An introduction to geotechnical engineering (holtz and kovacs)

AN INTRODUCTION TO
Geotechnical
Engineering
Robert D-Holiz
WillarrB Royacs

An Introduction
to Geotechnical
Engineering

PRENTICE HALL, Englemood Cl, New Jersey 07632

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DEDICATION: To Our Teachers, Past and Present

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Contents

PREFACE xi

1 INTRODUCTION TO GEOTECHNICAL ENGINEERING 7

LA GeowechnicalEopineeriog 2

12 The Unique Nature of So and Rock Materials 3

LD Sanseted Approach 1 the Sty of Geoecbical
Eagleson, 4

1a Scope of ths Book 5

15 Soi Formation and the Nature of Sol Coast 6

16 Historical Development of Geotechnical Engineering 7

17 Notes on Symbols and Units 9

2 INDEX AND CLASSIFICATION PROPERTIES OF SOILS 10

21 Inodetion 10
22 ase Definition and Phase Relations 1
23 Solution of Phase Problems 16
24 SolTexure 25
25 Grain Sue and Gran Sie Disbuton 26
26 Parle Shape 32
27. Aterberg Limits and Conssteney Indices 34
28 Ac a

Problems 41

3 SOL CLASSIFICATION 47.

31 Introduction 47
32. The Unified Sol Casieation System (USCS) 4

33 The AASHTO Soil Clusification System 64
34. Comparison of the USCS and AASHTO
sation Systems 72
Probleme 72

4. CLAY MINERALS AND SOIL STRUCTURE 77

41 Introduction 77
42 Cay Miners 78
43 Tenia of Cay Minerals 38
44 speci Sutace 9
45 traction Between Water and Clay Minerals 90
46 Interaction of Clay Parties 95
47. So Structure and Fabre 96
48 Cohesive So Fabrice 96
49. Covent Sol Fabrice 102
Probleme 107

5 COMPACTION 109

51 tateduction 109
32 Compaction 110
53 Theory of Compaction 111
34. Properties and Structure of Compactos
CCakesive Sous 117
55 Fil Compaction Equipment and Procedures IM
56 Field Compaction Cosirdvand Specifications 14!
57 Exiting Peformance of Compact Sol 153
Problems 161

$ WATER IN SOILS.
CAPILLARITY, SHRINKAGE, SWELLING,
FROST ACTION 166

61 Introdueton. 166
663 Shrinkage Phenomena in Sos 178
64 Engineering Signiicanc of Shrikage and
Sweling 196
65 From Action 190
Problems 195

Sort

7 WATER IN SOILS, lt:
PERMEABILITY, SEEPAGE, EFFECTIVE STRESS 199

11 totrodocion 199

72 Dynamics o Fl Flow 200

73 Darcy's Law for Flow Through Prout Media 203

74 Mesarement of Permeailig 205

75 Inergunular or Ellecive Sues 213

76 Relationship between Horizontal and Vertical
Sirenen 235

77 Meads and One-Dimensional Flow 227

18 Seepage Fores, Qucksand, and Liqefacion. 292

79 Seepage and Flow Nets: Two-Dimensional low 246

710. The Method of Fragments 238

TAL Control of Seepage and Files 270

8 CONSOLIDATION AND CONSOLIDATION
SETTLEMENTS 289

81 Intoducion. 287
82 Components of Seulement 244
#3 Comprenibiity of Sole 285
84 The Ociometr and Consolidaon Testing 209
85 Preconoldstion Pressure; Normal,
‘Overconsoation, Undercomolidaion 294
86 Consoidaon Behavior of Natural Soils 299
#7. Seilement Caluaions 209
8 Factors Allecting the Determination of y 126
89 Prediction of Field Consolidation Carver 328
$0. Sol Profiles 235
Kit Approximate Methods and Typical Values of
{Compression Indices 341
812. Sus Distritos 742
Problems 267

9 TIME RATE OF CONSOLIDATION 376
94 Intoducion 376
92 The Consolidation Process 377
93. Teragh’s One-Dimensional Consolidation Theory 309
94 Determination of the Cocfient of Consolidation cy

35

95 Determination ofthe Coefiient of Bermesbiliy 402
5% pol Values obey 405

9.7 Evaluation of Secondary Setlement_405
98 Comprehensive Example ola Tone Rate of
Setdement Problem 414
Problems 423

10. THE MOHR CIRCLE, FAILURE THEORIES,
AND STRESS PATHS. 437

101 tatodsetion 451
102 Stem ata Point 42
103. ‘Suess Stain Relationships and Failure Cri 446
104 The Motr.Coulomb Faure Criterion 449
105 Test for be Shear Stengh of Sols 458
106 Stress Pathe 473

Probleme 485

11 SHEAR STRENGTH OF SANDS AND CLAYS 490

114 Introduction 40
112 Ange of Repos of Sands 492
113 Behavior of Saturated Sands Dario Drained Shear 493
114 Btlect of Void Ratio and Config Pressure on Volume Change 496
115 Behavior of Saturated Sand During Undrised Shae 506
11.6 Factor that Ale the Shear Seen of Sands 514
117 The Caefiint of Earth Pressure at Res for Sands S19
113 Lgueacion and Cycle Mobility Bebavir of
Saturated Sands 522
119. Ste Deformatio and Steagih Characteristics of
= Saturated Cobesve Sl 536
119.1 Consldaed-Draned (CD) Tet Behavior 548
1192 Typical Valves of Drive Stength Parameters 543
1193 Use of CD Stenph sn Engineering Prat 43
1194 Consolidated Undrined (CU) Tes Behavior 545
1195 ‘Typical Values of the Undraned Su
1196 Useof CU Swengthin Engineering Practice
1197 Unconseldate-Undsine (UU) Tet Behavior 59
133 Typ Values of UU Sirengihs $68
199 Unconfined Compression Test
11910. Other Ways to Determine the UndrainedStearStength 570,
USA Senay SS
119.12. Use of Undrsined (UU) Shea Sen
Engineering Practice 94
11913. Special Problem ofthe Shar Strength ol Cobesve Soils 395

1110 Pore Pressure Parameter 509

HAL. The Coeticent of Earth Pressure at Rest for Clays 605

MAR, Sis Pats During Undrained Loading Normally
Consolidated Cage 610

1143, Stress Paths During Undrined Loading —
Overcomeldated Cys 630

116 Applications of Stress Paths to Engineering Pracice 634
Problems 640

APPENDIX A. APPLICATION OF THE “SI” SYSTEM
OF UNITS TO GEOTECHNICAL
ENGINEERING 665

A1 Introduction 665

A2 The SI Metic System 666

AB Basic and Deneed SI Mere Unis 667

AA SI Unis of Interest o Gectechnial Engineers and Their
Conversion Factors 49

APPENDIX 8.1 DERIVATION OF LAPLACES EQUATION 681

APPENDIXB-2 DERIVATION AND SOLUTION OF
TERZASMIS ONE-DIMENSIONAL
CONSOLIDATION THEORY 683)

BRA Assumptions 683
B22 Deren 87
B23. Mathematica Soluion 686

APPENDIX 8-3 PORE PRESSURE PARAMETERS 691

83.1 Derivation of Stemptons Pore Pressure Equation 697
22. Definition of de, and & or Rotation of Principal
1:33 Formulas for Bore Presse Parameters for Dirt
‘Stes Path Tests 696
BA rool dat Ay = dj aoû hag Ase 66
B33 Desation ofthe Henkel Pre Presur Eaton
and Coefients 696

REFERENCES 701

INDEX 719

Preface

An Introduction to Geotechnical Engineering is intended for use in the
first of à tworcourse sequence in geotechnical engineering usualy taught to
hird- and Tour year undergraduate Civil Engineering students. We as-
sume the students have a working knowledge of undergraduate mechanics,
especially statics and mechanics of materials (including Muid), À kaowi-
edge of basic geology, although helpful, isnot essential. We introduce the
“language” of geotechnical engineering in the first course, that is, the
classification and engineering properties of sols. Once the student has a
‘working knowledge of how soil behaves as an engineering material, he/she
can begin to predict soil behavior and, inthe second cours, to carey out
{the design of simple foundations and earthwork systems.

‘We fl that there is a need for more detailed and modern coverage
of the engineering properties of sis than is found in most undergraduate
texts. This applies to both the students “majoriag” in geotechnical en-
fineering and the general civil engineering undergraduate student, We find
that our students are involved in increasingly more complex projects,
especially in transportation, structural, and construction engineering. En-
Vironmentl, economic, and political constraints demand innovative solu-

ions to civil engineering problems. The availabilty of modern analytical
techniques and the digital computer has had an almost revolutionary effect
on engineering design practice, This development demands a better know.
tge of site conditions as well as better defined geotechnical engineering
design parameters

‘We have Wied to make the text easly readable by the average
undergraduate. To this end, An Inroduction 10 Geotechnical Engineering is
writen at a simple rather than sophisticated level, although the material
covered may be rather sophisticated at times. Involved derivations, unread

” Price

y the typical student are relegated to appendices where they are available
19 the interested student.

“The emphasis throughout is on the practical, and admittedly empii
cal knowledge of soi behavior required by the geotechnical engineer for
{he design and construction of foundations and embankments, Most of the
material in the text is descriptive, since most of the engineering design
applications are usually left to the second course in Foundation Engineer
ing. Consequently. in order to interest the student, we have tned to
indicate wherever possible the engineering significance and specific design
applications of the soil property being discussed. We have tied to em
plasize why such a property is needed, how its determined ox measured,
and, 10 some extent, how its actually used in practice, The only "design"
{ype problem we cover in a one-semester course (15 weeks) is estimating
the seulement of shallow foundations on saturated clays. The text Y
sulliciently flexible that innovative instructors can add additional design
examples should they so deste. I seems that units are always a problem
with geotechnical engineers. In ine sith the trend towards the use of SL
units encouraged by the American Society of Civil Engineers and Amer
an Society for Testing and Material, we have used this system in the text
‘The uninitiated may find the discussion of SJ. in Appendix A helpful In
addition tothe almost exclusive use of SL. units in examples and problems,
we have been careful to use the latest definition of density (mass/unit
volume) in phase relationships as well as in geostatic and hydrostatic
pressure computations,

We consider the laboratory portion of the fist course to be an
essential part ofthe neophyte engineer's experience with soils as a unique
engineering material. How else is the young engineer to begin to develop à
“fee” for sols and soil behavior o essential forthe sucessful practice of
seotechnical engineering? Thus, an emphasis on laboratory and field
testing is found throughout the text, The order of the laboratory partion of
our fist course has dictated the organization and development of the
material in the text. We begin with phase relations, visual classification of
soi, and simple classification tess. Thus, he early chapters introduce the
discipline of Geotechnical Engineering, Phase Relationships and Inder
Properties, Sol Classification, and Clay Minerals and Soil Structure. This
material provides the background and terminology for the later chapters,
Following a very practical discussion of Compaction in Chapter 5, Chapters
6 and 7 describe how water influences and affect soil behavior. Topics
presented include capllarity, shrinkage, swelling, and frost action as well
As permeabiliy, seepage, and effective stress, These {wo chapters again
serve as background for the next four chapters which deal with consolida.
tion and shear strength,

“The treatment of thes latter topics is quite modern and up-to-date
‘The Schmertmann procedure for determining field compressibility isin
cluded as is à modern treatment of secondary compression developed by
Prof. Messi and his co-workers. Prof, Lambe’ stress path method ls
introduced in Chapter 10 and used to advantage in Chapter 11, especially
‘when practical engineering applications of shear strength theory are dis.
cussed. The pioneering work of Profs. Seed and Lec on the drained and
Undrained strength of sands is presented in Chapter II, Also in this
chapter we discuss the stress deformation and strength characteristics of
‘cohesive sols. Although the treatment is modern, because thsi primarily
‘an undergraduate textbook, considerations of strength anisotropy, critical
state concepts, the Jürgenson-Ruledge hypothesis, and Hvorslevs srengih
parameters have been left 10 more advanced texts

Even though the book is primarily for the beginning student in
jgeotschnicl engineering. advanced students in other diteipines and en-
pincers desring a refresher in engineering properties may find the book
helpful. Because of the many fully worked example problems, the book is
almost “sell-teaching." This aspect of the text also ees the instructor in a
formal course from the necessity of working example problems during
lectures. I allows the instructor 10 concentrate on explaining basic princi.
ples and illustrating specific engineering applications of the points in
Question. The third group we hope wil fin this book useful are practicing
{geotechnical engineer. Typical valves are given for all clasufication and
Engineering properties or a wide variety of oils; we have found such a
‘compendiuen very useful in our own engineering practice

To acknowledge all who have contributed to this book isa formida
ble task. We have teed whenever possible to indicate by references or
‘quotations, concepts and ideas originating in the literature or with our
former teachers, especially Profs. A. Casagrande and H. B, Seed. We
apologize for any omissions. We must also mention the students in our
beginning geotechnical engineering course at Purdue who have graciously
sulfered through several versions of An Inroduction 10 Geotechnical En.
ineering in note form. Their entcism and helpful comments on the txt
have been very valuable. The authors have greatly benefited from discus-
sions wath Pro ME. Harr of Purdue University regarding the section on
‘the method of fragments in Chapter 7. We hope to bring forher attention
10 the profession of ths powerful design method. Dr. E Simiu of the US.
National Bureau of Standards entially read a recent version of the
‘manuscript and provided many helpful comments, It should be noted that
An Introduction lo Geotechnical Engineering was writen while William D.
‘Kovacs was on the faculty of Purdue University. The text has no connec:
tion with Kovacs’ present affiliation with the National Bureau of Stan

dards, Our faithful secretaries Mrs, Janice Wait Bollinger, Miss Cathy
Minth and Mrs. Edith Vanderwerp deserve special thanks for typing and
Correcting the several draft.” The frst author also wishes to gratetully
‘elnowledge the interest and encouragement of his wife Cricket Morgan
Her work with the proofreading and corrections is especially appreciated
We of course will appreciate any comments and eitiism of readers.

web. Kovecs

st Laye, Inia.

Introduction to
Geotechnical Engineering

1.1 GEOTECHNICAL ENGINEERING

Geotechnical engineering, the name implies, concern the applica-
tion of civil engineering tecology to some aspect of the earth. Usually,
the geotechnical engineer i concerned only with the natural materials
found at or near the surface of the earth. Civil engineers cal these earthen
materias sol and rock. Sol in an engineering sense, isthe relatively lose
agglomerate of mineral and organic materials and sediments found above
the bedrock. Sois can be relatively easly broken down into their con-
sitent mineral or organic particles, Rocks, on the other hand, have very
strong intemal cohesive and molecular forces which hold the constituent
mineral grains together. This is true wheter the rock i massive bedrock or
2 piece of gravel found in a clay soi. The dividing line between soil and
Fock is arbitrary, and many natural materials encountered in engineering
Practice cannot be easy clasfied. They may be either a "very soft rock"
for a “Very hard sol" Other scientific disciplines have different meanings
for he terms soil and rock. In geology, for example, rock means all the
materias found in the earth's crust, independently of how much the
mineral particles are bound together. Sols to a geologist are just decom-
posed and disintegrated rocks generally found inthe very thin upper part
ofthe erust and capable of supporting plant life Similarly, pedology (sit
science) and agronomy are concerned with only the very uppermost layers
of soi, that, hore materials relating to agriculture and forestry. Geotech-
ical engineers can learn much from both geology and pedology. Both
sciences, expecially engineering geology, are important adjuncs to geotech-
sical engineering and there is considerable overlap between these fields.
But differences in terminology, approach, and objectives may cause some
confusion, especially for the beginner.

2 Introduction 6 Geotchnca Enginering

Geotechnical engineering has several diferent aspects or emphases,
‘Soil mechanics is the branch of geotechnical engineering concerned with
the engineering mechanics and properties of sol, whereas rock mechanics
‘concerned with the engineering mechanics and properties of rock, usualy
Dut not necessarily the bedrock. Soil mechanics applies the basic principes
of mechanics including kinematic, dynamics, Muid mechanics, and the
mechanics of materials to sails. In other words, sil rather than water or
steel or concrete, for example, now becomes the engineering material
‘whose properties and behavior we must understand in order to build with
itor upon it A similar comment could also be made for rock mechanics. Tt
should be noted, however, that there are significant diferences between
the behavior of soil masses and rock masses, and in principle there i not
much overlap between the two disciplines

‘Foundation engineering applies peclog, sil mechanics, rock mecha-
nies and structural engineering 0 the design and construcion of founda.
tions for civil engineering and other structures. The foundation engineer
must be able to predict he performance or response ofthe foundation sol
‘oF rock to the loads impased by he structure, Some examples of the kinds
of problems faced by the foundation engineer include foundations for
industrial, commercial and residential buildings, and other types of sup.
port structures for radar towers, as well as foundations for oil and other
Kinds of tanks and offshore structures, Even ships must have a dry dock
during construction or repairs, and the dry dock must have a foundation,
‘The suppor of rockets and appurtenant structures during construction and
launch have led to very interesting and challenging foundation engineering
Problems. Related geotechnical engineering problems facing the founda
tion engineer are the stability of natural and excavated slopes, the stability
of permanent and temporary earth-etaining structures, problems of con-
struction, controlling water movement and pressure, and even the mainte-
‘nance and rehabilitation of old buildings. Not only must the foundation
Safely support the sta and construction loads, but it must alo
“adequately resist dynamic loads due to blasting, earthquakes, ete

If yu think about iti is impossible to design oF construct any civil
engineering structure without ultimately considering the foundation soils
and rocks o some extent and this is tue whether the structure is built on
(he earth or is extraterrestrial. The perlormance, economy, and safety of
any civil engineering structure ullmatly is affeied or may even be
‘controled by ls foundation,

Earth materials are often used as a construction material because
they are the cheapest possible building materal, However, ls engineering
Properties such as strength and compressibility are often naturally poor,
And measures must be taken to denily, suengthen, or otherwise stabilize
‘and reinforce sols so that they will perform satisfactorily in service

2 Tee Unique Mature of Solan ck atria 3

Highway and railway embankments, airfields, earth and rock dams, levees,
and aqueducis are examples of earth structures, and the geotechnical
engineer is responsible for their design and construction. Dam safety and
rehabilitation of old dams ae important aspects ofthis phase of geotechn-
al engineering. Also related, especially for highway and airfield engineers,
ls the design of the inal surface layer on the earth structure, the pavement.
Here the overlap between the transportation and geotechnical discipline is
apparent

‘Rock engineering, analogous to foundation engineering for sois is
concerned with rock as a foundation and construcion material, Because
‘most of the earth's surface i covered with sol (or water) rock engineering
usually oceurs underground (tunnels, underground power houses, pero.
Leu storage rooms, mines, ete). But sometimes rock engineering occurs at
the surface, such asin the case of building and dam foundations carie to
bedrock, deep excavations to bedrock, stability of rock slopes, ete.

Tn presenting some of the typical problems facing the geotechnical
engineer, we wanted you to see, fa, how broad the field i and, second,
how important itis 10 the design and construction of civil engineering
structures. In a very real sense, geotechnical engineering combines (he
basic physical sciences, geology and pedology, with hydraule, structural,
transportation, construction, and mining engineering.

1.2 THE UNIQUE NATURE OF SOIL
AND ROCK MATERIALS

Geotechnical engineering is highly empirical and is perhaps much
more ofan “at” than the other disciplines within civil engineering because
Of the basic nature of soil and rock materials. They are often highly
variable, even within a distance of a few millimetres, Another way of
Saying this stat soils are Aeterogencou rather than homuagenceut materias.
‘That is their material or engineering properties may vary widely from
point to point within a soil mass. Furthermore, soils in general are
nonlinear materials; thet siress-strain curves are not straight lines. To

ther complicate things ‘to make them interesting) soils are
rnonconsereaive materials; that is, they have a fantastic memory—they
remember almost everything thal ever happened to them, and this fact
strongly affects ther engineering behavior. Instead of being isotopic, soils
are Gpiclly aniotropie, which means that their material or engineering
properties ate not the same in all directions. Most of the theories we have
for the mechanical behavior of engineering materials assume that the
materials are homogeneous and iotropie, and that they obey linear stresse
strain laws, Common engineering materials such as steel and concrete do

“ Iren o Geotechnical Engineering

ot deviate 100 significantly from these ideas, and consequently we can
use, with discretion, simple inca theories Lo predict their response under
engineering loads. With sois and rock, we are not so fortunate. As you
‘hall se in your study of geotechnical engineering, we may aisume a lines
fHress-suain response, bul then we must apply large empincal correction or
“safety” factors to our designs to account for the rel material behavior.
Furthermore, the behavior of soil and rock materials in sty is often
governed or controlled by joints, fractures, weak layers and zones, and
ther “delecis” in the material; yet our laboratory tests and simplified
methods of analysis often do not take into account such real characteristics
‘ofthe soil and rock. That is why geotechnical engineering is realy an “art”
father than an engineering science. Successful geotechnical engineering
‘depends on the good judgment and practical experience of the designer.
constructor, or consultant, Put another way, the suecesful geotechnical
engineer must develop a “Tel” for soil and rock behavior before a safe and
economic foundation design can be made or an engineering sructure can
be safe bal

1.3 SUGGESTED APPROACH TO THE STUDY
OF GEOTECHNICAL ENGINEERING

Because of the nature of sil and rock material, both laboratory and
field testing are very important in geotechnical engineering. One way that
student engineers can begin to develop a fel for soil and rock behavior

lo get some experience in the laboratory by performing the standard tests
for clasification and engineering properties on many differen types of
soils and rocks. In this way the novice begins building up a “mental data
bank” of how certain soils and rocks actually look, how they might behave
should, for example, the amount of water present change, how they might
‘behave under diferent kinds of engineering loads, and what the range of
probable mumercal values is for the different et. This is sort of à
Se-calibraion process 0 that when you are faced with a new sail deposit
or rock type, you will in advance have some idea as to the engineering
problems you will encounter at that site. You can also begin 10 judge, at
Teast qualitatively, the validity of laboratory and field test results for the
‘material a that site. So laboratory as well as field experience is important
Tor you to help develop a “Tet” for sol and rock behavior. OF course, just
as with any other subject, this exposure in the laboratory to soil and rock
properties and behavior must be complemented by a diligent study ofthe
‘theoretical, empirical, and design components of geotechnical engineering

1.4 SCOPE OF THIS BOOK

Rather than attempt an all-inclusive approach to geotechnical en-
gineering, the primary emphasis in this text will be on the engineering
Behacior of soil materials Sol mechanics and the analysis and design of
foundations and earth structures i generally a fairly steaightforward, but
tive, application of mechanics, strength of materials, and elementary
Sructural engineering, Often the key in the successful practice and applica-
10 of geotechnical engineering lies ina sound knowledge and understand.
ing of the enginering properties and behavior of soils in sit, when they
re subjected 0 ther engineering loads and environmental conditions
Therefore we feel thatthe beginning student must fst develop an appre
ation for the engineering properties of soils as distinct from other common
ii engineering materials before proceeding to instruction in the analysis
“nd design phases of foundation and earthwork engineering.

