correlation of engineering properties of cohesive …
TRANSCRIPT
MISCELLANEOUS PAPER S-74-20
CORRELATION OF ENGINEERING PROPERTIES OF COHESIVE SOILS
BORDERING THE MISSISSIPPI RIVER FROM DONALDSONVILLE TO HEAD OF PASSES, LA.
by
R. L. Montgomery
June 1974
Sponsored by U. S. Army l:ngineer District, New Orleans
Conducted by U. S. Army l:ngineer Waterways l:xperiment Station
Soils and Pavements Laboratory
Vicksburg, Mississippi
ARMY-MRC VICKSBURG, MISS.
APPROVED FOR PUBLIC RELEASE; DISTRIBUTION UNLIMITED
FOREWORD
The study reported herein was authorized by the U. S. Army Engi
neer District, New Orleans (NOD), on 24 August 1970. The study was con
ducted for the NOD by the U. S. Army Engineer Waterways Experiment
Station (WES) during 1971. The soils data analyzed consisted of exist
ing data from the NOD files. There were no special soil samples taken
or tested for this study.
This report is essentially a thesis submitted by Mr. R. L.
Montgomery of the Engineering Studies Branch, Soil Mechanics Division,
to Mississippi State University in partial fulfillment of the require
ments for the degree of Master of Science in Civil Engineering.
Messrs. W. L. Hanks and D. E. Lillard, both of the Engineering Studies
Branch, made important contributions in preparing graphical presentations
and in preparing the report for publication, respectively. Mr. W. C.
Sherman, Jr., Research Consultant, provided valuable advice and sug
gestions. The work was performed under the general direction of ~rr. C. L.
McAnear, Chief, Soil Mechanics Division. Mr. J. P. Sale was Chief,
Soils and Pavements Laboratory.
The author wishes to express his appreciation to Messrs. H. A.
Huesmann (ret.), E. B. Kemp, R. P. Picciola, K. J. Cannon, and U. J.
Michel, Jr., of NOD for their advice and assistance in collecting the
soils data for analyses. The geological profiles presented herein were
developed from geological profiles prepared for engineering projects of
the NOD by Mr. Kemp, Chief, Geologic Section, NOD.
iii
Directors of WES during the conduct of the study and the prepara
tion and publication of this report were BG E. D. Peixotto, CE, and
COL G. H. Hilt, CE. Technical Director was Mr. F. R. Brown.
iv
\
TABLE OF CONTENTS
FOREWORD
PRINCIPAL NOTATIONS
CONVERSION FACTORS, BRITISH TO METRIC UNITS OF MEASUREMENT
SUMMARY
CHAPTER I. INTRODUCTION
1.1 Background
1.2 Purpose of Study
1.3 Scope of Report
1.4 Sources of Data
L h .l Lm·rer t'1ississippi River Valley
l. 4.2 Atchafalaya Basin
1.4.3 Field Investigations
l. 4. 4 Laboratory Investigations
ix
xi
xiii
1
1
2
3
3
3
5
6
6
CHAPTER II. RECENT DEPOSITS AND THEIR PHYSICAL CHARACTERISTICS 7
2.1 Geological History 7
2.2 Fluvial Environments
2.2.1 Natural Levee
2.2.2 Point Bar
2.2.3 Backswamp
2.3 Fluvial-Marine Environments
2.3.1 Prodelta
2.3.2 Intradelta
2.3.3 Interdistributary
v
9
9
10
10
11
12
12
13
2.4 Typical Properties of Fluvial and FluvialMarine Environments
2.4.1 General
2.4.2 Natural Water Contents
2.4.3 LiQuid Limit
2.4.4 Plasticity Index
2.4.5 LiQuidity Index
2.4.6 Dry Density
2.4.7 Specific Gravity
2.4.8 Void Ratio
2.4.9 s /P Ratio u 0
2.4.10 Consolidated-Undrained Shear Strength
2.4.11 Drained Shear Strength
CHAPTER III. ENGINEERING PROPERTIES OF SOIL AS A FUNCTION OF DEPTH
3.1 Natural Levee Deposits
3.1.1 Natural Water Contents and Atterberg Limits
3.1.2 Overburden and Preconsolidation Pressures
3.1.3 Undrained Shear Strength
3.2 Point Bar Deposits
3.2.1 Natural Water Contents and Atterberg Limits
3.2.2 Overburden and Preconsolidation Pressures
3.2.3 Undrained Shear Strength
3.3 Backswamp Deposits
3.3.1 Natural Water Contents and Atterberg Limits
3.3.2 Overburden and Preconsolidation Pressures
vi
14
14
20
23
26
29
33
36
39
42
46
49
52
52
52
54
54
54
54
56
56
57
57
59
3.3.3 Undrained Shear Strength
3.4 Prodelta Deposits
~
59
59
3.4.1 Natural Water Contents and Atterberg Limits 60
3.4.2 Overburden and Preconsolidation Pressures 60
3.4.3 Undrained Shear Strength 60
3.5 Intradelta Deposits 60
3.5.1 Natural Water Contents and Atterberg Limits 60
3.5.2 Overburden and Preconsolidation Pressures 63
3.5.3 Undrained Shear Strength 63
3.6 Interdistributary Deposits 63
3.6.1 Natural Water Contents and Atterberg Limits 63
3.6.2 Overburden and Preconsolidation Pressures 65
3.6.3 Undrained Shear Strength 65
CHAPTER IV. CORRELATION OF SOIL PROPERTIES
4.1 Statistical Method
4.2 Plasticity Index and Liquid Limit
4.3 Specific Gravity and Plasticity Index
4.4 Shear Strength Characteristics
66
67
69
71
80
4.4.1 Undrained Shear Strength and Liquidity Index 80
4.4.2 s /P Ratio and Plasticity Index 80 u 0
4.4.3 Drained Shear Strength and Plasticity Index 84
4.5 Consolidation Characteristics
4.5.1 Compression Index and Index Properties
CHAPTER V. DISCUSSION OF RESULTS
5.1 Frequency Histograms
vii
86
86
99
99
5.2 Soil Properties Versus Depth
5.2.1 Natural Water Content
5.2.2 Undrained Shear Strength
5.3 Correlations
5.3.1 Plasticity
5.3.2 Specific Gravity
5.3.3 Undrained Shear Strength
5.3.4 Drained Shear Strength
5.3.5 Consolidation Properties
CHA.PrER VI. CONCLUSIONS
LITERATURE CITED
PLATES 1-21
APPENDIX A. DEFINITION OF STATISTICAL TEill~S
viii
Page
100
100
100
101
101
101
102
103
104
105
107
Al
PRINCIPAL NOTATIONS
ALWP Average low water plane
c Unit cohesion
c' Effective unit cohesion
C Compression index c
e Void ratio
G Specific gravity of solids s
LI Liquidity index
LL Liquid limit
msl Mean sea level
pc Preconsolidation pressure
p0
Effective overburden pressure
PI Plasticity index
PL Plastic limit
Q Unconsolidated-undrained shear tests
R Consolidated-undrained shear tests
S Consolidated-drained direct shear tests
sd Drained shear strength
s Undrained shear strength u
S Degree of saturation
w Natural water content
yd Dry density
cr Standard deviation (see Appendix A)
0 Angle of internal friction
¢' Effective angle of internal friction
ix
CONVERSION FACTORS, BRITISH TO METRIC UNITS OF MEASUREMENT
British units of measurement used in this report can be converted to metric
units as follows:
Multi Ell By To Obtain
inches 2.54 centimeters
feet 0.3048 meters
miles (u.s. statute) 1.609344 kilometers
pounds per square foot 4.88243 kilograms per square meter
pounds per cubic foot 16.0185 kilograms per cubic meter
tons per square foot 9.764859 metric tons per square meter
xi
SUMMARY
The purpose of this study was to analyze available data on se-
lected cohesive deltaic plain soils and provide summaries of engineer-
ing data and correlations of engineering properties according to en-
vironments of deposition of the deltaic plain of the Mississippi River.
The Mississippi River deltaic plain is that part of southeastern Loui-
siana that borders the Mississippi River from near Donaldsonville to
Head of Passes.
The deltaic plain is a complexly interfingered mass of fluvial,
fluvial-marine, paludal, and marine deposits laid down in a variety [Ed! !'IdYl...,.,~ f
of environments directly above~ Pleistocene. This study focused 11
attention on the deltaic plain deposits that are most important from an
engineering standpoint. The deposits selected for study were the
natural levee, point bar, and backswamp deposits of fluvial environment
and the interdistributary, intradelta, and prodelta deposits of the
fluvial-marine environment. Engineering data were obtained from data
files on previous field and laboratory_investigations of these soils
for Corps of Engineers projects. The data were grouped according to en-
vironments of deposition based on the geological sections. No additional
field or laboratory investigations were undertaken for this study.
The data were collected and arranged in such a manner that it was
possible to describe the data mathematically. The best-fit curves or
lines, regression equations, and standard deviations presented for the
data were developed by use of a computer. Based on the analyses, a
xiii
number of important relations and trends appear to exist for the se-
lected Mississippi River deltaic plain fine-grained cohesive deposits.
Frequency histograms provide summaries of typical soil proper-
ties,and correlation plots show the relationships between the different
soil properties. A number of correlations were made between Atterberg
limits and data from relatively complex and more costly tests for
physical properties. Reasonable correlations were found to exist be-
tween data from Atterberg limits tests and specific gravity, uncon-
solidated-undrained shear (Q) strengths, drained shear (S) strengths,
and compression indexes (C ). Also, reasonable correlations between c
plasticity index and liquid limit were developed for each deposit.
Correlations between shear strength increase ratio (s /P ) and plastiu 0
city index proved inconclusive.
Important correlations between properties were found for soils of
similar geologic origin and depositional environment. However, suffi-
cient data were not available to establish conclusive relationships.
xiv
CAAP~RI
INTRODUCTION
1.1 Background
The Mississippi River deltaic plain is that part of southeastern
Louisiana that borders the Mississippi River from near Donaldsonville
to Head of Passes. The soils beneath the low, flat deltaic plain are
primarily cohesive. Unfortunately, these cohesive soils are relatively
soft and frequent foundation problems arise. The deltaic plain has
been intensively studied by engineers and geologists during past years.
Impetus for these studies was basically provided by industrial develop
ment along the banks of the Mississippi River and by oil companies
eager to exploit the petroleum resources in the area.
During the past few decades, the industrial and cultural develop
ment in this region has focused national attention on the economic po
tential of the river. It serves as means for cheap transportation and
provides a source for large quantities of fresh water. Extensive field
and laboratory investigations have been made to provide engineering
data on the deltaic soils so that foundation designs could be made for
industrial facilities and other structures, such as those built for
flood control. As a result of numerous foundation investigations in
the area, the Corps of Engineers has accumulated an abundance of engi
neering data on the soils of the deltaic plain. The geologic history
and sedimentary patterns of the study area have been intensively
1
1* studied in past years and fully discussed by Kolb, Kolb and Van
Lopik,2
Fisk,3 and Fisk et a1. 4
Significant advances have been made in correlating engineering
properties of some soils, but very few investigations of this nature
have been undertaken for the deltaic plain soils. There is a need for
summaries of physical properties and engineering correlations of these
soils.
1.2 Purpose of Study
The purpose of this study was to.analyze available data on se-
lected deltaic plain soils and to provide summaries of engineering data
and engineering correlations according to environments of Recent depo-
sition of the deltaic plain of the Mississippi River. Correlations of
engineering properties were made which will be useful for design, par-
ticularly for planning and preliminary design, of engineering projects.
Considerable geological data are available in various reports classify-
ing and describing the major environments of deposition of the Missis-
sippi River Deltaic plain. In this study, summaries and correlations
of data are presented to improve understanding of the nature and engi-
neering properties of deltaic plain soils. Correlations between soil
properties can frequently be helpful to the engineering designer.
* Raised numbers refer to similarly numbered items in LITERATURE CITED at the end of text.
2
1.3 Scope of Report
The Recent Mississippi River deltaic plain is a complexly inter
fingered mass of fluvial, fluvial-marine, paludal, and marine deposits
laid down in a variety of environments directly above the Pleistocene.
The scope of this study is to focus attention on those deltaic plain
deposits that are most important from an engineering standpoint. The
deposits selected for study were the fluvial (natural levee, point
bar, and backswamp) and fluvial-marine (interdistributary, intradelta,
and prodelta) deposits. The backswamp clays in the Atchafalaya Basin
are also included in this study.
Engineering data on the fluvial and fluvial-marine deposits were
obtained from data files on previous field and laboratory investiga
tions of these soils. No additional field or laboratory investigations
were undertaken for this study. Geological profiles are presented for
numerous sites along the Mississippi River mapping the distribution of
soil deposits. The soils data are grouped according to environments of
deposition based on the geological profiles. Summaries and correla
tions of engineering data are presented for each cohesive geological
deposit.
1.4 Sources of Data
1.4.1 Lower Mississip·pi River Valley
Study areas for this study were selected from sites of engineer
ing investigations and construction along and adjacent to the Missis
sippi River between Donaldsonville and Head of Passes, La. Study
3
areas were selected based on the nature and availability of soils and
geological data. The locations of study areas are shown in plate 1 and
geological soil profiles are shown in plates 2 through 21. The soils
data were grouped into environments of deposition based on these geo-
logical profiles.
Generally, the study areas between Donaldsonville and New Orleans,
La., are sites of Mississippi River revetment construction or sites of
investigations for proposed revetment construction. The study areas
below New Orleans consisted of proposed or existing revetment construe-
tion sites and areas of proposed grade increases for the main line
Mississippi River levees which were planned to provide additional hurri-
cane protection for the low-lying areas of the deltaic plain. A con-
tinuous geological profile for the east bank between Mississippi River
miles 66.2 and 10.1* is shown in plates 19 through 21. A continuous
geological profile for the west bank between Mississippi River miles
66.2 and 10.8 is also shown in plates 19 through 21.
The extensive levee and revetment construction along the Missis-
sippi River has resulted in numerous field and laboratory investiga-
tions. These investigations have enabled geologists to develop the
geology of the deltaic plain adjacent to the river more completely in
recent years. Selected data from field and laboratory investigations
and geologic soil profiles were obtained from the New Orleans District,
NOD, for this study. The geologic profiles presented in this report
were developed from geological studies by Mr. E. B. Kemp of NOD. The
* A table of factors for converting British units of measurement to metric units is presented on page xi.
4
soils data presented herein were obtained from the files of the NOD and
classified into individual environments of deposition based on the ref-
erenced geologic profiles.
1.4.2 Atchafalaya Basin
The Atchafalaya Basin backswamp deposits are an alluvial valley
feature; however, they developed in the deltaic plain. Because they
developed in the deltaic plain and they are a significant foundation
feature in this area, analyses of these backswamp deposits are con-
sidered within the scope of this study.
In recent years, increased construction in the Atchafalaya Basin
has resulted in the accumulation of large amounts of soils data on the
backswamp deposits. The NOD has been involved in an extensive levee
construction program in this area. The backswamp deposits, however,
are relatively soft and generally undesirable as a foundation material.
Consequently, settlement and stability problems have been associated
with levee construction in areas of these backswamp deposits. To gain
a better understanding of the settlement and stability problems in-
valved in levee construction on the soft Atchafalaya Basin soils, the
NOD constructed three test sections in typical locations to conduct
field studies. 5 The data analyzed and reported herein were obtained
from field and laboratory investigations made in connection with these
field studies. The general location of the study areas is shown in
plate 1.
Identification of the thick backswamp deposits overlying a
thicker substratum of sands and gravels was made by Fisk, Wilbert and
Kolb. 6 The entire top stratum in this area is backswamp deposits.
5
Therefore, the presentation of geologic profiles to identify the
backswamp deposits is not considered necessary.
1.4.3 Field Investigations
All data analyzed in this report are derived from tests on undis
turbed samples. Continuous undisturbed samples were taken with thin
wall, 5-in.-diam, steel-tube piston-type samplers. All borings were
made by the NOD. Soil borings are located in plates 2 through 21.
1.4.4 Laboratory Investigations
Laboratory tests were performed by NOD and the Waterways Experi
ment Station, WES. All triaxial shear data with the exception o~ the
unconsolidated-undrained (Q) shear data were obtained by WES. WES and
NOD laboratories performed the Q-tests and all other testing for data
presented in this study. No attempt was made to make separate analy
ses for the data tested by each laboratory.
In general, only those study areas were selected for which suf
ficient data were available to define soils and geological characteris
tics adequately. The studies and correlations in this report are based
primarily on data from clayey soils; however, no sharp line of distinc
tion between clayey and silty soils was employed in selection of data
for this purpose. In general, data from silty soils were included in
the correlations and studies wherever it appeared that the value of the
correlations or other relations would be enhanced by inclusion of such
data.
6
CHAPrER II
RECENT DEPOSITS AND THEIR PHYSICAL CHARACTERISTICS
2.1 Geological History
The scope of this study does not permit an intensive discussion
on the geological history of the study areas. It is recommended that
the reader refer to the geological studies by Kolb, 1 Kolb and Van
Lopik,2 Fisk,3 Fisk, Wilbert, and Kolb, 6 and others for detailed
presentations of the geological developments of the study areas. How-
ever, a brief abstract is presented to provide the reader with limited
information on the geological history which is necessary to set forth
the basic geological developments in the study areas. Discussions of
geological history presented herein are based on the previously refer-
enced geologic studies.
The Recent deltaic plain deposits are land surfaces built seaward
by past deltas and the present delta of the Mississippi River. Each
time the deltas extended seaward, the river abandoned its course in
favor of a shorter route to the Gulf. During the past 5000 years,2
seven major deltas were formed that reflect significant changes in the
course of the river and are discernible in coastal Louisiana. The re-
sult of these shifts on centers of deposition of the great quantities
of sediments from the river has been to distribute deltaic sediments in
a 200-mile arc2
in southeast Louisiana.
Delineation of soil conditions in the deltaic plain has gradually
progressed from correlation between relatively few soil borings to pro-
gressively more valid interpretations made by geologists based on
7
analyses of numerous soil borings and soils data. In the 1940's Fisk3
developed the general history of the Mississippi River alluvial valley
and developed comprehensive classifications for the environments of
deposition characterizing the middle and upper portions of the valley.
The lower portion of the valley was investigated only to the extent
necessary to establish that in southeast Louisiana the Pleistocene,
an ancient horizon with relatively high shear strength characteristics,
underlies normally-softer Recent sediments. These Recent sediments
were collectively classed as deltaic plain soils.
It was not until the 1950's that advances were made in recognizing
and delineating some of the environments that make up the deltaic plain
sediments. Kolb and Van Lopik2
studied the deltaic plain sediments and
described and classified the deltaic plain environments from the stand-
point of their associated engineering soil types. The environments of
Recent deposition of the deltaic plain are classified into broad cate-
gories of fluvial, fluvial-marine, marine, and paludal environments.
These are further divided into individual environments of deposition.
This report deals with deltaic plain soil properties separated into
their individual environments of deposition. As Terzaghi and Peck8
point out,
Two clays with identical grain-size curves can be extremely different in every other respect. Because of these conditions, well-defined statistical relations between grain-size characteristics and significant soil properties such as the angle of internal friction have been encountered only within relatively small regions where all the soils of the category, such as all the clays or all the sands, have a similar geological origin.
8
2.2 Fluvial Environments
The fluvial sediments are deposited mainly in the inland areas
within and along streams and in fresh to brackish waters. 2 They are
restricted to relatively narrow bands associated with active streams.
Sediments deposited in these areas are further divided into natural
levee, point bar, and backswamp deposits. The fluvial environments of
deposition associated with the final stages in stream history are fur
ther divided into abandoned courses and abandoned distributaries but
data were inadequate to present meaningful analyses of these deposits
in this study. The depositional characteristics of natural levee,
point bar, and backswamp deposits are discussed in the following paragraphs.
2.2.1 Natural Levee
The slightly elevated ridges that occur on both sides of the Mis
sissippi River have been identified as natural levee deposits by geol
ogists. These deposits were formed by near-channel deposition of sus
pended sediments carried by floodwaters that overflowed the riverbanks.
The coarsest of the sediments were deposited near the banks and the
finer grain soils were deposited further landward of the banks. There
fore, the grain sizes decrease in the landward direction away from the
river. The grain sizes of the natural levee deposit also decrease in a
downstream direction.
The height, thickness, and width of the deposit decrease signifi
cantly between Donaldsonville and the Head of Passes. 1 The width
varies between 4 and 2-1/2 miles between Donaldsonville and New Orleans
and becomes significantly narrower south of New Orleans. The growing
9
process of the natural levees has been altered or stopped by the con
struction of artificial levees along the river. These artificial levees
protect the natural levees from overbank flow during high-water periods,
thereby eliminating the source of building materials for the natural
levees. The vertical heights of the natural levee have been decreasing
because of the process of normal consolidation under its own weight and
consolidation caused by the applied weight of the artificial levees.
The vertical height of the natural levee decreases from about 20 ft
near Donaldsonville to about mean sea level at the Head of Passes.
