manhole survey was conducted during
the summer of 1970. A total of 1600 manholes was surveyed in the metro-
politan area of the City of New Orleans. This survey included 32 different
sewer systems that were selected on the basis of age, location, depth and
type of construction. The age of the manholes varied from one year to 67
years with 21 years as the average.
The land area in the systems surveyed represented approximately 22
square miles. Manholes in the Lakewood South System which had been
studied for infiltration were included in the survey. The manholes ranged
in depth from 3 to 24 feet with 10 feet being the average depth of the 1600
inspected.
Materials and Methods
Sections included in the survey ranged from those of the original sewer
systems constructed in New Orleans in 1903 to some constructed within
the last year. As the individuals collecting the information worked alone,
the survey for safety reasons was limited to collecting data that could
be observed from the street level.
Appendix N shows the form used in the survey. One of these forms was
filled out for each manhole inspected.
Results
The results of the inspection of the 1600 manholes are shown in Table B I.
All of the manholes inspected were constructed of brick and 48 were found
to have no cement mortar inner lining or the lining had deteriorated. A
total of 402 manholes were found to have interior cracks in the walls,
around the steps, around the inlets and outlets sewer pipes, inverts or
bottom. Castings on the top of the manholes were found to be cracked
in 15 installations.
Of the 1600 manholes inspected 56 or 3.5 percent were observed to have
infiltration at the time of the inspection. A greater number would no doubt
be subject to infiltration if inspections were made during periods of rain-
falls. Figure B 1 shows photographs of typical conditions found in the
survey.
153
-------
Displaced Manhole Collar
Poor Manhole Construction of Collar and Interior Wall
PHOTOGRAPHS OF MANHOLES
FIGURE B 1
154
-------
TABLE B 1
MANHOLE SURVEY
Percent of Total
Item Number Manholes Inspected
Total Inspected 1600 100.0
Brick - Cement Linings 1552 97.0
Brick - No Linings 48 3.0
Cracks
Walls 387 24.2
Around Steps 3 0.2
Inlets and Outlets 5 0.3
Invert 1 0.1
Bottom 6 0.4
Castings 15 0.9
Infiltration Observed 56 3.5
Steps
Iron 1540 96.3
Aluminum 42 2.6
None 18 1.1
This survey indicated that manholes do contribute greatly to infiltration
in sewers. The condition is the result mainly of poor manhole design,
construction practices and maintenance. The following is a listing of
some of the major causes of the infiltration that were observed during the
inspection:
a) Settlement of manhole because of poor foundations causing
breaks in the sewer pipe.
b) Settlement of sewer adjacent to manholes.
c) Improper construction of cement mortar linings inside and out-
side the manhole.
d) Deterioration of the cement mortar linings inside and outside
the manhole.
e) Cracks developing in the foundation, side walls and castings.
f) Improper seals for the inlets and outlets of sewers at the manholes,
g) Improper construction methods when manholes are raised or
lowered.
h) Dislodging of castings from top of manhole by heavy equipment
used for land clearing, filling or leveling the ground.
155
-------
LAKE PONTCHARTRAIN
HAYNE BLVD.
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APPENDIX C (CONTD.)
MAYO ROAD SYSTEM
Sheet 2 of 2
158
-------
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APPENDIX D
LAKEWOOD SOUTH SUBDIVISION
0 100' 200' SCO' 4OO'
-------
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PONTCHAR TRAIN
HAYNE BLVD.
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APPENDIX E
WEBER AVENUE SYSTEM
Sheet 1 of 2
161
-------
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BURKE STREET SYSTEM
Sheet 1 of 2
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APPENDIX G
BERG ROAD SYSTEM
Sheet 1 of 2
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165
-------
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APPENDIX G (CONTD.)
BERG ROAD SYSTEM
Sheet 2 of 2
166
-------
APPENDIX H
MAINTENANCE RECORD AND HOUSE CONNECTIONS
System
&
Line
Numbers
Weber
2-12
11-12
2-10
Lakewood
South ,
7-9
5-6
1-2
Burke
15-4
5-22-70 Raise manhole covers
Stub in manhole Left open - repaired
Tie - ins recorded
8-27-65 5666 Evelyn Ct. Choke freed
Tie-ins recorded
12-31-64 10714 Curran Rd. House
connection repaired
5-70 Manhole covers raised
Number
of House
Connections
in 1970
5
0
2
13
7
11
17
Mayo
4-5
4-10
7-8
5-26-70 Raise manhole covers
10-9-67 Mayo Rd. Repair casting
10-9-62 15" Pipe replaced
9-19-62 Line flushed
7-21-70 "Y" replaced at 7320 Mayo Rd,
0
0
Berg
17-18
19-20
5-27-70 Mercer St. Raise House
connection repaired
12-11-62 Repaired water seeping from
line in manhole to pump station conn.