“Ths isan elementary text, and the approach we have tried to follow
is to emphasize the fundamental, with an eye toward the practical
Applications that you as a praciing civil engineer are likey to encounter
in your engineering practice. Finally, we hope you will know enough about
foils and soil deposits to avoid serious mistakes or blunders in those
Sspects of your profesional career that involve soi and soil materi

Tn the fist part ol the book, we introduce some of the basic
Aetinitions and index properties of soi that are used throughout the book,
Then some common sol classification schemes are presented. Clasufcatión
of soils important because it is the “language” engineers use 10 com»
municate certain general knowledge about the engineering behavior of the
Soils at a particular site, The rest of the book is concerned with the
“engineering properties of sol, properties that are necessary for the design of
foundations and earth structure, Topics covered include how water affects
sol behavior, hei shrinkage and swelling characteristics, and their per-
‘meabilty (how water flows through sol). Then we get into the compres
bility of soil, which isthe important engineering property one needs 10
predict the settlement of engineering structures constructed on soil masses.
Finally, we describe some of the elementary strength characteristics of
both granular and cohesive soil. Soil strength i important, for example,
for the design of foundations, retaining walls, and slopes

Much of the practice of geotechnical engineering depends on topics
that include geology and the nature of landforms and soil deposits. You
are strongly encouraged to take a physical-geology or an engineering
eology course in connection with your studies of geotechnical engineer-
ing.

Its hoped that with the background of this text, you willbe prepared
for a follow-up course in foundation and,carthwork engineering: you
should know how to obtain the soil properties required for most designs,
and you should have a pretty good idea as tothe probable ange of values
for a given property if you know the general clasifcation of the soi.
Finally, you should have a fairly good idea of what to look for at a site,
how to avoid costly and dangerous mistakes, and be aware of your own
limitations and knowledge of sols as an engineering material

1.5 SOIL FORMATION AND THE NATURE
OF SOIL CONSTITUENTS

found above the bedrock. In a broader sense, of course, even shallow
bedrock is of interest to geotechnical engineers and some of these applien-
tions have already been mentioned.
our basic science courses thatthe earth
has a crust of granitic and basal rocks 10 o 40 km thick. Overying this
ively thin ayer of variable thickness of
‘what geologists call unconsoldated materials. These materials can vary in
size from sub-microscopie mineral particles to huge boulders. Weathering
and other geologic processes act on Ihe rocks at or near the earth's surface
form these unconsolidated materials, or sil, Weathering, which usually
results from atmospheric processes, alters the composition and structure of
these rocks by chemical and physical means. Physical ot mechanical
weathering causes disimegration of the rocks into smaller particle ies
Physical weathering agents include freeing and thawing. temperature
changes, erosion, and the activity of plants and animals including man.
‘Chemical weathering decomposes the mineral in the rocks by oxidation.
reduction, carbonation, and other chemical processes. Generally, chemical
weathering is much more important than physical weathering in soil
formation. In short then, sols ae he products of the weathering of rocks,
Soils ata particular site can be residuo? (iht is, weathered in place) or
transported (moved by water, wind, glaces, et), and the geologic history
ofa particular deposit significant affects its engineering behavior.

‘The nature of soil constituents is discussed in greater detail throughout
this text. For now, we want to make a few ponts just 10 set the stage for
‘what we are about 0 study. You already have a layman's idea about sol
[Atleast you know in general what sand and grove! are, and perhaps you
ven have a general idea about fine grained soils such as sil and cays,
‘These terms have quite precise engineering definition, as we shall later

18. Hain Development of estecnica Engine 7

se, but for now the general concept that sols are particles will suffice.
Particles of what? Well, usually particles of mineral matter or, more
simply, broken up pices of rock that result from the weathering processes.
wwe spoke of previously. If we just talk for now about the size of the
particles. gravels are small pieces of rock that typically contain several
minerals, whereas sands are even smaller and each grain usually contains
‘only a single mineral, I you cannot se each grain o si, then the sol
cither a sl of a clay or a mixture of each. In fact, natural sols generally
fre a mixture of several different particle ses and may even contain
Organic matter. Some soils such as peit may be almost entirely organic.
Futhermore, because sols are a particulate materia, they have voids, and
the voids are usually Filed with water and air. Iti the physical and
chemical interaction of the water and air in the voids with the particles of
soil, as well asthe interaction ofthe particles themselves, that makes soil
behavior so complicated and leads to the nonlinear, nonconservative, and.
anisotropic mechanical behavior we mentioned previously. Now, if You
add the variability and heterogeneity of natural soil deposits due 10 the
‘apriciousness of nature, you probably can begin to see that soils are
indeed complex engineering and construction materials. Helping you put
some order into this potentially chaotic situation is our primary objective
in this book

1.6 HISTORICAL DEVELOPMENT
OF GEOTECHNICAL ENGINEERING

{As long as people have been building thing, they have wed sois as à
foundation or construction material The ancient Egyptians, Babylonians,
Chinese, and Indians knew about constructing dikes and levees out of the
toils found in river flood plains. Ancient temples and monuments built all
Around the world involved soil and rock in some way. The Aztecs con-
ftructed temples and cites on the very poor soils in the Valley of Mexico
Long before the Spaniards arived in the New World. European architects
and builders during the Middle Ages leamed about the problems of
Settlements of cathedrals and lage buildings. The most noteworthy exam
ple is of course, the Leaning Tower of Pisa. Scandinavians used timber
piles to support houses and wharf structures on their soft lays. The
"design" of foundations and other constructions involving soil and rock
was by cule of thumb, and very litle theory as such was developed until
‘the mid-1700.

‘Coulomb isthe most famous name ofthat era. He was interested in
the problems of earth pressures against retaining wall, and some of his
calculan procedures are sill in use today. The most common theory for

. Iren 1 Omrchaict Engineering

{he shear strength of sois is named after him. During the next century, the
French engineers Collin and Darcy (D’Arcy) and the Scotsman Rankine
made important discoveries, Collin was the frst engineer to be concerned
With failures in clay slopes as well as the measurement ofthe shear strength
of clays. Darcy established his law for the flow of water (rough sands.
Rankine developed a method for estimating the earth pressure against
retaining wall. In England, Gregory utilized horizontal subdrains, and
‘compacted earth-fil buttresses to stabilize railroad cut slopes.

By the turn ofthe century, important developmen in the field took
place in Scandinavia, primarily in Sweden. Atterberg defined the con.
Sisteney limits for clays that are still in use today. During the period
1914-1922. in connection with investigations of some importan failure in
harbors and railroads, the Geotechnical Commission of the Swedish State
Railways developed many important concepis and apparatuses in geotech
sical engineering. Methods for calculating the stability of slopes were
developed, They developed subsurface investigation techniques such as.
‘weight sounding and piston and other types of samplers. They understood
important concepts such as sensitivity of lays and consolidation, which i
the squeezing of water out of the pores ofthe clay. At that time clays were
thought to be absolutely impervious, but the Swedes made field measure-
menta to show that they weren't. The Commission was the first 10 we the
Word geotechnical (Swedish: geotekriska) in the sense that we know it
Today: the combination of geology and civil engineering technology.

Even with these early developments in Sweden, the father of soil
‘mechanics is really an Austrian, Prol Karl Terzaghi. He published in 1925
the fist modern textbook on soil mechanies, and in fact the name “soi
mechanics” i à direct
Which was part of the
Very creative engineer. He wrote several important books and over 250
technical papers and articles, and his name will appear many times inthis
book. He was a profesor’ at Robert College im Istanbul, Technische
Hochschule in Vienna, M. LT. and at Harvard University from 1938 unt
is reirement in 1956, He continued tobe active as consultant until his
death in 1963 atthe age of 80.

"Another important contributor to the advancement of modera soi
mechanics is Prof, Arthur Casagrande, who was at Harvard University
from 1932 until 1969. You will se his name often inthis book because he
made many important contributions tothe at and science of soil mecha:
nies and foundation engineering. Other important contributors tothe field
include Taylor, Peck, Tschebotarff, Skempton, and Bjerrum. Since the
1950' the field has grown substantially and the names of thote responsible
for its rapid advancement ae 100 numerous to menton,

hotes on Symbols end Un .

Both Terzaghi and Casagrande began the teaching of soil mechanics
and engineering geology in the United States. Before the Second World
War, the subject was offered only as a graduate course in very few
universes. Alter the war, i became common for a east one course inthe
Subject to Be required in most schools of civil engineering In recent years
graduate programs in all phases of geotechnical engineering have been
implemented at many universities, and there has been a ral information
explesion inthe number of conferences, technical journals, and textbooks
published during the past two decades,

Important recent developments you should know about include de-
velopments in earthquake engineering and soil dynamics, the use of digital
computers for the solution ol complex engineering problems, and the
Introduction of probability and statistics into geotechnical engineering
analysis and design.

1.7 NOTES ON SYMBOLS AND UNITS

[At the beginning of each chapter, we list the pertinent symbols
introduced in the chapter. As with most disciplines, a standard notation is
‘ot universal in geotechnical engineering, so we have tried to adopt the
symbols most commonly used. For example, Ihe American Society for
Testing and Materials (ASTM, 1979) has a list of Standard Definitions ol
‘Terms and Symbols Relating to Soil and Rock Mechanics, Designation D
653, Which was prepared jointly some years ago with the American Society
of Civil Engineers (ASCE) and the International Society of Rock Mecha-
nics (SRM), Recently the International Society for Soil Mechanics and
Foundation Engineering (ISSMFE, 1977) published an extensive list of
symbols. Albough thee are some deviations from thelist because of our
personal preference, we have generally ted to follow these recommenda

Units used in geotechnical engineering can be politely called a mess
and, less politely, several worse things. There has developed in practice a
jumbled mixture of cgs-metre, Imperial or British Engineering unis and
Hybrid European metric units. With the introduction ofthe universal and
consistent system of units, "Le Systeme International d'Unités” (SD in the
United States and Canada, we believe its important that you learn Lo use
‘those Units in geotechnical engineering practice. However since Bei
Engineering units ae sill commonly used, its important hat you become
‘amuliae withthe typical values of both sets of units, To asset you with unit.
conversion where necessary, we have included a brief explanation of SI
‘units as applied to geotechnical engineering in Appendix A.

two

Index and Classification
Properties of Soils

2.1 INTRODUCTION
In this chapter we introduce the basic terms and definitions used by

‘geotechnical engineers 10 index and clasify si. The following notation is
sed in this chapter.

ci E93)
ect rate 2.0)
site of sara (21)
Dm or A ue Ey west
me fr a by ve

Bis fo 40% hue by ve
ol mo (E42)
uy nn 225)
gee
Toute
Peony (E422)
aan
Begue ton (64.2)
Stormy = Stange it
y Pa m Yémen
“ = ©, Vars 29
; MD alar Toa net o mob any (2420)
a MD Me Boyan dss Enr)
a MD Male) Dry dent 2
2 MD Me Da donen 27
D ME af State ey 310)
CR Dela 23)

Im thie list, = length and M = mass, When densities of soils and
water are expressed in kg/n?, Ihe numbers ase cathe large. For instance,
the density of water pi 1000 kg/m . Since 1000 kg = 1 Mg. to make the
numbers more manageable, we will usually use Mg/m for densities. If you
are unfamiliar with SI metric unite and their conversion factors it would
be a good idea to read Appendix A before proceeding with the rest of this
chapter.

2.2 BASIC DEFINITIONS AND PHASE
RELATIONS

In general, any mass of soil consists of a collection of solid particles
with voids in between. The soil solids are small grains of different mineral,
whereas the voids can be filled ether with water, ed partly with
both water and air (Fig. 21). In other words, the total volume ¥ of the sil
mass consists of the volume of sil solids Y, and the volume of voids Y

Ing ota partie (9) ano vols
wtih ana waar D

‘The volume of voids is in general made up of the volume of water Y, and
the volume of air Y. We can schematicall represent these three phases in
a phase digram (Fig, 22) in which each of the thee phases is shown,
Separately. On the let side we usually indicate the volumes of the three
phases; on the right side we show the corresponding masse ofthe phases
Even though only two dimensions are shown in the phase diagram, total
volume is any convenient unt volume such as m? orem?

Tn engineering practice, we usually measure the total volume ¥,, the
mass of water My, and the mass of dry solids M,. Then we calcule the
rest ofthe values and the mass-volome relationships hat we need. Most of
‘hese relationships are independent of sample size, and they are often
dimensionless. They are very simple and easy to remember, especially If

2 Indes and Ciao Propartion of Sle

ou draw the phase diagram. They probably should be memorized, but as
‘you work phase problems memorization wll occur almost automatically.
“There are three volumete ratios that are very useful in geotechnical
engineering, and these can be determined directly from the phase diagram,
Fig. 22.
1. The void ratio, e*, is defined as

en

where Y, =volume of the voids, and
Y, volume of the solid

“The void ratio e is normally expressed as a decimal. The maximum
possible range of eis between O and ac. However typical values of void
ratios for sands may range feom 04 to about 10: typical values for clays
vary from 03 to 1.5 and even higher for some organic sois

2. The porasty nis defined as

ET) ea
where Y, =volume of voids, and
Y, total volume of soi sample

Porosity is traditionally expressed as a percentage. The maximum

range of is between O and 100%. From 2.2 and Eqs. 2-1 and 22, ican be
shown that

a)
and
em)

‘Render wih British background wi aoe he comet mia sismo.

3. The degree of saturation Sis defined as
2
ía

100 (%) es

“The degree of saturation tells us what percentage of the total volume of
voids contains water Y the sol is completely dry then 5 = 0% and if the
pores are completely full of water, then the soil is fully saturated and
S= 100%

'Now lt us look atthe other side, the mass side, ofthe phase diagram.
in Fig, 22. Fi, let us define a mass ratio thats probably the single most
important thing we need to know about a soil. We want to know how
much water is present in the voids relative to the amount of solids in the
{oll so we define a ratio called the water comen 35

EA
Far) as)

where M, mass of water, and
M, mass of sol solid.

‘The ratio of the amount of water present in a sil volume to the
amount of sol grains is based on the dy mass of the soil and not on the
{otal mass. The water content, which is usally expressed as a percentage,
can range from zero (dry soi) to several hundred percent. The natural
‘water content for most soils is well under 100% although it an range up to
500% or higher in some marine and organic sis.

“The water content is easly determined in the laboratory, ASTM
(1980), Designation D 2216, explains the standard procedure. A repre-
Sentative sample of soil is selected and its total or wet mass is determined.
Then the soil sample is dried 10 constant mass in an oven at 110°C.
Normally a constant mass i obtained after the sample i left in the oven
‘overnight, The mass ofthe drying dish must, of courte, be subtracted from
both the wet and dry mes. Then the water content is calculated
according to Eq 25. Example 2. illustrates how the calculations for water
Content are actually done in practice.

EXAMPLE 2.1
Given:
A sample of wet soil in a drying dish has a mass of 462 , After drying in

an oven at 110°C overnight, the sample and dish havea mass of 364 g. The
mass of the dish alone is 39 8.

“ Inden and Cteateaton Proper Sot
Requires:
Determine the water content ofthe soi

Solution:

Set up the following calculation scheme; fill in the "given" or measured
quantities), (0), and (9, and make the calculations as indicated fr (9),
(x and

3. Mass of total (wei) sample + dish = 462 8
‘Mass of dry sample + dish = 364 g
Mass of water (a ~ 6) = 98 8
Mass of dish = 398
Mass of dry soil (6 — d) =325 8
Water content (c/e) X 100% = 302%
In the laboratory, masses are usually determined in grams (8) on an
‘ordinary chemical balance

reos

‘Another very useful concept in geotechnical engineering is density
You know from physics that density is mass per unit volume, so its Units
are kg/aP. (See Appendix A for the corresponding units in the cgs and
British Engineering systems) The density is the ratio that connects the
volumetric side ofthe phase diagram with the mase sie, There are several
commonly used densities in geotechnical engineering practice. Fist, we
define the tou, wet, of moist density p, the density of the particles, slid
density p, and the density of water py, Or, in terms of the basic masses
and volumes of Fig. 22:

es

en

es

In natural sols, the magnitude of he total density» will depend on
how much water happens o be in the voids as well asthe density of the
mineral grains themselves, but p could range from slighty above 1000.
g/m? 10 as high as 2400 kg/m? (1.0 10 24 Mg/m0). Typeal values ofp,
for most sols range from 2500 10 2800 kg/m? (25 to 28 Mg/m?). Most
sands have p, ranging between 26 and 27 Mg/m?. For example, à

22. Sat Datnonn and Phe alates .

‘common mineral in sand is quart sp = 265 M/mt. Most cay sol
have a value of p, between 265 and 240 Mg/m , depending on the
predominant mineral in he sol, whereas organic soie may have ap, 2 low
as 25 Mg/m’. Consequently, it usually close enough for geotechnical
work o assume à p, of 265 of 270 Mg/m? for mos phase problems, unless
2 speaiic vale ofp, e given.

‘The density of water varies slightly. depending on the temperature
AU 4°C, when water is at its densest, 9, exactly equals 1000 kg/m
(g/cm), and this density is sometimes designated by the symbol pa. For
‘ordinary engineering work, is sulfiienly accurate 1 take pz won, = 1000
g/m? = 1 Mg/m.

‚There are three other useful densities in sois engineering. They are
the dry density p,, the saturated density py, and the submerged oF
buoyant density 9!

na e
A)
A TA am

Suit speaking. total p should be used insted of fy in Eq, 2-11, but in
‘most cases completely submerged soils are als completely saturated ar at
least ii reasonable to assume they are saturated, The dey density py 5 a
‘common bass for judging the degree of compaction of earth embankments
(Chapter 5) A typical range of values of py Aan and 9° for several sol
‘types is shown in Table 21

From the basic definitions provided in this section, other useful
relationships can be derived, as we show in the examples in the next

TABLE 2:1 Some Typical Vales for Ditecont Denies of Some
‘Common Soi Matera

EDITO
Sand rr Un in
Fer ok oats
‘Gace 123 10a
E 0103 0001
Grae and coe Oss oon

Mote at ano (97)

2.3 SOLUTION OF PHASE PROBLEMS

Phase problems are very important in sols engineering, and in this
section, with the help of some numerical examples, we illustrate how most
‚Phase problems can be tolved. As is tue for many disciplines, practice
Felps: the more problems you solve, the simpler they become and the more
proficient you will become. Also, with practice you soon memorize most of
the important definitions and relationships, thus saving the time of looking
‘up formulas later on.

‘Probably the single most important thing you can do in solving phase
problems is 10 draw a phase diagram, This is especially true for the
Beginner. Don't spend time searching for the ght formula to plug into
Instead, always draw a phase diagram and show both the given values and
the unknowns of the problem. For some problems, simply doing this leads
almost immediately to the solution; at leas the correct approach to the
problem is usually indicated. Also, you should note that Bere often are
Alternative approaches to the solution ofthe same problem as illustrated in
Example 22.

EXAMPLE 22

Given:
p= 1.76 Me/m (total density)
= 10% (water content)

Requires:

Compute py (dry density) e (void ratio), (porosiy), S (degree of satura»
tion), and py (saturated density).

Solution:

Draw the phase diagram (Fig. Ex 22s). Assume that j= 1 m.