2.2.2 Point Bar
Point bar deposits are the direct result of lateral migration of
the river. During the migration process, erosion occurs from bank
scouring, and the coarser materials are redeposited immediately down
stream at the convex sides of river bends. The river velocities are
considerably less in these areas, and the coarser sediments are readily
deposited and form point bar deposits. The rate of lateral migration
is much more rapid in the deltaic plain in the vicinity of Donaldson
ville than it is downstream. Downstream of Donaldsonville, the river
is attempting to scour Recent or Pleistocene clayey materials, which
effectively resist erosion. Point bar deposits in the lower reaches of
the river are much less extensive.
2.2.3 Backswamp
Backswamp deposits are formed by deposition of sediment in shal
low ponded areas during periods of overbank flow. They consist primar
ily of thinly laminated fat clays and silts, which sometimes have a
high organic content. Overbank flows trapped between high natural
10
levee ridges and other outer boundaries, such as the valley wall, gen
erally result in thick accumulations of sediment. The coarser material
from overbank flow settles quickly near the stream, while the finer ma
terial settles slowly in low-lying areas as the ponded water gradually
drains, evaporates, or seeps into the ground.
Geologists have stated that use of the term (backswamp) is
inappropriate for soils downstream of College Point, La. Basically,
backswamp deposits are formed from the alluvial valley soils and not
the deltaic plain soils. However, the Atchafalaya Basin backswamp
deposits formed between two meander belts that bordered an elongated
freshwater basin situated in the deltaic plain. Thus, it is an allu
vial valley feature, though it developed in the deltaic plain.9
Krinitzsky and Smith10
studied the geology of the backswamp de
posits in the Atchafalaya Basin and proposed that, based on deposition
and other features, the deposits could be subdivided into correlatable
horizons of lake, well-drained swamp, and poorly drained swamp. These
correlation horizons were identified through the use of radiography.
Radiography also brought out details of fracturing and plastic deforma
tion, including voids and desiccated layers. The backswamp deposits
are believed to have been developed continuously over the past 15,000
years in an environment of shallow lakes and low-lying swamps.10
2.3 Fluvial-Marine Environments
Fluvial-marine deposits are laid down off the mouths of deltas
in fresh to brackish waters.2
Although the fluvial-marine deposition
results in a complexly interstratified deposit, geologists have
ll
subdivided the fluvial-marine deposits into three main environments of
depositions: prodelta, intradelta, and interdistributary. Geologists
estimate that the fluvial-marine environments make up about 75 percent
of the Recent deposit of the deltaic plain. These soils are a signifi
cant foundation material along the Mississippi River from New Orleans
to the Head of Passes. A good understanding of the geology and engi
neering properties of fluvial-marine deposits is required before engi
neers can design foundations on these soils with confidence. The depo
sition characteristics of the three environments are described below.
2.3.1 Prodelta
The fine-grained deposition swept seaward by the Mississippi
River preceding each deltaic advance is the prodelta deposits.2
They
are deposited underwater at the mouth of the river and redistributed by
tidal currents. The clays are deposited some distance from the mouth
and the silty clays are deposited nearer the mouth. These deposits are
the first sediments introduced into a depositional area by an advancing
delta. Each ancient delta that contributes to the makeup of the del
taic plain was preceded by a wave of prodelta deposits resulting in a
widespread areal extent of prodelta deposits in the subsurface. Mud
flats and mud lumps are two phenomena in the deltaic plain that are as
sociated directly with the prodelta deposits. The scope of this study,
however, does not permit inclusion of these interesting phenomena.
2.3.2 Intradelta
The continuous seaward advance of the delta results in the depo
sition of bars of coarser materials over the prodelta deposits. These
intradelta deposits form near the mouths of the distributaries when the
12
current velocity becomes significantly less as the river water joins
the Gulf water. The coarser sediments fall from suspension and form
distributary mouth bars.11
Sediments continue to build seaward on the
bar crest. Some sediments, however, are distributed as submerged fans
on the seaward sides of the bars. As the distributary builds seaward,
the bars may be scoured through and a new seaward bar deposited. At
times, the channel may split around the bar, resulting in the formation
of additional distributary mouth bars. As a result of this bifurcation
of the stream channel and the resultant formation of additional bars
laterally away from the original bar, widespread wedges of silty sand
and sand called "sand sheets"12 are formed over the deltaic plain.
Kolb and Van Lopik2
found that in most instances, the position of the
intradelta deposits in the subsurface is marked on the surface by
fairly well-defined abandoned distributaries.
2.3.3 InterdistributarJC
Interdistributary deposits occur in areas between the past and
present channels of the Mississippi River. Where sediment-laden waters
flow over the subaqueous or low natural levees, the coarsest material
is deposited near the distributaries as part of the intradelta se
quence. The finer materials are carried in suspension into the basins
between distributaries and settle out. Deposition of interdistributary
deposits is very similar to that of the backswamp deposits of the flu
vial environment. Fine materials may also be supplied into the inter
distributary basins by overflow from the main channels upstream and
from materials originally discharged at the mouths of the distribu
taries and gradually worked inland by tidal action.
13
2.4 Typical Properties of Fluvial and Fluvial-Marine Environments
2.4.1 General
A considerable amount of field and laboratory data was reduced
and separated so that typical properties of each depositional environ-
ment could be established. The major portion of the data represents
saturated soils because the groundwater table is located near the ground
surface at all of the study sites. However, the natural levee deposits
probably occur more in a partially saturated state than fully saturated.
The study sites, with the exception of the sites in the Atchafa-
laya Basin, are located along the banks of the Mississippi River. The
groundwater tables established in the geological profiles shown in
plates 2 through 21 correspond to the average low water plane (ALWP) of
the river at each study site. There was sufficient data for the study
sites in the Atchafalaya Basin to establish a groundwater table quite
near the ground surface.
Preconsolidation pressures (pc) were compared to existing effec
tive overburden pressures (p ), which were based on the groundwater at 0
ALWP, to determine the state of consolidation of the soils. The p c
values were computed from laboratory consolidation tests using the pro-
8 cedure proposed by Casagrande. Values of pc were plotted versus p0
for each of the deposits, and the results are shown in fig. 2-1. The
following criteria were used to define the degree of consolidation:
Normally consolidated Overconsolidated Underconsolidated
14
0.67 to 1.5 >1.5 <0.67
I-' Vl
0 1.0 2.0 3.0 4.0 4.0,, I I I I I I
3.0 1-----t---+----t------1
2.0 1-.... a rn ..... 1- 1.0
~ "'~ a: ::;) rn rn 0 "' a: a.. z "' 0 ~ 4.0 Ill a: "' 15 "' > 3.0 t= u "' .... .... "'
2.0
r.o I / - 'P' /' I I I
1.0 2.0 3.0 4.0
PRECONSOLIOATION PRESSURE, Pc, T/SQ FT 0 1.0 2.0 3.0 4.0
0 I .0 2.0 3.0 4.0 PRECONSOLIOATION PRESSURE1 Pel T/SQ FT
0 1.0 2.0 3.0 4.0
,, I I I 14 "0
1------+----+----1----13.0
2.0 1-.... a rn .....
1.0 1-,J "'~ a: ::;) rn
0 Cl)
"' a: a.. z "' 0
4.0 ~ Ill a: "' 15 "' 3.0 > t= u "' .... .... "'
2.0
r---+-r--7~~r---_, ___ -41.0
~----~--~~--~~--~0 ~0 0 2.0 3.0 1.0
Fig. 2-1. Effective overburden versus preconsolidation pressures
The major portion of the data points falls within the range of ap-
proximately normally consolidated soils. However, the natural levee
and backswamp deposits have an appreciable number of ratios in the
range of overconsolidated soils. Preconsolidation data on the natural
levee deposits were insufficient to establish the depth of overconsoli-
dated soils. Sufficient data were available to define the overconsoli-
dated soils of the backswamp deposits. The deposits also experience
cycles of wetting and drying as the groundwater table fluctuates. The
process of desiccation can result in consolidation, the same as if an
external load were applied, and overconsolidation can occur after re
peated cycles of wetting and drying. 8 Accordingly, the natural levee
clays and the backswamp clays, within the range of groundwater fluctua-
tions, were considered to be slightly overconsolidated resulting from
the process of desiccation.
Based on the data shown in fig. 2-l, the point bar, interdistrib
utary, intradelta, and prodelta deposits appear to be approximately
normally consolidated. The data also indicate that some of the back-
swamp soils have not fully consolidated under the existing overburden
load. These soils are considered to be slightly underconsolidated but
still in the process of consolidating. The data for the underconsoli-
dated soils were not sufficient to permit adequate analyses.
Organic materials were found in various amounts in all the de-
posits. The backswamp deposits, however, contained considerably more
organic materials than the other deposits. Abundant quantities of peat
and organic clays containing partially decayed vegetation were present
in the backswamp deposits. Since there was sufficient information
16
available for such identification, the data from backswamp deposits
were classified and analyzed as either organic or inorganic deposits.
The organic backswamp soils were identified on the basis of visual in-
spection and plots of plasticity index versus liquid limit. Organic
backswamp deposits were included in this study because there is a need
for a better understanding of these soils. Peat deposits were not
considered within the scope of this study. Organic materials were
found in the other deposits, but not in sufficient quantities to war-
rant division of the data into organic and inorganic groups.
Statistical analyses* were performed on data from selected envi-
ronments of deposition within the Mississippi River deltaic plain to
determine average properties. Typical properties are summarized in
table 2-1. Frequency histograms were used as the basis for selection
of the typical properties presented herein. Frequency histograms are
a meaningful way to present the variation in soil properties so that
the researcher (as well as the reader) can draw reasonable conclusions
concerning certain typical properties of a given deposit. All of the
data plotted as histograms did not form the normal histogram distribu-
tion, which is a bell-shaped curve with 63.3 percent of the data (i.e.,
68.3 percent of the area under the normal curve) contained within plus
or minus one standard deviation of the average. Some of the data
showed very erratic distributions when plotted as histograms.
* Statistical terms and procedures used in this report are briefly defined in Appendix A. References 13-16 are cited as sources of complete definitions and thorough explanations of the statistical procedures used in this study.
17
-~ "' M
"" " ·:;; +' M
"' "' '"' "' > ·.-<
"' ·.-<
"' I-' j·~ co ·.-<
" " "'" :>:
Table 2-1
!lEical ProEerties of Selected Environments of DeEosition
Within the MississiEEi River Deltaic Plain
Natural Water Liquid
Content Limit DeEosit Grain Size and Or11anic Content ____:L_ _L_
Natural levee W###P".1.1====vid 18-83 29-129 (45) (66)
Point bar t0%l u 26-79 31-87 M (silty} (44) (54)
"' ., ~ Back swamp Insufficient data 42-367 58-397 r;! (organic} (127) (152)
Backswamp 31-98 27-148 Wffbo/&'/&WA=IJ (inorganic) (59) (83)
Prodelta W#$#$$#A=n 31-70 39-100 (53) (79)
"' " "'" '"' "' Intradelta W& t/Xt'::Y:] 24-132 25-212 ~ (58) (77) ';;! ·.-<
~ I Inter- W#####h§%·1 24-113 38-179 rz.. distributary (57) (82)
LEGEND
~ Clay (0.005 mm)
k'-'\(\/1 Sand (2.0-0.05 mm)
~ Silt (0.05-0.005 mm)
- Organic material
Void Shear Stren~h Plasticity Dry Ratio g., R +-Index Liquidity Density Specific c c
% Index ~ Gravity e
0 sufo Ratio T/sq ft T/sq ft ~~
2-90 0.14-1.18 50-92 2.62-2.74 0.82-6.16 -- 0.08-0.68 0.01-0.50 8-22 16-31 (42) (0.54) (76) (2.69) (1.46) (0.20) (13) (24)
7-63 0.22-1.6o 54-98 2.65-2.77 0. 70-2.12 0.14-0.37 0.11-1.24 0.01-0.50 8-22 16-31 (33) (0.74) (78) (2.69) (1.12) (0.27) (0.20) (13) (24)
43-218 0.16-1.41 16-73 2.10-2.74 1. 36-6.73 -- 0.03-0.27 o.oo-o.4o 7-20 13-35 (106) (0.70} (43) (2.46) (3.11) (0.14) (13) (22)
19-86 0.03-1.26 48-91 2. 52-2.75 0.85-2.57 0.07-0.76 0.1-0. 72 0.00-0.50 4-27 13-36 (56) (0.55) (65) (2.68) (1.62) (0.26) (0.13) (12) (21)
16-72 0.12-1.08 49-90 2.67-2.80 0.84-2.06 0.11-0.39 0.18-0.85 0.01-0.50 8-22 16-31 (51) (0.51) (72) (2.72) (1.32) (0.22) (0.20) (13) (24)
5-164 0.39-1.52 33-98 2.57-2.76 0.64-2.84 0.07-0.65 0.05-0.4 0.01-0.50 8-22 16-31 (52) (0.69) (67) (2.70) (1. 57) (0.29) (0.20) (13) (24)
19-162 0.13-1.03 45-94 1.59-2.74 1.01-2.59 0.22-0.85 0.12-0.5 0.01-0.50 8-22 16-31 (59) (0.61) (66) (2.64) (1.58) (0.37) (0.20) (13) (24)
Notes: (l) Numbers in parentheses are average values.
(2) Insufficient consolidated-Wldrained and drained shear strength data were available for the natural levee, point bar, prodelta, intradelta, and interdistributary deposits. The data shown represent all five deposits.
(3) Insufficient data >rere available to clearly establish the amo\Ult of organic matter typically occurring in each deposit.
(4) Shear strengths are given in cohesion (c), tons per square foot and angle of internal friction (¢) in degrees. Q. denotes unconsolidated-Wldrained triaxial compression tests. R denotes consolidated-undrained triaxial compression tests. S denotes consoJidated drained direct shear tests.
(5) n.rain-size characteristics based on references 2 and 10.
Frequency curves have certain characteristic shapes. Some of
these shapes are described as normal curve, skewed to the right, skewed
to the left, J-shaped, reverse J-shaped, U-shaped, bimodal, and multi
modal. The degree of peakedness of a distribution is called kurtosis
and can be described as leptokurtic, platykurtic, or mesokurtic. Def
inition of the above histogram descriptive terms are presented in
Appendix A. These descriptive terms are used in the following para
graphs to provide standard means for discussing the histograms.
Computation and plotting of the frequency histograms were accom
plished by computer. In some areas, the values selected for typical
properties represent a minimum amount of data. Nevertheless, the values
presented in table 2-l are considered to be reasonably indicative of
the typical properties of each soil deposit and are good empirical
data. These data, supplemented by other data presented herein, are
considered pertinent to a better understanding of the soils of fluvial
and fluvial-marine environments.
19
2.4.2 Natural Water Contents
Frequency distributions of natural water contents for selected
deltaic deposits are shown in figs. 2-2 and 2-3. A summary of natural
water content investigations is given in table 2-2.
40
•o
40
•o
20
10
NATURAL LEVEE
WATEft CONTENT IN PEII:Cf.NT
NO. TESTS 109 AVERAGE 44· 7:! 510. DEY. 11.93
f'U(:[tH Of TOTAL Sf!nPLE9 WIIH PI:E3PECJ TO ONE UP• OEV. f1
BACK SWAMP (ORGANIC)
IIELOW WI THIN ABOVE 5.50 77.08 11-U
~---AVERAGE
I . ·-- CT __ --l.-- __ 0:
I I I
NO. T£5T9 142 AVERAGE 127.U 3JQ, O£V, 71.12
f'UCCNT Dr JOYAL SAMPLES NfTH RE9PECJ TO ONE UP. QEV. Q lfLON WI THIN AllOY£
4.95 71.46 17-81
50~ [ POINT BAR
<0
•o
40
•o
10
WATER CONTENT IN PERCENT
NQ. T£515 88 AVERAGE t9.51 sro. oev. I0-69
PERCENT OF TOTAL 3At1PLE9 WITH RESPECT TO ONE STD. OEV. 0 BELOiol WITHIN A!!DVE:
ll-36 72-" 15.91
t--AVERAGE
o:._ .. L_o:_-----1 I I
I I I
0o 10.00 20.00 WATER CONTENT IN PEII:CENT
HQ. TESTS 200 AVERAGE. 59. 05 9JQ, OfV, 14.25
Pf!IC[!fl Of ID!Ab Sf!MPL£9 WITH @E:IrECJ TO ONE Sip. OEV. Q BELOW WITHIN ABOVE
('1.50 '"·SO 15.00
Fig. 2-2. Natural water content frequency histograms for natural levee, point bar, and backswamp deposits
20
<O
~ 20
10
00
<O
90
PRODELTA
10-00 20-00 WATER CONTENT IN P'fltCENT
NO. TESTS 190 AYEII:AGt. 52. 91 STD. DEY. 'L~9
ao.oo ao.oo too.oo
PEIIIC!MI pr lOIBL !AMeLU WITH f!E!PfCJ TO ONE UP. OC:y. q II!. LOW N I THIN A60Yf u. H 75.\S 12.11
INTERDISTRIBUTARY
WATER CONTENT IN PERC!:NT
NQ. TESTS 8! AYEIIACE 56. 65 STD. Qf'V. 17.69
,.C"trCfNT 0' IQTSL 3MrtU h'/TH Rf5r'EC[ TQ Q!tf !HO. plY. 0 II!.LOM WI THIN RBOVf
15-25 72-29 14.46
•o
90
INTRAOELTA
t.IATER CONTENT IN PERCENT
1\10. TE~HS 1;7 AVERAGE 58.30 sro. oEv. t9-24
f'EfiCENI OF TOTAl SR"P!,ES WITH RE3PECf TO ONE STD. DEY. Q BELOW WITHIN RBOYE
\3.56 71.\9 15.25
Fig. 2-3. Natural water content frequency histograms for prodelta, intradelta, and interdistributary deposits
21
TABLE 2-2
SUMMARY OF NATURAL WATER CONTENT FREQUENCY HISTffiRAMS
Number % Within of Range Average Standard Standard Histogram
Deposit Figure Tests _L_ % Deviation Deviation Description
Natural Levee 2-2 109 18 - 83 45 11.9 77.1 Positive Skewness
Point Bar 2-2 88 26 - 79 44 10.9 72.7 Positive Skewness
Back swamp (Organic) 2-2 142 42 - 367 127 71.1 77.5 Positive Skewness
Back swamp (Inorganic ) 2-2 . 200 31 - 98 59 14.3 63.5 Bimodal
Prodelta 2-3 190 31 - 70 53 7.4 73.0 Negative Skewness
Intradelta 2-3 177 24 - 132 58 19.2 71.0 Positive Skewness
Interdistributary 2-3 83 24 - 113 57 17.7 72.3 Normal
2.4.3. Liquid Limit
In figs. 2-4 and 2-5 liquid limit frequency distributions are
presented for selected deltaic deposits. A summary of this investiga-
tion is presented in table 2-3.
••
NATURAL LEIIEE
MQ, TUU 101 AYU:Aiif. 015.10 STD. DE'f. 20.'74
PC:p:C!MT Of TOTAL SA!trL(,! IIIlTH ru:;!Jpt:CT TO ONE .!liD· OCY. q
BACK SWAMP (ORGANIC)
BELOW WlfHIN AIIOYf 17.81 II.St IS.U
LIQUID LII'IIT
NO. TEST3 14S AVfJIA~ 152.!0 ~no. on. 15-19
PCBH!H Of IQIAL SAnrLU WITH l!C!fECJ IQ QNt !JD. DB. q llr:LOW WITHiN AllOY[ 1.n ·u.u te.te
••
••
"
••
POINT BAR
HQ, f[ST5 78 AVERAGl 54-21 SJQ, DEY. 15.88
Pf!!CfNI Ofa~~~~L SAMrLE!I w!ITHi5"!!CJ ro QNE '!iOv~Ev. a
BACK SWAMP (INORGANIC)
ts.31s as.se tB.2S
NO. TESTS 200 AV[l!AGf. 82.711 5JQ. Q[V. Ul.l9
P!l!ClNT Of TOTAL SA!ti"LU H!IH !!UrlCJ JO QNf 2JO. OfV. 0 II[LOW WITHIN AIOV[
15-00 7!1.00 12.00
Fig. 2-4. Liquid limit frequency histograms for natural levee, point bar, and backswamp deposits
23
··~~ PRODELTA
••
INTRADELTA
30
••
fi so
LIQUID llt1U
HQ. Tf,T!I 200 AVERAGE 19. 48 STD. DEY. 12.8:!11
r'£RC[NI Of TOTAL SAMPLE:! WI IH RE5fECJ TO ONE UQ. QfY. 0 BELOW ~!THIN ABOVE
15.00 74..00 11-00
INTERDISTRIBUTARY
LIGUJD LlftiT
No. run 11 AYEIIII'IIif. 12.20 !TQ. ou. 24.11
~CB[C!T 0'ale!t SAftrLU ,.!J¥Hifitr!CI IQ QN! !!!HDJ!Y. q 12. se 'lt.l!l u. ee
i :!110.
