CORRELATION OF ENGINEERING PROPERTIES OF COHESIVE …

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




3.3 Backswamp Deposits



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


3.4 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




3.6 Interdistributary Deposits 63




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


5.3 Correlations

5.3.1 Plasticity




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


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


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


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"


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


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


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


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


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


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


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


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


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


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


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



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


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


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


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


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.


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'


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


<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


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.


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.


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


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


(T /SQ FT) 120 0 1.0 2.0 3.0 0


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.


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.


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.


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£


(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


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.


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.


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.


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.


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


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 ~·~ . .. ~· . ..

\ • .. -•


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


(T /SQ FT) 120 0 1.0 2.0 3.0

I r: .. .. ..

• " PRECONSOLIDATION • OVERBURDEN

0

•


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.


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.


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


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 . \ \ • • ~ •


(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


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


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.


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


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


• •

• .........

"'~ • • • • •

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


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


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


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


•

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


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


• •'/ • 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


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


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%


• 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


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


•

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


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


~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.


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.


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


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.


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

~ )> fTI - OJ 0 :::i ~ 5 NOTE_', SEE PLATE 2 f'OR NOTES AND LEGENDS. ;:... "' G) m r-10n ~ c (J)

(J) fTI - n ~ )> --l 0 z 0 ~ )> z

DISTANCE, fT 0 5000 \0,000 15,000 20,000 ,----~- I --,--- - l---,---,----,--,---,-----,--,-----,---,--,---,----,,---,----,-----,

R-163.0-L R-16e.4-LU R-16Z.I R-161.9 R-160.9-L R-160.4-L R-159.8-LU R-159.Z-L

<ll t<i ~ lu ::;:!

~ _,t ~ >(

~ "-_ -4-0

[ z '1'

I I I I I I I I

GROUNO SURFACE--......

NATURAL LEJ/EE

r----REWORKED PLEISTOCENE Cl.L/1/B_ sz &_L t_.Q ---

ACCRETIONARY

DEPOSITS

C) J:: o)

~ lu -lO :::::1 ~ )( t• ~ ~ -4-0 ~-'1' z

0 0

~ -60 >

PLEISTOCENE -60 ~ > w w

_J w -80

POINT BAR ..J -80 w

I -100 -100

-120 -120

/ -I <in -14-0

NOTE.: SEE PLATE Z FOR NOTES AND LEGEND.

:::0 0

~ ~ (;)

1"'1 1"'1

< 0 m - r w r o . r (;) 1\) 1"'1 -I ~ ()

~ r (/1 0 1"'1 c ()

1J

I (}'I - .,

r <D ~

~ b )> 0

z z 1"'1

)>

(}'I

DISTANCE, FT 0 10,000 . zo,ooo ~0,000 I-~

40 R-160.0-UR R-159.3-R R-158.8-R R·\:58.3-R R-157.9-R R-157.4-R R-156.9-R 3 R-156.4-UR R-156.2-R R-155.9-R R-155.4-R R-154.8-UR R-154.2-R

zof--- <:i ~· 1.(1

Of- ~

~ -eo f- ~

' ~ -' -40

"' ::; I-LL_ -60 z 0

i= ~ -80 w --' w

-roo

-120

-140

I I I I I I I I I I I I I I

N~TURAL LE;'££

POINT BAR

PLEISTOCENE {Cfl)

.--------r-AL/1/P "

--

BACKSII'AMP

PL£/STOCF.N£ {CII)

PL£/STOC£N£ (SP)

', ~ ',,~~-------

/

/ /

::u -160

~ () C) I rr1

0 m OJ r 0 rr1 0 . z C) - 0-I ()

~ 5 (j) c rr1 - ()

""0 I (JI (j) --~ r w--)> • )> 0 -1 01 zZ rr1 )>

0)

NOTE: SEE PLATE 2 FOR NOTES AND LEGEND.

40

0

c20

-40 _J

"' ::;:

-60 t;: z 0

-80 i= ~ w -'

-IOOW

-120

-140

-160

""U r ~ [TI

.--.~

DISTANCE, FT 0 5000 10,000 i5,000 20,000

I 40 R-155.1-L R-154.6-L R-154.0-L R-153.5-L R-153.1-L 152.6 152.2 R-151 .85-LU

1 I 1 I 6ROUND SURFACE-I 1 I I

20 NATURAL LEJ/EE

R-1513-L I

40

20

0 4LIYP sz EL. 1.0 ----8/ICKSIY/l!WP --- ----- ----- ---+---- 0

I ' 4.1

~ '"t~ '( f-- -40 () lL 9:: 2 & 9 -60 ">::

POINT BAR

f--<( > uJ -80 --' uJ

-100

-120

-140 - - - - PTEISTOCENE- -

Ill ~ 1"'1 (;) r [TI

~ 0 (]I o r (]I z 0 N u~ £! I r n ~ 0 (J)

~ [TI

·~ (J) ()

~ ): :::! (]I z 0

~ z

__] Vl

2

f-lL

40

20

-80

-100

-120

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N

X·

X

Kurtosis

Leptokurtic

Platykurtic

Mesokurtic

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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

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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

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Unclassified Security Classification

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CORRELATION OF ENGINEERING PROPERTIES OF COHESIVE …