From the definition of water content (Eq. 2-5) and total density (Eq
2.6) we can solve for M, and Mf. Note that in the computations water
Content is expressed as a decimal

Votre m Ps pi
y Es
rou

s Dun
Fo. ex 220

Substituting M, = 0.10M, we get

176 Mg/n? =
7 Pr

M,=160Mg and M = 0.16 Mg
“These values re now placed on the mass sde ofthe phase diagram (Fig.

[Ex 22), andthe rest ofthe desired properties are calculated.
From the definition ofp, (Eq 2-8) we ean solve for Y

ne

0

0.16 Mg
a OO

Place this numerical value on phase diagram, Fig. Ex. 226.
"To ealeulate V,, we must assume a vale of the density of the slide
Here assume p, = 270 Mg/m0. From the definition ofp, (Eq. 2-7) we

vette a

E AIN

A TES
3 .

Dres

index and ClanttatonPropartin ot Soto

can sole for Y, directly or
M L6Mg
D" 270Me/m?

Since = Ya + Ve + Y,, we can solve for Y, since we know the other

0.93 m

”

Van Wim Ve = B= 10-0893 — 0.160 = 0247 m

‘Once the phase diagram has been filled in, solution ofthe rest of the
problem involves just plugging in the respective numbers into the ap-
Dropriate definition equations. We recommend that when you make the
‘Computations, you weite out the equations in symbol form and then inser
the numbers in te same order as writen in the equation. Also, it sa good
idea to have the units accompany the calculations.

Solving for the remainder of the required items is easy.

From Eq. 29,

From Fa. 24.
% 1.160
SO nr

‘The saturated density u, isthe density when all the voids are filled
with water, that i, when S = 100% (Eq, 2-10) Therefore, i the volume of
Ai Y wer filed with water, it would weigh 0287 m? x 1 Mg/m or 0247
Mg. Then

Met M,

qu M M ET + OEM + LEME a ga”

m
‘Another, and perhaps even easier way to solve this example problem,
is to assume ¥, is a unit volume, 1 m. Then, by definition, M, = 9, = 2.7

(hen p, is assumed to be equal to 270 Mg/m?). The completed phase
diagram is shown in Fig. Ex. 2.2.

Since w = M/M, = 0.10, M, = 027 Mg and M, = M + M, = 297
Mg. Also Ko = Mz since p, = 1 g/m; that, 027 Mg of water Gccupies

à volume of 027 m?. Two unknowns remain to be solved before we can
proceeds they are Y, and Y, To obtain these values, we must we the given
Information that p = 1.76 Mg/m?. From the definition of total density
CE

p= trés = Mi = 257M
Sotving fo Y,
=,
ne IE ste
DEL)
“Therefore

Be Y Ve Y, 1688 = 027 - 10 = 0418 m

‘You can use Fig, Ex. 2.2 to verify thatthe remainder of the solution is
‘dential tothe one using the data of Fig. Ex. 2.26.

Vitae Des
8-2 | * SY gle
| s | ae |
EXAMPLE DS

Requires

Expres the porosity nin terms of the void rao e (Eg. 2-33) and the void
ratio in terms of the porosity (Eq. 2-30).

Solution:

Draw a phase diagram (Fig. Ex. 232).
For this problem, assume Y = 1 (units arbitrar). From Eq. 21,
Ve esince ¥, = 1, Therefore V;~ 1 + e. From Fq. 22, the definition ol

roman

men

mis BJ oF
(238)

Equation 2.36 cin be derived algebraically or from the phase dia-
gram (Fig, Ex 2.30), For this case assume Y = 1

From Eq, 22, Y, = n since Y, = 1. Therefore From Eg,
2-1, the definition of € = Y/Y, So.
a)
EXAMPLE 2.4
Giver:

6062, w= ISK, = 265 Mm.
Requires:

À pau for 5 = 100%
Solution:

Draw phase diagram (Fig. Ex. 24).

2. Since no volumes are specified, assume Just as in

Example 23, this makes the Y, = € = 062 m and = 1 + 6 162m
From Ea. 29,

eh
ms

and M, = pf rom Eq, 2-7), So

A since hy min
nun Mem ne Y= min Fig Bao
MET
T+08

“The relationship

636 Ma/m

Not
=

en

is often very useful in phase problems.

M+ Me
F

We know that

Mu = WM, (trom Eq.25) and M, pi,

alls)
Tre

since ¥, = 1 a?

201019
pu 6028 ayn?

“This relationship is often well to know
BES)

re en)

2 Index and Cleateation ropas ote

Pen am

LEE 6 Mgr
You should verify that py = 9/01 +»), Which is another very useful
relationship to remember.
©. Water content for $ = 100%, From Eq. 2-4, we know that Y, =
Yom 062 m). From Eq. 28, Me = Vp, = 062 n° (I Mg/m) = 062 Mg.
Therefore w for $ = 100% must be

Pi
none #28 como

4. pur From Eg, 210, we know pau = (M, + M)/V, or

DRE 3019 0202 Malm?

Check, by Eq, 2-13:
28) 8 2.02 Mg/n?

EXAMPLE 2.5
Required:

Derive a relationship between 5, €, and p,

Solution:

Look at the phase diagram with Y, = 1 (Fig. Ex. 25),
From Eq. 24 and Fig 2.5, we know that Y, Se. Frora the
ions of water content (Eq. 2-5) and p, (Eq. 2-7), we can place the

y DE

equivalents for M, and M, on the phase diagram. Since from Eq. 24,
Me = pubs we now can write the following equation
Me = BF, = WM, = nV,

= A

Since Y,

Sw, e15
Equation 2-15 is one of the most useful of all equations for phase
problems. You can also verify its validity from the fundamental definition

OÙ pes 5, e,» and,
"Note that using Eq. 2-15 we can write Eq. 2-13 another way:

(oe)
a, au

CRE UN
ae em

Given:

A silty lay sol with 9, = 2700 kg/m), 5 = 100%, and the water content =
46%,

Required:

Compute the void ratio e, the saturated density, and the buoyant or
submerged density in kg/m.

Solution:

Place given information on a phase diagram (Fig, Ex. 29).
Assume F, = 1 m’; therefore M, = Hp, = 2700 kg. From Eq. 2-15,
we can solve fore directly
2m, „ 046 x 2700 |
ES
But e also equals Y since Y, = 10; Likewise M = 1242 kg since Mu is

120

numerically equal to Y, because pa.
‘unknowns have been found, we may readily calculate the saturated density
(Es 210.

= 1758 kg/m?

‘When a soi is submerged, the actual unit weight is reduced by the buoyant
efect of the water. The buoyancy effects equal to the weight ofthe water
‘isplaced. Thus, in terms of densities, (Eos. 2-11 and 2-17):

D = pu = Be = 1758 kg/m = 1000 kg/m? = 758 kg/m?

ragen
in

soil will be found to be very important later on in our discussion of
‘consolidation, settlement, and strength properties of sois

In summary, forthe ety solution of phase problems, you don't have
to memorize lots of complicated formulas. Most of them can easily be

derived from the phase diagram as was iustrated in the preceding exam-
ples, Just remember the following simple rules:

1. Remember the basic definitions oF m, e, pS, et.
2 Draw a phase diagram.

3. Assume either Y, = 1 or Y 1 if not give.

4. Often use Se a

2.4 SOIL TEXTURE

So far we haven't sad very much about what makes up the “solids”
part of the soil mass. In Chapter 1 we gave the usual definition of soil from
Zn engineering point of view: the relatively loose agglomeratio of mineral
And organic materials found above the bedrock, We briefly described how
‘weathering and other geologic processes act on the rocks at or near the
“arts surface to form sol. Thus the sold part of th soil mass consists
primarily of particles of mineral and organic matter in various sizes and

"The texture ofa sol its appearance or “Tel” and it depends on the
relative sizes and shapes ofthe particles as well asthe range or distribution
‘of those aies. Thus coarse-grained soil such as sands or gravels obviously
“appear coarse textured, while a fine tetured soil might be composed of
predominantly very tiny mineral grains which are invisible to the naked
ye. Sits und clay sols are good examples of fine textured sois

“The so texture, epccally of eosrse grained soil, has some relation
to their engineering behavior. In Tact, sol texture has been the basis for
certain soil classification schemes which are, however, more common in
sgronomy than in soils engineering. Stl, textural classification terms
(Gravel, sands sits, and clas) are useful in a general sense in geotechnical
engineering practice. For fine-grained wi, the presence of water greatly
affects their engineering response—much more so than grain size or
texture alone. Water affects the interaction between the mineral grains,
and this may affect thee plate and their cohesiveness.

Texturally, soils may be divided into coarse grained versus fine-
trained sols. A convenient dividing line isthe smallest grain that i visible
{o the naked eye. Sois with particles larger than this size (about 0.05 mm)
are called coarse-grained, while soils finer than the size are (obviowly)
called fine-grained, Sands and gravels are coarse grained while sls and
‘lays ae fine grained. Another convenient way to separate or classify sois
is according to thee plasticity and cohesion (physics: cohesion— sticking

= Inden and Ciortcaton ropero of Sle

TABLE 22 Textura and Omer Characteites of So

EL a se En
“Grime Tae ped Fae wad | Foe pained
Eyes EE
Fre ‘Sima | Cod
Da mo moe
nc | Common eon | Cave
Er caer |
A | Imparası | Way impos
cn: ae
‘te pane ater
tu
pore
ites twine | opor Ready | Rent
or = Tras | “eps
Eid

together of like materials), For example, sands are nonplastc and non-
‘cohesive (cohesionless) whereas clays are both plastic and cohesive. Sits
fall between clays and sands: they are at he same time fine-grained yet
onplastic and cohesionless. These relationships as well as some general
engineering characteristics ae presented in Table 2-2. You will need 10

best done in the laboratory, in identifying sois
according to texture and some ofthese other general characteristics such as
plasty and cohesiveness Also you should note thatthe term clay refers
Both 10 specific minerals called clay minerals (discussed in Chapter 4) and
Ko sois which contain clay mineral, The behavior of some sols is strongly
affected by the presence of clay minerals. In geotechnical engineering, for
Simplicity such soil are usually called clays, but we really mean soils in
‘which the presence of certain lay mineral affects their behavior.

2.5 GRAIN SIZE AND GRAIN SIZE
DISTRIBUTION

As suggested in the preceding section, the size of the soil particle,
especially for granular sos, has some effect on engineering behavior.
‘Thus, for classification purposes, we are often interested in the particle or
gran sizes present in a particular soil as well asthe distribution of those

# br) BEE EL
me «bop el

3.23 Gran sa ranges according severa engineering sn
Caro aye eating ar ARS 1a

“The range of posible particle sizes in sois is tremendous. Soils can
range from boulders or cobbles of several centimetres in diameter down 0.
‘ultrafine rained colloidal materials, The maximum possible range is on
the order of 101, so usually we plot grain size distributions versus the
Iogrihm of average grain diameter. Figure 23 indicates the divisions
‘between the various textural size according to several common engincer-
ing classification schemes. I: should be noted that taditonally in the

a index and Cieacntin Propane ie

United Stats the units fo the various sizes depend on the grain size. For
materials greater than about $ mm (about 1/4 in). inches are commonly
ed, although mllimeres could be used just as well. Grain size between
S mim and 0074 mm are classified according to US. Standard sieve
number, which of course can be related toa specific gain size as shown in
Fig, 25. Soils finer than the No, 200 sieve are usually. dimensioned in
mifimeires or forthe very fine-grained colloidal particles, in micrometres,

iow isthe particle size distribution obtained? The proces is called
mechanical analysis or the gradation test. For coatsegrained sois, à sieve
Tmabsis is performed in which a sample of dry si is shaken mechanically
through a series of woven-wiresquate-mesh sieves with successively smaller
‘openings Since the total mass of sample is known, the percentage retained
for passing each size sieve can be determined by weighing the amount of
Soil retained on each sive after shaking, Detailed procedures for this test
fre specified by ASTM (1980), Designations € 136 and D 422. The
corresponding AASHTO (1978) es standards are T 27 and T 88. The US,
Standard sieve numbers commonly employed for the particle size analysis
fof sois are shown im Table 2-3. Since sol particles are rarely perfect
Spheres, when we speak of particle diameters, We really mean an equivaent
particle diameter as determined by the sieve analysis.

TABLE 23 US. Standard Save Sizes and
‘Their Coresponding Open Dimension

US Sabido
See. en

E
ioe
ors

It turns out that the sieve analysis is impractical for sieve openings
less than about 005 to 0075 mm (No. 200 US. Standard sieve), Thus for
the fine-grained sois, sit, and clays, the Adrometer anis is commonly
sed. The basis for this testi Stoke's law for falling spheres in a viscous
Fluid in which the terminal velocity o fll depends on the grain diameter
and the densities of the grains in suspension and of the fluid. The grain
diameter thus can be calculated from a knowiedge ofthe distance and time
of fall. The hydrometer also determines the specific gravity (or density) of
the suspension, and this enables the percentage of particles of a certain
equivalent parle diameter to be calculated. As withthe seve analysis,

the percentage of total sample stil in suspension (or already out of
suspension) can therefore readily be determined. Detaled procedures for
the hydrometer test are given by ASTM (1980) Designation D 422, and
AASHTO (1978) Standard Method T 88. The US.BR. (1974) and US,
‘Army Corps of Engineer (1970) also have similar standardized procedures
for this test.

“The distribution of the percentage of the total sample less than a
certain sieve size or computed grain diameter can be ploted in either a
histogram or, more commonly, in a cumulative frequency diagram, The
equivalent grain sizes are plotted to a logarithmic sale on the abscissa,
Whereas the percentage by weight (or mass) of the total sample either
passing (mer han) of retained (coarser than) is potted arithmetically on
{he ordinate (Fig. 28). Note that this figure could just as well be plotied
withthe smaller grain sizes going towards the right. Some typical grain size
distributions are shown in Fig. 24, The wellgraded soil has a good
representation of particle sizes over a wide range, and its gradation cure i
smooth and generally concave upward, On the other hand, a poorly graded
soil would be one where thee i either an excess or deficiency of certain
sites où if most of the particles are about the same sie. The uniform
Eradation shown in Fig. 24 is an example of à poorly graded soil. The
Bap-araded or skip gaded sil in that Figure s also poorly graded: in this
ate the proportion of grain sizes between 05 and O1 mm is elaively
tow.

We could, of course, obtain the usual statistical parameters (mean,
median, standard deviation, ec) For th grain size distributions, but Uns
more commonly done in sedimentary petrology than in soil mechanics, Of
‘course the range of particle diameters found in the sample is of interest.
Besides that, we use cerain grain diameters D which correspond to an
equivalent “percent passing” on the grain size distribuion curve. For
example, Day is the grain size that corresponds 10 10% of the sample
passing by weight, In other words, 10% of the particles are smaller han the
diameter Day, This parameter locates the grain size distribution curve
(GSD) along the grain sine axis, and its sometimes called the effective size.
“The coefficient of uniformity € is etude shape parameter, and itis defined

Da
> em)

where Dyy =grain diameter (in mm) corresponding to 60% passing, and

Da =grain diameter (in mm) corresponding to 10% passing, by
weight (or mass)

Actually, the uniformity coefficient is misnamed since the smaller the

number, the more uniform the gradation, So itis really a coefficient of

“disunilormiy” For example, a €, = 1 would be a soil with only one
grain size Very poorly graded sis, for example, beach sands, have G.s of
or 3, whereas very well-graded soils may have a C, of 15 or greater.
‘Occasionally the €, can range up to 1000 or so. As an example, the clay
core material for Oroville Dam in California has a C, of between 400 and
500; the sizes range from large boulders down to very fine-grained clay
partes.

‘Another shape parameter that is sometimes used for sol classifi
tion isthe coeficent of curvature defined as
(Do)
Dig Da)
‘where Di = grain diameter (in mm) corresponding to 30% passing by
‘weight (or mas). The other terms were defined premously.

‘A soil with a coefficient of curvature between | and 3 is considered
Lo be well graded as long asthe C, is also greater than 4 for gravels and 6
for sands.

Ge

220)

EXAMPLE 2.7

Given:

“The grain size distribution shown in Fig. 24

Requires

Determine Di, C., and €, for each distribution.

Solution:

For Eqs. 2-19 and 2-20 we need Diy, Day, and Dag foreach gradation curve
in Fig. 24.
Well graded sol; simply pick off the diameter corresponding to
10%, 30%, and 60% passing
Dyy™002mm, Dy = 0.6mm, Dy= 9mm
From Eq. 219, -
DO

Den

= Index and Clean Propre Sot

From Ex 228,
= Pah (06 >
(Die) Dee) (0.02K9)
Since €, > 18 and Gi betwen 1 and , Ns ois nded el sade.
À Gap gel sit we ume procedure a
Den 0022. Dy 0052, Dy 12

From Eq. 220,

PCS
BND)” PAID

Even though by the uniformity coefficient criterion, this soil is well
graded, 1 fails the coefficient of curature enterion. Therefore itis indeed
poorly graded

€: Uniform soil: use same procedure as in (a)

Demo) Dy 043, Dy 055
From Eg. 219,
Da _ 055

eus

[CATS

TR ~ Waxes)”

‘This soil is stil poorly graded even though the C, is slightly greater
‘than unity; the, i very small

2.6 PARTICLE SHAPE

“The shape ofthe individual particles is a least as important as the
gain size distribution in affecting the engineering response of granular
Soil. I is possible to quantify shape according to rules developed by
sedimentary petrlogists, but for geotechnical engineering purposes such

28 parce Shape =
refinements are rarely warranted Only a qualitative shape determination is

Usually made as part of the visual classlcation of soils. Coarse-grained
Soils are commonly classified according tothe shapes shown in Fig. 2.5

eo 00

u.

Er Lo gained Buy paris Pratogaz

A distinction can also be made between particles that are bully and
those which are needlelike or flaky. Mica flakes are an excellent example
of the latter, and Ottawa sand is an example ofthe former. Cylinders of
ach dilfer drastically in behavior when compressed by a piston. The bulky
rains hardly compres at all, even when in avery loose sate, but the mica
Flakes wil compress, even under small pressures, up to about one-half of
their orignal volume, When we discuss the shear strength of sands, you
al Learn that grain shape is very significant in determining the frictional
Characteristics of granular soil

2.7 ATTERBERG LIMITS AND
CONSISTENCY INDICES

We mentioned (Table 22) thatthe presence of water inthe voids of a
soil ean especially affect the engineering behavior of fine-grained soils. Not
Only ist important to know how much water is presenti, for example, a
tural soi deposit (he water content), but we need to compare or sale
this water content against some standard of engineering behavior. This is.
what the Atterberg limits do—they are important limits of engineering
behavior. If we know where the water content of our sample i relative 10
the Atterberg limit, then we already know a great deal about the engineer

limits. then, are water contents

fine-grained sol. They ae used in clasifiation of such sis, and they are
sel because they cortelate with the engineering properties and engineer-
ing behavior of fine-grained soils.

"The Atcrber limits were developed inthe early 1900's by a Swedish
soil scientist, A. Auerberg (1911). He was working in the ceramics in
dustry, and at that time they had several simple tests to describe the
plasticity of a clay. which was important both in molding clay into Bricks,
for example, and to avoid shrinkage and cracking when fed. After many
experiments, Aterberg came tothe realization that at last two parameters
were required to define plasticity of clays—the upper and lower limite of
plasticity. Infact, he was able to define several limits of consistency or
behavior and he developed simple laboratory tests 10 define these limits.
They are:

1. Upper limit of viscous flow.

2. Liquid limit—lower limit of viscous flow.

3. Sticky limit—elay loss its adhesion to metal blade.

4. Cohesion limit grains cease to cohere to each othe.

$. Plastic limit—lower limit of the plastic state

6. Shrinkage limit—lower limit of volume change.

He also defined the platico index, which is range of water content
where the soil is plas, and he was the first to suggest that it could be
used for sol classification. Later on, in he late 1920 K. Terzaghi and A.
Casagrande (19320), working for the US, Bureau of Public Roads, san
dardized the Atterberg limits so that they could be readily used for soil
classification purposes. In present geotechnical engineering practice we
usually use the liquid limit (LL Or »,), the plastic hit (PL orp) and
sometimes the shrinkage limit (SL or wy). The sticky and the cohesion
limits are more useful in ceramics and agriculture.

a Index and Citation Propane of Sots

Since the Attrberg limits are water contents where the soil behavior
changes, we can show these limits on a water content continuum as in Fig
26 Also shown are the types of sal behavior for the piven ranges of water
Contents. As the water content increases, the state of the soil changes from
ont solid to plastic solid und then 10 à viscous liquid. We can also
Show on the same water content continuum the generalized material
response (suesestrain curves) corresponding to those states.