LIQUID lii'HT
NO. T[STS 188 AYERAGf 77.11 5TQ. OfV. :!111.49
PERCENT Of TOTAL :!JRMrLE:!J WITH RE:!IIrtCJ TO ONE :!JJQ, OEV. 0" BELI.IW WITHIN ABOVE
10.24 1!10.12 9.84.
Fig. 2-5. Liquid limit frequency histograms for prodelta, intradelta, and interdistributary deposits
24
TABLE 2-3
SUMMARY OF LIQUID LIMIT FREQUENCY HISTCGRAMS
NtUnber "/o Within of Range Average Standard Standard Histogram
Deposit Figure Tests _L ~ Deviation Deviation Description
Natural Levee 2-4 101 29 - 129 67 20.7 66.3 Normal
1\) Point Bar 2-4 78 31 - 87 54 16 65.4 Positive Skewness V1
Back swamp (Organic) 2-4 143 58 - 397 152 65 74 Bimodal
Back swamp (Inorganic) 2-4 200 27 - 148 83 16.7 73 Negative Skewness
Prodelta 2-5 200 39 - 100 80 12.8 74 Bimodal
Intradelta 2-5 116 25 - 212 77 31.5 80 Leptokurtic
Interdistributary 2-5 79 38 - 179 82 24.7 74.7 Positive Skewness
2.4.4 Plasticity Index
Frequency distributions of plasticity index are shown in figs.
2-6 and 2-7, and summarized in table 2-4.
10
•o
20
<O
•o
20
10
NATURAL LEVEE
r- .JL
I
··AVERAGE
PLASTJCITT INDEX
NQ. JESTS 103 AYflltAGf. 4.2.05 :no. oev. JS.Js
PERCENT OF TOTAL 9A .. rLEs WHH RESPECT TO ONE SJQ, Of'f, q
BACK SWAMP (ORGANIC)
BELOW WITHIN AllOY£ 20.39 64-08 15.53
~
PLASTICITY INDEX
NO. TESTS 92 AYfiiiAG[ 1 :)8. IS STD. DEY. 48.1:!1
PERCCNT Of TOJRL SAf\nES Wl!H liE SPEC I TO ONC, STD. OEV. Q IIELOM WI THIN ABOVE
10.81 66.30 22-83
so
20
10
10
•o
20
10
POINT BAR
f- - ·AVERAGE
I fl. -l- cr
I I
PU-ISIJC!TT INDEX
NO. TI:STS ·:3 AVERAGE 32.55 STD. DEY. 14.34
PERCENT Of TOTAL SAI'IPL[S WITH RESPECT TO ONE STO. ['[V. 0
BACKSWAMP (INORGANIC)
BELOII WITHIN ABOVE J&.u ss.;s n.aa
I----AVERAGE
I J! -
PLASTIC! TY INDEX
NO. TESTS 122 AVERAGE 56.\1 sro. oev. 13.92
cr
~OTAL SAMPLES WIIH RESPECT TO ONE STD. Ofv,(J BEL OM WI Tli/N ABOVE
!9.93 71.31 14.75
Fig. 2-6. Plasticity index histograms for natural levee, point bar, and backswamp deposits
26
"
30
20
10
••
30
20
10
PRODELTA
!-"- ·-·AVERAGE
i (/"...\-
PLAST ICITT INDEX
"10. TESTS 14!1 1-iVfRRGE SD-90 STD. OfV. 12.16
PERCENT OF TOTAl. SRnrLp W!TH RE!IPECT TO ON£ UQ. QE'f. Q BELOW WITHIN ABOVE ., ... s 69-95 12-59
INTERDI STR I BUTARY
)'---AVERAGE
I (J"-1---'"-"1
I I I I
PLRSTIClTY INDEX
NQ. TESTS 81 AVERAG[ 58-81 sTo. oev. 25-14
PEpCENI OF TOTAL 9RMf'lfS WITH RESPECJ TO ONE STO. OEV. Q BELOW WITMIN ABOVE
12.3s ?,.o., u.sa
..
30
20
INTRADELTA
!----AVERAGE
PLASTICI TT INDEX
1~0. TESTS 151 AVERAGE 51.64 STO- DEv. 23-15
140-00 160.00 180.00 200.00
PERCENT OF TOTAL SRnPLES WITH RESPECJ TO ONE STD. OEV.CI" BELOW WITHIN ABOVE
ll.ol6 11."71 10-BS
Fig. 2-7. Plasticity index frequency histograms for prodelta, intradelta, and interdistributary deposits
27
TABLE 2-4
SUMMARY OF PLASTICITY INDEX FREQUENCY HISTOORAM3
Number % Within of' Range Average Standard Standard Histogram
Deposit Fi~ Tests - Deviation Deviation Description -Natural Levee 2-6 103 2 - 90 42 19 64 MJ.ltirnodal
[\) Point Bar 2-6 23 7 - 63 33 14 65.8 Multirnodal OJ
Backswamp (Organic) 2-6 92 43 - 218 106 46.7 66 Bimodal
Backswarnp (Inorganic) 2-6 122 19 - 86 56 13.9 71.3 Normal
Prodelta 2-7 143 16 - 72 51 12.2 69.9 Negative Skewness
Intradelta 2-7 157 5 - 164 52 23.8 77.7 Leptokurtic
Interdistributary 2-7 81 19 - 162 59 25 74 Leptokurtic
2.4.5 Liquidity Index
The liquidity index is the ratio of natural water content minus
plastic limit to plasticity index. It is possible to compute the
liquidity index (LI) from the following equation:
(l)
where:
w = Natural water content
PL = Plastic limit
11 = Liquid limit
The liquidity index is a good indicator of the consistency of a soil.
If the natural water content of a soil is greater than the liquid limit,
the LI is greater than 1.0; when remolded at constant water content
such a soil turns into a thick viscous slurry. If the natural water is
less than the plastic limit, the liquidity index is negative. Soil
with a negative liquidity index cannot be remolded at the natural water
8 content. The liquidity index is also a useful indicator of sensitivity
of clays and of undrained shear strength. This point will be discussed
later in paragraph 4.4.1. Frequency distributions of liquidity index are
shown in figs. 2-8 and 2-9, and summarized in table 2-5.
29
NATURAL LEVEE
40
"
10 t- AVERAGE
I .L " I I
10
oo~~~~~~~~~~~~~~ •. ~1~0~1w·w•o~~,~ .• ~o~·,.~,~0~1~.oo LIQUIOITT hiDE ..
40
~ 10
10
oo
NO. TE"! 105 AYUFIIZ .5. !!TO. OEV •• 22
PERCENT OF TOTAL !AftrLf.S WITH RE!fECT TO ONE UQ. OEV. q
BACK SWAMP (ORGANIC)
BELOII WITHIN AIIOVE l!i,QS 62o86 JII,JQ
LIQUID ITT IIIIOEX
NQ. TESTS Ul!l AYE«AG£ • ?0 !JTQ. Of\', .22
t.to 1-80 J.ao 2.00
P'UC!,NI OP IQIAL !AftrbE! WITH Rl!!rECJ IQ QNE !Jp. pc:y.O' II(LOW WITHIN A8DYl.
15-114 68.51 14-tl
40
"
20
10
40
POINT BAR
LIOUIOITT INDEX
NO. TESTS 78 AVEIHIC.E • 74 STQ. DEY. -28
1.60 1-80 2.00
PERCE~T OF TOTAL ~AI"'PLES I-IlTH RESPECT TO ONE STQ. DEV. 0"
BACK SWAMP (INORGANIC)
BELOW WITHIN ABOVE 14.10 69-23 16-67
1.20 1.410 t.ao 1.80 2.00 LIQUIOITT INDEX
NQ, Tf.!TS 182 AVERAGE: ,55 sro. or:v •• 20
rUCEt!l Of IQIAL !AftPLC:! WITH RE!rf:CJ TO ONE !JO. QCY. 0" l!lfLON WITHIN AIIO'ff:
lll.tll ss.se l&.u
Fig. 2-8. Liquidity index frequency histograms for natural levee, point bar, and backswamp deposits
30
"! PRODELTA
t ··f
AVERAGE
,[~~~~~~~.~~~~~~~~~~~~~ o .ao t-oo 1.20 t.to t.ao t.ao 2.oo
40
••
20
10
LIQUIDITY INDEX
~0. TE!IH 198 AVERA&£ , 51 !TO. DEY •• 12
I'ERCENI OF TOTAL !IRP!rLE' WITH RE3PECJ TO QNC, JID. DEV. q BELOW WITHIN AeOV[
!3. IS 16. ?1 10. 10
INTEROI STRIBUTARY
1--·- ---AVERAGE
I "-1- "-"1
I I I I
·.~~~~~~~~~~~·~~~ •. ~.~.~.~-~ •• ~~.~ .• ~.~7 •. ~.~.~.~ .•• LIQUIDITY IMDEII:
MO. Tf3TS Btl AV(IUU;E .61 3JQ, Q[V •• 18
l"fJ!!iENT OF TOTAL !AI":rlC,S WITH !!ESPECI IQ ON! 3JD. OEV.O" BELON WI THIN jqQYI!:
18.2! 8?.44 18-28
••
"
"
I NT RADEL TA
LIQUIDITY INDEX
NO. TESTS ISS AVERA&f. .69 sro. oEv .. 20
PEtfCC"NT OF TOTAL :JB.P!f'Lf3 WJIH I!ESPECf TO ONE UP- DEY. 0 BELOW WITHIN ABOVE
11-88 14.-23 14-11
Fig. 2-9. Liquidity index frequency histograms for prodelta, intradelta, and interdistributary deposits
31
TABLE 2-5
SUMMARY OF LIQUIDITY DIDEX FREQUENJY HISTOORAMS
Number % Within of Range Average Standard Standard Histogram
Deposit Figure Tests -- Deviation Deviation Description
Natural Levee 2-8 105 0.14 - 1.18 0.54 0.22 62.9 Multi modal
w Point Bar 2-8 78 1\)
0.22 - 1.60 0.74 0.28 69 Positive Skewness
Back swamp (Organic) 2-8 138 0.16 - 1.41 0.70 0.23 69.6 Normal
Back swamp (Inorganic ) 2-8 182 0.03 - 1.26 0.55 0.20 65.4 Normal
Prodelta 2-9 198 0.12 - 1.08 0.51 0.12 76.8 Leptokurtic
Intradelta 2-9 163 0.39 - 1.52 0.69 0.20 74 Positive Skewness
Interdistributary 2-9 86 0.13 - 1.03 0.61 0.18 67.4 Multimodal
2.4.6 Dry Density
Frequency distributions of dry density are shown in figs. 2-10
and 2-11, and summarized in table 2-6.
..
••
••
~ 20
10
NATURAL LEVEE
NO. TEST!I 97 AVEftAGl 15. II'J sro. au. s.1e
~ERC[MI Qfe~e~:L )AnrLU w!fQtti5'1"ECI TO ONE 'AXOv~f.v. q
BACK SWAMP (ORGANIC)
20.&2 64-95 u .• ,
"---AVERAGE
(T "1
I I
MO. 1!515 135 AVf.fiAiiE 42.88 STD. Q[Y, 15-155
P'UICUT or111eacl 5A11P'LE5 "!lVtti~SrECT TO or:E 'lXovrv· 0
U,U 54.07 2lo411
..
~ 20
&
0
tO
••
~ 20
10
POINT BAR
AVERAGE
_<T ---;
I
NQ. TESTS 85 AVEftAGE 78.55 sro. DEY. s.7t
I"Ef!CENI Of TOIF!L 9AI1PLE5 MITt! RE9rECT TO ONE SID· OEV. Q
BACK SWAMP (INORGANIC)
BELOW. WITHIN ABOVE \9.?.8 68-27 U-48
I--AVERAGE
_j____l[_ __ , l I I I I I I I
NO. TI!:STS 200 AVUAG! 8'5.25 STD. O(Y. El-111
tCIICfMI or111each. sennn W!1Vtt15'"CT TO Qff( '~@ovrv· 0
17.50 r.!!I.QO 1'7.50
Fig. 2-10. Dry density frequency histograms for natural levee, point bar, and backswamp deposits
33
40
3D
10
•o
20
PRODELTA
ORT DENSITY IN LBStCU FT
NO. TESTS 131 AVERRGf 71.67 STQ. DEY· 'LSB
PERCENT OF TOTAL SAnPLES WtTH RESI"ECT TO ONE STD. OEY. (J BELOW WITHIN ABOYE
9.92 17.86 12.21
INTERDISTRIBUTARY
r -AVERAGE
I '! ----4-- . ___ '!-
I
PRY DEWS ITT IN L831CU f T
NO. TESTS 71 AVERAGE: 66.08 ~ITO. DEY. 10. 71
PERChiT Of TOTAL 2AMPL£S Wll11 f!ESPECf TO ONE SIP. QU. (J BELOW WITHIN A80VE
as-•e se.e' 11.&9
10
•o
20
10
I NT RADEL TA
I-----AVERAGE
I '!_ --+--R--;
I I
DRY DENS! TT IN LBS/CU FT
NO. TESTS 163 AVERAGE 66.88 STD. DEY. 12.89
I I
PERCENT OF TOTAL SAJ'!PLES WITH RESPECT TO ONE S!Q. DE\'. q BELOW WITHIN ABOVE
ts.s4 ss.st u.n
Fig. 2-ll. Dry density frequency histograms for prodelta, intradelta, and interdistributary deposits
34
TABLE 2-6
SUMMARY OF DRY DENSITY FREQUENCY HISTOGRAMS
Number % Within of Range Average Standard Standard Histogram
Deposit Figure Tests _E£!_ pcf Deviation Deviation Description
Natural Levee 2-10 97 50 - 92 75·9 9.8 65 Negative Skewness
w Point Bar 2-10 83 54 - 98 78.3 9.7 66.3 Bimodal \Jl
Back swamp (Organic) 2-10 135 16 - 73 42.7 15.6 54 Multimodal
Back swamp (Inorganic) 2-10 200 48 - 91 65 9.2 65 Multimodal
Prodelta 2-ll 139 49 - 90 72.3 7.6 77.8 Leptokurtic
Intradelta 2-ll 163 33 - 98 66.9 12.9 66.9 Nonnal
Interdistributary 2-ll 77 45 - 94 66 10.8 68.8 Multi modal
2.4.7 Specific Gravity
Frequency distributions of specific gravity are shown in figs.
2-12 and 2-13, and summarized in table 2-7.
SUI,., ~,,,-,.-,..,--r ,...,.....,..... • •·ro-r·T..,-,-y-~
I NATURAL LEVEE
~ J!l
"
10
•o
20
10
SPE:::JFIC GRAVITY
NO. 1£315 47 AVERAGE 2.69 ST!). OfY .. 03
f- AVERAGE
<T <T
PERCENT OF TOHll SAMPLES WITH RESPECT TO OHf 510. DEY. g
BACK SWAMP (ORGANIC)
BELOW WITHIN ABOVE 14-89 74-47 10-64
J- -·AVERAGE
I <T_ -- .+. <T
I I
~l
f.oo 2.80 2-SIO S.OO 51"ECIFJC GIIRVIU
NO. T£519 88 AVERAGE 2.4.6 !HO. DEY. -19
I"ErtC£NI or 8~e~=L !AI1rLES w!I~tt~~srrcr ro ONE 'AXOv~cy. q 20-45 62.50 1?.05
POINT BAR ~I
~ 30
J AVERAGE
<T "1 r-, I
I I I
20
I I
~ I
D! I I I I
0 .l n 2.60 2.62 2-64 2-66 2-66 2.70 2.12 2-74 2.76 2.78 2.80
SPECIFIC GRAY! TT
10
>o
NO. TESTS 52 AVERAGE 2.69 STQ. OEV- .02
PERCENT OF TOTAL SAMPLES loi!TH RESPECT TO ONE STD. DEY. 0
BACK SWAMP (INORGANIC)
BELOW loi!THJN ABOVE 13-46 67.31 19.23
SPECifiC GRAVITY
NO. TESTS 123 AVERAGE 2.67 STD. OEV. -04
ruilll OF TOTAL 5AMPlE5 W!fH RESPECT TO ONE 5TO. OEV.Q" BELOW WITHIN R80YE
14.63 68-29 \7.0?
Fig. 2-12. Specific gravity frequency histograms for natural levee, point bar, and backswamp deposits
36
"
"
20
10
f ...
..
0
10
PRODELTA
t--AVERAG£
I
31'ECIFIC GIIIAYITT
NQ. TfSTS 92 AVERAGE 2· 72 STD. OEV •• 02
PEfiCENT Of TOTAL !IAP!I'LES WITH llf!!r[Cl TO ONE STD. OE't. q BELOW lUTHI• ABOVE
17-39 65.22 17.59
INTERDISTRIBUTARY
r- 60.71"'
t t
r-'
AVERAGE-----.
17 I
r--- 17
I I I I I I I I I I I I I I I
n .n I I I I 0 J,SQ 1-15 I·IG 1.15 2.10 2.2'5 2-tO 2.55 2.10 2.15 ,,00
Sf'!CJPIC GIUrtiTT
NO. JUTS 21 AVfltAG( 2·14 sro. ot:w •• 21
PUCCNT or:.:e&C'" serrLU "A""'5vc:cr tp 1M 'iav~~U· Q
1 •. u ez.se o
tO
10
INTRADELTA
!-----AVERAGE
I
z.se 2.10 SPECJF(C GfiAV!TT
NO. TESTS 76 AVERAGE 2. 70 STD. OEV. -04
f'ERC:fNI Of TOTAL SAMPLES WITH RESPECJ TO ONE STD. OEV. 0 BELOW WITHIN ABOVE
10-53 'J7,63 11.84
Fig. 2-13. Specific gravity frequency histograms for prodelta, intradelta, and interdistributary deposits
37
TABLE 2-7
SUMMARY OF SPECIFIC GRAVITY FREQUENCY HISTOGRAMS
Number %Within of Range Average Standard Standard Histogram
Deposit Figure Tests -- Deviation Deviation Description
Natural Levee 2-12 47 2.6~ - 2.74 2.69 0.03 74.5 Multimodal
w Point Bar 2-12 52 2.65 - 2.77 2.69 0.02 67.3 MJ.ltimodal co
Back swamp (Organic) 2-12 88 2.10- 2.74 2.46 0.19 62.5 Multimodal
Back swamp (Inorganic) 2-12 123 2. 53 - 2. 75 2.67 0.04\ 68.3 Multimodal
Prodelta 2-13 92 2.67 - 2.80 2.72 0,02 65.2 Normal
Intradelta 2-13 76 2.57 - 2.76 2.70 0.04 n.6 Negative Skewness
Interdistributary 2-13 27 l. 59 - 2. 74 2.64 0.26 92.6 Multimodal
2.4.8 Void Ratio
Frequency distributions of void ratio are shown in figs. 2-14
and 2-15, and summarized in table 2-8.
..
,.
10
NATURAL LEVEE
t- AVERAGE
I I"" cr 11-- !! .. "1
I I I I I I : n:
.n n l .i . .lJ. I.l 0o t.oo 2.oo 3.oo t.oo s.oo s.oo 1.00 e.oo s.oo 10-00
••
,.
VOID RAHO
NQ, TESTS 46 AVERRG£ \.46 !ITO. oev. t.os
PERCENT Of TOTAL SAMPLES WIJH !!E!IPfCT TO QNE SJQ, OEV. q
BACK SWAMP (ORGANIC)
BELOW WITHIN ABOVE o 93-4.8 s.s2
VOID RATIO
NQ, TESTS 68 AVEIIRG£ 3, 10 STD. QfV. \.51
I'EfiCENT Of IOTf!L Sf!Mf'LE' WITH R£5f'ECT TO ONE STD. DCV.Q Df.LOW WITHIN ABOVE
10.29 61.65 22-06
40
,.