7-19-65 Marquis St. rodded
7
20
167
-------
APPENDIX I
CIAM SHELL
ANALYSIS
Percent
Dry
Material Basis
Aluminum Oxide as AlO (R 0 = Fe 0 ) 12.99
Z o It o u O
Silica, as SiO. 50.01
Iron Oxide, as Fe 0 5.13
b O
Calcium, as CaCO 21.17
O
Calcium, as CaO 0.53
Magnesium Oxide as MgO 1.79
Sulfate as S04 2.31
Chlorides, as Cl 0.44
Carbon Dioxide as CO 9.91
Lt
Loss on Ignition 600 C as organic 6.58
Loss on Ignition 1000°C 14.47
169
-------
APPENDIX J
WYOMING BENTONITE
TYPICAL PHYSICAL AND CHEMICAL PROPERTIES
X-RAY ANALYSIS
85% Montmorillonite
5% Quartz
5% Feldspars
2% Cristobalite
2% Illite
1% Calcite and Gypsum
SCREEN ANALYSIS - (Ground Material)
99.6% thru 100 mesh
91.4% thru 200 mesh
76.2% thru 325 mesh
CHEMICAL ANALYSIS
55.44%
Al 0 20.14%
£» o
Fe 0 3.67%
£* o
CaO .49%
MgO 2.49%
Na 0 2.76%
£
K20 .60%
Bound Water 5.50%
Moisture at 220 F 8.00%
Total 99.09%
MISCELLANEOUS PROPERTIES
Specific gravity of dried material 2.79
Specific gravity of natural material 2 .00
Fusion temperature 2444 F
Weight of dried bulk unpulverized 71 Ib per cu ft
Weight of pulverized material 61 Ib per cu ft
Weight of crude, crushed, undried
material 80 Ib per cu ft
Refractive index 1.557
pH of 6% water suspension 8.8
Liquid Limit 500 - 700%
171
-------
APPENDIX
BORING NC-1 IOTA STREET
r-H
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-------
APPENDIX L
BORING NC-2 IOTA STREET
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APPENDIX M
BORING ND-1 HESSMER AVENUE
1
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e § „ $£ £ § & SsS&la RECORD
<0 l< O B. »; >'-l.rH i—i -rt t, C u
COPM H coO
-------
APPENDIX N
BORING ND-2 HESSMER AVENUE
2 -a
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Drilled Through
Soft Gray Clay witt
^ Rootlets.
CO
2 10 12.5 2.53 50 Gray Clayey Silt - Sample Kept
in Plastic Bag.
3 12.5 15 39 54 25 Soft Gray Clayey Silt.
4 15 17.5 2.60 61 47 20 4°24' 61 Soft Gray Clayey Silt.
5 17.5 20 No Sample Obtained.
6 20 22.5 No Sample Obtained.
7 22.5 25 64 56 23 Soft Gray Clay - Sample Kept
in Plastic Bag.
-------
00
APPENDIX O
BORING ND-3 HESSMER AVENUE
CO
1— 1
a
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to
CO
1
2
3
4
5
6
7
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CD
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0
7.5
10
12.5
15
17.5
20
22.5
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15
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22.5
25
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211
46
78
2.73 75
68
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24
27 1°43'
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O
Drilled Through
75 Soft Gray Clay with Traces of Humus,
Gray Clayey Silt.
Gray Clayey Silt.
Gray Clay with Silt Lenses.
Soft Gray Clay with Silt Lenses -
Sample Kept in Plastic Bag.
No Sample Obtained.
46 Gray Clay with Silt Lenses.
-------
APPENDIX P
MANHOLE SURVEY FORM
I. Identification
A. Location
1. System Area
2 . Street and number
II. Characteristics and Condition
A. Depth
B. Material
1. Brick with interior finish
C. Water
2 . No flow
3. Depth
D.
Off center
Cracked or broken
E.
Major cracks
Cracks around casting
Cracks around steps
Cracks around entrances
Signs of infiltration
F.
Cracked or leakage
Needs flushing
G. Bottom (exclusive of invert)
1. Cracked or leakage
_2. Excessive debris
H. Entrances and Outlets (number)
Line manhole
Junction manhole
Drop manhole
Terminal manhole
I.
Iron
Aluminum
Bad condition
J. Remarks
183
«U.S. GOVERNMENT PRINTING OFFICE: ?97r 7.°] -
-------
1
Accession Number
w
5
2
Subjec* Field & Group
SELECTED WATER RESOURCES ABSTRACTS
INPUT TRANSACTION FORM
Organization
Tulane University, New Orleans, Louisiana
Title
Sewer Bedding and Infiltration Gulf Coast Area
10
Author(s)
Mayer, John K.
Macdonald, Frank W.
Steimle, Stephen E.
iz Project Designation
EPA Contract 80-04-68, Project 11022 DEI
21 N
22
Citation
Descriptors (Starred First)
1 Infiltration, Sewers, Manholes
25
Identifiers (Starred First)
Sewer Bedding
27
Abstract
Problems of excessive infiltration are found in the Gulf Coast Area.
Infiltration can cause problems of water pollution and economic ex-
penditures. Cost of sewage treatment and sewerage systems can be
adversely effected in both capital and operating costs by infiltration.
The primary cause of infiltration found in this study was poor con-
struction methods used by contractors and by the "tapin" practices
of plumbers in making service connections.
Abstractor
Institution
WR:I02 (REV. JULY 1969)
WRSIC
SEND. WITH COPY OF DOCUMENT, TO: WATER RESOURCES SCIENTIFIC INFORMATION CENTER
U.S. DEPARTMENT OF THE INTERIOR
WASHINGTON. D. C. 20240
* GPO: 1970-3B9-830
------- |