"You may recall the curves shown in Fig. 27 from fluid mechanics,
where the shear velocity gradients plotted versus he shear stress, Depend
Ing on the water conten, st is possible for sols to have a response
represented by all of those curves (except possibly the ideal Newtonian
quid), Note, too, how different this response is from the stress-strain
behavior of other engineering materials such as steel, concrete, or wood,

Atterbergs original consistency limit tests were rather arbitrary and
mot easily reproducible, especially by inexperienced operator. As men
tioned, Casagrande (1952, 1958) worked to standardize the tests, and he
{developed the liquid limit device (Fig. 28) so thatthe test became more

” Indes and Ciessincnton Properton 1 Sot

‘operator.independent. He defined the LL as that water content at which a
Standard groove eut in the remolded soil sample by a grooving tool (Figs.
2800) will dose over a distance of 13 mm (E in.) at 25 blows of the LL.
up falling 10 mm on a hard rubber or micarta plastic base (Fig. 2.8). In
practic, is dificult to mix the soil eo thatthe groove closure occurs at
act 25 blows, but Casagrande found that if you plot the water contents
‘tests where you get closure at other blow counts versus the logarithm of
the number of blows, you get straight line called the flow curve, Where
the flow curve crosses 25 blows, that water content is defined as the liquid
limit

“The plaie limit test is somewhat more arbitrary, and it requires
same practice to get consistent and reproducible results. The PL is defined
35 he water content at which a thread of soil just erumbles when it is
‘heefully rolled out 0 a diameter of 3 mm (4 in. I should break up into
Seaments about 3 to 10 mm (3 in. to } in) long. If the threads can be
rolled toa smaller diameter, then the si 5 100 wet (above the PL); fit
Crumbles before you reach 3 mm (} in.) ia diameter, then you are past the
PL. Property rolled out PL threads should look like those shown in Fig.
288,

Even though the liquid limit and plastic imit tests appear simple,
both tests do take some practice to get consistent results. In Sweden, the
fallcone test is used to determine the liquid limit (Hansbo, 1957) I seems
to give more consisten results than the Casagrande device, especially for
Swedish clays, and it is somewhat simpler and faster 10 use. Karlsson
{1977 presents an excellent discusion of the reliability of both procedures.

‘Sometimes a onepoint guid lini est can be used because, for sols
of similar geologic origin, the slopes of the low curves are similar. Then all
Jou have to-do is obtain the water content, of the sample with closure of
the groove at any blow court m, and use the following relationship,

us) am

where tan Bis the lope of the flow curve. For best results the blow count
Should be between about 10 and 40, Lambe (1951), US. Army Corps of
Engineers (1970) and Karlson (1977) provide good discussions of the
one-point liquid limit est

"You may have noticed that we have not mentioned the ASTM
procedures fr the Atterberg limits tests. We do not recommend the ASTM.
procedures because, for one thing, they require that the limits be con-
Aveted on air-dried specimens. For some sol, such a procedure wil give
Very different results than if the limits are conducted atthe natural water
‘Content (Karisson, 1977. The other problem with ASTM is the grooving
100 for the liquid limit test. I does not allow for any control of the height

127. Atar Lint and Conaelancy nee =

of the groove, and therefore it will give inconsistent results. For this
feasoa, we recommend the Cassgrande grooving tool (Fig. 2.) be used.

“The range of guid limits can be from zero to 1000, but most soils
have LL' less than 100, The plastic limit can range from zero 10 100 or
more, with most being less than 40. Even though the Atteberg limits are
real water contents, they are also boundaries between different engineer
ing behaviors, and Casagrande (1948) recommends that the values be
reported without the percent sign. They are mumbers to be used to classify
Fine-rained soi, and they index sol behavior. You will, however, se the
limits reported both ways and sing both symbols: LL and PL, and w, and
wp with à percent sgn

"The other Aterberg limit sometimes wed in geotechnical engineering
practice, the shrinkage limi, is discussed in some detal in Chapter 6

We mentioned earlier that Aiterberg also defined an index called the
plasticity index o describe the range of water content over which a sil was
Plastic. The plasticity index, PI off, therfore is numerically equal to the
Siffecence between the LL and the PL, or

PL=LL~ PL e

“The PI is usefol in engineering classification of fine-grained sois, and
many engineering properties have been found o empirically correlate with
the PL

‘When we fist started the discusion on the Atteberg limits, we said
that we wanted tobe able to compare or scale our water content with some
(defined limits or boundaries or engineering response. In this way. we
‘would know if our sample was likely to behave as x plastic, a brite solid,
or even possibly a liquid. The index for scaling the natural water content
‘of a soil sample ithe liquidity index, LI or Z, is defined as

PL

us en)

A
here mis the natural water content of the sample in question the LI is
less than zero then, from the water content continuum of Fig. 26, you
‘would know thatthe soi wil have a bri fracture if sheared. Ifthe LI is
between zero and one, then the sil will behave Hike. plastic. I LI is
greater than one, the soil will be essentially a very viscous liquid when
heared, Such soils can be extremely sensitive 10 breakdown of the soil
Structure, As long as they are not disturbed in any way, they can be
‘elatively strong, but if for some reason they are sheared and the structure
‘of the sol breaks down, then they iterally can flow like a liquid. There are
“epost of lira sente (quick clay in Eastern Canada and Scandinavia
Figure 23 shows a sample of Leda elay from Ottawa, Ontario, in both the

a 29 (9 Undated an) Warovgny remotos ame ot

undisturbed and remolded sites atthe same water content, The undis-
turbed sample can carry a vertical stress of more than 100 KPa; when
thoroughly remolded, 1 behaves like a quid.

Tr wasn't emphasized previously, but the limits are conducted on
thoroughly remolded soils, and when we discuss the structure of clays in
CChopter 4, we will see thatthe natural structure of à soil very strong
fgovern ts engineering behavior. So then how come the Atterberg limits
Work? They work empirically; that is they correlate with engineering,
properties and behavior because Both he Aterberg limits and the engineer.
In properties are affected the same things, Some ofthese “things” include
the clay minerals the ion inthe pore water, the stress history of the sol
deposit ee. And these factors are discussed in detail in the chapter on soi
Structure (Chapter 4), For now, Just accept that these very simple, arb
vary, end empirical Atlerberg limits are most useful in classifying soils for
engineering purposes and that they comelate quite well wth the engines
ing behavior of soils.

2.8 ACTIVITY

ln 1953, Skemplon defined de activi À ola clay as
eae
CE
here the cla fraction is usually taken as he percentage by weight of the
foil es than 2 um Clays which have an acvity around 1 (0.79 < À <
125) are classified as “normal”; À < 05 ate inactive clays and À > 125
are active clays. Actif has been useful for certain Classification and
‘engineering property corelations, especialy for inactive and active clays.
Also, here 1 fat/ good correlation ofthe activity and the type of lay
mineral (Chapter ), However, the Aterberg limits alone are usually
saficient for these purposes, and the actwity provides no really new
information

(29

PROBLEMS

2:1. A water content test was made on a sample of silty clay. The weight
‘ofthe wet soil plus container was 175) g, and the weight ofthe dry
Soll plus container was 1484 g. Weight of the empty container was
7,34 y. Calculate the water content of the sample
22. During plastic Himit es, the following data were obtained for one
of the samples:
Wet weight + container = 22.122
Dry weight + container = 20422.
Weight of container = 1308

What isthe PL ofthe soil?

22. A sample of fully saturated clay weighs 1380 gin its natural state
nd 975 g alter drying. What is the natural water content of the

soir

2.4, For the soil sample of Problem 23, compute (a) vod ratio and (b)
porosity

2-5. For the soil sample of Problem 2-3, compute (a) the total or wet
density and (5) the dry density. Give your answers in Mg/m?,
kg/m), and 101/10,

e Inden and lantenton Prope ot oi

26. A 1 m sample of mois sil weighs 2000 kg, The water content i
10% Assume p, is 270 Mg/m. With this information, fill in al
blanks inthe phase diagram of Fig. P26.

the information given in Problem 2-6, calculate (a) the void
io. (9) the porosity, and (c) the dry density

2-8. The dry density ofa compacted sand is 1.82 Mg/n? and density of
the solids s 2.67 Mg. What is the water content of the material
when saturated?

2.9, À 100% saturated oil has a total density of 2050 kg/m? and a water
coment of 25%. What is the density of the solide? What is the dry
density of the si?

2-10, What is the water content of a fully saturated soil with a dry
density of 1.70 Mg/1? Assume p, = 271 Mg/m!

21. A dry quartz sand has a density of 168 Mg/m?. Determine its
(density when the degree of saturation i 78%. The density of solids
for quart à 2.65 Ma/m.

212. The dry density of a soi is 165 Mg/m and the solids have a
density of 268 Mg/m?. Find the (a) water content, (8) void ratio
and (6) total density when the soi is saturated.

2.13, À natural deposit of soil was found to have a water content of 20%
and 10 be 90% saturated, What isthe void ratio of this sil?

“The void ratio of clay sol is 0.5 and the degree of saturation is 70%,
‘Assuming the density ofthe solids is 2750 kg/m, compute (a) the
‘water content and (9) dry and wet densities in both SI and British
Engineering units

2.5. The volume of water in a sample of moist soil is 0056 m?. The

volume of solids Y, is 0.28 m’. Given that the density of soil solids
Pis 2590 kg/m’, find the water content.

216

am.

218

2

22.

221

22,

Verity from first principles that:

Derive an expression for p, in terms ofthe porosity n andthe water
content w for (a) a fully saturated soil and (b) a partially saturated
i

Derive an expression for (a) dry density, (9) void ratio, and (9)
degree o saturation in terms of D, Pes and.

Develop a formula for (a) the wet density and (9) the buoyant
density in terms ofthe water content, the density of the soil solids,
and the density of ws

From Archimedes’ principle show that Eq. 211, 9 = fay = pes 6
the same as (o, ~ 9.)/(0 +6).
‘The “chunk density” method is often used 10 determine the unit
weight (and other necessary information) ofa specimen of irregular
shape, especialy of friable samples. The specimen at its natural
‘water content is (1) weighed, (2) painted witha thin coat of wax or
paralin (o prevent water from entering the pores), (3) weighed
again (W, + M). and (4) weighed in water (0 ge the volume of
the sample + wax coating-—remember Archimides?). Finally, the
tual water content ofthe specimen is determined. A specimen of
Silty sand is treated in this way 0 obtain the “chunk density.” From
the information given below, determine the (2) wet density, (0) dry
density, (6) void ratio, and (d) degree of saturation of the sample
Given:

‘Weight of specimen at natural water content = SLR 2
Weight of specimen + war coating = 2159
Weigh of specimen + wa in water = 589
Natura water content 238
Soil solid dens. p. = 2700 kg/m
Wax solid density. Ban = 940 kg/m"

Hint: Use a phase diagram,

‘The total volume ofa oil specimen is 80000 mu? and it weighs 145
8. The dey weight of the specimen is 128 g, and the density of the
sal solids is 268 Mg/m?. Find the (a) water content, () void rai
(©) porosity, (A) degree of saturation, (e) wet density, and (D) dry
density. Give the answers to parts (e) and ($) in both SI and British
Engineering units.

22.

22,

235,

226

228,

22,

arte Propuso ote

The values of minimum e and maximum « for a pure silica sand
were found to be 046 and 0.66, respectively. What isthe corre:
sponding range in the saturated density in g/m?

A 588 cm? volume of mois sand weighs 1010 gts dry weight is
918 4 and the density of solids i 2670 kg/m). Compute the vo
ratio, the porosity. water conten, degree of saturation, and the total
densiy in kg/m

A sample of saturated glacial clay has a water content of 47% On
the assumption that 9, = 270 Mg/m’, compute the void ratio,
porosity, and saturated density

A sensitive volcanic clay soil was tested in the laboratory and found
to have the following properties:

GO = 128 Ma/m (me
(0 a 275 Me/m? PRES

CRE

In rechecking the above values one was found to be inconsistent
with the rest. Find the inconsistent value and report it correctly

1 The saturated density Yu o a so is 135181/10. Find the buoyant

density ofthis ol in both 191/10 and p/m?

A sand is composed of solid constituents having a density of
268 Mg/m’. The void ratio is 0.58. Compute the density of the
sand when dry and when saturated and compare it with the density
‘when submerged,

A sample of natural glacial til was taken from below the ground
water table The water content was found to be 55%. Eximate the
wet density, dry density, buoyant density, porosity, and void ratio.
Clearly state any necessary assumptions

Calculate the maximum possible porosity and void ratio for a
collection of (@) ping pong balls (assume they are 30 mm in
diameter) and (6) tiny ball bearings 03 mm in diameter

A ylinder contains $00 em? of loose dry sand which weighs 750 8.
“and under a static load of 200 kPa the volume i reduced 15% and
then by vibration itis reduced 10% ofthe original volume, Assume
the solid density of the sand grins is 265 Mg/m, Compute the
void ratio, porosity, dry density, and tual density corresponding to
each of the following cases

(a) Loose sand. (6) Under sti loa.
(©) Vibrated and loaded sand,

22.

233,

The natural water content of a sample taken from a sol deposit was
found tobe 115%, Ithas been calculated that the maximum density
for the sil will be obtained when the water content reaches 21.5%.
‘Compute how many grams of water must be added to each 1000 g
‘of sol (im is natural tae) in order 1 increase the water content 10
215%

(On five-eyete semilogarithmic paper, plot the grain size distribution.
‘curves from the following mechanical analysis data on the six sis,
‘A through F. Determine the effective size as well asthe uniformity
coefiient and the coefficient of curvature for each soi Determine
also the percentages of gravel, sand, sl, and clay according to (2)
ASTM, (b) AASHTO, (6) USCS, and (4) the British Standard.

“Tica see, Teen Pain bo Wei
10
A
" m
“ 5 4 .
A 2 2900
2 2 5 2
i i > 8

234. () Explain briefly why itis preferable, in plotting GSD curves, to

plot the grain diameter on a logarithmic rather than an arme
sele.
(0) Are the shapes of GSD curves comparable (for example, do
they have the same C, and C,) when plotted arthmetically? Ex-
pain.

s

236

27.

Inder and Casaca Proparton of Sota

‘The sols in Problem 2-33 have he following Aterberg limits and
tural water contents, Determine the PL and LI foreach soil and
‘comment on their general activity

recy SIA Bann SIC SSIES

u Fa
a 5 à ao

Comment on the validity ofthe results of Aterberg limits on soils
Gand H

“8

‚The following data were obtained from a liquid mit test on à sty
el

CIA

‘Two plastic limit determinations had water contents of 23.1 and
236%. Determine the LL, PI. the flow index, and the toughness
index, The flow index isthe slope ofthe water content versus log of
number of blows in the liquid limit ts, and the toughness index is
‘the PI divided by the flow index.

Soil Classification

3.1 INTRODUCTION

From the discusion in Chapter 2 on soil texture and grain size
distributions, you should have atleast a general idea about how soils are
classified. For example, in Sec. 24 we described sands and gravels as
coarsegrained soil, whereas silts and clays were fine grained. In Sec. 25,
we showed he specific size ranges on a grain size scale (Fig. 23) for these
Soils according to the standards of ASTM, AASHTO, ete, Usually, how
‘ever, general terms such as sand or clay include such a wide range of
‘engineering characteristics that additional subdivisions or modifiers are
required to make the terms more useful in engineering practico. These
terms are collected into so classification systems, usually with some specie
engineering purpose in mind

‘A soil classification system represents, in effect, a language of com
‘munication between engineers. It provides a systematic method of cate
goriing sols according to their probable engineering behavior, and allows
engineers access to the accumulated experience of other engineers. A
classification system does not eliminate the need for detailed sols investie
tations or for testing for engineering properties, However, the engineering
Properties have been found to correlate quite well with the index and
classification properties of a given sil deposit. Thus, by knowing the soil
classification, the engineer already has a fairly good general ¡dea of the
way the soil will behave inthe engineering situation, during construction,
under structural loads, ete Figure 3.1 illustrates the role of the classifica:
‘ion system in geotechnical engineering practice.

Many sol classification systems have been proposed during the past
50 years or so. As Casagrande (1948) pointed out, most systems used in

“ ‘ot Cda

1.23, ot cra stem geen! ring

civil engineering had their rots in agricultural soi science. This is why the
firat systems used by civil engineers classified soil by grain size or soil
texture. Alterberg (1905) apparently was the first 10 suggest that something
‘ther than gran size could be used for soil classification. To this end, in
1911 he developed his consisteney limits for the behavior of fine-grained
soils (Sec, 27), although at that time for agricultural purposes. Later the
US. Bureau of Public Roads based the classification of fine-grained sois
almost entirely on the Auterberg limits and other simple tests. Casagrande
(1548) describes several other systems that have been used in highway
engineering, airfield construction, agriculture, geology, and sol scence.
"Today, only the Unified Soil Classification System (USCS) and the
“American Association of State Highway and Transportation Officials
(AASHTO) system are commonly used in civil engineering practice, The
Unified Soil Classification System is used mostly by engineering agencies
of the US. Government (U.S, Army Corps of Engineers and US. Depart.
ment of the Interior. Bureau of Reclamation) and many geotechnical
engincering consulting firms and soil testing laboratorio With slight
modification this system is al in Fairy common use in Great Britain
and ckewhere outside Ihe United States. Neatly all of the state
Departments of Transportation and Highways in the United States use the
AASHTO system, which is based upon the observed behavior of soils

22. The Unido Caire Sytem (USCS) “

under highway pavements. The Federal Aviation Administration (FAA) of
the US, Department of Transportation had ite own soil classification
system for the design of airport pavements, but it now uses Ihe Unified
Soil Clasiiation System.

‘Once you become familiar with the details, both the USCS and
AASHTO systems are easy to use in engineering practice

3.2 THE UNIFIED SOIL CLASSIFICATION
SYSTEM (USCS)

‚This system was originally developed by Professor A. Casagrande
(948) for use in aifeld construction during World War Il, It was
modified in 1952 by Professor Casagrande, the U.S. Bureau of Reclama
tion, and the US. Army Corps of Engineer to make the system also
applicable to dams, foundatiors, and other construcion (U.S. Army En-
ineer Waterways Experiment Station, 1960). The bast for the USCS is
that coarse-grained soils can be classified according to ther grain size
distributions, whereas the engineering behavior of fine-grained. sols is
primary related to ther plasticity, In other words, sols in which "fines"
Gils and clays) do not affect the enginering performance are classified
according 10 their grain size characteristics, and soils in which fines do
control the engineering behavior are classified according to thei plasticity
characteristics, Therefore, only a sieve analysis and the Atterberglimuts are
necessary to completely clasiy a sol inthis system,

The four major divisions in the USCS are indicated in Table 3-1
They are (1 conse grained, (2) fine grained, (3) organic ols, and (4) peat
Classification is performed on the mateal passing the 75 mm sieve. and
(he amount of “aversze” material í noted onthe dil logs or data sheets
Particles greater than 300 mm equivalent diameter are termed boulders,
‘while materials between 75 mm and 300 mm are called cables. Coarse
rained sols, sands, and gravels ate those having 50% or more material
retained on the No. 200 sieve, These fractions have been arbitrarily but
conveniently subdivided as shown in Table 3-1. Finegrained sois are
‘those having more than SO% passing the No. 200 sieve. The highly organic
soils and peat can generally be identified visual.

‘The symbols in Table 3-1 are combined to form oil group symbols
“hich correspond tothe names of typical soils as shown in Table 3-2.

‘The course-grained soils are subdivided into gravels and gravelly soils
(G) and sands and sandy sols (9. The gravels are those having he greater
percentage of the coarse fraction (parles larger than 4.75 mm diameter)
tetained on the No, 4 sieve, and the sands are those having the greater
Portion passing the No. 4 sieve. Both the gravel (G) and the sand (5)

TABLE 31 USCS Dotntons of Parle Size Size Ranges, and Symbol

oF Component Symbol Sue Range
Bad Fe rte
Ce Ne mod
0) Corel ir
eo e mm No Asie
(Ismay
Come amo am
Foe Damiano. tse
aan
Sond s Notes mano
No 200008 mim)
Con Ne LG ame
No 10 Dam)
Meth NOT ETS
Ke 40028 mm)
Foi NO
DETTE)
0) Feegained i:
Fr Les an No, 00er
Ona
su ™ (is papi
‘se Ar ini)
ES e No pag
‘Seater ini)
© Opa Sot: o (ie peti prin)
CES rn (ie pete pin)
‘radian Se Tp iat Som
andes eL
Po des. P kenn

groups are divided into four secondary groups, GW and SW, GP and SP.
GM and SM, GC and SC, depending on the grain size distribution and
nature of fines the sols. Wellgraded (W sois have a good representa-
tion of all particle sizes whereas the poorly graded (P) sois are either
uniform or skip- or gap-graded (Fig, 24) Whether a gravel or sandy sol is
well graded can be determined by ploting the grain size distribution curve
And computing the coefficient of uniformity €, and the coefficient of
‘curvature C, These coefficients are defined in Chapter 2

oz es)

and the coefficient of curvature is

De

On er e.)

32 Te Uno Sa Cisco Sytem (99) ”

where Di = grin diameter at 60% passing,

D = gran diameter at 30% passing, and

Dig = grain diameter at 10% passing by weight (or mass).

(Gradation enter for gravelly and sandy soils ate shown in Table 32
(column 6). The GW and SW groups are well-graded gravely and sandy
‘oils with less than 5% passing the No. 200 sieve. The GP and SP groups
‘te poorly graded gravels and sands with litle or no nonpastic fines.