••
••
POINT BAR
HO. TESTS 60 AVERAGE 1-12 STD. DEY •• 27
PEI!CfNT OF TOTAl SAMPLES WITH RESPECT TO ONE STQ. OEV. q
BACK SWAMP (INORGANIC)
BELOW WITHIN ABOVE 1!1.!13 70.00 16.67
VOID RATIO
NQ. TESTS 155 AVERRG£ 1.61 !JQ. DEY •• 38
P[RCENT QF TOTAL :SRftrL£5 IHTH !!E3PECJ TO ONE !TO. OfY, (J BELOW WITHIN ABOVE
11.t2 ss. 45 16-13
Fig. 2-14. Void ratio frequency histograms for natural levee, point bar, and backswamp deposits
39
PRODELTA
10
30
~20 .to .60
0
40
•o
20
10
NO. TESTS 94 AVERAG£ I • 32 ~no. Dfv •. 21
Pff!CENT QF TOTAL SRnPLE! WITH RESPECT TO ONE STD. DEY. Q 11£LON WITHIN ABOVE
14-1!19 10.21 u.eg
INTERDISTRIBUTARV
t--·AVERAG£
I IT -" I I I I I I
I I
~ I I I I I I I I I I I
2.20
~1fl 0o .so .so .go 1.20 t.so t.eo 2.10 2.40 2.10 s.oo VOID RATIO
NO. TESTS 20 AVERAG£ 1.58 STD. OEV. -52
PUCCN! Or IQIAL !AftrL£2 WITH I!UPCCJ TO ONE :no. QEV. Q BELOW WJfHJN ABOV[
.a.oo 1o.oo zo.oo
10
90
INTRADELTA
NO. TESTS ?8 AVERA&£ !.57 sro. ocv .. so
PEf!CENT Of TOTAL SAnPLf.S WITH RpPECf TO ONE 910. DEY. 0 BELOW WI THIN ABOVE
12-82 74.36 12.82
Fig. 2-15. Void ratio frequency histograms for prodelta, intradelta, and interdistributary deposits
40
TABLE 2-8
SUMMARY OF VOID RATIO FREQUENCY HISTOGRAMS
Number % Within of Range Average Standard Standard Histogram
Deposit Figure Tests -- Deviation Deviation Description
Natural Levee 2-14 46 0.82 - 6.16 1.46 1.05 93.5 Positive Skewness
~ Point Bar 2-14 60 0.70 - 2.12 l.l2 0.27 70 Positive Skewness I-'
Back swamp (Organic) 2-14 68 1.36 - 6.73 3.10 1.51 67.7 Positive Skewness
Backswamp (Inorganic) 2-14 155 0.85 - 2.57 1.61 0.38 66.5 Platykurtic
Prodelta 2-15 94 0.84 - 2.06 1.32 0.21 70.2 Normal
Intradelta 2-15 78 0.64 - 2.84 l. 57 0.50 74.4 Normal
Interdistributary 2-15 20 l.Ol - 2.59 1.58 0.52 70 Multimodal
2.4.9 s /P Ratio u 0
The ratio between undrained shear strength (s ) and effective u
overburden pressure p is known as the s /P ratio. Reference 8 sug-o u 0
gests that a constant s jp ratio should exist for normally consolidated u 0
natural deposits. It has been found that a constant s /P ratio does u 0
exist for normally consolidated soils provided the plasticity index re-
21 I mains constant. Correlation of s p ratio with plasticity index ' u 0
will be discussed in later paragraphs. Frequency histograms of s /P u 0
ratio are presented in figs. 2-16 and 2-17. Histograms for the natural
levee and organic backswamp deposits were omitted since these deposits
are slightly overconsolidated.
table 2-9.
A summary of s /P data is provided in u 0
42
POINT BAR
40
~ 30 f
20~ ~ AVERAGE
I
t r'"t'"
]~' ' ~r!l~& ~~~ ~ 0 .OS -10 .IS .20 .40 .45 .SO
VALUES 'lf
"
30
NO. TESTS 33 AVERAGE .27 SID. DEY •. 07
PERCENT OF TOTAL S~rlf'L[S WITH RESPECT TO ONE STO. OEV. 0"
PRODELTA
BELOW WI THIN ABOVE 24-24 57.5!1 18-18
VALUES OF
NO. TESTS 110 AVERAGE -2Z !ITO. O[V .• OS
I"Efi'CfNT OF TOTAl 9/Hif'LES W/TH RfSPlCI TO ONE :uo. OEV. (J BELOW WITHIN ABOVE
17.27 6'J.21 15.45
40
•o
Fig. 2-16. su/P0 ratio frequency inorganic backswamp,
43
BACKSWAMP (INORGAI'IIC)
VALUES OF
NO. TESTS 106 AVERAGE .26 sro. oe.v .. to
PERCENT OF TO!RL SAMPLES WrTf1 RESPECT TO ONE SJO. OfV. C1 SELOW WJT~TN ABOVE
7-55 79.25 19.21
histograms for point bar, and prodelta deposits
50
40
lO
-20
50
~··~ I INTRADELTA INTEROISTRIBUTARY
40
AVERAGE
VALUES Of
NO. TE!ITS E12 AYERFIGE .29 STD. D£V •• J2
PERCENT Of TOTAL SAI'IPLES WITH RESPECT TO ONE STQ• OEV. q BELOW WI THI!i ABOVE s. 7& 73. 11 n.o7
30
20
VALUES OF
NO. TESTS 3:1 AVERAGE .37 STQ. DEY •. 16
PERCENT OF TOTAL SAMPLES WITH RESPECT TO ONE 5TO. DEY. (J"
BELOW WITHIN ABOVE U Bl-82 J8.1B
Fig. 2-17. su/Po ratio frequency histograms for intradelta and interdistributary deposits
44
j j
TABLE 2-9
SUMMARY OF s /P RATIO FREQUENCY HISTCGRAMS u 0
Number % Within of Range Average Standard Standard Hi~togram
Deposit Figure Tests -- Deviation Deviation Description
Point Bar 2-16 33 0.14 - 0.37 0.27 0,07 57.6 Multi modal
+ Back swamp \J1 o.o7 -·a. 76 (Inorganic) 2-16 106 0.26 0,10 79.3 Leptokurtic
Prodelta 2-16 no O.ll - 0.39 0.22 0.05 67.3 Multimodal
Intradelta 2-17 82 0.07 - 0.65 0.29 0.12 73.2 Positive Skewness
Interdistributary 2-17 33 0.22 - 0.85 0.37 0,16 81.8 Positive Skewness
2.4.10 Consolidated-Undrained Shear Strength
Consolidated-undrained shear (R) strengths are obtained from tri
axial compression tests. Drainage of the test specimen is permitted
and full primary consolidation is allowed to take place under the ini
tially applied confining pressure. Drainage is stopped, and the axial
stresses are increased until the specimen experiences shear failure.
The R-shear strength is equal to the shear resistance of the specimen
at the point of shear failure. The shear strength parameters from tests
on a series of specimens at different confining pressures are described
by both a friction angle and a cohesion value. The R-tests were conso
lidated under pressures of 1, 2, and 3 tons per sq ft. The shear strength
parameters were obtained by a straight line approximation of the data.
Frequency histograms for friction angles and cohesions are shown in figs.
2-18 and 2-19. Unfortunately, insufficient data were available to ade
quately analyze the R-shear strengths for the natural levee, point bar,
prodelta, intradelta, and interdistributary deposits individually. The
R-shear strengths for these deposits were analyzed collectively and called
deltaic soils.
Deltaic. Based on 80 tests, the friction angle ranged between 8
and 22 degrees with an average of 13 degrees. The cohesion ranged be
tween 0.01 and 0.50 ton per sq ft with an average of 0.20 ton per sq ft.
The friction angle histogram in fig. 2-18 shows that the data are
distributed relatively normal. The standard deviation of plus or minus
2.62 degrees from the average contains 65.2 percent of the data. The
cohesion histogram in fig. 2-18 shows that the data are skewed to the
46
<O
•o
20
10
J'.oo
•o
30
20
10
DELTAIC
l,QQ
FltiCT ION ANGLE IN DEGREES
NO. T£91580 JIYf.RRGE 1~. 26 !ITQ. Df.Y. 2.62
PERCENT Of TOTAL !IIU1fbE5 W!Jtt R~£ SJQ, 0['1. q
DELTAIC
BELOW WITHIN AOOYE 14-49 65.22 20-29
t--·-AVERAG£
I r--__ q:__ -1-· ,__.!1:, __ -<-j
/ I
...
I I 1--,1
: L I I I
. 20 .25
COHESION IN TISO FT
NO. ![5T'3 80 AYlRAGE .201 sro. DEY •• Jo
I'Efi:CENT Of IO!fi.L !IAnP\.ES oi!Tii IIESPECT TO ONE SJQ. OEV.q BELOW WI THIN ABOVE s.zs 77.50 16-25
•o
•o
20
10
J'.oo
<O
!0
20
10
BACK SWAMP (ORGANIC)
7.00 21.00 2!1.00 zs.oo FRICTION ANGl.E IN OEG«f.£5
NO. TESTS 55 AVERAGE 12.94 :no. oev. ,,,g
f'EIIICENI Of TOTAL SIU!PLE' WITH RE!PECJ TO ONE UQ, QEV. (I
BACK SWAMP (ORGANIC)
BELOW WITHIIIII ABOVE 12-12 12.73 15.15
f----AVERAG£
I
COHESION IN T/50 FT
NO. JUTS !19 AVERAGE: .141 STD. Q[V. -II
...
PEIICfNI or 11~e6Cl senrL£5 w~l~tt~5'"Cl TO QNE 'lKDv~EV. q 24-24 60-61 15.15
. ..
Fig. 2-18. R-test shear strength frequency histograms for deltaic and organic backswamp deposits
47
BACK SWAMP (INORGANIC)
FRICTION ANGLE IN DEGREES
NO. TESTS 90 AVERAGE: 11.81 sro. oev. 3,12
PERCENT OF TOTAL SA11PLES WITH RESPECT TO QNE SJQ. OfV, a BELOW WITHIN ABOVE
11.11 'J3.33 15.56
so
30
BACKSWAMP (INORGANIC)
COHESION IN T/SC FT
NQ, T!:STS 90 AVERAGE -203 SJQ. OEV .. ]3
PERCENT OF TOTfR SAftPLES lo.ll TH RESPECT TO ONE STD. DEY. a BELOW WITHIN RIJOVE
14- 12 69.41 \6.41
Fig. 2-19. R-test shear strength frequency histograms for inorganic backswamp deposits
right. The standard deviation of plus or minus 0.10 ton per sq ft
from the average contains 77.5 percent of the data.
Backswamp (organic). Based on 33 tests, the friction angle
ranged between 7 and 20 degrees with an average of 13 degrees. The co-
hesion ranged between 0 and 0.40 ton per sq ft with an average of 0.14
ton per sq ft. The friction angle histogram in fig. 2-18 shows that
the distribution of data is multimodal. The standard deviation of plus
or minus 3.2 degrees from the average contains 72.7 percent of the
data. The cohesion histogram in fig. 2-18 shows that the standard dev-
iation of plus or minus 0.11 ton per sq ft from the average contains
60.6 percent of the data. The data are distributed multimodally and
are skewed to the right.
Backswamp (inorganic). Based on 90 tests, the friction angle
48
ranged between 4 and 27 degrees with an average of l2 degrees. The co
hesion ranged between 0 and 0.50 ton per sq ft with an average of 0.20
ton per sq ft. The friction angle histogram in fig. 2-19 shows that
the data are normally distributed with a leptokurtic shape. The stand
ard deviation of plus or minus 3.1 degrees from the average contains
73.3 percent of the data. The cohesion histogram in fig. 2-19 shows
that the data are multimodally distributed. The standard deviation of
plus or minus 0.13 ton per sq ft from the average contains 69.4 per
cent of the data.
2.4.11 Drained Shear Strength
Drained shear strength is normally obtained by means of the
S-test performed in either direct shear apparatus or triaxial appara
tus.7 The drained shear strengths presented herein were obtained from
S-tests using the direct shear apparatus. The term ''direct shear'' is
used because failure is induced on a specific plane on which the normal
and shear stresses at failure are known. The shear strength para
meters from the direct shear strength test are designated as the
angle of internal friction ¢' and cohesion c'. These parameters
are affected significantly by the amount of preconsolidation pres-
sure to which the samples have been subjected; therefore, care was
taken to separate the data based on consolidation test data. Insuffi
cient drained strength data were available for the natural levee, point
bar, prodelta, intradelta, and interdistributary deposits to adequately
present them individually. The drained shear strengths for these soils
were combined and presented as deltaic soils. The data presented in
fig. 2-20 include deltaic, organic backswamp, and inorganic backswamp
deposits. The data presented for the deltaic deposits are from tests
on reasonably normally consolidated soils; the organic backswamp depos
its are considered slightly overconsolidated; and the inorganic back
swamp deposits are reasonably normally consolidated.
Deltaic. Based on 22 tests the friction angle ranged between 16
and 31 degrees with an average of 23.7 degrees. The histogram in
fig. 2-20 shows that the data are distributed in a multimodal shape.
The standard deviation of plus or minus 4.86 degrees from the average
contains 63.6 percent of the data. Cohesion values ranged between 0
and 0.16 ton per sq ft but were not presented in histogram form.
Backswamp (organic). Based on 25 tests, the friction angle
ranged between 13 and 35 degrees with an average of 22 degrees. The
histogram in fig. 2-20 shows that the data are distributed in a multi
modal shape. However, it is reasonably good presentation of data. The
standard deviation of plus or minus 5.23 degrees from the average con
tains 72 percent of the data. Cohesion values ranged between 0 and
0.15 ton per sq ±~ but were not presented in histogram form.
Backswamp (inorganic). Based on 86 tests the friction angle
ranged between 12 and 36 degrees and averages 20.6 degrees. Based on
the histogram shown in fig. 2-20, the data are distributed in a reason
ably normal shape, but the Kurtosis is leptokurtic. The standard devi
ation of plus or minus 3.48 degrees from the average contains 75.6 per
cent of the data. Cohesion values ranged between 0 and 0~30 ton per
sq ft but were not presented in histogram form.
50
•o
20
10
•o
30
DELTAIC
r- ·--AVERAGE
<7 I
I ---""---~
I I I
FRICTION RHULE IN DEGREES
NO. TE~TS 22 RVERRC.E 23.'73 sro. DEv. -t.es
34-00 31.00 40.00
PEf!CENT Of TOTAL SRttPLE.S WITH RESPEC' 10 ONE :no. OfV. (J'
BACK SWAMP (INORGANIC)
I!IELOW WITHIN ABOVE 18.18 63-64 ]8. 18
fiUC!ION ANGLE IN DEGREES
NO. TESTS 1!16 AVERAGE 20.60 SID. O[V. 3-48
r'EIIICENf OF TOTAL SRttPL!:S W/JH lll;!rfCT TO ONE SIQ. pEV. q BELOW WITHIN ABOVE
12.19 15-58 11-83
.o
30
20
10
BACK SWAMP (ORGANIC)
<7
f---AVERAG£
I u
NO. TESTS "S AVERAGE 22.00 STQ. OEV. 5-23
~EtH Of TOTRL SAMPLES WITH RESPECT TO ONE STD. O[V. 0 BElOW WITHIN ABOVE
12.00 72-00 16-00
Fig. 2-20. S-test shear strength frequency histograms for deltaic and backswamp deposits
51
CHAPTER III
ENGINEERING PROPERTIES OF SOIL AS A FUNCTION OF DEPTH
If it can be established that in fact, the distribution of perti
nent soil properties of fluvial and fluvial-marine deposits do vary sys
tematically with depth, this knowledge can be of great value in engi
neering design problems. The number of laboratory tests to establish
soil properties of these deposits could be greatly reduced, and the re
sults of these tests could be applied to permit designs with greater
confidence. Generally, it is desirable to know whether any relation-
ship between natural water content and plasticity characteristics with
depth can be established. If so, the shear and consolidation character
istics of the soil then can be determined by correlations such as those
described in later paragraphs. Studies were made to determine not only
the distribution of natural water content and Atterberg limits but also
the distribution of preconsolidation pressures and undrained shear
strength with depth. The preconsolidation pressures and effective over
burden pressures are discussed previously in Chapter II. The undrained
shear strengths included in this study were determined from unconsolidated
undrained triaxial compression Q-tests (also called quick, undrained, or
UU test).
3.1 Natural Levee Deposits
3.1.1 Natural Water Contents and Atterberg Limits
The range of natural water contents and plastic range are shown
in fig. 3-l. It should be noted that the plastic range is based on the
52
\Jl LA> ....
0 0
10
20
30
t:l4o ... ~ :I: .... 0.. 50 loJ 0
110
70
60
eo
NATURAL WATER CONTENT AND ATTERBERG LIMITS (.,.o DRY WEIGHT)
20 40 60 60 100
~ ' ~ v 1/
/ MIN ( \ ~MAX
PLl LL
/ \ If I
/_ LNATURAL WATER
I
CONTEITS
! f----PLASTIC RANGE---j
I I
OVERBURDEN AND PRECONSOLIDATION PRESSURES
(T/SQ FT) 120 0 1.0 2.0 3.0 0
• jlr, • . f~ .. . ·.
•• -.. •
• I
I
I
LEGEND I
• PRECONSOLIDATION
• OVERiURDEN
I I
UNDRAINED SHEAR STRENGTH (T/SQ FT)
0.2 0.4 0.6 -• •
• .. • •• • . . .,.. ~ •• • • • . • • •
•
•
Fig. 3-1. Soil properties versus depth for natural levee deposits
0.6 0
10
20
30
.... 40 t:l ...
z :I: I-
50 0.. loJ 0
60
70
60
90
minimum values of plastic limit and maximum values of liquid limit based
on numerous data. This range does not necessarily correspond to plasti
city index. The plastic range appears to decrease slightly with depth.
The natural water contents are basically concentrated near the center of
the plastic range.
3.1.2 Overburden and Preconsolidation Pressures
Based on the data shown in fig. 3-l the preconsolidation pres
sures generally exceed the computed effective overburden pressures, thus
indicating an overconsolidated soil. There is an appreciable amount of
scatter in the data for the overburden pressures. These soils have not
experienced overburden pressures greater than those imposed by the
existing overburden, and any excessive preconsolidation exhibited by
them is caused solely by desiccation either during or after their
deposition.
3.1.3 Undrained Shear Strength
The undrained shear strengths plotted against depth, as shown in
fig. 3-l, do not exhibit an increasing trend with depth. In fact,
there is no correlation with depth. The data exhibit a rather random
pattern down to about a depth of 10 ft. Below that there is a slight
indication of a trend. The slightly overconsolidated nature of this
deposit is a reasonable explanation for the random pattern of data.
3.2 Point Bar Deposits
3.2.1 Natural Water Contents and Atterberg Limits
The natural water contents and plastic range are shown in fig. 3-2
plotted versus depth. Based on this plot, the plastic range for point
54
\Jl \Jl
0 0
10 1- -
NATURAL WATER CONTENT AND ATTERBERG LIMITS ('P'o DRY WEIGHT)
20 40 60 80 100
v . ~ \ --- • .-- --
.)--~ . M~~ NATURAL WATER 1 MAX LL PL CONTENT~-----..._
20
30
1-
t:: 40 .... ! J: 1-~ 50
• • ( ... •
• • ) •
••• v • I •
0
eo )
• •
( • •
-· \
) • \
70
J_."''\'C R~NO< ~ 80
90
OVERBURDEN AND PRECONSOLIDATION PRESSURES
(T /SQ FT) 120 0 1.0 2.0 3.0 0
UNDRAINED SHEAR STRENGTH (T/SQ FT)
0.2 0.4 0.8
~
•
:\ . • • 1\·' •
• . \--...~~ '\ •
• •
\ • •
• \ • \ Sv.x. •0.19
0.8 0
J I
•
l
10
20
30
1-40 t:: ....
! J: I-
50~ 0
80
70
. \ U!l 80
-- -- -I 90
Fig. 3-2. Soil properties versus depth for point bar deposits
bar deposits appears to narrow with depth. The data were insufficient
to establish a range of natural water contents within the plastic range
for this deposit. Thus the natural water contents are plotted indivi-
dually. They generally plot nearer the upper limit of the plastic
range above a depth of about 40 ft; below that depth, they are located
nearer the center of the plastic range. The lower limit (plastic
limit) of the plastic range is relatively constant with depth while the
upper limit (liquid limit) decreases with depth. Fig. 3-2 shows that
the silty point bar deposits exhibit an appreciable decrease in plas-
ticity below a depth of about 40 ft.
3.2.2 Overburden and Preconsolidation Pressures
Effective overburden and preconsolidation pressures are plotted
versus depth in fig. 3-2. The effective overburden pressures (p ) are 0
represented by a best-fit straight line located by the method of least
squares. The method of least squares is discussed in more detail in
Chapter IV. Below a depth of ten feet, the relation between effective
overburden pressure and depth can be expressed by a linear line of
regression. The preconsolidation pressures lie very close to the re-
gression line in fig. 3-2. Based on these data, the point bar soils
included in this study can be considered to be normaliy consolidated.
3.2.3 Undrained Shear Strength
The undrained shear strength values plotted versus depth in
fig. 3-2 show an increasing trend with depth. The trend of the change
in undrained shear strength (s ) with depth can be represented by a u
linear line of regression. The standard deviation from regression is
0.19 unit of s . This line of regression represents the trend of s u u
56
below a depth of 10 ft; above that depth, the s showed no trend with u
depth. Based on the data shown in fig. 3-2, the su ranges between 0.11
and 1.24 ton per sq ft. The s increased with effective overburden presu
sure according to the relation defined by the ratio s jp ~ 0.30. u 0
This ratio is also known as the shear strength increase factor. The
higher shearing strength in the upper 10 ft is associated with a·
slight overconsolidation effect resulting from desiccation. There is
appreciable scatter in the strength data which could indicate that the
sediments are still undergoing primary consolidation or could represent
anomalies that occurred during testing. Although the trends developed
in fig. 3-2 appear reasonable, the writer feels that insufficient data
were available to fully analyze the undrained shear strengths of silty
point bar deposits. Use of this data should be restricted to making
rough estimates and as supplemental data for preliminary designs.
3.3 Backswamp Deposits
Fig. 3-3 includes data from both organic and inorganic backswamp
deposits. A composite_presentation of the properties of backswamp de-
posits was considered to be more indicative of natural conditions.
3.3.1 Natural Water Contents and Atterberg Limits
Fig. 3-3 shows that the natural range of water contents and the
plastic range vary considerably down to a depth of about 30 ft. The
soils within these ranges are slightly organic to highly organic. Be-
low 30ft, the plastic range is reasonably constant and natural water
contents appear to have a decreasing trend approaching the lower limit
of the plastic range.
57
0
10
20
30
40
50
1-
'Jl loJ
co ~ 60
~ J: :i: 70 loJ 0
80
90
100
110
120
130
NATURAL WATER CONTENT AND ATTERBERG LIMITS ("fo DRY WEIGHT)
0 50 100 150 200 250 300 350
) " A [) M~~ h_NATURA~~~~ --........ PL
I I CONTENTS-~ / ~~
~ v I-MAX
\ LL
7
( II)
I I I
I
/(
I I
~ I I F:!-PL1STIC R~NG£
OVERBURDEN AND PRECONSOLIDATION PRESSURES
(TISQ FT) 0 I .0 2.0 3.0 4.0 5.0
~'! LEGEND
• PRECONSOLIDATION • OVERBURDEN
I~
""· =~ .. ~
't' I ~ •• :
I •
~ II- .... ..
I .. ~ • t , .. ~
·~~: I -~ .. .. I .. I .
~' .. ..
·~ .. .. I 'r- ..
~~- Sv.x.•O.I4
J
I
UNDRAINED SHEAR STRENGTH (TISQ FT)
0 0.2 0.4 0.6 0.8 1.0 .. .. I 0 .. , .. .
I , .. ....... 10 .. --:. .. 20 .. . . . . .. . . 30
,..l- . I . •• !\.. .. ~~: ·-. . -.\·· ... . . . . :r- .
5~"'0.26
. .. y. . ·~· • .. , ..
\ .. . .
',\.
40
50
1-loJ
60 ~ ~ J:
70 t loJ 0
80
90
. .. .. . . 100
J\ . . . '\. Sv.x.•O.I2
\.
110
120
130
Fig. 3-3. Soil properties versus depth for backswrump deposits
3.3.2 Overburden and Preconsolidation Pressures
The effective overburden and preconsolidation pressures are plot-
ted versus depth in fig. 3-3.
and depth, below a 30-ft depth.
A linear relationship exists between p 0
The preconsolidation pressures (p ) c
plot on both sides of the line of best-fit for the data, thus indicat-
ing that the backswamp deposits consist of underconsolidated, normally
consolidated, and overconsolidated soils. Overconsolidation is much
more prevalent in the upper more organic portion of the deposits.
3.3.3 Undrained Shear Strength
The undrained shear strengths are plotted versus depth in fig.
3-3. Below a depth of about 30ft the strength increase is reasonably
constant with depth and the trend can be represented by a linear line
of regression. The standard deviation from the regression line is 0.12
unit of s . The shear strength data between 0- and 30-ft depth were u
omitted. Based on the data shown in fig. 3-3 the s range between u
0.03 and 0.27 ton per sq ft for the organic soils and 0.10 and 0.72
ton per sq ft for the inorganic soils. The shear strength increase
factor for the inorganic backswamp soils is expressed by s /P ~ 0.26. u 0
These soils have never experienced overburden pressures greater than
those existing at the time of this study. The overconsolidation of
soils in the upper portions of the deposits and the slight overconsolida-
tion of soils in the lower portions can be associated with desiccation
during and after deposition.
3.4 Prodelta Deposits
It was pointed out earlier in this study that the prodelta deposits
59
are the most homogeneous of the deltaic deposits. This fact is ex-
emplified clearly by the data plotted in fig. 3-4.
3.4.1 Natural Water Contents and Atterberg Limits
The natural water content range and the plastic range are reason-
ably constant with depth. Although the natural water contents seem to
have a slight trend toward the lower limit of the plastic range with
depth. The range of natural water contents at all depths is closer
to the lower limit of the plastic range.
3.4.2 Overburden and Preconsolidation Pressures
The overburden and preconsolidation pressures are plotted versus
depth in fig. 3-4. The overburden pressures can be represented by a
straight line. The preconsolidation pressures lie reasonably close to
the overburden pressures, indicating that the prodelta deposits are
normally consolidated.
3.4.3 Undrained Shear Strength
The plot of undrained shear strengths versus depth in fig. 3-4
shows an increasing trend with depth. The strengths range between 0.18
and 0.85 ton per sq ft. The standard deviation from the regression
line is 0.09 unit of
as s /P ~ 0.22. u 0
s . u The shear strength increase factor is expressed
3.5 Intradelta Deposits
3.5.1 Natural Water Contents and Atterberg Limits
The natural water content range and plastic range are shown
versus depth in fig. 3-5. Both these ranges appear to decrease with
depth. The lower limit of the plastic range is reasonably constant
60
0\ 1---'
NATURAL WATER CONTENT AND ATTERBERG LIMITS (..,o DRY WEIGHT)
00 20 40 80 60 100 120 140
10
20
30
r--Li NATURAL WATER CONTENTS I
40
1/ 50
1-w ~ 60
; J: li: 70 w 0
'tf~ r- MAX LL
1 \
\ 80 .. ~· ..
90
I
100 I)
I \
110
120
130
( I I \ I H l---PL
1AST/C fANG£-
OVERBURDEN AND PRECONSOLIOATION PRESSURES
(T/SQ FT) 0 1.0 2.0 3.0 4.0 5.0
I LEGEND I " PRECONSOLIDATION • OVERBURDEN
_\
-~ !
~~~ ... ..
·~1· ·~
.. ... tot .. .. • • t·· .~
o4 ~· .. .. . • •I .. ·~l~ ' . • •
Sv.x.•0.28 ~·~ . .. ~· . ..
\ • .. -•
UNDRAINED SHEAR STRENGTH (T/SQ FT)
0 0.2 0.4 0.8 0.8 1.0
I
·\: . :\ • • • • • '· .
•• vs~,.0.22 \ .
•
·.' ft• .. • • -.,; J·· . • • • • • •• -1· ..
•
:~. • I •
I • • . ~ •• I • Sv.x.s0.09 • I I
I \~ I I
1 I
0
0
20
30
40
50
1-w
60 ~ z J:
70 1-Q.
~
80
90
00
10
20
30
Fig. 3-4. Soil properties versus depth, prodelta deposits
0\ !\)
t-
0 0
10
20
30
t:l4o ... ~ :r t-:!; 50 0
60
70
60
90
NATURAL WATER CONTENT AND ATTERBERG LIMITS (.,.o DRY WEIGHT)
20 40 60 80 100
OVERBURDEN AND PRECONSOLIDATION PRESSURES
(T /SQ FT) 120 0 1.0 2.0 3.0
I r: .. .. ..
• " PRECONSOLIDATION • OVERBURDEN
0
•
UNDRAINED SHEAR STRENGTH (T/SQ FT)
0.2 0.4 0.6
•• •• • • •• ... •
': ~· • . . ••• • , ... \
1\ .. •
• • 1\·: • ..
·r so/p:D.U
• . \
• . •• •
•• •
·r s •.•. •0.09 \
•
Fig. 3-5. Soil properties versus depth for intradelta deposits
0.6 0
-
!
I
I
10
20
30
t
"' 40"' ... z :r t-
50 Q.
"' 0
60
70
80
90
with depth. Natural water contents appear to be confined to the middle
of the plastic range. A highly plastic range is noted between the
10-15 ft depths. This can be attributed to the presence of organic
materials.
3.5.2 Overburden and Preconsolidation Pressures
The overburden and preconsolidation pressures are plotted versus
depth in fig. 3-5. Preconsolidation pressures agree reasonably well
with overburden pressures, with the exception occurring between depths of
10 and 15ft where preconsolidation pressures are appreciably larger,
thus indicating a range of overconsolidated soils. At other depths, the
soils appear to be normally consolidated.
3.5.3 Undrained Shear Strength
Undrained shear strengths are plotted versus depth in fig. 3-5.
The strengths increase with depth, below 15 ft depth. The standard
deviation from the regression line is 0.09 unit of s . The shear u
strength increase factor is represented by s /P ~ 0.24. The strengths u 0
range between 0.05 and 0.40 ton per sq ft.
3.6 Interdistributary Deposits
3.6.1 Natural Water Contents and Atterberg Limits
The plastic range shown in fig. 3-6 is slightly erratic in re-
gard to its upper limit. The lower limit remains reasonably constant
with depth. Insufficient data were available to establish a range of
natural water contents with depth; thus, the individual data are shown.
The writer feels that there were insufficient data available to permit
conclusive analyses.
63
0\ ~
1-
0 0
10
20
30
t:l40 ... ~ J: 1-~50 0
60
70
eo
90
NATURAL WATER CONTENT AND ATTERBERG LIMITS ("!o DRY WEIGHT)
20 40 60 80 100
I . \ \ • • ~ •
OVERBURDEN AND PRECONSOLIDATION PRESSURES
(T/SQ FT) 120 0 1.0 2.0 3.0 0
• 1\ MIN • • PL •
J • • . . -~ • c: •• !--MAX
) LL
~· I • \ NATURAL WATER
CONTENTS----
•• I \
I •
• 1\
• \ I---PLASTIC RANGE
LEGEND
" PRECONSOLIDATION • OVERBURDEN
UNDRAINED SHEAR STRENGTH (T/SQ FT)
0.2 0.4 0.6
• • •
• ~ • • • .rl : . ~ . :t •
5"/f..=O . .J5
"\ \
s •.•. =o.og \ I
Fig. 3-6. Soil properties versus depth for interdistributary deposits
o.e 0
10
20
30
1-
40 t:l ... z J: I-
50 D..
60
70
eo
90
"' 0
3.6.2 Overburden and Preconsolidation Pressures
In fig. 3-6, the effective overburden and preconsolidation pres-
sures are plotted versus depth. The preconsolidation pressures
determined from laboratory consolidation tests agree closely with the
computed overburden pressures, indicating that the interdistributary
deposits analyzed herein are normally consolidated.
3.6.3 Undrained Shear Strength
The undrained shear strengths plotted versus depth in fig. 3-6
show an increasing trend with depth. This trend can be represented by
a straight line. The standard deviation from the regression line is
0.09 unit of s . The strength increase factor is indicated by s /P ~ u u 0
0.35. The strengths ranged between 0.12 and 0.50 ton per sq ft.
65
CHAFTER IV
CORRELATION OF SOIL PROPERTIES
Man has used soil as a construction material since the beginning
of civilization, although its employment as such is more hazardous than
the use of any other construction material. More money is spent on
earthwork construction than on any other type of construction and the
failures of such construction cause a greater loss of life and property
than the failure of any other construction. This is true today, even
though such men as Terzaghi, Casagrande, and others have contributed
much knowledge toward better understanding the properties of soils and
the interaction of soil properties. Because of the heterogeneous nature
and characteristics of soils, the design engineer must have more know-
ledge and a better understanding of the fundamental properties of soils
than of other construction materials. Correlations to identify the
relationships between soil properties can frequently be of significant
help to the design engineer. Correlations permit the design engineer
to make preliminary estimates and designs based on a minimum of soils
data with more assurance. Investigations by Sherman and Hadjidakis18
showed that there are reliable correlations between soil properties in
the meander belt and backswamp deposits of the Mississippi River alluvial
plain. 19 McClelland reported correlations for the prodelta clays of
the Mississippi River deltaic plain that were encountered on the con-
tinental shelf in the Gulf of Mexico. Correlations have been found to
exist between index properties (determined from simple and relatively
inexpensive laboratory tests) and shear and consolidation properties
66
(which must be determined from more complex and costly laboratory tests).
Such correlations are of great value to an engineer for use in the design
of minor projects where economy does not warrant extensive laboratory
testing. Correlations also make possible a significant reduction in
the amount of laboratory testing required on all projects. In general,
correlations contribute greatly toward better understanding the nature
of soils.
4.1 Statistical Method
The data presented in this report generally involved two variables.
The data were collected and arranged in such a manner that it was pas-
sible to describe the data mathematically. Data showing corresponding
values of variables were collected; then the corresponding variables
were plotted as points on a rectangular coordinate system. With only
two variables involved, there was the potential for simple correlation
and simple regression.
The method of least squares* is a powerfUl method for obtaining
the most reliable possible information from a set of experimental ob-
servations. Curve fitting by this method simply involves choosing a
curve for which the sum of the squares of the deviations of data from
the curve is minimum. A curve satisfying this criterion is said to be
the best-fit curve or is said to fit the data in the least square sense.
The resulting curve is called the regression curve. The best-fit curves
* References 13-16 are cited as sources of complete definitions and thorough explanations of the statistical procedures used in this study. Statistical terms and procedures are briefly defined in Appendix A.
or lines and regression equations presented in the following paragraphs
were developed by use of a computer. Standard deviations in the Y-axis
are presented. Generally, the lines of regression were described by the
equation:
however, in some instances, the second degree polynomial,
Y = a 0
+ a1
X + a2-i!-
(2)
(3)
was found to fit the data better. The second degree polynomial gives a
parabola whose axis is vertical; however, only small segments of such a
parabola appear in the process of fitting the data. The data were cor
related by either linear or nonlinear regression lines based on the
lowest computed standard error of estimate between each. The least
square lines or curves presented herein are regression lines or curves
of Y on X. The standard error of estimate is therefore a measure of
deviation from the regression line or curve in the Y axis. The standard
error of estimate has the same properties as the standard deviation of
a frequency histogram in that, if lines were constructed parallel to
the regression line or curve of Y on X at a vertical distance of the
standard error of estimate, they would contain 68 percent of the data
points~ 17 Correlation of relationship between soil properties are re
presented by regression lines or curves. In some instances, the scatter
diagram, which shows the location of points (X, Y) on the rectangular
coordinate system, showed no correlation. In some cases, the mathemati
cal nonlinear curves of regression were modified near the outer limits
of the curves to provide smooth positive or negative correlation curves
68
that best fit the data. Therefore, the equations are only applicable
to approximately the two-thirds of these correlation curves that is
nearest the axis.
4.2 Plasticity Index and Liquid Limit
One of the best known methods of classifying soils on the basis
of plasticity is the use of the plasticity chart (fig. 4-1). It has
been observed that many properties of clays and silts can be correlated
with the Atterberg limits by means of the plasticity chart. 8 It has
been found that the data for soils of a given geologic origin tend to
fall on a line more or less parallel to the A-line. The U-line is the
expected upper limit below which most soils plot on the plasticity
chart. As the liquid limit of soils represented by such a line in-
creases, the plasticity and compressibility of the soil also increase.
Inorganic clays plot above the A-line and organic clays and silts plot
below. Organic soils are also distinguished by their characteristic
odor and dark color.
A summary of the correlations between liquid limit and plasticity ·
index is shown in table 4-1. An equation is presented for each correla-
tion. Standard deviations are given for each line of regression. The
plasticity charts for each deposit studied are shown in figs. 4-2a
through 4-4b.
The regression equation for the prodelta deposits compares favorably
with the regression equation of PI = 0.831LL - 14.0 which was developed
by MCClelland. 19 MCClelland's work was oased on 53 samples of prodelta
clays from the continental shelf in the Gulf of Mexico. The standard
69
-..:J 0
C·'.::.cj~r- D~ ·;::;io:-.:
~~ ~
Group Sy,-:bol~
Gt:
GT'
'1'-Jr~cu.l lltU"".cs
Wc-11-;~raded c:·-;:,vel:;, ..:;ravel-sand t;",ixtures, little or ne ~~ncs.
F'~cld Identification Procedure:; (Excluding particles larger t.han 3 in.
and ba~lng fraction~ on estimated wci,::hts)
Wide range in grain si::e:; and ~ubstr:tntial
ilr.lOU!Jt~ of all intermediate particle dzc~.
Po~~~~1~r~c~0£>~~~=;~ or r:ravcl-:;~d mixture:;,~ Pr~~~~!.~~~~~e~~~t:i~~z~~ ~i~~~~-of ~i::e::; with
;~ ,_,] ~ ;....... "~-> ~ U~·l 3"lty cravels, ,;~ wcl-~anci-:;ilt mixture. ilo(f~;s~~~n~~~~~n~~0~i;;~c~~:c;o~e~l~~t~~i~~).
Information Required for De~Cl"ibir.g Soils
For und.i.::;turbed sell~ add inlor~::..tion on ~tratiflcution, dee;ree of compaci..ncss, cementation, moi::;ture conditions, and drainage charr:tcteristicG.
;' :::::... =";:: g <:: ~ .S Give typical n;;une; indicate upproxi:nnte
~ mi!~ ~ :S 5 ~ ~ ~ ~ ~- § ~ :;c~~~~e:n~:~~y an~~;~~=l~0~~=-3j ;:, ~ "~ .§- 0 GC Cl!.lyey 10:rll.vel.s, t;ravcl-:;nnd-cluy rr.i}:turcs. Pln.stlc fines (for identification procedures i_i · ~ d h d •• ~ ~h ,. · -
~~-~- ~.:; ~~ ~ see CL belo~·). gr~~;u;:nloc~ ~;u~e~iogi~ ~=-~d ..... " _,; ..c=- other pertinent de:o.criptive infc!'nln-
:: ~ ~ -:~ ~;~ !)-:;; :A,' f!e~!-~~~~~~ sami~, gruvclly sunds, l!.ttle or tli:~ ~~~C~n~~~~~i~t!i;:r~~l:u~~~:~~ial llJToOU.'Jts tion; and symbol in parentheses.
~~~;g~ ?~ ~ .: ::... .::l ~ SP g-: B -....-
i~g s u:,_
3~-1
~ c.
'~
5~ sc
;~ ~ _:; ~ ......
?~orl.:r c;:-aded suncis or grn•Jelly S[!!Jd.s, little or no I'incs.
Silty G::O..'ldG, :and-silt f"liXturcs.
Clay<:y r:=ds, sand-clay m.:.xtur<:s.
Predomimmtly one size or u range of ~i:,:es
l.lith so:t:e intermediate sizes misslnc;.
l/onplar:tic fine.s or fines with lo'ol ple.:ticity (for identiflcatio:J procedures :::ee 1-\L below).
Pln..:th• Enc_. {ror iderlt.ification uroccdures .:;ee CL belo;:). -
Exumple; Silty sand, tVD.Velly; about ZJ% hard, nn~ur l!l"evel purticles 1/2-<..n. mro:i:num ::;izc; rounded ll.!ld :;ubangular sand grain~, course to fine; about 15'% nonpla::;tic fines with low dry .strength; \."Ci.l compacted und moist in place; alluvial sand; (SM). I ' " !ll I I I I
~ ~ ..__ Identification Procedures
" Ur! Fraction Sr.mllcr thnn No. If() Sieve Si:!e
Dilutnncy (ReOJ.ction
to ::;hlll-;lng)
Tou,_VJneo:~
{ConsiGto:ncy near PL)
'2 i; T!lor.;:::.n!e silt; a:1d •;cry f:'.nc .:;~JJd:::, rock
:::
~-~L
~
flour, ;llty or cl:,yey ~·:.n·~ sr:..nd::; or elaycy :;.ilts vith sliV!t- plu~t.iclty.
I 3 dtc "''d occonic c:lty clc.yc of lou
~ ..,:; CL Inor~~cn:c cluy~ of lo;; to medillr.l pln:::ticit.y,
·~l·n·,ell:r cluy:, ~OJ.~.d:; clay.>. c::lty cle.ys, L~<L'l clayJ.
None to sli,::ht
Nedi Ul'l to high
Quic~. to slo1·
!lone to very slow
ilonc
l·!ed1Wn
For W1di:;turbed ::;oils add infom[!tion on :;trueture, :.tr'"-tificL.tion, consi:;tcncy in und.i:;turlled nnd re:nolded stutes, r.mi::;ture o.nd dn:..ina;~e condit!.o~n;.
Give t.ypic::.l nrunc; .iudicnte dcgrc:c otr.d C"---------+----t---------------+------j--------1C"---------1 che.rr.ctcr of plust~c~ty; f.l·r.oun<. :_.nd
WJ..X~rr:un .;ize ol coarse grains: colo!" ln \ret. condition; odor, if' t~ny; lc.clol
0 ~~ CE
"}, Ci:
';: ::->.:.~· J:- _:;.r.:c .::0~1: ,,._
I!JCJ ::..::1lc c:l:;y.: cf hi,_j} pl:.o.~t.icity, f:.o.t clay~
Or,~:..:~:.c c:l;,y:::- of ~.o:!diu::r to hi,~h pl:...~ti:city,
n·:::;n!llcsilt.:;.
P·~nt. :;r:d oth<.:r !oL~hl:; or,;::.~:c ~oil:.