“The fine-grained sols, those having more than 50% passing the No.
200 sieve ae subdivided into sis [M for the Swedish terms mo (= very
fine sand) and mata (= si) and clays (C) based on their liquid limit and
plasticity index. Organic sois (0) and peat (Pt) are also included in this
fraction although, as shown in Table 31, no grain size range is specific,
Fine-grained sos are site (M) if their quid limite and plasticity indices
plot below the A-line on Casagrande’ (1948) plasticity chart (Fig. 3.2). The
Fines are clays (©) ifthe LL and PL plot above the Adine, The Adine
generally separates the more claylike materials from those that are silty
‘and also the organic from the inorganics. The exception is organic «
(OL and OH) which plot below the Aline. However, these soû do behave
Sim to sis of lower plasticity. The sl, la, and organi actions are
further subdivided on the basis of relatively low (L) or high (H) liquid
limits, The dividing line between the low and high quid Fists has Been
arbitrarily etat SO, Representative sol types for ine-grained soils ae aso
Shown in Fig. 32. This figure, columns 4 and 5 of Table 3-2 and Table
33, willbe helpful in the visual identification and classification of fine-
trained sols. You can see fom Fig. 32 that several different sol pes
tend to plot in approximately the same area on the LL-PI chart, which
ian that these sols tend to have about the same engineering behavior.
“This is why the Casagrande chart itso Useful in the engineering classifica
tion of sos. For example, Casagrande (1948) observed the behavior of
soils atthe same liquid limit with plasticity index as compared with their
behavior at the same plasticity index but with an increasing liqid limit,
and he obtained the following results

ETS
arce seth area
bowers

Fong eae PL face
Compre bout he wine
Fa vo change Dee

‘Touphnes near the PL and dry strength are very useful visual
cassation properties, and they are defined in Table 3-3. The other
‘characteristics are engineering properties, and they are discussed in great

eo cheatenton

TABLE 32. United Sol Clssitcaton System“

‘ater US. Army Page Waters Esperen Sin (1960) and Howard (1977.

22. The Units So Colon Sten (SCH)

TABLE 32 Continued

“cus, eno pun pet 20008
ceo won pedo) ea RO, wanes Sumous ung Han span EE Bd

22. Te Uns So Cotton Sytem (0868) se

TABLE 33 Fila Idetcaton Procedures tor Fins Grain Sols e Fractone"
"Thee procedures ate 1 be performed on the minus No. 40 sieve
ae pario. approsinately 04 mim For ld classicaion pur
Pose, srenig 5 ao intended; imp remove by hand the couse
Paris that tere wit te test

Dime DoS
pre (eri carr:
Alter roving paris ger as Alu cora paris rer ua

a solo a Soe. Add comite) lp, nding mate U ner
Ltd ec o mate he ssf atta Alow te patty compet Oy
[etsy Pace the at inte ope pun fof oo at then te rend
fone nd abd shake oy spas tbe breaking ted crumbly Bss ge
Se Rad eel un À ponte sion ‘Thi En y ar tte char
cot of he apesar of mae om Be And quisas fe cal cion com
Sree of te pt och changer toa vey laca lo des. Te dy og octet
cates) tod became ge. When Be wh ra pas,

Ampere Dance the loge he High dy aeg carte for
‘ete an pies appar rom he ta. dy of de CH prop A peal sra
etc stay cater pw on ey By a
Al ry seg at eam be drampues
byte el when pondering he ed pe
a cet eee

At enon parte re han he No. 40 ve se, à 8 ab
Jin bein te poled he size of pty eo dy water mu ad nd.
His de secs sad be pend ou a di hes pond ce moe
‘yn e epee ad mb e
Foly, Dey ir Sagas de montos e proa, rbd 2 de
es ses, Hal bes psy and sis when te pti Us pct.
he rc, Se pene se ped ope ads
vor he red or Be ae nd ier e lam wen aly
rumble he mre eet he tal y fro ed, Wes fe red a e
hate Lt nd uc bn ef ebenen oe Jump eos De pase mt nae ter
‘Ronan lay oom tho mania sch as kanye las and organ aya wich
iy spa ays havea ey waka pony fs plat int.

“Aer US. Ary Engines ren pit San (Nand Hoa TD,

= sait Cineaticaton

til late in this book. For now, just sey on your general knowledge and
Ingenuity to igure out what those words mean.

“The upper limit Hine (Uline) shown in Fig, 3,2 indicates the upper
range of plasticity index and liquid limit coordinates found thus far for
foils (A. Casagrande, personal communication). Where the limits of any
foil plot to the left of the Uslne, they should be rechecked. Some highly
Acte days such as bentonite may plot high above the Acline and close to
the Using. It is shown in Chapter 4 that Casagrande’s plasticity chart can
ven be used to identify qualitatively the predominant clay mineral in a
sol.

Coarse-grained soils with more than 12% fines are classified as GM
and SM ifthe fines are sly (mits plot below the A-line on the plasticity
Chart) and GC and SC if the fines are elayey (limits plot above the A-line).
Both wellgraded and poorly graded materials are included in these two,
groups

Sois having between 5% and 12% passing the No. 200 sieve are
classed as “borderline” and have a dual symbol. The first part of the dual
Symbol indicates whether the coarse faction is well graded or poorly
Frades, The second part describes the nature of the fines. For example, a
Soil classified as a SP-SM means that it is a poorly graded sand with
between S% and 12% sily fines. Similuly a GW-GC is a welleraded
‘travel with some clayey fines that plot above the A-line

Fine grained sos can also have dual symbols. Obviously, if the limits
plot within the shaded zone on Fig. 32 (PI between 4 and 7 and LL
Between about 12 and 25), then the sol clasifies as a CL-ML. Howard
(1977) makes the practical suggestion that ifthe LL and PI values fall near
the Aline or near the LL = 50 line, then dual symbols should be used,
Possible dual symbols then ae:

chon
Borderline symbols can also be used for soils with about 50% fines
and coarse grained fractions, In thi case possible dual symbols are
SM
cect
stem
ENT
sa
en

32 Te Untied Sa Camion Sytem (USCS) ”

Figure 33 is a practical guide for borderline cases of sol clasica»

usted SOIL CLASSIFICATION SYSTEM

‘conse ram all + ir rame Si

A step-by-step procedure for USCS classification of sois, conveni-
em presented in Fig, 34, shows a process of elimination of all the
possbiities until the only one left imdiates the specific clasifiation. The
Following steps, adapted from the Corps of Engineers, may help in this
process (US. Army Engineer Waterways Experiment Station, 1960). Cas
‘ication should be done in conjunction with Table 3-2 and Fig. 34:

1. Determine if the soil is coarte grained, fine grained, or highly
Organe. This is done by visual inspection and/or by determining
the amount of soil passing the No. 200 sieve,

2. Wreoare grained:

a. Perform a sieve analysis and plot the grain size distribution
Curve, Determine the percentage passing the No. 4 sieve and
ls the sol as grave (greater percentage retained on No. 4)
‘or sand (greater percentage passing No. 4)

». Determine the amount of material pasing the No. 200 sieve. If
less than 5% pases the No. 200 sive, examine the shape of the
grain size curve if well graded, classify as GW or SW; if poorly
traded, classify as GP or SP.

between S% and 12% ofthe material pases the No, 200 seve,
it isa borderline case, and the classification should have dual

symbols appropriate to grading and plasticity characteristics
(GW.GM, SWSM, ete)

a W more than 12% passes the No. 200 sieve, perform the Auer-
berg limits on the minus No, 40 sieve fraction. Use the plastic.
Ay chart to determine the correct clasifeation (GM, SM, GC,
SC. GM-GC, or SMSC)

3. Wine grained

3. Peiform Aterber limits tests on minus No, 40 sieve material
Te guid limits less than $0, classify as Land if the liquid
miis greater than SO, classify as H.

b. For Le ifthe limits plot below the Aline and the hatched zone
fn the plasticity chart, determine by color, ador, or the change
Sn guid mit and plastic limit caused by oven-drying the soi,
Sheiher ii organie (OL) or inorganic (ML). If the limits plo
In he hatched zone, classify as CI-ML. If the limits plot above
the Aline and the hatched zone on the plasticity chart (Fig,
32), classify as CL.

eo For Hr if the limits plot below the Actine on the plasticity
‘Ghat, determine whether organic (OH) or inorganic (MH). IT
the limits plot above the Alin, classify as CH.

a. For limits which plot in the hatched zone on the plasticity
chart, close tothe Aline or around LL = 50, use dual (border-
Tine) symbols as shown in Fig 33.

[Although th letter symbols in the USCS are convenient, they do not
completely describe a soll o soi deposit. For this reason, descriptive terms
Show also be used along with the letter symbols for a complete soil
{lasification, Table 3-4 from US. Army Engineer Waterways Experiment
Station (1960) provides some useful information for descibing ols.

Ta the cue of all sols. such charaterisics as color, oder, and
homogeneity of the deposit should be observed and included in the sample
description.

For coarse-grained sois such items as grain shape, mineralogical
content, degree of weathering, in sito density and degree of compaction,
nd presence or absence of fines should be noted and included, Adjectives
Sich as rounded, angular, and subangular are commonly used to describe
rain shape (ee Fig. 29). The in situ density and degree of compaction is
Formally obtained indirectly by observing how difiult the material isto
ate orto penetrate with devices calle peneometers. Terms such as
Sho late, lose, medium, dense, and very dense are wed to describe in situ
der, A granular deposit which can, for example, be excavated readily

22, Te Unas Sot Casaca Sytem (0008) “

TABLE 34 Information Required or Describing Sots"

ee: en
RE un mn TÜRE um nam don
ie ee „ee
a ea
en rare
es ter
Sie plat nope tt a fee adn de
ele aren
End ru wowed ly a ee
Ta ee er Soe Set meee ot dene
Soe er Se ears a eid aid

Lane Aloma. and symbol m a, movie and drag cono
seis ample
sami yo st brow, shy plas,

“iy and, gravely. About 20% hard, small percentage of at sand, numerous
angular Pava paris 12 mm mani vertical rot bole firm and dry im place,
‘mom sae rounded and subangular sand lees (MI),

{gains soar afin, sbout 19% rompt

fines with low de swength well com

fasted and moist in pce ova! ná,

EN

M ey lave hr one ay fae ig
er US. Army Espiner Waterss Experiment Son (160.

by hand would be considered very Loose, whereas a deposit of the same
material which requires power tools for exeavation would be described as.
very dense or perhaps cemented.

For the fine-grained fraction, natural water content, consistency, and
remolded consistency should be noted in the sample desenption. Con-
siency in the natural slate corresponds in some respects to degree of
‘Compaction in coarsegrained sis and is usually evaluated by noting the
tase by which the deposit can be excavated or penetrated. Such terms as
en sft, sof, medium, sf, ver st, and hard are employed o describe
‘consistency, (Sometimes the word firm is used synonymously wth the term
ff) Fine-prined sois may be additionally described by using the tests
explained in Table 33 for dlatancy, toughness, and dry strength. Other
techniques for visual casificatio of sols should be learned and practiced
in the laboratory. Excellent descriptions of visual classification and identi-
fiction procedures are found in the US.B.R. (1974) Earth Manual, Ap-
pendix E, and ASTM (1980) Designation D 2488.

EXAMPLE 3.1

Requires:

Classify th tree sois according to the Unified Sol Classification System.

Solution:

Use Table 32 and Fig. 34

1. Plot the grain size distribution curves forthe three sois (shown in
Fig Ex 31),

2. For soi 1, we see from the curve that more than SOR passes the
No, 200 sieve (60%); thus the soil is a fine-grained soll and the
Aterberg limits are required to further classify the sol. With
LL = 20 and PI = 5, the soil plots in the hatched zone on the
plasticity chart. Therefore the sol is a CL ML.

3: Soil2is immediately sen to bea coarse-grained sol since only 5%
passes the No. 200 seve. Since 97% passes the No. À sieve, the sol
ls a sand eather than a gravel. Next note the amount of material
passing the No. 200 sieve (5%). From Table 3-2 and Fig. 34, the
soil is “borderline” and therefore bas a dual symbol such as
SP-SM or SW.SM depending on the values of C, and C.. From
the grain size distribution curve, Fig. Ex. 3.1, we find that Da =
O71 mm, Dyy= 034 mm, and Diy 0.18 mm. The coefficient of

vera tu .

uniformity Gis
Da „om

Gegen <é

and the coefiient ol curvature G is

PEE

ETS

Fora soil to be considered well graded, it must meet the criteria
shown in column 6 of Table 32: it does not, so the soil is
considered poorly graded and is classification is SP-SM. The soil
is SM because the fines are siiy(nonplasti).
‘A quick glance at the characteristics for soi 3 indicates he sili
fine grained (97% passes Ihe No. 20 seve) Since the LL is greater
than 100 we cannot directly use the plasticity chart (Fig. 32). Use
instead the equation forthe Acne on Fig. 32 to determine ifthe
soil isa CH or MH.

P= O.73(LL ~ 20) = 0:73(124 — 20) = 759
Since the PI is 78 for soil 3, it ies above the A-ine and thus the
tolls classified as a CH.

3.3 THE AASHTO SOIL CLASSIFICATION
SYSTEM

Im the ate 1920's the U.S. Bureau of Public Roads (now the Federal
Highway Adminstration) conducted extensive research on the use of sois
special in local or secondary road construction, the so-called "farm-to-
market” roads, From that research the Public Roads Classification System
was developed by Hogentogler and Terzaghi (1929). The original system
was based on the stability characteristics of soils when used as a road
surface or with thin asphalt pavement. There were several revisions since
1929, and the latest in 1945 is essentially the present AASHTO (1978)
system. The applicability of the system his been extended considerably;
‘AASHTO slates that the system should be useful for determining the
relative quality of sil for ute in embankments, subgrade, subbases, and
Bases. But you might Keep in mind its orginal purpose when using the
system in your engineering practice. (See Casagrande, 1948, for some
‘comments on this point

Fe Team Ne 10 eve Rome)
(Coe sn Re dam) Ne 0025 mm)

Fans 0.0043 am) 10 No 2903 mm
Sit Combioed Mae! asia te 0015 mm (No. 200

stand ey) ‘ioe

Soil factions recognized in the AASHTO system are listed in Table
3:5, Boulders should be excluded from the sample to be elasifed, but as
‘with the USCS the amount of boulders present should be noted. Fines are
Silty if they havea PI ess than 10 and clayey ifthe PL is greater than 10.

"The AASHTO system classifies soils into eight groups, A- through
(A4 and itincludes several subgroups. Sols within each group are evaluated
according o the group index, which is calculated by an empiical formula.
‘The only tests required are the sieve analysis and the Atterberg limits,
‘Table 3: states the current AASHTO (1978) sl classification,

“Granular materials fall unto casses A-I to A. A-! materiale are well,
graded, whereas A-3 soils are clan, poorly graded sands, A-2 materias are
lo granular (ese than 35% passing Ihe No. 200 sieve), but they contain a
Significant amount of sits and clas. Ad to A-7 ae fine-grained soils the
siltclay materials. They are differentiated on the basis of thet Atterberg
Timits, Figure 35 ean be used to obtain the ranges of LL and PI for groups
ALA to AT and for the subgroups in A-2. Highly organic soils including
peats and mucks may be placed in group AS. As with the USCS,
lssfcation of A-8 sis is made visually.

‘The group index is used to further evaluate soils within a group. It is
based on the service performance of many sis, especially when used as
pavement subgrades. It may be determined from the empiicl formula
Even at the op of Fig. 3.6, or you may use the nomograph direct.

Using the AASHTO system to easily sois snot dificult. Once you
ave the required test dat, proceed from let to right in the chart of Table
136, and find the correct group by the process of limination. The first
group from the lft to fit the test data isthe correct AASHTO clasica»
tion. A complete classification includes the group index to the nearest
whole number, in parentheses, alter the AASHTO symbol, Example are
A263), AA), AID}, A-7 SCID, ie

Figure 37 will be helpful in classifying’ sois according to the
AASHTO system,

el Rs] I
EE BEN E
Fg 35, Atooor eno ranges fr subgrade subgroups AA AS, AS,

ERST. Note mal Casngrande hie and Use have bah sure
on on chen ar Lu. 1970 and Ana, 1879

EXAMPLE 3.2

Given;

‘The following data for soils 4 and 5. See Fig. Ex. 31 forthe grin size
distribution curves.

Required

Classify the soil according to the AASHTO Soil Classification System.

Grau dos (= (F-91102 OODSIL - 0) ONE 1811-10,
GRR EM nm dove, LE adm nd PL puy nde

en working wih A2 6 and A27 spouse Pr Grou index (PE)
L'an rom be Pon

3

3 8

20

Expte The:
"Soins 007 mme — "PSL 89 or LL
far BEER

Fig 38 Group inde char (anos AASHTO, 1970) American Associ
SE Bo ay nd rms ic. aa Und oy pr.

Pecent omg No, 200 eve

avn UG NAPO 105 OLNEY 0 sungen ur Loin Kane ‚or uno LE OU

= 3 Fea we E ad T au |

TABLE 37. Comparabi Sol Groups in the AASHTO and USCS Systems"

Comparte Sa Groups

a
A ara
m EZ a
u m Tash

ae
má. Ham
aa
ferred pores
oo
œ num num AA
mm ne um
M ques au ses
“más em pe
mu pee aa
ve mas mung me
ar mecca
= “ss mm
Œ Oum mé
a — ane
on je ar

Improsuie

Sm

ir

1. mm — om.or.
ws

n26 Ce Ewa
Swe

Ra ow. cr,
A4 MLOL cs MOC
aS om — sum
ATS UMR MLOL OMS,
oH Ex

Ms ame MOL OM
se Kom,

Solution:
1. Because more than 35% of sol 4 passes the No. 200 sieve, from
Table 3-6 we see thatthe soil isan A4 or higher. Since the LL is
49, the soi is either A-S or AT. wilh a PI of 25, the sol an AT.
A check of Fig, 35 shows the soil is classified as an A-T-6
2, Because sol 5 has less than 35% passing the No. 200 seve, it is
granular. (A glance at Fig Ex 31 provides the same information!)
Proceeding from let to right in Table 3-6, we see tha the fist
group from the left that meets the criterio is A-la.

3.4 COMPARISON OF THE USCS.
AND AASHTO CLASSIFICATION SYSTEMS

There are several significant differences between the USCS and
AASHTO soil classification systems, which is not surprising considering.
the differences in their history and purpose. You can see the differences in
the treatment of conrsegrained sols by comparing Table 3-1 with 3-5. The
major differences in the fine-grained soils are shown in Fi. 35, where we
have superimposed both the Adine and the U-line on the LL-PI chart
AASHTO (1978) actualy plots LL versus PL but we have turned the chart
90° for easy comparison with the Casagrande plasticity chart (Fig. 3.2).
‘The differences ate significant. Also, use of PI = 10 as the dividing line
between silty and clayey sois seems rather arbitrary and probably does not
realistically relate to the engineering properties of fine-grained soils.
‘AL-Hussaini (1977) discuss several other significant differences between
the two systems.

“Table 3-7 shows a comparison of the 160 systems in terms of the
probable corresponding sol groups.

PROBLEMS

3-1. Classify sols 4 and 5 in Example 32 according to the Unified Soil
Classification System. Explain your steps. Compare with Table 3-7
and Example 31

32. Classify soie 1, 2, and 3 in Example 3.1 according to the AASHTO
Soil Classification System. Compare with Table 3-7 and Example 32.

33. Given the grain size distribution curves of Problem 2-33 and the
‘Atterberg limits data of Problem 25, classify sols À through F using
the USCS and AASHTO soil classification systems.

324. For the data below, classify the soils according to the USCS.

(2) 100% material passedNo.4 (6) 65% material retained on

sieve, 25% retained on No. No, 4 seve, 32% material
200 seve. ‘tained on No. 200 sieve.
Fines exhibited: Gener

Medium to low plasticity.
Dilataney—none to very slow,
Dry strength—medium to high

(©) 100% passed No. 4 sieve
90% passed No. 200 sieve
Dry strength—low to medium.
Dilataney- moderately quick
LL=B.PL=M.

(©) 100% material passed No. 4
sieve, 20% retained on No
200 seve
Fines exhibit high plasticity

Dilatancy—none
Dry strength—high.

(2) 5% material retained on
No. sieve, 70% passed
No. 4 sieve and retained on
No. 200 seve.

Fines exhibited medium dry
strength, medium toughness
Dilatancy—none
LL =25,PL= 15

(9 5% retained on No. 4sieve,
70% passed No. 4 and re.
tained on No. 200 seve.

Fines exhibited low plasticity
and high dlstaney.

(© 90% material passed No. 4
sieve, and retained on No.
200 eve.

Grace

10% passed No. 200 sieve,
Fines exhibited high
ilataney.

0) 70% material retained on
No. 4 sieve, 27% retained
on No. 200 sieve
GSC als,

3-5. For the soils of Problem 3-4, estimate the compressibility, permeabil

y, and toughness.