E.i.,:;h to very hi~h
i'ione
~·!eciiU!:l to hiifr< I i/o~~0~0 YC:'!'Y
H.i,jl
Sli;:;ht to rr.cdiurn
Re"'.dily identitled Uy colo1·, mlor, _pcnc;y feel :..:nd f!'cquently by fibrous texture.
or GCOlOGiC numc nnd other pertinent. cie:::criptive informo.tion; and :.;;rmbol in yarenthese:;.
Exwnplc: Clcyey :;ilt, br01m: ~lic;ht.ly plust:c; small perccnt:J{:e of fine !";!ind; numerous vert.icnl root hcle::; firm nnd O:ry in pluce: loe::~; (JI,L).
~ ~
c ~
.5
~ § ..
~~ ~ -~ §.:
1~g 13~~ t.!l'd<;:; 5 ~ ';i
~ -~ ~ ~~~ 1:~ ~~! s'o -~ ·~ ~ ~ ~~ ~
~ [ ~ ~~~ u~
i:i B H
6o
50
40
~ I~ ~ ~
30
"' 10 T 4
0
~
Labora~ory Cla~~if:..cation
Cr-:.terin
D60 Cu =~Greater t.han 4
""' (D )2
1 ~ Cc = D10
3~ DGo 3etwcen 1 o.nci 3
i~ AtterOe~:t l::::~r:c::: ~~l~::::n rc:::::rn~:~.s 1::~ :: th
1-o .g or PI le:::s than 4 ?I betveen 4 and ·r , . ~ ~ are borderl~ne ease:;
fu g ~ .., requir:!.ng u~e c.or dual ~ ~ <! g Att.erber,:: limits above "A" line .:;ymbols.
~0~0~----------~---------L--------------~
~ t7i .5,: with PI creater thv.n 7
: .. ~~] g C " ;e. Greater th&n 6 c c :Il u 10
1'i\~ .§~10-:5:5 .....
~ (D / I Cc=~Betveenland3
Not meeting all (';l'"Et.dut.ion requirements for ,sy;
0
g~$ ~~ ~1?.: A~~~r~~rfe~~!r·~~:nb4lO\.' "A" line I ;, 0 ~'!cr,~,~~: .. ?~~nf :~~il",'
'lrcicr:\erl:.n.:-criJ..CJ rc;J_uirinr• u.: :;f ,l\n'
Att.erberG limit~ abol.'e ''A" line I .o:r:r.bolJ. w!.th PI greater tho:1 7
Comparin:; Soil:: at Equul Liquid Li:r.i t Touc;hncss and Dry StrenGth Increase ~~_;_th Increasi~ Plasticity Index
CH~nf ·-
10
CL
CL-ML ML
20 ]0 l10 5C 6o
LICUID L!~·:IT
?U~ICI'I'Y CiUIIl7
OH & l·li
TO
For la"ooruto!-y clu:.:if:c .. t:cn o:' fir;c-c;r«i~.eC. -~c:L
;N lOO
(!) 3yt::,;i: .. ~: cl·.--::·:c- .. t: So~l: po::~c:;~ ,,,~ ch~:o.c~<..ri:t.:c. cf ;.;:o 7-"0U)l.': :o.rc dc.·::i.G!1atcd b;: cc!:lbin::.tiGn~ of ,:roup ,,ymboL. For cxto.mpl-:: -:;;:.GC, ;,•cll-c;rr.dc:d crnvcl-:;::cnd r.:oi:-:ttu·e •:.it)l clay tinder. (2) All ~:eve :;L:cr; un th:.: cl:t..!"t or<: U. ~-cu'ld•u·d.
Fig. 4-l. Unified Soil Classification Sy~0
deviation for the equation developed by McClelland was not reported.
Sherman and Hadjidakis18 reported an equation of PI 0.7951L -
8.09 with a standard deviation of 5.71. Their work was based on 125
tests on backswamp deposits at the Morganza Floodway Control Structure.
This equation compares reasonably close to the equation reported in
table 4-1. Thus indicating that similar soils (although the backswamp
deposits at Morganza Floodway are alluvial valley deposits) fall on a
line approximately parallel to the A-line and can be represented by a
line of regression equation.
TABLE 4-l
SUMMARY OF CORRELATION BETWEEN LIQUID LIMIT
AND PLASTICITY INDEX
DEPOSIT FIGURE LINE OF REGRESSION STANDARD DEVIATION
Natural Levee 4-2a PI = 0.86LL 14.46 3.45
Point Bar 4-2b PI = 0.87LL 14.99 3.48
Interdistributary 4-3a PI = 0.79LL 9-27 4.69
Intradelta 4-3b PI = 0.81LL - 11.3 3.80
Prodelta 4-4a PI = 0.79LL 8.48 5.70
Back swamp 4-41; PI = 0. 73LL 6.81 6.32
4.3 SEecific Gravit;y: and Plasticit;y: Index
All calculations involving the fundamental properties of a soil
mass require the use of the specific gravity (G ) of the solids. The s
specific gravity mus~ be known with reasonable accuracy for the reduc-
tion of data from laboratory shear and consolidation tests. Ranges and
71
a. Natural levee
1&0
/ / v
/v L v
~ / v
180
140
120
80
@) Pi•O .• TLL7 t7' v
U-LIN£-
~ / ~A-LINE' /
/~ ~ v
@
/ l0-v ~··
100
eo
/ ~ ~ v 8•€
~ V4'
--~·€) Sy x. =3.48 ~ _L
20
0 o 20 40 eo ao 100 120 1 40 110 1ao zoo 220 240 210 zao
LIQUID LIMIT
b. Point bar
Fig. 4-2. Plasticity charts for natural levee and point bar deposits
72
,.. t-o
180
180
140
120
~ 80 .. ~
eo
40
20
0
/ v
/ / //
~o/ v /
PI•O.T>LL-•.1'7-~/ / / . U-LINE-v ."/ / 1--/
@ v ~/. ~ v @ ~~ ~ KA-LIN£
/ ~ •/ /
Wb&@
/ ~ ~ / v v i--- @•@ ~ I-' Syx = 4.69
I o 20 4o eo eo too 120 t40 teo teo 200 220 240 2eo zao
LIQUID LIMIT
a. Interdistributary
180
180
140
120
~ 0 ~ 100 ,.. t-o ~ 80
~
eo
40
20
@
/
.¢! {P
ti-LINE-
@) K: /~ ~
/ ~ v ~ ~ / ?.· v v
@•@
/ /
v
/ ·v_ PI•O.OILL-17
v ,/. v ~/ /
/ v / v / / v // ~ v A-LIN£
v/ / v
v
~·@>
Syx = 3.80 I
20 40 60 &0 100 120 1 ... 0 180 180 200 220 240 280 280
LIQUID LIMIT
b. Intradelta
Fig. 4-3. Plasticity charts for interdistributary and intradelta deposits
73
! ! I I /
v v i I
i I I !
f--! ! v I / -++ I
/ I
U-LINE-v v i
i / PI-O,.,.LL-6J./ v/ v
180
100
140
120
@ @) v l.-/)' 0-lA-L/N£ f----
/
~~ [,,/ v /
100
eo
20
/ l;;~ v ~ ~ v. e~€3
/ v ~
v . ~ f@&@ Svx=5.70
!-""'" . I
00
40
0 0 20 40 eo eo roo r2o r4o roo reo 200 220 24o 2eo 2eo aoo
LIQUID LIMIT
a. Prodelta
12>
0
/ ~t~.;) / / .~~..~ lo /•
!!!-./~
/ v . b/' .../~
.. ~
Pl•O.ULL-._.'7-- ;;> v . 'C ~· . -~ v 13.9
7.• .. : . .. . .
~ 'y U-LINE-v. ~-LINE
. . € 0 .
V~; . -' v . . ~
v·~ v. .. t? .
/ r--;;;
22>
200
17>
100
100
~ . .
/
/. ~ .. 8• @ . .
~ ~ v . Sy X= 6.32 ·.~ . I
0 0 2!t ~0 7~ 100 12~ l!tO 17!t 200 22!t 2!tO 27!t 300 32!t l!tO 37!t
LIQUID LIMIT
b. Backswamp
Fig. 4-4. Plasticity charts for prodelta and backswamp deposits
averages of specific gravity were presented in Chapter II of this
study. For this discussion, specific gravity was correlated with plas-
ticity index. A summary of the correlations is provided in table 4-2.
In figs. 4-5 through 4-8, it is shown that the specific gravities for
inorganic deltaic deposits have a positive correlation with plasticity
index; while a negative correlation is shown for organic deltaic deposits.
Reasonably good correlations exist for all the deposits, with the greatest
scatter reflected in data for the organic backswamp deposits. The cor-
relations shown in figs. 4-5 through 4-8, supplemented by the specific
gravity frequency histograms shown in figs. 2-12 and 2-13, provide some
basis for estimating specific gravities for the deltaic deposits.
TABLE 4-2
SUMMARY OF CORRELATIONS BETWEEN SPECIFIC GRAVITY
AND PLASTICITY TI!DEX
DEPOSIT FIGURE LINE OF REGRESSION STANDARD DEVIATION
Natural Levee 4-5a G 2.66 + 0.0007PI 0.02 s
Point Bar. 4-5b G = 2.66 + O.OOlPI 0.02 s
Interdistributary 4-6a G = 2.66 + O.OOlPI 0.02 s
Intradelta 4-6b G = 2. 68 + 0. 0003PI 0.04 s
Prodelta 4-7 G = 2.68 +O.OOlPI 0.02 s
Back swamp (Inorganic) 4-8a G = 2.65 + 0.0004PI 0.04 s
Back swamp (Organic) 4-8b G = 2.81 - 0.003PI 0.11 s
75
2.8!1
2.80
.. ,-· 2.7!1 >-~
1-
~ ~ 2.70
~ ~ u .... ~ 2.8!1
2.80
,__-;-;
•
• • •
• • ~
~--~--- •• •
• • •
• --~-----• ~-_..- ..-;- • ~ • • ............_Gs•2.66+0.000T PI •
•
Sv.x. = 0.02
I 2.5!1 0 10 20 30 40 80 70 80 90
a. Natural levee
2.85
2.80
.., .. 2.75
>-~ 1-
> <( •
•
• • • • -.~ . ~ 2.70
u ... . -f.--.· .. ~
~·· • • u .... l); 2.65
2.60
2.!15 0
--- •
10
b. Point bar
• • . .. • • •
20 30
PLASTICITY INDEX, PI
•
~-< -
• ---.:--:- Gs •2.66 +0.001 PI
• •
Sy X = 0.02 .. , 70 80 90
100
100
Jig. 4-5. Correlation between G8
and PI for natural levee and point bar deposits
76
2.85 ~
2.80
~:>"'2.75
>~
t-
~
• • ~-1-
• • ~.-• ~- •
•• ·-- • • !!i 2.70
~ 1---;-1---. ~G 5 •2.66 +0.001 PI
~ u w :li 2.65
2.60
2.55 0
-
10 20 30
a. Interdistributary
2.85
2.eo
1:)011
2.75
>t-
~ ~ 2.70
~
'"' u w :); 2.65
2.60
- -
• . 1-• •
• • •
2.55 0 10 20 30
b. Intradelta
•
• •
•
•• • •
Sy X = 0.02 .. I
40 50 60 70 eo 90 100 PLASTICITY INDEX, PI
• • • • / G5 ~~68 +0.000.1 PI
• :/ • • • • • • . • ••• .!..---
r-.--~ • • • • •
• •• • •
• • .
--
Svx = 0.04 .. )
40 50 eo 70 80 110 100 PLASTICITY INDEX1 PI
Fig. 4-6. Correlation between Gs and PI for interdistributary and intradelta deposits
77
2.85
2.80
0 2.75
~-1-
~ • -·
• ~ .. •• • __....---< ~ • •
• •• • ..... ·~ --·~ • .... ..
-G5•2.66 fO.OO/ PI • • ••
:§ 2. 70
~ ~ •• •• • •
~ u "' g; 2.65
2.60
2.55 0 10
Fig. 4-7.
• • • • •
Sv.x. = 0.02
I 20 30 40 50 60 70 80 90
PLASTICITY INDEX1 PI
Correlation between G and PI for prodelta deposits s
100
2.9
2.8
>~
~ 2.7
~ a: C)
u !;; 2.6 u "' Q. <I)
2.5
2.4 0
Gs•2.65 .,.0.0004 PI\
• \ • • •• - - • •
• •
10 20 30 40
a. Backswamp (inorganic)
2.8
• • • • • 2.7
le ....... •• • • ~· ... 2.6
I
• • . Jr •• • •
l!se~ • _.• -:. • • • • t .•• -, .•. r--- --.--. .. • • • I -:a:. • .: • • •• • • • • • •
Sv.x. = 0.04
I 60 70 80 90 100
PLASTICITY INDEX, PI
• •
• .........
"'~ • • • • •
J'2.5
> 1-
~ ffi 2.4
u ... u ~ 2.3
2.2
2.1
2.0 0 20
• • • •
40 60
b. Backswamp (organic)
• •
•
80
.. -............... • • •• • r---~
~Gs =2.81-0.00.1 PI
• •
'~ • • •• ~ • ...... ~
~""' • • • • • ••
• •
Sv.x. = 0.11
I 100 120 140 160 180 200
PLASTIC lTV INDEX, PI
110
~
220
Fig. 4-8. Correlation between Gs and PI for inorganic and organic backswamp deposits
79
4.4 Shear Strength Characteristics
4.4.1 Undrained Shear Strength and Liquidity Index
Relationships between liquidity index (LI) and unconfined com-
pressive strength for Chicago clays are given in reference 21. This
suggested that similar correlations could be made for other soils that
have the same geological origin. A well-defined relationship between
undrained shear strengths and the index properties of soils is needed.
Means for accurately estimating s would be helpful to design engineers u
as a supplement to laboratory shear strength data. The plots of liqui-
dity index versus s in figs. 4-9 through 4-ll permit estimates of s u u
for the deltaic deposits based on re~atively inexpensive laboratory
tests. Based on the least squares method, the resulting best-fit line
is nonlinear. This nonlinear correlation of data is represented satis-
factorily by the second degree polynomial. The best-fit curves resulted
in negative nonlinear correlations for all the deltaic deposits
investigated.
4.4.2 s jp Ratio and Plasticity Index u 0
In reference 8 Skempton is quoted as suggesting that a constant
ratio should exist between the undrained shear strength and the effec-
tive overburden pressure for normally consolidated soils of similar ge-
ologic origin that have a constant plasticity index. It has also been
found that a correlation exists between s /P ratio and plasticity inu 0
dex for reasonably homogeneous normally consolidated deposits. 8 This
correlation has been found to exist over a wide range of types of sedi-
mented clays. Such a correlation makes it possible to roughly estimate
80
~
..J ,.~
l!l
1.8
1.4
1.2
1.0
~ 0.8 ,.. ... 0
:> ~ 0.8 ..J
0.4
0.2
0 0
. .
~ . . . . -~ . . . . . 1'-.. .
-~ . ... K "-..,
~ .. --..........
0.1 0.2 0.3 0.4 0.~ 0.6 0.7 UNDRAINED SHEAR STRENGTH, Su T/SQ FT
a. Natural levee
~
..J
,[
"' 0
1.8
1.4
1.2
1.0
~ 0.8 ,.. ... 0
:> ~ 0.8 ..J
0.4
0.2
0 0
• • •
• ....... K t-..
• . .
0.1 0.2
b. Point bar
•
• . ~
~ . . 1--. . . . . • r---t----
•
.
0.3 0.4 0.~ o.e 0.7 UNDRAINED SHEAR STRENGTH, Su TISQ FT
Fig. 4-9. Correlation between point bar deposits
s and LI u
81
Sy X= 0.19 .. I 0.8 0.9 1.0 I. I
1.18 -----~
Svx=022 .. , 0.8 0.9 1.0 1.1
for natural levee and
... ...J
x' ... 0
I.e
1.4
1.2
1.0
~ 0.8 > .... Ci 5 !? 0.6 ...J
0.4
0.2
0 0
.
•
•• •
""' : , . • •
K • • • . ~
• • • . • • ···~
. ~
• • • • 1-• !'-·:_) • • • . .. • • . \ ~ --•
• • . •
•
0.1 0.2 0.3 0.4 0.5 0.6 0.7
UNDRAINED SHEAR STRENGTH, Su. T /SQ FT
a. Backswamp (inorganic)
... ...J
x"
~
I.e
1.4
1.2
1.0
~ 0.8 > .... 0
::> !? 0.8 ..J
0.4
0.2
0
~ . ..
r---...... ••• • _jl_
.-......e_
~ . . • . . .. . . .
. . . .. . • .. . . • ~ • . ~ • . . . •••• . . . . .
0.8
0 0.1 0.2 0.3 0.4 0.5 0.6 0. 7 0.8 UNDRAINED SHEAR STRENGTH, Su. T/SQ FT
b. Prodelta
Svx.=0.17 I
1.0
Svx=O.I4 . I
0.9 1.0
Fig. 4-10. Correlation between su and LI for inorganic backswamp and prodelta deposits
82
I. I
1.1
:; XOJ 0
J.8
1.4
1.2
1.0
~ 0.8 ,.. t-o :> ~ 0.6 ...J
0.4
0.2
. . . ~ . . .
. . . . . . . .. . . ~ . ~ • • . . .. . . . .. ~ ... ~ ... .. ' .. 1-
0 0 0.1 0.2 0.3 0.4 0.~ 0.6 0.7
a. Intrad.elta
~
...J x-"' 0
1.6
1.4
1.2
1.0
~ 0.8 ,.. t-o :> ~ 0.8 ...J
0.4
0.2
' . ~
.. . ~
. ~ ... . .
UNDRAINED SHEAR STRENGTH, Su T /SQ FT
. . . ~ ~ . . r---.
0.8
0 0 0.1 0.2 0.3 0.4 0.!1 0.6 0.7 0.8
UNDRAINED SHEAR STRENGTH, Su T /SQ FT
b. Interdistributary
Sy X.= 0.16 I
0.9 1.0 1.1
Sv.x.=0.16 I
0.9 1.0 1.1
Fig. 4-11. Correlation between su and LI for intradelta and interdistributary deposits
83
the undrained shear strength of normally consolidated deposits on the
basis of results from Atterberg limit tests; however, if undrained shear
strengths are available from laboratory tests, it may be possible to
determine whether the deposit is normally consolidated or overconsoli-
dated by comparing the laboratory data with the correlations shown in
fig. 4-12. Undrained shear strengths from normally consolidated soils
should agree reasonably well with the correlation trends, overconsoli-
dated soils would not correlate. Plots of s jp ratio versus plasticity u 0
index are shown in fig. 4-12. In contrast to the positive correlation
suggested in reference 8, the data for the deltaic deposits indicate
both positive and negative, and no correlation. There is no apparent
explanation for these relations. The natural levee deposits were not
investigated because of their overconsolidated nature.
4.4.3 Drained Shear Strength and Plasticity Index
The shear strength parameters from drained shear strength tests
(S-tests) are designated as the angle of internal friction ¢' and co-
hesion c'. These shear strength parameters used in this report were
obtained by a straight line approximation of the data. The drained
shear strength for normally consolidated cohesive soils can be expressed
with satisfactory accuracy by Coulomb's eQuation in which c' = 0. 8
Thus
where
sd = shear strength
s = p tan ¢' d 0
p0
= effective overburden pressure
84
(4)
co \Jl
0
0 0.5
0.4
i= 0.3 < a:
'fo.2 .. 0.1
0
0.5
0.4
0 i= 0.3 < a:
~0
0.2
0.1
0
0.5
0.4
0 i= 0.3 < a:
1-02 0.1
0 0
...........
PLASTICITY INDEX 10 20 30 40 50 60 10 eo 90 100 110
. . . . . ' t-- I • . r~ -"-:-- . 1-!--- /'<Y.. w0.343-0.003 PI . .. ~ . .
I
I J sv.x. -o.oe r POINT BAR I
•: • I • •
I INTRAOELTA I
. . • j.62
. . . . . +--. . . .
1--...-. . . --·. . . . ~ f·~ >;-."-~•% w0./Sr0.002 PI
._....! •• 1 .... . . · . ~ . . - .. .. : . . . : ·. .
I BACKSWAMP I SY.X.i0.1 (INORGANIC)
10 20 30 40 50 60 70 eo 90 100 110 PLASTICITY INDEX
0
0
PLASTICITY INDEX 10 20 30 40 50 60 10 eo 90 100 110
. . . . I
- 1--~ a .. • ;:_:.:_ ~· :.:.-. -;:---.;. r.:.--;..; .. . . .. -· · . . . ': •. i I . . Sv.x.iO.OS
. I_ I _I •
'%._ =0.19r0.002 PI~ . ~ -·
~-1- .
~ lt''<y,; w0.25-0.0005 PI • I
. -
r PRODELTA l
. . f.---·--~----. . . .
I I NTERDISTRIBUTARY I
0.5
0.4
0 0.3 ~
a:
0.2f.
0.1
0
0.5
0.4
0
0.3 ~ a:
0.2-f.
" 0.1
Sv.x.i0.06
90 100 110° 10 20 ":3o 40 50 60 10 eo PLASTICITY INDEX
Fig. 4-12. s /p ratio versus plasticity index for point bar, intradelta, inorganic backs~am~, prodelta, and interdistributary deposits
It is, therefore, considered reasonable to omit the c' parameter when
defining the drained shear strength, although the c' values ranged
between 0 and 0.30 ton per sq ft. Bjerrum and Simmons,22 Sherman and
Hadjidakis, 18 and others have reported correlations between¢' and
plasticity index for normally consolidated clays. The values of¢' seem
to decrease as plasticity increases. Correlations of¢' with plasticity
index are shown in figs. 4-13 and 4-14. Insufficient data were available
for individual types of deltaic deposits located along the river, so
they were correlated as a group and called "deltaic". The data rep-
resenting this group is from tests on reasonably normallY consolidated
soils. Correlations of¢' and PI for the inorganic backswamp deposits
are shown in fig. 4-14. The correlation of data for the inorganic
backswamp deposits shown in fig. 4-l4a is based on data from normally
consolidated soils. The correlation of data shown in fig. 4-l4b
should be used with caution because the inorganic backswamp soils rep-
resented by this plot are slightly overconsolidated. The c' parameter
was not correlated with PI. No correlations existed between ¢' and
PI for the organic backswamp deposits. The standard deviations from
the regression lines varied from 1.75 to 3.84 units of friction angle.
4.5 Consolidation Characteristics
4.5.1 Compression Index and Index Properties
Relationships between compression index and index properties such
as natural water content and liquid limit have been established in public
8 literature. Terzaghi and Peck reported a correlation between compres-
sion index and liquid limit for normally consolidated soils and suggested
86
45
40
35
(/)
::130 a: C)
"' 0
z -25 $.
20
15
10 0
............. •• •
I> I • ~
•
10 20 30
I I LEGEND ---
I NATURAL LEVEE • INTRADELTA A PRODELTA • UNIDENTIFIED
• '--..._
1---- • • r----• • --1---• r---• 1--t-•
Sv.x. = 3.B4
I 40 50 80 70 80 100
PLASTICITY INDEX,PI
Fig. 4-13· Correlation of drained shear strength with plasticity index for deltaic deposits
-
110
40
3~
30 '
~ • •
~· '[.;-_._ • • • • ~
• • • • ~= • • • ·-·· • . • • ~ • •
20
r--.. ... 1---• r---
I~
10 0 10 20 30
• • • •
40 ~0 flO PLASTICITY INDEX, PI
• •
Sv.x. = 3.0
I 70 80
a. Normally consolidated inorganic backswarnp deposits
U) w w a: 1-'
40
3~
30
~ 2~
~
&
20
I~
10 0
' r--.. ~
~ '
10 20 30
•
"" 1'---1-----: 1---.,._
•
Sv.x. = 1.7 S
I 40 ~0 flO 70 flO
PLASTICITY INDEX, PI
b. Overconsolidated inorgani~ backswamp deposits
90
90
100
100
Fig. 4-14. Correlation of drained shear strength with plasticity index for inorganic backswamp deposits
88
that the line of regression can be represented by the e~uation:
C = 0.009LL- 0.09 c (5)
Sh d H d .. d k. 18 t d . . l l t . f th Mi . erman an a Jl a 1s repor e s1m1 ar corre a 1ons or e ss1s-
sippi Valley alluvial soils, as well as correlations between natural
water content and compression index for the alluvial valley soils. Ap-
preciable differences were found between correlations of compression
index and index properties of normally consolidated and overconsolidated
soils. Sherman and Hadjidakis18
suggested that the correlation between
compression index and li~uid limit can be represented by a linear line
of regression with an e~uation of:
C = O.OllLL - 0.176 c
The standard deviation from the regression line for their data was
(6)
0.137 unit of compression index. This correlation is in reasonably
close agreement with that reported by Terzaghi and Peck. Correlations
between compression index and natural water content and between com-
pression index and liquid limit for deposits in the study area are dis-
cussed in the following paragraphs.
Correlations between compression index and soil index properties
permit engineers to estimate the order of magnitude of settlement in a
cohesive stratum caused by some applied external load without making
any tests other than li~uid limit and natural water content tests. These
correlations have proven useful for estimating settlement in normally
consolidated soils. The correlations of compression index with li~uid
limit appear to be more reliable than the correlation of compression
index and natural water content. Based on the data presented herein,
positive correlations exist between compression index and natural water
content and compression index and liQuid limit for the deltaic deposits.
The correlations can be represented by linear lines of regression.
Summaries of correlations between water content and compression index,
and liQuid limit and compression index are shown in tables 4-3 and 4-4,
respectively. The correlation plots are shown in figs. 4-15 through
4-21.
TABLE 4-3
SUMMARY OF CORRELATIONS BETWEEN WATER CONTENT
AND COMPRESSION INDEX
DEPOSIT FIGURE LINE OF REGRESSION STANDARD DEVIATION
Natural Levee 4-l5a c 0.017w 0.46 0.28 c
Point Bar 4-'l6a c = O.Ollw 0.12 0.19 c
Interdistributary 4-l7a c = O.Ol5w 0.13 0.19 c
Intradelta 4-l8a c O.Ol4w 0.056 0.20 c
Prodelta 4-l9a c O.Ol6w 0.14 0.13 c
Back swamp 4-20a c = - 0. 91 + 0. 027w 0.74 (Organic) c 0.000045w2
Back swamp (Inorganic) 4-2la c = 0.02w - 0.36 0.33 c
90
TABLE 4-4
SUMMARY OF CORRELATIONS BETWEEN LIQUID LIMIT
AND COMPRESSION INDEX
DEPOSIT FIGURE LINE OF REGRESSION STANDARD DEVIATION
Natural Levee 4-150 c = 0,013LL - 0.37 0.40 c
Po:int Bar 4-16b c = O.OllLL - 0,04 0.24 c
Interdistributary 4-17b c = O.Ol4LL 0,22 0.21 c
Intradelta 4-18b c 0. 012LL 0.12 0.19 c
Prodelta 4-19b c = O.OlLL - 0.09 0.12 c
Back swamp 4-20b c = - 1.215 + 0.024LL 0.75 (Organic) c 0.000035LL2
Back swamp 4-2lb c = 0.013LL - 0.28 0.36 (Inorganic) c
The equation shown in table 4-4 for prodelta deposits closely agrees
with a correlation reported by McClelland19 for prodelta clays from
the continental shelf off southeastern Louisiana. McClelland's cor-
relation is represented by equation:
C = O.OllLL- 0.176 c (7)
Sherman and Hadjidakis18 found the same correlation to exist between
compression index and liquid limit for the Mississippi River alluvial
deposits as noted from equation 6.
91
3.~
3.0
u 2.5 u X UJ 0 z - 2.0 z Q U) U) UJ
g: 1.~ :::!! 0 u
1.0
0.~
0 0
. / v
20 40
•
v v Cc zO.OI T...,.-0. 46
~ v /
v v
/ v
•
/ 17
•
Sv.x.=0.28 I
60 80 100 120 140 160 180 200 NATURAL WATER CONTENT ,ur Ofo
a. Compression index versus natural water content
3.5
/
220
~-
u u X llJ 0
3.0
2.5
~ 2.0 z Q U) U)
"'
•
Cc "0.01.1LL -0 . .1T--.__
i'Y v
/ /-
v v
y
g: 1.5 :::!! 0 u
1.0
/. /
_/
/ 7
/
0.~
0 0 20 40 60 80 100 120
LIQUID LIMIT, LL
b. Compression index versus liquid limit
•
Sv.x.= 0.40 I
140 180 180 200
Fig. 4-15. Compression index correlations for natural levee deposits
92
220
u u x ...
1.4
1.2
1.0
~0.8
z 0 iii ell ~ 0.8 D. ::::e 0 u
0.4
0.2
1.4
1.2
1.0
0 0
u u ,; ... ~ 0.8
z Q ell en ::! 0.8 Q.
::::e 0 u
0.4
0.2
0 0
• •
-Cc•O.OII cv-0.11- y v
• • • : /
.V [7 •
•
v. v •
v •• . /
Sv.x.=O.I9 I
10 20 30 40 50 60 70 80 90 100 110
NATURAL WATER CONTENT1 u.r 'Vo
a. Compression index versus natural water content
•
v v
-Cc•0.0/1 LL -0.0~>
/ v..
• • v • ~ • v •
/ • / •
Sv. x.=0.24 I
10 20 30 40 50 80 70 80 DO 100 110 LIQUID LIMIT, LL
b. Compression index versus liquid limit
Fig. 4-16. Compression index correlations for point bar deposits
93
~ u X~
LIJ 0
1.4
1.2
1.0
! 0.8 z 0 iii II) LIJ
8: 0.11 ::lE 8
0.4
0.2
~ u X~
LIJ 0
0 0
1.4
1.2
1.0
~ 0.8 z Q V) V) LIJ
If 0.11 ::lE 8
0.4
0.2
0 0
• • / v
Cc=O.O/S...,.-0,/.J---._
IY v·
•
/ v. • •
•
v. •
/ v.· • •
/ •
Sv.x. iO.III
10 20 30 40 50 eo 70 80 110 100 110 NATURAL WATER CONTENT1ur "To
a. Compression index versus natural water content
• •'/ • v Cc •0.014LL-0.2~y
• • v- 122
/ •
V· •
/
• v • • /.
I/
I Sv.x.
1
-o. 21
10 20 30 40 !>0 eo 70 80 110 100 110 LIQUID Llt.41T1 LL
b. Compression index versus liquid limit
Fig. 4.17. Compression index correlations for interdistributary deposits
94
3.!!>
3-0
~2-!!1 u X w 0
~ 2.0 z Q Ul Ul w
•
g: 1.!!> :::11
8 C., w0.0/4...--0.0~ :----~
~ u X~ w 0
1.0
0.5
0 0 10 20
-~ • •
30
• •• • !.
~ ......-~
•
~ .. • . -• • •
40 50 60 70 80 NATURAL WATER CONTENT,u.r%
a. Compression index versus natural water content 3.5
3.0
•• .
•
Sv_x_=0.20 _[ 90
~ ~ 2.0 z Q • / v Ul Ul w g: 1.5 :::11
Cc•O.OI2LL -0./2~
8
1.0
0.5
0 0 20
• • v v •
• - I/
~ ~ -. • ~ ••
/
/ ~,
40 60 80 100 120 LIQUID LIMIT, LL
b. Compression index versus liquid limit
140
Sv.x. = 0.19 l
160 180
100
200
Fig. 4-18. Compression index correlations for intradelta deposits
95
110
220
1.4
1.2
1.0 u
u )( ... 0
~ 0.8 z Q ll! ... g: 0.8 li 8
.J )(~ ... 0
0.4
0.2
0 0
1.4
1.2
1.0
~0.8 z Q U) U) ... g: 0.6 li 8
0.4
0.2
0 0
c. •0.016..,. -0. 14----...._______ v v • • Y'
• • /. ... • • » •
• • • • ·~ •• v. •
/ v. •
/ • •
Sv.x.= 0.13 I
10 20 30 40 !)0 80 70 80 90 100 NATURAL WATER CONTENT ,ur%
a. Compression index versus natural water content
• Cc•O.OILL -0.0.9~ v~ . ·-· 0
~. • • • • • •
/ • •
/ /. •
/ •
Sv.x.= 0.12 I
10 20 30 40 !>0 60 70 80 90 100 LIQUID LIMIT, LL
' b. comwression index versus liquid limit
Fig. 4-19. Compression index correlations for prodelta deposits
110
110
u u
15 0 ~ z Q If) If) ... a: Q.
::e 0 u
u u X ...
7.0
6.0
~.0
• . ~
1----
:_-. l---- • • • • • . . • ~ • y • • • •• • • • • • •
.x ~ f...... Cc• -0.11 +0.027 ~ -0.000045..,-1
• • v • • • • • Sv.x.= 0.74 • • I
4.0
3.0
2.0
1.0
40 80 120 180 200 240 280 320 380 400 NATURAL WATER CONTENT,....,. "''o
a. Compression index versus natural water content
7.0
6.0
~.0
• . ---~---
~ 4.0
---- • • • ~ •
z 0 iii :3 3.0 a:
• • _,....
~ ~ -Cc•-1.215 +o.o,us LL-o.ooooJs LL 2
Q.
::e 0 u
2.0
1.0
0 0 40
• • • v. ~
/""' • • • • r·,· • • • / ,.• •
80 120 180
••• • ,/' • • •
•
200 240 LIQUID Llt.AIT1 LL
b. Compression index versus liquid limit
•
Sv.x.= 0.75 I
280 320 3110 400
Fig. 4-20. Compression index correlations for orgainc backswamp deposits
97
440
440
u u x w 0 ~ z Q II') II') .... a: a. :::!! 0 u
u u X ....
3.!1
3.0
2.5
• 2.0 •
• • • • • •
• .. ~
v • • • ~ • . • • •
~ ~ • . .. • ... .. Cc•0.02..,.-0 • .N~ •• •• • • • •
•
~ ~· .. . •
• Sv.x.ar-33
1.5
1.0
0.5
0 0 10 20 30 80 70 80 ' 90 100
NATURAL WATER CONTENT, u.r "7'o
a. Compression index versus natural water content
3.!1
3.0
2.5
• • v • v ~ 2.0
z 0 iii :!) 1.5 a: a. :::i! 8
1.0
0.5
0 0 20
• • • • . • . • / • ~ ... ,
• . ~ ~ • . "' •
0 .. ..... ~ ••
• v. iio • •• • I I • •
/ fee •
40 80 80 100 120 LIQUID LIMIT, LL
b. Compression index versus liquid limit
~Cc =0.0/.JLL -0.26
•
Sv.x.j0.36
140 180 180 200
Fig. 4-21. Compression index correlations for inorganic backswamp deposits
110
220
CHA.Pl'ER V
DISCUSSION OF RESULTS
5.1 Frequency Histograms
Typical properties of the deltaic deposits in the study area are
summarized in table 2-1 and the variations in soil properties are pro
vided by fre~uency histograms shown in figs. 2-2 through 2-20. They
are presented for use by foundation design engineers who have limited
laboratory data on deltaic soils and are in need of supplementary data.
These histograms are intended only as supplemental data and for use in
making rough approximations of soil properties. In no instances should
these data be used in lieu of laboratory test data for making final
foundation designs. If, however, the engineer selects data from the
histograms based on his best judgment as to its applicability to his
particular field conditions, the data should be ~uite useful in provid
ing additional confidence in limited laboratory data. The mode values
of the fre~uency distributions are the values that are most likely to
occur for a given deposit. These values can be used in lieu of average
values with reasonable confidence.
As pointed out in Chapter III, some soil properties such as water
content, Atterberg limits, li~uidity index, void ratio, and others, can
be a function depending upon depth. Therefore, this should be con
sidered if data are selected from the histograms. The engineer should
select data within the range of plus or minus one standard deviation
from the average but he must also take into account the effect of soil
properties within the limits of variations that have been encountered.
99
Statistical presentations of data in the form of fre~uency histograms
provide a better understanding of the variations in soil properties of
deltaic soils.
5.2 Soil Properties Versus Depth
5.2.1 Natural Water Content
The range of natural water contents appeared to decrease slightly
with depth and the range generally narrowed significantly as depths in-
creased. Near the surface the water content data occupied a wide
range, which can be attributed to the presence of organic matter.
5.2.2 Undrained Shear Strength
The undrained shear strengths of the deltaic soils, with the ex-
ception of the natural levee deposits, tend to increase with depth.
Typical shear strength profiles are shown in figs. 3-1 through 3-6.
They show that the shear strengths are either constant or decrease
from the surface through a weathered zone and then increase linearly
with depth. The undrained shear strengths of the natural levee de-
posits showed no variation with depth because of the overconsolidated
nature of the soils represented by the test data.
Shear strength increase factors (s /P ) were computed for each u 0
deltaic deposit with the exception of the natural levee deposits. They
ranged from 0.22 ton per s~ ft for the prodelta deposits to 0.35 ton
per s~ ft for the interdistributary deposits. Shear strength increase
factors were only developed for the normally consolidated soils and are
not intended to apply to the slightly overconsolidated soil near the
surface.
100
5.3 Correlations
5.3.1 Plasticity
The plasticity values of all the deposjts except the backswamp
deposits generally plotted close to but above the A-line, indicating a
classification of CH or CL. Plasticity values for the backswamp de
posits generally plotted nearer the A-line with an appreciable quantity
plotting below it, thus indicating significant quantities of organic
material present in these deposits. Reasonable correlations between
plasticity index and liquid limit were developed for each deposit.
5.3.2 Specific Gravity
In general, it was found that for the deltaic soils, specific
gravity increased with increases in plasticity. This holds true for
the inorganic deltaic soils. However, the organic backswamp deposits
displayed a reverse trend in that specific gravity decreased with in
creases in plasticity. The correlations shown in figs. 4-4 through 4-7
are considered to be reasonably typical for each deposit. Appreciable
scatter, however, is noted in the data used for.the correlations for
intradelta and the organic backswamp deposits as shown in figs. 4-5b
and 4-7b, respectively. The correlations between specific gravity and
plasticity index provide a means of estimating specific gravity from
relatively economical Atterberg limit tests. Extrapolation of the re
gression lines is not recommended. Reasonable assurance can be ob
tained from values selected from the regression lines only within the
range of data.
101
5.3.3 Undrained Shear Strength
Reasonable correlations were established between undrained shear
strength and liquidity index as shown in figs. 4-8 through 4-10. Al-
though appreciable scatter is noted in the data shown in the plots for
the point bar, inorganic backswamp, and intradelta deposits it is con-
sidered that reasonable estimates of undrained shear strength can be
made from the nonlinear curves of regression. A correlation was
developed for the slightly overconsolidated natural levee deposits
(fig. 4-9), which indicated that such correlations can be made regard-
less of degree of consolidation of the soil. Nevertheless, estimates
based on these correlations should be considered as only rough esti-
mates of shear strength and should be verified by other correlations
and laboratory data. The use of these correlations in conjunction with
the su/p0
ratio should result in a predicted shear strength that can be
used with more assurance.
Plasticity index was plotted versus s /P ratio in fig. 4-12. It u 0
has been suggested that a correlation exists between s /P and plasticu 0
ity.8 Correlations were developed for several of the deltaic deposits,
however, the data indicated both negative, positive, and no correla-
tions. This is in contrast to the positive correlation of such a
statistical relation between s /P and plasticity reported in referu 0
ence 8. The reason for the variation between s /P and plasticity inu 0
dicated for the deltaic soils is not fully understood. However, such
correlations of s /P with plasticity have been questioned previously u 0
by Kenney,24
and Narain and Ramanathan. 25 Kenney suggests that the
plasticity index of a soil is measured for remolded soil by tests that
102
depend on the mineralogical nature of the constituent particles of the
soil; whereas, the undrained shear strength is dependent on soil struc-
ture. Although correlations were developed between su/p0
and plastic
ity index, they do not completely verify the theory that positive
correlations exist between these two variables. Additional studies
are needed to provide more conclusive data in this regard. A greater
quantity of data would probably have permitted a more accurate and
conclusive study of these properties. Estimates of undrained shear
strength based entirely on the regression lines shown in fig. 4-12
are not recommended.
5.3.4 Drained Shear Strength
The small quantity of S-data available for the natural levee,
intradelta, and prodelta deposits provides only inconclusive results.
No S-test data were analyzed for the point bar or the interdistributary
deposits. Adequate data were available for a reasonable correlation
between ¢' and plasticity index for the normally consolidated inorganic
backswamp deposits.
Based on the data shown in figs. 4-13 and 4-14, there appears to
be a relation between the effective angle of internal friction ¢' and
t d b B . d s .. 22 d th PI as sugges e y Jerrum an lmons, an o ers. However, appreci-
able scatter of the data is noted in the plots. The scatter in fig.
4-13 may be attributed to the fact that data from the slightly over-
consolidated natural levee deposits and data from unidentified de-
posits a~e included.
Correlations are shown for the normally consolidated inorganic
backswamp deposits (fig. 4-l4a). Although appreciable scatter of data
103
occurs about the line of regression, it is considered that ¢' values
can be estimated from this correlation with reasonable assurance. Cor
relations for the overconsolidated inorganic backswamp deposits are
shown in fig. 4-14b. Although there appears to be a good correlation
between ¢' and PI, insufficient data are presented to permit a con
clusive analysis.
5.3.5 Consolidation Properties
Simple correlations between natural water content and compression
index and between liquid limit and compression index were found to exist
for the deltaic deposits (figs. 4-18 through 4-24). The correlations
appear to be quite good, although a greater quantity of data would have
provided a better basis for more conclusive opinions. Appreciable
scatter is noted in the data shown in all the plots. The correlations
between compression index and natural water content, and compression
index and liquid limit are markedly different for overconsolidated soils
shown in fig. 4-20 than for normally consolidated soils shown in figs.