3-6. Grain size distributions and Aterber limits are given for 16 soils in
the six graphs comprising Fig P3.6 Clasiy the soils according to (3)
USCS and (2) AASHTO systems. (All data from USAEWES, 1960)

ER
Teh

jo

is

B

ig

ie

oct ine wih or mam)
ossesssages ©

‘Gime Org Be ELIO PIS run mar content: LSS, PID Loven de

more

Rea Sse aoe magn EO

Perce a oc

CENT TETE

nt on i ma)

Fo P38 conos.

four

Clay Minerals and
Soil Structure

4.1 INTRODUCTION

At this stage its useful o again define the term ely. Clay can refer
to specific mineras such as kaolinite or lite, as are discussed in detail in
this chapter, However, in civil engineering. ely often means a clay sa
soil which contains some clay minerals as well as other mineral con-
tuent, hs plasticity, and is “cohesive” Clay sols are fine rained, as
indicated in Chapter 2 (Table 22), but not all fine-grained soils are
‘cohesive or lay, Sills are both granular and fine grained. The individual
[St grains, like clays, are invisible o the naked eye but silts are noncohe-
sive and nonplastic, Rock flour is another example of a very fine-grained
ohesioness si.

‘Also remember that certain characteristics of granular soils such as
the grain size distribution and the grain shape affect the engineering.
behavior of these soils. On the other hand, the presence of water, with a
few important exceptions, is relatively unimportant in their behavior. In
contras, for clay soils the grain size distribution has relatively litle
influence on the engineering behavior, but water markedly affects their
‘behavior, Sits are an "in between” material. Water affects their behavior
they ae dilatant yet they have lite oF no plasty (PI = 0), and their
strengths, Ike sands, are essentially independent of water content.

"As we indicate inthis chapter, clay minerals are very small particles
‚which are very active electochemicaly. The presence of even a sms
amount of clay minerals ina sol mass can markedly affect the engineering
“properties ofthat mass. As the amount of clay increases, the behavior of
the sol is increasingly governed by the properties of the clay. When the
clay content is about 50%, the sand and sl grains are essentially floating
in a clay matrix and have Ile effect on the engineering behavior

” Cie Minerals e So Sucre

In this chapter, we briefly describe the important clay minerals, how
‘hey are identified, and how they interact with water and with each other.
‘We also, describe some of the latest thisking about so fabric and struc
ture, concepts which are fundamentally important fora good understand.
ing of cohesive soil behavior. Finally, cohesionless sol structures and the
concept of relative density are discussed.

introduced inthis chapter.

= Aa

42 CLAY MINERALS,

Clay minerals are very tiny eryslline substances evolved primarily
from chemical weathering of certain rock-forming minerals, Chemically,
they are hydrous aluninsilicates plus other metalic ions. All clay minerals
are very small, cllodalszed erytals (diameter less than | um): and they
‘an only be seen with an electron microscope. The individual exystals ook
like tiny plates or flakes, ad from X-ray diffraction studies scientists have
determined that these flakes consist of many crystal sheets which have a
tepeating atomic structure. In fac, there are only two fundamental crystal
sheets, the rerahedval or sea, and the octahedral or alumina, sheets. The
particular way in which these sheets are stacked, together with different
bonding and diferent metalic ions in the erystalIatice, constitute the
different elay mineras
‘The tetrahedral sheet is basically a combination of silica tetrahedral
units which consist of four oxygen atoms at the corners, surounding a
Single sicon atom, Figure 4 a shows a single silica tetrahedron; Fig. 4.15
shows how the oxygen atoms atthe base ofeach ttrahedron are combined
O form a sheet structure. The oxygens at the bases ofeach tetrahedron are
in one plane, and the unjoined oxygen comers all point in the same
direction. A common schematic representation of the tetrahedral sheet
hich is used later is shown in Fig 4.10. A top view of the silica sheet
showing how the oxygen atoms atthe base ofeach tetrahedron belong to
two tetrahedroas and how adjacent silicon atoms are bonded is shown in
Fig. 4.14, Note the hexagonal “holes” in the sheet.
‘The octahedral sheet is basically a combination of octahedral units
‘consisting of six oxygen or hydroxyls enclosing an aluminum, magnesium,
fon, or other atom. A single octahedron is shown in Fig 424, while Fig.
420 shows how the octahedrons combine to form a sheet structure, The
ows of oxygens or hydroxyls in the sheet are in two planes. Figure 42 is

Ouen ane above ions
Oxygen term eo

etn teens scanner, no
Sa ene ir
‘are ope

Fg 42, (1) Sngi ston tavanedion (otr Om. 1969) (9) noma
1 ow Sn tovaneart or sien sect (mer Se, 89) 6)
Sein parton twice sen ae rig, SD 6)

A Schematic representation ofthe octahedral sheet which we use later. For
à top view of the octahedral sheet showing how the different atoms are
Shared and bonded see Fig. 420

‘Substitution of different cations in the octahedral sheet is rather
‘common and leads to different clay minerals. Since the ions substituted are
approximately the same physical size, such substitution i called Lomar-
‘hous. Sometimes no all thé gctahedrons contain a cation, which results in
& somewhat diferent crystalline structure with slightly diferent physical
properties and a different clay mineral. If all the anions of the octahedral
Sheet ate hydroxsls and two-thirds of the cation positions are filed with
Aluminum, then the mineral is called gihhete. If magnesium is substituted

18 Marvin not atone

© ran inion ane

rot

mn es e
Ben en rem re D
nens ome
=a

fren se antl a hon rons he he

sa mete estab ee ncn Dae

a ety moon ea Un tee tems A cy

so a eat hee si asus ne a

sae an ns ha tin psa ooo

cream na fay ca pune o ae 0

‘ete Oe nl a o

clay soi.

42 cay teeta "

N
t
Zs

Er

fp, 42, Seremate agan H
(Gree ame 199) 1

Keone consists basically of repeating layers of one tetrahedral
(la) shet and one octahedral (alumina or gibbsite) sheet. Because of the
Stacking of one layer of each of the two baste sheet, kaolinite is called a

1 clay mineral Fi. 43). The two sheets are held together in such a way
tha the tps ofthe sia sheet and one of the layers ofthe octahedral sheet
form a single aye, a shown in Fig. 44. Ths layer is about 072 nm thick

O ones
O treo
O nn
Osa

Fig. 44. Atom ctr e Lacio anar Gm, 958.

ogro br MD. Ho

“nd extends indefinitely in the other two directions. A kaolinite crystal,
then, consists of a stack of several layers of the basic 072 nm layer.
Successive layers ofthe basic layer are held together by hydrogen bonds
between the hydroxyls of the octahedral sheet and the oxygens of the
eirahedral sheet Since the hydrogen bond is very strong, it prevents
hydration and allows the layers to stack up to make a rather large crystal.
‘A typical kaolin crystal can be 70 to 100 layers thick. Figure 45 is a
Scanning electron micrograph (SEM) of kaolinite.

‘Kaolinite is the primary constituent in china clay; it is also used in
the paper, paint, and pharmaceutical industries. For example, as a phat
maceutial it used in Kaopectate and Rolaids,

‘Another 1:1 mineral related to kaolinite is halle. I differs from
kaolinite in that when it was formed it somehow became hydrated between
the layers, causing a distortion or random stacking in the crystal aceso.
that itis tubular in shape (Fig. 46). The water can casly be driven out
from between the layers by heating or even air drying. and the proces is
irreversible. That is, the halloyste will not rehydrate when water is added
Halloyate, although not very common, occasionally plays an important

Son of hoya rom Coiorado.
ogro fe ban bare Ep
on à SH

42 Chey mens e

engineering role. Classification and compaction tests made on irried
Samples can give markedly diferent results than tests on samples at thee
natural water content. Ifthe sol wil not be air dried inthe fed, it can be
extremely important that laboratory tests be carried out atthe feld water
‘contents so that the results wll have some validity.

Montmorilenite, also sometimes called smectite, is an important
mineral composed of two silica sheets and one alumina (gibbsite) sheet
(Fig, 47) Thus montmorilonie is called a 2:1 mineral. The octahedral
het is between the two silica sheets with the tips of the tetrahedrons
combining with the hydroxyls of the octahedral sheet to form a single
layer. as shown in Fig. 48. The thickness of each 2:1 layer is about 096
fm, and lke kaolinite the layers extend indefinitely in the other (wo.
directions. Because the bonding by van der Waals forces between the tops
‘ofthe silica sheets weak and there isa net negative charge deficiency in
the octahedral sheet, water and exchangeable ions can enter and sepa

Mount f

Fig 47 Serenate saga of ho structure of monmotlonte
Cle Lande. 10)

42 Gay tad Di

from yon Tne ng of
‘Gres gm oo

other important industrial and pharmaceutical applications. I is even used
in chocolate bars!

ite, discovered by Prof. R. E. Grim of the University of lines, i
another important constituent of clay soils. I also has a 2:1 structure
Similar 10 montmorillonite, but the interlayers are bonded together with
potassium atom. Remember the hexagonal hole inthe sica sheet (Fig
AG) Te has almost exactly the ight diameter so that a potassium atom
just ills that hexagonal ole and rather strongly bonds the layers together
(Fig. 410), In addition, there is some omorphous substitution of
aluminium for silicon in the slica sheet,

Illes have a eu structure similar to the mica minerals but with
less potassium and less somorphous substitution: thus they are chemically
much more active than the other mias. Figure 411 is a SEM of illite

Emir. relatively common in clay sil is made of repeating layers
of a sia sheet, an alumina sheet, another sica, and then either a gibbsite
(A or brucite (Mg) sheet (Fig. 4.12). It could be called a 2:1:1 mineral
Ohlorite can also have considerable isomorphous substitution and be
missing an occasional brute or gibbsite layer: thus it may be susceptible
to swelling because water can enter between the sheets. Generally, how.
ver iis significanly less active han montmerillon

‘As mentioned previously thee ae iterally dozens of
with virtually every conceivable combination of substituted io:
Grater, and exchangeable cations. Some of the more important from an
engineering viewpoint include vermieulite, which is similar to montmori
Tonite, a 21 mineral, but st has only two interlayers of wate. After itis
ri at high temperature, which removes the intedayer water, “expanded”
‘ermicuite makes an excellent insulation material. Another clay mineral,
litapulpte, Fig. 4.13, does nat have a sheet structure but sa Chain siete

Consequently has a needle or rodlike appearance. Mixed per minerals

oie A

= Clay Marae end sot Structure

are relatively common: they would include, for example, montmorillonite
mixed with chlorite or lie. Because alophane is an aluminosilicate, it is
Often classified as a clay mineral. However, iis amorphous, which means it
has no regular erysaline structure. Under specialized conditions of
‘weathering, it may be a locally important constituent of clay sil.

4.3 IDENTIFICATION
OF CLAY MINERALS

Since the clay minerals are so very small, their identification by the
sual optical mineralogial techniques Used in geology is not possible 50
Other means must be employed to identify them. From your engineering
Materials courses, you may remember that materials with regular or
‘repeating pattems of crystal structure wll difract X-rays. Different mine.
[with different enstaline structures wil have different X-ray diffraction
pattern, and in fact these different pateras were how the minerals were
ented in the fist place. The pauerns for the common minerals are
Published, and it is relatively simple to compare the diffraction patter of
Sour unknown with the patterns of kaown minerals. There is a problem,
however with soils which are mixtures of clay minerals, soils which
contain organics and other non-clay mineral constituents, and soils with
mixed layer minerals, Usually a detailed quantitative analysis is impossible
“about all that one can tell is which minerals are present and roughly

how much of each

“Another technique that is sometimes used to identity elay mine
fferenil thermal analysis (OTA). A specimen of the unknown soil
‘Sith an inert contro substance is continuously heated to several hundred
degrees in an electric furnace, and certain changes in temperature occur
because ofthe particular structure of the clay minerals. The changes occur
At specific temperatures for specific minerals, and the record of these
Changes may be compared with those of known mineras

“Electron microscopy, both transmission and scanning, can be used 10
idenuly clay minerals im a Soil sample, but the process is not easy and/or
‘quantitative

'A simple approach suggested by Prof. Casagrande is to use the
Atterberg limits, It was mentioned (Sec. 28) that the activity has been
{elated to speifie active or inactive clays. Montmorilonites willbe highly
[clive since they are very small and have large plasticity indices. Use of
‘Casageande’s plasticity chart (Fig. 32) can also tell you just about as
much, at leas from an engineering point of view, as the more sophisticated
lation and DTA analyses. The procedure is shown in Fig 4.14. You
Simply locate your sample on the LL-PI char, and compare is location

u cin Bunce ”

norte

sy char forlopea rom Casngranae 548 and an ln
itches

With those of known minerals. If your sample has Atterberg limits that plot
high above the Acne near the Uline, then chances
lot of active clay minerals such as montmorillonite. Even ifthe sol is
«lassiied as a CL, for example a sandy clay (CL), and sill plots near the
Uline, the elay portion of the sol is predominantly montmorillonite. The
tlacial lake clays from around the Great Lakes region in the United States
and Canada are predominantly illic and they plot right above the A-line.
Scandinavian marine clays which are ¡ie also plot in this region
Kaolinite, which are relatvely inactive mineral, plot right below the
1. Even though they are technically clay, they behave like ML-MH
materials

4.4 SPECIFIC SURFACE
‘Specific surface is the ratio ol the surface arca of a material to ether
its mass or volume. In terms of volume

specific surface = surface area/volume en

‘The physics! significance of specific surface can be demonstrated
‘using a 11 I em cube,

m)

= 6/em = 06/mm
eh 7

If he cube is 1 mm on a side, the specific surface would be

specifi surface = O

Em) mm
Im 7

It the cube is gm on a ide, the specifi surface would be
sen = 6/um = 6000/mm

“This stats that large partis, whether cos or si particles, have

smaller surface areas pr unit of volume and thus smaller specie sacs

than smal pares. To oan the specie surface in terms of mass, Jo

Jus vide the value in teens of volume by the mass density pun

would thes be m/e or md

‘Now if suficent waer was preset to just dampen the surface aca
of the cubes in the above example it would ake tn tines as much water

the surface of all the gras when the cubes wee Imam on a side
‘hen the same volume ocepied à single cube of 1 om? Not also
one were tying to remove water Irom the surface wet tol, hee
Would e ten tines as much water L remove from the smaller gains,

Specie surface is inversely proportional 10 the grain size of sol
‘We general do not compute the speie surface for practical eases since
{he soi grin are woo regla in shape todo 0. Bui should be eat
{hata sol mass made up of many small aries wl have on he average à
larger specie srfac than the same mass made up of lar partes

From the concept of specific srface, we would expect larger moi
ture contents for fine grained sis than for care grind si ll ober
things such as void rado and si sucre Being Sal.

You may recall rom your materials courses that specific surface a
primary factor in concrete and asphalt mix design. In both cases ib
cesary 1 provide sufiientcement pase or asphalt o coat the age
te surfaces

4.5 INTERACTION BETWEEN WATER
AND CLAY MINERALS

‘As mentioned previously, water usually doesn't have much effect on
the behavior of granular soils. For example, the shea strength of a sand is
approximately the same whether itis dry or saturated. An important

AS nern Basen Water an Cy rss

‘exception to this fact is the case of water present in lose deposits of sand
‘subjected to dynamic loadings such as earthquakes or Blass.

‘On the other hand, fine-grained soils specially clay soil are strongly
inluenced by the presence of water, The variation of water content gives
rise to plasticity, and the Atterbrg limits are an indication of dis in
fluence. Grain size distribution only carly is governing factor in the
behavior of fine-grained sis,

"Why is water important in fine-grained soils? Recall the discussion of
specific surface, in the previous section, where the smalie he particle, the
larger the specie surface. Clay minerals, being relatively small particles,
have large specific surfaces, and everything ese being equal, you might
expect that they would have very active surfaces,

“the relative szes of four common clay mineral and thee specific
surfaces are shown in Fig. 415, Kaolinite the largest clay mineral, bas a

pa A
E m
ES
Gn wen am

F9 416 Average van frente io, icknasen, tnd specie
fines o Common day mts er Yong rd arn,

= Chey Mara nd a Suar

thickness or edge dimension of about 1 um, while montmorillonite, the
has a thickness of ony a few nanometres. Since the
Crystals have roughly the same average “diameter,” atleast within an order
‘of magnitude, itis not surprising thatthe specifi surfaces are so diferent
(Of course, there are rather wide variations in the sizes of the crystals
depending on weathering and other factors, but the values given are
Average values, Since surface activity is related tothe particle size, you can.
ce why montmorillonite, for example, is more “active” than Kaolinite,
Similarly the surface activity ofa sand or si grain is practically ero.
In Sec. 28, we defined the acc ola cla

024)

where the clay fraction is usually taken as the percentage of the sample less
than 2 um (Skemplon, 1953), We mentioned that there was a preity good
correlation between activity and the type of clay mineral. This correlation
de shown in Table +1.

"Now, it seems that clay particles are almost always Aydrated in
ature; that is, there are layers of water surrounding each crystal of ely,
This water is called adsorbed water. As discussed in the next section, the
structure of clay soil and thor their engineering properties ultimately
‘depend on the nature of this adsorbed water layer

How is water adsorbed on the surface of a clay particle? First, you
may recall from chemistry or materials courses that water is à dipolar
molecule (Fig. 4.16). Even though water is electrically neutral, it has two
Separate centers of charge, one positive and one negative. Thus the water
molecule is eeeirostaically attracted to the surface of the clay crystal
Secondly, water is held tothe clay cristal by drogen bonding (hydrogen,

TABLE 4 Actives of Various Minerals?

monton 1
le 513
estate 3208
Moye span) 03
Mate bye) ot
Apu 0512
lease fear
cs scie) =
Ce =
ur >

Aer Stompin (195) and Miel 197)

{45 Inseln Between Wale and Cay Minerale =

Fig 436 Seramste diagram
Ea or molec (er Lambe,

‘of the water is attracted 10 the oxygens or hydroxyls onthe surface ofthe
lay) The third factor is that the negatively charged clay surface also
ucts cations present inthe water. Since al cations are hydrated to some
extent, depending on the ion eations also contribute 10 the atracion of
‘water to the clay surface, OF these three factors, hydrogen bonding is
‘probably the most important factor.

The attraction of water to the clay surface is very strong near the
surface and diminishes with distance fom that surface. I seems that the
Water molecules right atthe surface are very tightly held and strongly
onented. Measurements show that some thermodynamic and electrical
properties of the water next 10 the lay surface are different than that of
tree water” (Mitchell, 1976)

The source of the negative charge atthe surface of the clay crystal
results from both somorphovs substitution, mentioned easier, and imper-
fections in the crystal latte. especially at the surface. “Broken” edges
contribute greatly to unsatisfied valence charges atthe edges ol the crystal
Since the crystal wants to be electrically neutral, cations in the water may
be strony attacted 10 the clay. depending on the amount of negative
charge presen. Different clas have different charge deficiencies and this
have different tendencies to attract the exchangesbe cations. They are
called exchangeable unce one cation can easly be exchanged with one of
the same valence or by two of one-half the valence of the original cation.
[As might be expected from their relative sizes and specific surfaces,
‘montmorillonite has a much greater charge deficiency and thus a much
reste attraction for exchangeable cations than Kaoliite. Mie and chlo-
Fit are intermediate in this respect

Caleium and magnesium are the predominant exchangeable cations
in sols, whereas potassium and sodium are less common. Aluminium and
hydrogen are common in acidic oil. The depositional environment as.
well as subsequent weathering and leaching will govern what ions are
Present in a particular soil deposit, As might be expected, marine clays are
predominately sodium and magnesium since these are the most common
tations in sca water. Cation exchange or replacement is further com-
plicated by the presence of organic mater.

” toy Minera and ot Scar

“The case of replacement or exchange of cations depends on several
factors, primarily the valence of the cation. Higher valence cations easily
replace cations of lower valence For ins of the same valence, the size of
the hydrated fon becomes important: the larger the ion, the greater (he
replacement power À further complication i the fact that potassium, even
though it is monovalent, fits into the hexagonal holes in the silica sheet.
Thus i will be very strongly held on the clay surface, and it will have a
greater replacement power than sodium, for example, which is also mono-
Valen. The cations can be listed in approximate order ofthis replacement

ity. The specific order depends on the type of clay, which ion is being
Feplaced, and the concentration ofthe various ions inthe water. In order
of increasing replacement power the ions are

Lit E Nat < HY € KT € NH] Mg € Gat Alt

“There are several practical consequences of ion exchange. The use of
chemicals 10 stabilize or srengihen soils is possible because of ion ex
Change. For example, lime (CaOH) stabilizes a sodium clay soil by re-
Placing the sodium fons in the clay since calcium has a greater replacing,
power than sodium. The swelling of sodium montmorillonite clays can be
Significantly reduced by the addition of lime.

‘What does a clay particle look lke with adsorbed water on it? Figure
17 shows a sodium montmorillonite and Kaolinite crystal with layers of
adsored water. Note that the thickness of the adsorbed water is a
proximately the same, but because of the size differences the montmoril-
fonite will have much greater activity, higher plasticity, and greater sell
ing. shrinkage, and volume change due to loading.

In this section only a bref overview of the very complex subject of
the interaction between water and clay minerals has been presented. For
‘dditional information, you should consult Yong and Warkentin (1975)
and Mitchell (1976) and references included therein,

1000 2 100 mm

ME om)

Po. 417 Patte aies of aauorbes water ayers on tectum
‘mBnumoraonte end Sodem hasnt ora Lumen, 1060).

46 INTERACTION OF CLAY PARTICLES.

‘The association of clay minerals and their adsorbed water layer
provides the physical bass for soil structure. The individual clay particles
Tmierac through their adsorbed water layers, and thus the presence of
{Mfereat ions, organic materials, different concentrations, et. affect or
Sontibute wo the multitude of soil structures found in natural sol deposits
Clay particles can repulse each other elecwostatically but the process
“depends on the ion concentration, interparticle spacing. and other factors.
mar. there can be attraction of the individual particles due 10 the
tendency for hydrogen bonding, van der Was

‘chemical and organic bonds. The interparticle force or potential fields
decrease with increasing distance from the mineral surface, as shown in
Fig 4.18. The actual shape of the potential curve will depend on the
valence and concentration of the dissolved ion and on the nature of the
bonding forces.

22. potential vers tance

Particles can flocculate or be repelled (disperse. separate). They
«an fioceulate in several possible configuration; edge-o-ace is the most
‘Common, but edge-to-edge and {ace-toface flocculation are also possible
‘The tendency towards flocculation will depend on increasing one or more
of the following (Lambe, 1984).

Concentration ofthe electrolyte
Valence of the ion
“Temperature

or decreasing one or more of the following:

Dielectric constant of the pore uid
Size of the hydrated ion

pH

‘Anion adsorption

Just about all natural clay sois ae floceulated to some extent. Only
in very dite solutions (at very high water content) is dispersion of clay
partes possible. and this might occur in a sedimentary deposit during.
Sepostion.

4.7 SOIL STRUCTURE AND FABRIC

In geotechnical engineering practice, the sure of a soi is taken 10
can both the geometric arrangement ofthe particles or mineral grains as
SEN as the interparticle forces which may act between them, Soil fabric
‘eters only to the ¿cometio arrangement of the particles. In granular or
ohesionfess soils the interparticle forces are very small, so both the fabric
Sha autre of graves, sands, and to some extent silts are the same. On
the contrary, however, interparticle forces ate flatvely large in fine-grained
{herve wis. and thus both these forces and the fabric of such soils must
be considered as the structure ofthe soi. The structure strongly affects oF
Seine would say. governs the engineering behavior of a particular soi. All
{he lay trucures found in nature and described inthe next section result
from tome combination of these factors, the geologic environment at
Ulpenition, the subsequent geologic and engineering stress history, and the
ature of the clay mineral. We study these very complicated factors
Because they fundamentally affect soi behavior and the engineering prop.
Chics of sol. Geotechnical engincers must conside the soll structure and
fabric at least quahtaively when cohesive soils are encountered in en-
gineering practice.

Tk complete description of the structure ofa fine-grained cohesive soil
requires a Knowledge of both the interparticle forces as well as the
Geometrical arrangement (fabric) of the particles. Since it is extremely
cute not impossible to directly measure the interparticle foree fields
Surrounding clay parties, most studies of cohesive sol structure involve
‘Only the fabric of these oils, and from the fabric certain inferences are
‘made about the interparticle forces.

4.8 COHESIVE SOIL FABRICS

Classification of cohesive sil fabrics into simple systems involving
only 2 few clay particles is not really possible. Single grain or single
particle units occur only rarely in nature and then in only very dilute
Ghaycwater systems under special environmental conditions. From recent
“adie of real elay soils withthe scanning electron microscope (SEM), the

individual clay particles seem to always be aggregated or flocculated
together in submicroscopic fabric units called domains. Domains then in
turn group together to form clusters, which are large enough to be seen
vih a visible light microscope. Clusters group together to form pedo and.
‘ven groups af pes. Peds can be seen without a microscope, and they and.
ther macrostructural features such as joins and fisures constitute the
macrofabrie system. A schemati sketch ofthis system proposed by Yong
And Sheeran (1973) i shown in Fig. 4.19: a microscope view of a marine
‘ay is also included (Pusch, 1973) Collins and McGown (1974) suggest a
Somewhat more elaborate System for describing mirofabric features in
natural sels They propose tte typeof features:

1. Elementary particle arrangement, which consis of singe forms of
partice interaction at the level uf individual clay, silt, or sand
Particles (Figs. 4204 and b) or interaction between small groups of
‘hay platelets (Fig. 4209) or elothed sit and sand particles (Fig
4200)

2, Particle astemblages, which are uns of particle organization hav-
ing definabl physical boundaries and a specific mechanical func-
tion. Paruce assemblages consist ol one or more forms of elemen-
tary particle arrangements or smaller particle assemblages. and
they are shown in Fig 421

3. Pore spaces within and between clementary particle arrangements
and particle assemblages

Collins and McGown (1974) show microphotographs of several natural
soils which illustrate their proposed system.

"A SEM photograph of «silty clay ped from Norway is shown in Fig.
422, Note how complex the structure appears. which suggests that the
engineering behavior is also probably quite complex

“Macrovrucare, including the statigraphy of fine-grained soil de-
posits hasan important influence on sol behavior in engineering practice.
Joint, fissures, sit and sand seams, too holes, varves, and other “defects”
‘often control Ihe engineering behavior ofthe entice sil mass. Usually, the
Strength of a soil mass i significantly les along a crack or fissure than
‘through the intact material, and thus ifthe defect happens o be unfavora-
bly onented with respect to the applied engineering tresses, instability oF
failure may occur. As another example, the drainage of a clay layer can be
markedly affected by the presence of a silt or sand layer or seam.
‘Consequently, in any engineering problem involving stability, settlements,
or drainage, the geotechnical engineer must investigate carefully the clay

‘Microstructure is more important from a fundamental than an en-
gineering viewpoint, although an understanding of the mirostucture aids

a mn

rangement (yma ny gant murs 0) edi
Sit’ sand patio Iran: (0) ea pata group trac,
(a) mea st or and pure Tannen. e) party once
Banc mero ater Ex and Meow ra)

in a general understanding of soil behavior. The microstructure of a clay
reflets the entire geologic and stress history of that deposit. Virtually
cverything hat ever happened o that cl which wil affect the engineering.
response of the clay is imprinted ia some männer on the microstructure
‘The microstracture reflects the depositional history and environment of the
‘epost, its weathering history, both chemical and physical: in effect ite
stress history that is, all changes caused both geologically and by man.
Recent research on clay microstructure suggests that the greatest
single factor influencing the final structure ofa clay isthe electrochemical
environment existing at the time of sedimentation, Floceulatd structures
or aggregations can result during sedimentation in vitally all depositional
environment, whether marie, brackish or in fresh water. The degree of

EY

Sener sesenta o pare amenas Cd.
nda tetas se e,

(her Gonna and om, 1874)

‘telat pr don tno hoe anh

‘openness of the structure is apparently influenced 10 a large degree by the
‘lay mineralogy as well as Ihe amount and angularity of silt grains present.
Sit particles have been observed to have a thin skin of apparently strongly
Orient clay particles or even amorphous materials parallel to their
surfaces. Some grain-to-grain contacts of silt particles have been observed
(Gee Fig. 423) bat at present it dificult to asceruin whether actual
‘mineral contact occurs in lays

‘Tn summary, the structure of most naturally occureing clay deposits is
highly complex. The engineering behavior of these deposits is strongly
influenced by both the macro- and the microstructure. AL present, no
‘quantitative connection exists between microstructure and the engineering

ar

properties, but it is important forthe engineer to have an appreciation of
The complexity of the structure of cohesie soils and thei elation to
engineering behavior

4.9 COHESIONLESS SOIL FABRICS

Grains of oil which can settle out of a sila suspension indepen-
ently of other grains (generally larger than 0.01 10 002 mm) will form
Sia is called à single groined structure. This is the structure of, for
sample, a sand of gravel ple, and some sandsit mixtures. The weight of
fhe grains causes them to sto and come to equilibrium in the bottom of
the fluid as soon as the velocity can no longer support the particles in
suspension

Deponition media include both air (loess deposi, sand dunes: grain
size generally © 005 mm) and water (rivers, beaches, et)

Single grained structures shown in Fig. 424, may be “loose” (high
void rato or low density) or “dense” (ow void ratio or high density)
Depending on the grain sue distribution as well asthe packing or arrange
ment of the grains, a wide range of vod ratios is possible. Table 4-2 lists
Tome typical valves for a variety of granular soils. (tis possible, under
Tome conditions of deposition, for a granular material o achieve a honey-
‘ombed structure (Fig 425) which can have a very high void ratio. Such a
Structore is meta-stable. The grain arches can support static Toads, but the

49. Cohesaniags Ba Fabs 1

9 424 Single ganes sos cher

structure is very sensitive Lo collapse when vibrated or loaded dynamically
The presence of water ın very loose rain structures also can alter the
engineering behavior. Phenomena typical of lose pain structures, such as
‘bulking. a capillary phenomenon, and quicksand are discussed in Chapters
and

‘The greatest posible void ratio or looses posible condition af a soi
is called the maximum cold ratio (Sm). Tis determined in the laboratory
by pouring dry sand very carefully with no vibration into a calibrated
molá of known volume. From the weight of sand inthe mold, eu, can De
calculated. Similarly, the minimum cod ratio (eq) isthe densest possible
condition that a given soil can attain. The value of en, is determined by
‘vibrating a known weight of dry sand into a known volume and calelating
the void ratio. The range of possible void ratios fer some typical granular
soils are shown in Table 42

The relative density D, also called the density index Jp. is used 10
‘compare the void ati of à given soil with the maximum and minimum
‘void ratios. Relative density is defined as

Dolo

000%) Ce)
and is usually expressed as a percentage. Relative density can also be
Stated in terms of maximum and minimum dey densities as
DESTA
rom
where py “dey density ofthe sol with void ratio e,
Peron = minimum dry density of the soil withthe Void 1880 Em, and
Dana, = maximum dry density of the soil withthe void ratio ene

AS

x 100(%) (5)

1 soil deposit very strongly afecs its
I is important to conduct laboratory

ang Ka oy ons q

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tests on samples of the sand at the same relative density as in the fel
‘Sampling of loose grasular materials, especially at depthe greater than a
few metres, is vey difficult. Since the materials are very sense lo even
the sie. vibration, ones never sue the sample has the same density as
the natural soil deposit. Therefore different kinds of penetrometer: are
used in engineering practice, and the penetration resistance values are
‘oughly correlated with relative density. For deposits at shallow depths
where direct access is possible, other techniques have been developed to
measure the inplace density of compacted soils. These techniques are
discussed in detail im Chapter $.

nally, it should be noted in this discusion of the structure of
Branular sols that relative density alone is not sulficiet to characterize
their engineering properties e is posible for two sands, for example, 10
have identical void ratios and relative densities but significanty different
fabrics and thus significant different engineering behaviors. Figure 426
is a twordimensional example of such a fabric. Both “sands” are dential
— they have the same grain size distributions and the same void ration. But
heir fabrics are obviously very diferent. Ses history is another factor
(hat must be considered when dealing with sands and gravels in engineer.
in practice. Deposits of granular materials which have been preloaded by
nature or man will have very diferent stresestain properties and therefore
very different setlement responses (Lambrechts and Leonard 1978).

PROBLEMS

41, Calculate the specific surface of a cube (4) 10 mm, (6) 1 mm,
(© 1 um, and (6) 1 nm on a side, Calculate the specific surface in
rms of both areas and m?/kg. Assume for the later case that ÿ, =
265 Me/m.

42. Calculate the specific surface of (a) tennis bals, (5) ping pong ball,
(©) bal bearings 1 mm in diameter, and (fly ash with approximately
‘spherical particles of $0 ym in diameter.

43. The values of em. and em, for a pure slica sand (p, 265 g/m?)
were found to Be 046 and 066, respectively. (3) What isthe core
sponding range in dry density? (b) I the in situ void ratio is 0.63,
‘what is the density index?

mn tay inert nd ol nr

44, Describe briefly the ersaline or atomic structure of the following.
ten minerals. Also list any important distinguishing characteristics.

(a) Smecite @) Bruce (9 Gibbsite
(8) Atapulgie (© Bentonite (O Allophane
(9) Halloysite ©) lite © Mica
© Chlosite

45. Describe the following. types of bonding agents found with clay
minerals
(a) Hydrogen bond (6) Covalent bond
(© van der Waals forces (8) James bond

46. The wet density of a sand in an embankment was found 10 be
19 Mg/m and the field water content was 10% In the laboratory,
the density of the solids was found to be 266 Mg/n?, and the
maximum and minimum void ratos were 062 and 044, respectively.
CCatelate the relative density ofthe sand in the field

4-2. Which sheet. sica or alumina, would you wear to a toga party? Why?

48. Given the particles in Fig, 426, is it realistic (0 show that al the
particles are in contact with each other for this given plane? Any
ven plane? Why?

five

Compaction

5.1 INTRODUCTION

In geotechnical engineering practice the soils at a given site are often
tess than ideal for the intended purpose. They may be weak, highly
‘compressible, or have a higher permeability than desirable from an en
Eineeing or economic point of view. It would seem reasonable in such
fnstances to simply relocate the structure or facility. However, considera:
tions other than geotechnical often govern the location ofa structure, and
the engineer is forced o design forthe sie at hand. One possiblity isto
“gap! the foundation to the geotechnical conditions atthe ste, Another
possibility i to try to stabilize or improve the engineering properties ofthe
Soils at he site. Depending on the ctcumstanees, this second approach
may be the most economical solution to the problem. Stabilization is
Usually mechanical oF chemical, bot even thermal and electrical stablza-
tion have occasionally been used or considered.

inthis chapter we are primarily concerned with mechanical stabilca-
tion of densification, also called compaction. Chemical stabilization in
lues the mixing or injecting of chemical substances into the soil. Port
land cement, lime, asphalt, calcium chloride. sodium chloride, and paper
mil wastes are common chemical stabilization agents

‘Other methods for stabilizing unsuitable foundation soils include
dewatering, which isthe removal or reduction of unwanted excess ground
‘rater pressures, and preloading, in which the foundation soils are surcharged
Wh à temporary overload so as to increase the strength and decrease
Anticipated settlement. The detils of these and other, methods are der
Series in textbooks on foundation and highway engineering A good sate

ve Compacte

of he art discusion and reference to methods for improving the engineer
ing characteristics of silt is provided in the ASCE (1978) commitee
report "Sol Improvement — History, Capabilities, and Outlook.”
Compaction and stabiizatio are very important when soils used as
an engineering materia; thst, the structure il! is made of soi. Earth
‘Same and highway embankments are examples of each srucrre, 1 sis
re dumped or otherwise placed at random in a fl, the result will be an
tmbankment with low stability and high settlement In fa, prior tothe
1930's, highway and eilroad hil were usually constructed by enddumping
soils from wagons or truck, There was very itl attempt to compact or
ens the sol and failures of even moderately high embankments were
‘common. Of course earthworks such as levees are almost as old as man,
but these structures, for example in ancient China or India. were con-
structed by people carrying small baskets of earth and dumping them in
the embankment. People walking over the dumped materials compacted
And thus strengthened the sos. Even clephants have been used in some
to compact soils, but research has shown that they are not very
it (Meehan, 1967.
‘The Following symbols ae introduced inthis chapter.

co

Rene pg; ni
Aaron 59)
Keen
nen vts mei le e

nor mt sat (OM)
tiem «M/E Maja) Mises da
MD MP Misa ra

5.2 COMPACTION

Compaction isthe densification of sil by the application of mecha
sical energy. I' may also involve à modification of the water content as
sell as the gradation ol he soi. Cohesionless soï are efficiently com-
pacted by vibration. In the field, hand-operated vibrating plates and
‘motorized vibratory rollers of various sizes ae very efficient for compaet-
ing sand and gravel soil, Rubberaied equipment can also be used
elicienly 10 compact sands. Even large frectaling weights have been
‘used to dynamically compact loose granular fils. Some o these techniques
are discused ater in this chapter

53 mar ot Compaction oo

Fine-rained and coh:.ive sols may be compacted in the laboratory
by falling weights an? nammers, by special “kneading” compactors, and.
even statically on a common loading. machine or press. In the field,
Sommer compaction equipment includes hand-operated. tampers,
Shespsfoot rollers, rubber-ited rollers, and other types of heavy compac.
tion equipment (ec. 5.5). Considerable compaction can also be obtained
by proper routing of the hauling equipment over the embankment during

“The objective of compaction is the improvement of the engineering
properties of the soil mass. There are several advantages which occut
through compaction:

Detrimental settlements can be reduced or prevented.

Soi strength increases and slope stabi

can be improved.
Be

In capacity of pavement subgrades can be improved.

Undesirable volume changes for example, caused by frost
action, swelling, and shrinkage may be controle,

5.3 THEORY OF COMPACTION

‘The fundamentals of compaction of cohesive soils are relatively new.
RR. Proctor in the carly 1930 was building dams for the old Bureau of
Waterworks and Supply in Los Angeles, and he developed the principes of
compaction in a series of articles in Engineering News-Record (Proctor,
1933). In his honor, the standard laboratory compaction test which he
developed is commonly called the Proctor test

Proctor established that compaction isa function of four variables:
(9 dry density pa, (2) water content w, (3) compactive effort, and (4) soil
type (gradation, presence of clay minerals, ete). Compactice effort is à
measure of the mechanical energy applied to a soil mass. In countries
‘where British Engineering units are used, compactive effort is usually
reported in flbl/{0, whereas the SI units are J/m (= joules). Since
TT Nom, and using the conversion factors in Appendix A, we can
determine that 1 IC101/T0 = 47.88 3/01. In the fil, compactive effort is
the number of passes or “coverages” of the roller of a certain type and.
‘weight on a given volume of soi Im the laboratory, impact or manic,
Ancadng, and static compaction are usually employed. During Impact
‘compaction, which isthe most commen type, a hammer is dropped several
times on a sol sample in a mold. The mass of the hammer, height of drop,
number of drops. number of layers of soil, and the volume ofthe mold aye
Specified. For example, inthe standard Proctor tet [ako standard AASHTO

m compaction

(1978), Designation T 98, and ASTM (1980), Designation D 69. the mass
‘ofthe hammer is 2495 kg (55 1) and the height of fall s 309.88 mm (1 10.
‘The soi i placed jn thee layers in an approximately 1 lite (0944 x
10°? wor 1/30 10) mola, and each layer is tamped 25 times. Compactive
fort can then be calculated as shown in Example $.

EXAMPLE 5.1
Given
Standard Proctor test hammer and mol.
Requires

CCaleulate the compactive effort in both SI and British Engineering unis

Solution:
a. Sr amis
«ompactive 249 ke(9.81 m/s*)(0-3048 m)(3 layers(2S blows ayer)
‘lor 0.988 x 10 7m
2713/00

A exact values of g and the volume are used, the standard Proctor
compacsve effort is 592.576 kl 1

D British Engincering unis:

compactive PEO

“This caution is strictly speaking, incorrect since the 5. lb hammer is
really a mass nota weight, However, the differences are negligible.

For other types of compacton, the caleulation of compactve elfor is
ot so simple, In kneading compaction, for example, the tamper kncads
the soil by applying a given pressure for a fraction of a second, The

53 Theoret Compaction w

Aneuding action is supposed to simulate the compaction produced by
sheepsfoot roller and oer types of field compaction equipment. In static
Compaction. the soi is simply pressed into a mold under a constant static
Sees in a laboratory testing machine

“The process of compaction for cohesive soils can best be illustrated
by considering the common laboratory compaction or Proctor test, Several
samples of the same si, but at different water contents, are compacted
“according to the standard Proctor compaction test specifications. given
previously. Typically, the toral or wet density and the actual w
fent of each compacted sample are measured. Then the dry density for
tach sample can be calculated from phase relationships we developed in
Chapter 2

pat as

ane eo

When the dry densities of cach sample are determined and plowed
‘versus the water contents fr each sample, then curve called a compaction
‘ire for standard Proctor compaction is obtained (Fig. 51. curve A)

Daye ot GON BON 100 Torn, 270 Wim?
Zu no
1 a
ho
13
“E 0s
(a) smart
1s ike So

er content 8)

ron

m compucton

ach data point on the curve represents a single compaction test, and
úsually four or five individual compaction tests ae required to completely
“termine the compaction curve. This cure is unique fora given soil ype,
tnethod of compaction and (constant) compactive effort. The peak point of
the curve is an important point, Corresponding to the maximum dy density
Panne is water content known as the optimum water content Wip, (ISO
{hat as the optimum moisture content, OMC). Note that the maximum
‘Sry density is Only a maximum for a specific compactive effort and
method of compaction. This does not necessarily reflect the maximum dry
density hat can be obtained in the field

“Typical values of maximum dry density are around 1.6 10 20 Mg/m®
(100 1 125 Ibt/fÜ) with the maximum range from about 13 10 24 g/m’
(80 to 150 101/10). (Densities are also given in British Engineering unite
because you are likely to encounter them in practice) Typical optim.
ater contents are between 10% and 20%, with an outside maximum range
OF about 5% to 40%. Also shown on Fig. 5.1 are curves representing
iterent degree of saturation of the so. From Eqs, 2-12 and 2-15, we ea
‘derive the equation for these theoretical curves.

oS

mn

e. co)

“The exact poston of the degree of saturation curves depends only on the
value of the density of the sot solids p, Note that at optimum water
Content for this particular soil, is about 75% Note too thatthe compac-
on curve. even at high water contents, never actually reaches the curve
lor “100% saturation” (traditionally called the zero ar void curve). And
this is true even fr higher compactive efforts, for example, curve B of
SA Curve Bis the compaction curve obtained by the modified, Proctor
compaction est [modified AASHTO (1978), Designation T 140. and ASTM
(1360). Designation D 1557]. This test utilizes a heavier hammer (4536 kg
Geto ba greater height of fall (457 mm or 1.510, and 5 layers tamped 25
nes into a standard Proctor mold. You should verify thatthe compactive
{forts 2603 KJ/a? or $6250 fe Ib{/1C. The modified test was developed
during World War II by the US. Army Corps of Engineers to better
represent the compaction required for ares to support heavy aircraft
‘The point is that increasing the compacive effort tends 10 increase the
maximum dry density, as expected, but also decreases the optimum water
Content. A kine drawn through the peak points of several compaction
Cones at different compactive efforts for the same soil will be almost
‘parallel toa 100% S curve. Its called the line of oprimums.