4-15 thr.ough 4-19 and 4-21. Such correlations for overconsolidated
soils appear to be best represented by nonlinear curves of regression.
Sufficient data were not available to define clearly the correlations
for the overconsolidated natural levee deposits. The correlations
shown in fig. 4-15 appear quite good, even though based on a limited
amount of data. A probable explanation for the wide scatter of data is
that water content and liquid limit determinations were made on
materials that did not truly represent the consolidation test specimen.
104
CHAPrER VI
CONCLUSIONS
Analysis of the soil test data representing important segments
of fine grained cohesive deposits of the deltaic plain of the Missis-
sippi River and backswamp deposits of the Atchafalaya River indicates
that a number of important relationships and trends exist that appear
to be characteristic of the deposits studied. Based on the data pre-
sented in this report, the following conclusions appear warranted:
a. Natural water contents appear to decrease slightly with
depth and the range generally narrowed significantly as depths
increased.
b. Undrained shear strengths for the normally consolidated del-
taic soils tend to increase with depth. Based on the shear
strength versus depth plots, the average shear strength in-
crease factors (s /p ratio) varied from 0.22 to 0.35 for u 0
the deposits studied.
c. A study of the variation of s /P and plasticity index for u 0
the various deposits indicates that such a correlation does
not necessarily exist even for soils of the same geologic
origin.
d. Undrained shear strengths from Q-tests are related to liquid-
ity index. Thus reasonable estimates of Q-strengths can be
made from the natural water content and Atterberg limit tests.
e. The relationship between liquid limit and compression index
and also water content and compression index was found to be
105
f.
g.
linear for all deposits studies, except the backswamp deposits,
which gave nonlinear relationships.
Correlations have been developed between the following:
(1) Plasticity index and liquid limit.
(2)
(3)
(4)
(5)
(6)
Plasticity index and specific gravity.
Liquidity index and undrained shear (s ) strength. u
Plasticity index and drained shear (sd) strength.
Natural water content and compression index.
Liquid limit and compression index.
It is thought that much of the scatter of data for correla-
tion of natural water contents and liquid limits with compres-
sian index is due to difficulties in obtaining materials for
liquid limit and water content determinations that truly
represent the consolidation test specimen.
h. Correlations presented in this report may be used with confi-
dence for preliminary estimates and planning of investigations.
106
LITERATURE CITED
l. Kolb, C. R. , "Distribution of Soils Bordering the Mississippi River from Donaldsonville to Head of Passes," Technical Report No. 3-601, June 1962, U. S. Army Engineer Waterways Experiment Station, CE, Vicksburg, Miss.
v-"2. Kolb, C. R. and VanLopik, J. R. , "Geology of the Mississippi River Deltaic Plain, Southeastern Louisiana," Technical Report No. 3-483, July 1958, U. S. Army Engineer Waterways Experiment Station, CE, Vicksburg, Miss.
/3. Fisk, H. N. , "Geological Investigation of the Alluvial Valley of the Lower Mississippi River." Conducted for Mississippi River Commission, Vicksburg, Miss., 1945.
4. Fisk, H. N., McFarlan, E., Jr., Kolb, C. R., and Wilbert, L. J., Jr., "Sedimentary Framework of the Modern Mississippi Delta," Journal of Sedimentary Petrology, Vol 24, 1954, pp 76-99.
5. U. S. Army Engineer District, New Orleans, "Atchafalaya Basin Floodway, Louisiana, East Atchafalaya Basin Protection Levee, Field Tests Sections I, II, and III," Interim Report, January 1968, New Orleans.
/6. Fisk, H. N., Wilbert, L. J., Jr., andKolb~ C. R., "Geological Investigation of the Atchafalaya Basin and the Problem of Mississippi River Diversion," April 1952, prepared for the Mississippi River Commission by the U. S. Army Engineer Waterways Experiment Station, CE, Vicksburg, Miss.
7. Headquarters, Department of the Army, Office of the Chief of Engineers, "Engineering and Design, Laboratory Soils Testing," Engineer Manual No. EM 1110-2-1906, 1970, Washington, D. C.
8. Terzaghi, K. and Peck, R. B., Soil Mechanics in Engineering Practice, 2d Ed., John Wiley and Sons, New York, 1967.
9. Krinitzsky, E. L., "The Effects of Geological Features on Soil Strength," Miscellaneous Paper S-70-25, November 1970, U.S. Army Engineer Waterways Experiment Station, CE, Vicksburg, Miss.
via. Krinitzsky, E. L. and Smith, F. L., "Geology of Backswamp Deposits in the Atchafalaya Basin, Louisiana," Technical Report S-69-8, September 1969, U. S. Army Engineer Waterways Experiment Station, Vicksburg, Miss.
ll. McFarlan, E., Jr., Kolb, C. R., and Wilbert, L. J., Jr., "Sedimentary Framework of the Modern Mississippi Delta," Journal of Sedimentary Petrology, Vol 24, No. 2, June 1954, pp 76-99.
107
12. Fisk, H. N. and McFarlan, E., Jr., "Sand Facies of Recent Mississippi Delta Deposits," Proceedings, Fourth World Petroleum Congress, Rome, Italy, 1955.
13. Snedecor, G. W., Statistical Methods, 5th Ed., Iowa State College Press, Ames, Iowa, 1957.
14. Bryant, E. C., Statistical Analysis, 2d Ed., McGraw-Hill, New York, 1962.
15. Young, H. D., Statistical Treatment of Experimental Data, McGrawHill, New York, 1962.
16. Spiegel, M. R. , Theory and Problems of Statistics, Schaum 1 s Outline Series, McGraw-Hill, New York, 1961.
--- 17. Taylor, D. W., Fundamentals of Soil Mechanics, John Wiley and Sons, New York, 1948, p 26.
/18. Sherman, W. C. and Hadjidak.is, C. G., "Engineering Properties of Fine-Grained Mississippi Valley Alluvial Soils, Meander Belt and Backswamp Deposits," Technical Report No. 3-604, June 1962, U. S. Army Engineer Waterways Experiment Station, CE, Vicksburg, Miss.
19. McClelland, B., "Process of Consolidation in Delta Front and Prodelta Clays of the Mississippi River," Marine Geotechnique, University of Illinois Press, Chicago, 1967.
v 20. U. S. Army Engineer Waterways Experiment Station, CE, "The Unified Soil Classification System," Techn~cal Memorandum No. 3-357, April 1960, Vicksburg, Miss.
21. Leonards, G. A., Foundation Engineering, McGraw-Hill, New York, 1962.
22. Bjerrum, L. and Simons, N. E., "Comparison of Shear Strength Characteristics of Normally Consolidated Clays," ASCE Research Conference on Shear Strength of Cohesive Soils, Colorado, 1960, p 711.
23. Kolb, C. R. and Kaufman, R. I., "Prodelta Clays of Southeast Louisiana," Marine Geotechnique, University of Illinois Press, Chicago, 1967.
24. Kenney, T. C. , Discussion of "Geotechnical Properties of Glacial Lake Clays," Transactions, ASCE, Vol 125, 1960 .
..- 25. Narain, J. and Ramanathan, T. S. , "Variation of Atterberg Limits in Relation to Strength Properties of a Highly Plastic Clay," Journal of Soil Mechanics and Foundation Engineering, Indian National Society, 1970, pp 117-128.
108
.t N
~ 30°
""'~'!;- 0 .. ...'9~•.. 30'
(JI
-I )> fTI ::0 r )>1"'1 0 z)> () Os:: L~~-~ £.'1"~'V'i M£XICo
"U
I ~ )> i • "l_ ' r ~\•7• a~ • ' • r J io· ~ • \-!.i!.."'J.., ~ ·.,- . .'!' t " '
r "U ,, " . . . .. , r ..:...g- . I f 0 ! l 0 - ' - -~ ... •• _,i. ·. -\0 -:::::>~ - 0
~ 1 ... lF ..,• .... ..t • ,_). • "c. • <-- .d ~ • • t • '\. ·-""IJ •"/AU '0.~""! .... z
fTI
1J r ~ (TI
1\)
40
20
_] 0 (f)
2 -20
f-ll-
Z-4-0 0
f-~-60 w __j w_so
-100
-120
3: 3: )> (;)
~8 I r
().) )> 0 - z (;) <» -1 -I ~ ()
3: r (J) o(TI ~ ()
-...1 (j) -1 ~ ); 0 0 z z
)>
0 DISTANCE, FT
5000 ,------ I
R-1817-UL 1815 181.1 1810 180.9 I I I I I
R-180.6-L I
10,000 T
R-1803 I
R-180.0-L I ~40
~
~ ----....L.L_ GROUN~ SURFACE --------
NATURAL LEVEE 20
~~----c:=-~~-~L /.0 ~-----~~ --- ---:>.<: ~I POINT BAR
~ "(
-......_/
40
20 __] (f)
2 1-- 0 lL
z ~ -20 f-::; w -40 __] w
-50
BACKSfi/AMP
-------------------- -SUBSTRATUM
DISTANCE, FT 15,000
R-179.6-L I
R-179.1-UL I
<::)
~ GROUND SURFACE MIL.E 1790
NATURAL LEVEE
ALIV P ----lL_ ____f;L_.LQ_ __ _
COHESIYE TOPSTRATUM
POINT BAR
/ NON-COHESIVE SUBSTRATU!vf
'-lu :::! ~
~ ----------- I ~ ""-....~
40 _] (j)
20 ::; f-lL
0 z-0 f--
-20~ w _j w
-40
-60
---- ____sz__ 0 _j
~/ (f) ::;o
C2Q f-lL
-406-
POINT ~ BAR
\ -60~
--' w
-80
-100
-120
LEGEND
NATURAL LEVEE- soft to stiff cloys with lenses and layers ML.
POINT BAR
MARSH
-silts, silty sands, and sands with lenses and toyers clay.
-very soft cloys with organic moller and peal.
INTEROISTRIBUTARY- very soli to soft cloys with lenses and loyers of Ml, SM, and SP
INTRADELTA - soft alternating cloys and silts with layers SM and SP.
SHELL REEF -shell and shell fragments.
PRODELTA -medium to stiff cloys.
NEARSHORE :.. sands w1th shell and shell fragmenls.
PLEISTOCENE -stiff to very stiff cloys w1lh lenses and layers ML.
NOTE: ALWP represent-s ~he Mississippi River avera9e
low water plane and grout-~dwal-er surface.·
The. number loco-led above each .soil profile idenkf<j
sOd borings.
Undis,+urbed bol"';n9.s ore ;dent;~\.<ad. by (u..)~ aU othe.r
bor;nss ore. general sample.. iype.
"'0
I r ~ 1"'1
w
(/l
~
DISTANCE, FT 9--------------------~5~oFo~o------------------~~~o~p~o~o------------------~'5~oro~o~----------------~2~o~,o~o~o----------~
<\j
Ri '
~ ~ ~ "'
R-179.0-R I
POINT BAR
---
J
R-1785-R 178.1 R-177.9-RU R-177.2R R-176.6-R R-176.1-R r<-175.4-R
! I I 1
GROUND SURF/ICE\ I I
' ---i NATURAL LEVEE - I
ALIVP 2 EL
i >.. I
9::: l ~ ~ Cl;)
POINT BAR 9:: BACKStVAAIP f..: ~ ':)
~ ~
\ ~ ;jl "'
SUB-STRATUM SANDS
3:: 0 G) :;,;: 1"'1
NOTE: SEE PLATE 2. FOR NOT.ES AND LEGEND. 1"'1 0 r
..... OJ 0 <0 1"'1 G) ru z -I 5J ()
3:: r C/l 0 1"'1 c ()
..... - -1 (}I (/l -. - 0 ~ )> z
z )>
40
20
0
-20
-40 ui ~
1--60 lL
z-0
-BO f= :;; w
-IOOllJ
-120
-140
-160
"'0 r ~ fTI
~
DISTANCE., FT 0 5.000 IQOOO 15,000 20,000
R-17<L5-R R-173.8-R R-173.3-R R-172.9-RU R-172.5 R-171.9-R R-170.9-R 4 0 I I I I I I I 40
GRO(IND SURF/ICE
2 <c I>. 20 O tt NATURAL LEVEE ~
' ~ O ~ ALJ'/P sz EL 10 ~ O
~ ~ x ~
-20 ~ ~ -20 [ ~ ~ ~
-40 ~ -40
ij{ ACCRETIONARY DEPOSITS BACKSWAMP flJINT BAR ~
2 -60 -60 2 r r ~ ~
z -80 -80 -0 z
0 r :;; -100 -100 ~ w > ~ w w ~
-IZO -120 w
StJ8STRATl/M 5UBSTR//Tl/J,.f
-140
-160 I , -160 / '
1 PLE!STOCE/VE 7 G) / -------------------------- -180
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------____,____
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Dl STANCE, FT 0 10,000 20,000 30,000 40,000 50,000 60,000 70,000 80.000 90,000 100,000 ~----- -1 I 1 I I
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DISTANCE, FT 220,000 230,000 240,000 250,000 260,000 27QOOO 280,000 290,000 300,000
I ----~1
5/~MHL R~24.0LU R-228L R·21.2L R·20.0LU R~I8.9L R~I7.7L R·I7.0L R·I5.9LU 54-MHUL R·l40L R·I28L R·II.GLU 5G·MHL .58-MHUL SO·MHUL I R-24.8L I R23.4L 152·MHUL I R·20.6L I R·l9.5L I R-18.4L 153·MHULIR-IG.4L I R-15.3L IR-14.7L I R-13.4L I R·IZ.ZL 155-MHL 157-MHLI5.9·MHL
I I I I I I I I I I I I It I I I I I I
~ ~ ~ ::: ~
PRODELTA
LEI/E£---
POINT BAR
7fl.NP 'V
/11/TRAOELTA
EAST BANK
DISTANCE, FT
0.
ACCRETIONARY 1
I~ !NTRA1J£LTA
~
PRODELTA
22o,ooo 230,000 24o,ooo 25o,ooo 26o,ooo ZTqooo 280,ooo Z9o,ooo 3oo,ooo
IO·MHU 8·MH 7-MH 4-MH 5-A 4 3 2·MH I I I I I II I
~
"' ~ iii "' " '::> iii ~
"'
56 7 6 II I I
~ <>;
2 I
3 I
5 6 7 I I
8 9-U 10 II I I I I
INTR/IOEL TA
PRODELTA I I \'i. I I PRODELTA
WEST BANK
15 13 14116
I I I
20
0
-20
J '-<!
+40: "::! ~
U..
·60 z 0
f--80 ~
w .J
"' -100
-120
-140
20
0
ro -4-0 ~
f-LL
-Go z-0
i= -ao <(
> w ..J
~roo lu
I -120
·140
NOTE: SEE PLATE 2 <'DR NOT£.5 AND LEGEND.
N
X·
X
Kurtosis
Leptokurtic
Platykurtic
Mesokurtic
Symmetrical Shape
Positive Skewness
Negative Skewness
Bimodal Shape
Multimodal Shape
APPENDIX A
DEFINITION OF STATISTICAL TERMS
Frequency Histogram
Number of measurements, observations, or test values.
Individual,value of a measurement, observation, or test value.
N
Arithmetic mean or average,
rx. i=l ~
N
Standard deviation or root-mean-square deviation for
a given group of values, N - 2 L (X. - X) /N . The
j=l J
standard deviation represents a distance on the scale of values which is indicative of the amount of dispersion.
Degree of peakedness of a distribution.
Description of a distribution having a relatively high peak.
Description of a distribution having a relatively flat curve.
Description of a normal frequency distribution, a bell-shaped curve.
Normal bell-shaped curve.
The longer tail of the curve occurs to the right, skewed to the right.
The longer tail of the curve occurs to the left, skewed to the left.
Frequency curve has two maxima.
Frequency curve has more than two maxima.
Al
Curve Fitting and Correlation
Curve Fitting
The Method of Least Squares
The Least Square Line
The Least Square Parabola
Simple Correlation
Positive Correlation
Negative Correlation
Linear Correlation
Nonlinear Correlation
Regression Line
The problem of finding equations of approximating curves which fit given sets of data.
Finds the most probable value of a quantity for a set of measurements by choosing the value which minimizes the sum of the squares of the deviation of these measurements.
y = a 0
Y =a 0
+ a X 1
2 +aX+ aX
1 2
Constants determined by solving equations simultaneously.
Degree of relationship between two variables.
Where Y tends to increase as X increases.
Where Y tends to decrease as X increases.
All the points seem to lie near some straight line.
All the points seem to lie near some curve.
A line which permits estimation of a variable Y based on a variable X . Thus the line is called a regression line of Y on X , since Y is estimated from X . In general the regression line or curve of Y on X is not the same as the regression line or curve of X on Y •
A2
Standard Deviation from Regression
Commonly known as the Standard Error of Estimate. It is a measure of the scatter about the regression line. It has properties analogous to those of the histogram standard deviation. For example, if lines were constructed parallel to the regression line Y on X at respective vertical distances Sy,x , 2 Sy,x , and 3 Sy.x from it, 68%, 95%, and 99-7% of the sample points should be included between the lines.
Standard Deviation from Regression of y on X:
_JLCY- y )2 es
8Y.X - N
Standard Deviation from Regression of X on Y:
-JLcx- X )2 es
8x.Y- N
A3
Unclassified Security Classification
DOCUMENT CONTROL DATA- R & D (Security classification ol tltle, body of abstract and index in~$ annotation must be entered when the overall report Is classJ/ltJ~)
1. ORIGINATING ACTIVITY (Corporate author) Za. REPORT SECURITY CLASSIFICATION
u. s. A:rrrry Engineer Waterways Experiment Station Unclassified Vicksburg, Mississippi 2b. GROUP
3. REPORT TITLE
CORRELATION OF ENGINEERING PROPERTIES OF COHESIVE SOILS BORDERING THE MISSISSIPPI RIVER FROM DONALDSONVILL TO HEAD OF PASSES, LA.
4. DESCRIPTIVE NOTES (Type of report and Inclusive dates)
Final report 5- AU THOR(S) (First name, middle initial, Ia at name)
Raymond L. Montgomery
e. REPORT DATE ?a. TOTAL NO. OF PAGES rb. NO. OF REFS
June 1974 140 25 Ba. CONTRACT OR GRANT NO. 9a. ORIGINATOR"S REPORT NUM"'BER(S)
b. PROJECT NO. Miscellaneous Paper S-74-20
c. 9b. ~J8H!~o~t~PORT NO(S) (Any other numbers that may be aas/gntJd
d.
10. DISTRIBUTION STATEMENT
Approved for public release; distribution unlimited.
II- SUPPL.EMENTARY NOTES 12. SPONSORING MILITARY ACTIVITY
u. s. Army Engineer District, New Orleans New Orleans, La.
13. ABSTRACT
The purpose of this study was to analyze available data on selected cohesive deltaic plain soils and provide sununaries of engineering data and correlations of engineering properties according to environments of depo-sition of the deltaic plain of the Mississippi River. The Mississippi River deltaic plain is that part of southeastern Louisiana that borders the Mississippi River from near Donaldsonville to Head of Passes. The deltaic plain is a complexly interfingered mass of fluvial, fluviaJ.-marine, paludal, and marine deposits laid down in a variety of environments directly above the Pleistocene. This study focused attention on the deltaic plain deposits that are most important from an engineering standpoint. The deposits selected for study were the natural levee, point bar, and backswamp deposits of fluvial environment and the interdistrib-utary, intradelta, and prodelta deposits of the fluvial-marine environment. Engineering data were obtained from data files on previous field and laboratory investigations of these soils for Corps of Engineers proj-ects. The data were grouped according to environments of deposition based on the geological sections. No additional field or laboratory investigations were undertaken for this study. The data were collected and arranged in such a manner that it was possible to describe the data mathematically. The best-fit curves or lines, regression equations, and standard deviations presented for the data were developed by use of a computer. Based on the anaJ.yses, a number of important relations and trends appear to exist for the se-lected Mississippi River deltaic plain fine-grained cohesive deposits. Frequency histograms provide sum-maries of typical soil properties, and correlation plots show the relationships between the different soil properties. A number of correlations were made between Atterberg limits and data from relatively complex and more costly tests for physical properties. Reasonable corr~lations were found to exist between data from Atterberg limits tests and specific gravity, unconsolidated-undrained shear (Q) strengths, drained shear (S) strengths, and compression indexes (Cc). Also, reasonable correlations between plasticity index and liquid limit were developed for each deposit. Correlations between shear strength increase ratio (s /p ) and plasticity index proved inconclusive. Important correlations between properties were found fo¥ s8ils of similar geologic origin and depositional environment. However, sufficient data were not available to establish conclusive relationships.
DD FORM 1473 REPLACES DD FORM 1473. I JAN 64, WHICH IS I NOV 65 OBSOLETE FOR ARMY USE. Unclassified
Security Classification
IJpcl assi fj eQ Security Classification ... LINK A LINK 8 L I hi K c
KEY WORDS ROLE WT ROLE WT ROLE WT
Cohesive soils
Deltas
Geological sedimentation
Mississippi River
Soil properties
-
Unclassified Security Classification