#3 Teor ot Compaction we

‘Typical compaction curves for different types of soils are iustrated
in Fig. 52. Notice how sands that are well graded (SW soil, top curve)
havea higher dr censity than more uniform sols (SP soils, bottom curve)
For clay 9-35, the maximum dry density tends to decrease as plasticity

Why do we get compaction curves such as those shown in Fig. 5.1
and 52? Starting at low water content. asthe water content increases, the
Parties develop larger and larger water films around them, which tend to
"lubricate” the particles and make them easier to be moved about and
recriented into a denser configuration, However we eventually reach a
ater content where the density does not increase any further. At Uns
point, water starts to replace soil particles in the mold, and since p. = p,
{he dry density curve starts o all off as shown in Fig. 3.3. Note that no
matter how much water is added, the soil never becomes completely
saturated by compaction,

‘Compaction behavior of eobesive soils as described above is typical
for both feld and laboratory comp

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154 Properties and Saure o Compactos Canasta Sa ur

Someuha, that is, have different shapes and positions on the py versus w
plot, but ia general he response will be similar to that shown ia Fig. 54,
where the same soil is compacted under diferent conditions. The standard
and modified Proctor laboratory tests were developed as a standard of
‘comparison for field compaction, thats 10 se ft rolling or compaction
‘was sufficient The approximation to field compaction is not exact, as.
mentioned, since the standard laboratory compaction is a éynamicimpact
‘ype, whereas field compaction is esentally a kneading-ype compaction.
‘This difference led tothe development ofthe Harvard miniature compac-
tor (Wilson, 1970) as well as larger kneading compactors. Field compac-
tion control procedures are described in See. 3.6.

5.4 PROPERTIES AND STRUCTURE
OF COMPACTED COHESIVE SOILS

‘The structure and thus the engineering properties of compacted
cohesive sols will depend greatly on the method or type of compaction,
the compactive effort applied. the soil type, and on the molding water
content. Usually the water content of compacted soils is referenced to the
‘optimum water content for a given type of compaction. Depending on
their position, soils are called dy of optimum, ear Or af optima, or et of
optimum. Research on compacted clays has shown that when they are
Compacted dry of optimum, the structure ofthe sili essentially indepen-
¿ent ol the type of compaction (Seed and Chan, 1959). Wet of optimum,
however, the type of compaction has a significant effect on the Soil
structure and thus on the strength. compressibility, ete, of the si.

“The comments in his section are very general, and you should keep
in mind that the real fabric of compacted clays is about as complex a the
Fabric of natural clays described in Chapter 4. At the same compactive
effort, with increasing water content, the soil fabric becomes increasing}
‘oriented, Dry of optimum the sois are always locculated, whereas wet of
Spimum the fabric becomes more oriented or dispersed. In Fig 53, for
‘example, the abri at pont Cis more orented than at point. Now. if the
Compactive effort is increased, the sil tends to become more oriented,
ven dry of optimum. Again, referring to Fig 55, a sample at point £
more orented than at point 4. Wet of optimum, the fabri at point D will
be somewhat more orented than at point B, although the effect is less
significan than dry of optimum.

Permesbiliy (Chapter 7) at constant compactive effort deereases
with increasing water content and reaches a minimum at about the

m compaction

‘optimum. If the compactive effort is increased, the coefficient of permea.
ly decreases because the void ratio decreases (increasing dry unit
ei. This change in permeability wth molding water content is shown
in Fig. 569, where i can be seen thatthe permeability is about an order of
‘magnitude higher when this soi is compacted dry of optimom than when it
is compacted wet of optimum,

‘Compressibikty (Chapter 8) of compacted clays is a function of the
Stress level imposed on the soil mass. AL relatively low sress levels, clays
‘compacted wet of optimum are more compressible, At high svess levels,
the opposites true In Fig 5.6b it can be sen that a lager change in void
ratio (a decrease) takes place in the sil compacted wet of optimum for a
given change (increase) in applied pressure.

‘Swelling of compacted clays is greater for those compacted dry of
‘optimum. They have a relatively greater deficiency of water and therefore
have a greater tendency to adsorb water and thus swell more, Soils dry of
optimum are in general more sensitive 0 environmental changes such as
changes in water content, This i jus the opposite for shrinkage as shown
in Fig. 573, where samples compacted wet of optimum have the highest
Shrinkage. Also illustrated in the upper part of this figure isthe effect of
lterent methods of compacting the samples,

‘The strength of compacted clays is rather complex. However, fo
now, just remember hat samples compacted dry of optimum have higher
Srengths than those compacted wet of optimum. The strengh wet of
‘optimum also depends somewhat on the type of compaction because of
blferences in sol structure, the samples are soaked. the picture changes

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‘due to swelling, especially dry of optimum. The strength curves for a silly
lay compacted by Kneading compaction for thre different compactive
forts are shown in Fig. 570, They show the sess required to cause 25%
Strain (upper) and 5% strain (middle) fo the three compactive efforts. The
Strengths are about the same wet of optimum and increase significantly on
the dry ide of optimum.

"Note too that at a given water coment wet of optimum, the stress at
19% strain is actualy les for the higher compaction energies, This fact is
also shown in Fig, 58, where strength is measured by the CBR (California
bearing rato) test Im this tes, the resistance 10 penetration of a 3 in?
piston developed in a compacted specimen is compared to that developed
by a standard sample of densely compacted crushed rock. The CBR is a
‘common pavement design test In Fig. 58 a greater compactive effort
produces a greater CBR dry of optimum, as you would expect. But notice
Row the CBR is actually less wet of optimum for the higher compaction
energies. This fact i important in the proper design and management of a
‘compacted earth fill; we shall discuss its implication later in this chapter.

"Table $-1 from Lambe (1958) is a summary of the effects of wet
versus dry of optimum compaction on several engineering properties

5.5 FIELD COMPACTION EQUIPMENT
AND PROCEDURES

Soil to be used in compacted fil is excavated from a borrow area.
Power shovels, draglines and self-propelled scrapers or “pans” are used (0
‘excavate the borrow material. A sell-oading scrape is shown in Fig. 5:93
And an elevating scraper in Fig. 596. Sometimes "dozers” are necessary 10
help load the seraper. Scrapers may cut through layers of different mater:
als, allowing several grain sizes o be mixed, for example. The power shovel
‘mixes the soil by digging along a verücal surface, whereas the scraper
mixes the sil by Cutting across sloping surface where different layers
may be exposed.

“The borrow area may be on sie or several kilometres away. Scrapers,
of the road vehicles, are often used to transport and spread the soil in ft
fon the fill area, Trucks may be used as well, on or off the highway, and
hey may end dump, sie dump, of bottom dump the fill material (Fi, 5103)
For economic reasons, the hauling contractor usually tres (0 spread the fil
‘material when dumping in order o teduce spreading time. However, unless
the borrow materials are already within the desired water content range,
the soil may need to be welted, dried, or otherwise reworked. Where
possible, the contractor directs is earth-moving equipment over previously

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Fig, 510 Exameles of equipmant used fr hauling and sore na
Intel: (a) A matara beng Rae by end dump tse) motor
Ei sentra ee rap cone

uncompacted soil thereby reducing the amount of compactive effort
required later.

Once borsow material has been transported to the fill area, bull
users front loaders, and motor grader, called blades (Fig. 8.108), spread
{he material o the desired layer ov 4 thickness. Lift thickness may range
from 150 to 500 mm (6 to 18 in) or so, depending on the size and type ot
‘compaction equipment and on the maximum grain size of the

‘The kind of compacting equipment or rollrs used on à job will
depend on the type of sol 19 be compacted. Equipment is available to
apply pressure, impact, vibration, and kneading. Figure 5.11 shows two.
types of rollers.

A smooth wheel, or drum. roller (Fig. 5113) supplies 100% coverage
under the wheel with ground contact pressures up to 380 kPa (55 ps) and
may be used on all soil types except rocky sois. The most common use for

o

Cros (notogragre courtesy el er Company, Caravan
Soma Owe).

28. rita Compaction Equipment ond Procedures 7

large smooth wheel rollers is for proofoling subgrades and compacting
asphalt pavements The pneumatic, or rubber ied, roller (Fig, 5110) has
about 80% coverage (80% of the total area is covered by tres) and tire
prestures may be up to about 700 kPa (100 psi) A heavily loaded wagon
Wh several rows of four to sx closely spaced tres is self-propelled or
{owed over the soil to be compacted. Like the smooth wheel roller. the
fubberied roller may be used for both granular and cohesve highway
filas well a5 for earth dam construction.

Probbly the fist roller developed and perhaps the most common
‘ype of compactor used today ı the ahecpeoos role. This roller
ame implies. has many round or rectangular shaped protrusions
(Fig, 5.123) attached to a sel drum. The
from 30 to 80 en? (5 to 12 in). Because ofthe 8% to 12% coverage, very
high contact presures are possible, ranging from 1400 to 7000 KPa (200 to
1000 ps) depending on the drum size and whether the drum is filled wit
water The drums come in several diameters. Surprisingly enough. a "4 by
4° (which means 4 ft long and 4 fin diameter) roller provides a higher
strength compacted fill in clay sols than a heavier, higher pressure "5
$" roller because there is les kneading or shearing action sith the "4 by
than the *S by 5° roller, which produces a different sol structure (see Fig.
SB) Shoepsfoot rollers are usualy towed in tandem by crawler tractor or
are self-propelled as shown in Fig. 5.120.

“The sheepsfoot roller starts computing the soil below the bottom of
the foot (projecting about 150 to 250 mam from the drum) and works its
ay up the lift as the number of passes increases. Eventually the roller
walks out” of the Fil as the upper part of the lift is compacted, The
sheepsfoot roller is best suited for cohesive sil

‘Other roller: with protrusions have also been developed 10 obtain
high contact pressures for better crushing, kneading, and compacting of a
rather wide variety of soils. These rollers can either be towed or sel
propelled. Temping foot rollers (Fig. 5.13) have approximately 40% cover.
“ge and generate high contact prestures from 1400 to 8400 kPa (200 to
1200 px, depending on the size ofthe roller and whether the drum filled
for added weight. The special hinged feet (Fig. 5.133) of the tamping foot
roller apply a kneading action tothe soi, These roles compact simlarly
o the sheepsfoot in that the roller eventually “walks out” of a well
compacted Ift. Tamping foot tolles are best for compacting fine-grained
sol

Sill another kind of roller is the mesh, or grid pattern, roller with
about SO% coverage and pressures from 1400 10 6200 KPa (200 to 900 psi)
(ig. 5.14, The mesh roller i ideally suited for compacting rocky soil,
grave, and sands. With high towing speed, the material is vibrated,
‘rushed, and impacted,

o
Fp 33 Taping toot rota) ea of a tanping loot D) st propa
{trong foo compactor hist Row tu ado toned 10 area the
‘tater eters compaction bythe role (Gina and photograph
ay Esmas Factor Co)

va Compaction

Den von

Several compaction equipment manufacturers have attached vertical
vibraton to the smooth whee! and tamping foot rollers so as to more
“ificenty densify granular sois. Figure 515 shows a vibrating drum on a
Smooth wheel roller compacting a gravelly material. Also available are
tibating plates und rammers hat range in size from 230 to 122 mm? © to
Sin?) and weigh from 50 to 3000 kg (100 to 6000 1). Compaction depth
or even the larger plates is les than I mete. These devices are used in

Fig. 5:5 varsing dum on mostra rer Ghatagra counter of
a! Company, Sarnen Equant On)

148. mota Compaction Equipment and Procedures en

areas where ie larger roles cannot operate Broms and Forssblad (1969)
ave listed the different types of vibratory soil compactors (see Table 5-2)
and also indicate the common frequency of operation. In Table 5-3, they
Älustrat the practical application of these machines.

Probably the best explanation of why roller vibration causes densi
cation of granular sois is that particle rearrangement occurs due to cylie
Äkformation of the soil produced by the oscilations of the roller. In
déron. vibratory compaction can work in materials with some cohesion
(Selig and Yoo. 1977) When oscillation is added to a static componer
Compaction is significantly increased, as shown in Fig 5.16, For soils
Compacted on the dry side of optimum. adding the dynamic component
sus in increased density

There are many varables which contol the vibratory compaction or
densification of soils, Some are compactor dependent and some depend on
the sol being compacted. The lst of variables would include:

Characteristics of the compactor:
Mass, size
‘Operating frequency and frequency range
Characteristics of the soi:
Trial density
Grain size and shape
Water content

Construction procedures:
"Number of passes ofthe roller
Tit hickness
Frequency of operation of vibrator
Towing speed

“The compactor characteristics influence the stes level and depth of
influence of the dynamic force, and the initial density strongly influences
the final Sens, For example, the upper 30 em of medium dense sand
may never become compacted higher than the initial density, whereas
‘lense Sands will be vibrated loose in the top 30 cm. Once the compactor is
chosen, the actual construction procedures essentially govern the results.
‘The influence of operating frequency for various Sol types s shown in Fig,
517. Note how a peak in the denity-requency curve develops for most of
the sols, even clays. The Frequency at which a maximum density is
achievedis called the optimum frequency. Isa function ofthe compactor:
Sol system. and it changes a the density increases during the process of
Compaction, Cleuly ts desirable for a compactor to have the capability
to vary its operating frequency and have the range required 10 obtain

‘ae Bae
simon
pmo o

ke rta pons
Po

regent
un soe Bu
a a EE rs
coma ma Der
Eid es Kann JO nah wen, 25 ZIEL

TABLE $3, Applcaions 0! Vibratory Sol Compaction*
ype ac =

cng pr (sm St i Fi ad ede ig

ting ple coc

Sd tando! Base and blas compact foc, sidewall, ee
‘Stee repair Pls behind bag ebene, eng
nd scent mal. ul bw fore. Trench fi

Mappe Bite and eh compaction or gra

ann ates
Sopas had gudes Ds, obs nd spl compaction fa ss, dde
‘sparking ars, are drenar e. Pl
Vin bre abres and ening als ls bom
Seltgrogeled, tandem type Base, subie, and asphalt compaction for highways,
‘cei rca, punga, peon»,
Pe bow oor
Sal popa, bie terse ube and enbakment compaction for igh,
Ste pain aren sti te, Re ila
Fistor) wed s ovate for een ad

Tandem

ie park ara, sii ee, Bar and roch
{shame ol rok ede foundation or
‘eto nu bla ep pac

“Aer Bon ad Forbin (1.

E
ry ty an?)

A 108
CO u u DE
ae content 06)

Pia. 518 Compaction seua on 30 em (12 In ayers of ay san. win.
‘ins ost vaio. sing 8 7700 hy (7-00) ea Veran roter
anne. 182" as tad y Stig and Ya 187

se compaction

MORT ee

DE Te

=
FH: zes

ES

"| i EN ne Ir. la

D

on en

a ha, Le N
ma == ss
ones tec

ng 817 Varaton wi avance compactos by snoot dun Wie
FR de sora sodas au cid by Sg and Yoo. 197)

maximum density. However, ihe peaks are gentle and. percentagemiso, &
Wide frequency range is not al that important
‘The influence of the number of passes of a roller and the towing
speed are shown in Fig, 5.18 for a 7700 kg roller compacting a “heavy”
(ish LL) clay and a well graded sand, Notice how the density increases as
the numberof passes or coverages increases, up toa point. Not so obvious
3 that for a given number of passes, à higher density is obtained if the
bras is towed more slowly?
ect of lift thickness may be illustrated by the work of
tal. (1969), shown in Fig. 5.19. Here a 5670 kg roller
operating at a frequency of 27.5 He is used to compact a 240 cm thick
liver of northern Indiana dune sand. The inital relative density was about

8 noté Compacton Equipment and Procedures sr

On dey 1)

CEE:

{Pcs my tomes vera Taler ar Baro 1.180 ce
Soi and Yoo 1977

50% 10 60%. Field density ests were made in test pits before and after
ompadtion, Note how the density varies with depth. Inthe upper 15 cm (6
in). the soli vibrated loose, whereas the sol reaches its maximum density
for given number of coverages at about 45 cm; thereafter the increase in
density tapers of. When compacting past five or so coverages, here is not
a great increase in density

EXAMPLE 52

Given:

I is decide, based on economics, that five coverages of a cert
and operating frequency shall be used.

je compaction
Roquires

What would be the maximum lift thickness 10 obtain a minimum relative
density? Use the data shown in Fig. 5.19

Solution:

“Trace the relative density versus depth curve for five passes on onionskin
paper Superimpose that drawing over the original one, and dei up and
‘own unt the desied relative density is obtained (shown in Fig. Ex. 52)
About 45 cm (18 in) is indicated as the maximum thickness. Actually.
however, the lft could be thicker as compaction of the top layer denses
the lower layer the second time around,

4
|

=" m Seen

1

F2 519 Denaty. sep rotor to 57059 lt opereta 275
Fira 240 om in eight oor Apocrine 809)

5 Mais Compaction Equipment and Procedure m

Ant deity (8) Poe en (8)
" ee mn san m

oot

|
[

a 4
i

get hehe

an comedias rare deny ot TOR wh foe raat
pence, cing ata fora ange In Regt (eer Appear 1000

Figure 520 summaries the applicability of various type of compac-
tion equipment as a function of soll type, expressed as a percentage of
sand to clay. These “zones” are not absolute, and itis possible for a given
Piece of equipment 10 compact satisfactorily outside the given zone.

‘When structures are to be founded on relatively deep deposits of
loose granular materials, densification by even heavy surface vibratory
rollers is usually insufficient, and other techniques must be employed.
‘Excavation and replacement of the soi in compacted layers may be eco-
nomieal under certain conditions Blasting has also been used at some sites
(Michel, 1970). Vibro orion (Mitchell, 1970) is often used to increase
the density of building foundations on loose sand. Another technique
“which is gaining in popularity is dynamic compaction. Basically, the method
‘consists of repeatedly dropping a very heavy weight (10 to 40 tons mass)
Some height (10 10 40 m) over the ste. The impact produces shock waves
that cause densification of unsaturated granular soils. In saturated granu
lar soils, the shock waves can produce partial liquefaction of the sand, a
condition similar to quicksand (discussed in Chapter 7), followed by
onslidation (discussed in Chapter 8) and rapid densification. The varia-
les include energy (drop height and weight of pounder, the number of
“drops at a single point ( to 10), and the patter ofthe drops at the surface
(5:10 15 m centerto-center). Figure 521 shows a pounder just impacting
the surface of à loose sand layer. Eventually this ste will look like a set of

we ‘compaction

COMPACTOR ZONES OF APPLICATION terse
100% 100%
arte SR sun on ding

Seres

Eo see tara oot Stee needing inst wat on

1,520 App ot vous types ol compacton equipment tor a
(een sou ype mowed ane En ri C2. 1077)

‘organized moon craters, The craters can be fled with sand and adition-
Ally tamped or the area between them smoothed out by the pounder iz

Dynamic compaction was apparenty first used in Germany in the
mid-1930% during construcion ofthe Autobahns (Loos, 1936) I has also
been used in the USSR 10 compact loesial soils up 10 $ m deep (Abele,
1957). The technique was further refined and promoted in France and
elsewhere by Louis Ménard (Ménard and Brose 192). who pioneered in
the development of very heavy pounders (up to 200 metic tons mass) and
massive eranes and tripods for lifting them 10 drop heights up to 40 m.
Improvement is claimed to depths down to 40 m. Inthe United States,
<dynamie compaction has been used on a more modest scale by contractors
using ordinary equipment (Leonards, Cutter, and Holt, 1980; Lukas,
1980)

“The depth of influence D, in metres, of the soil undergoing compac-
tion is conservatively given by Leonards tal (1980) as

Dtm” (52)

where W mass of falling weight in metic tons, and
drop height in metres.

“The heavier the weight and/or the higher the drop height, the greater
the depth of compaction. Leonards, ei al. (1980) also found that the
amount of improvement due to compaction in the zone of maximum
improvement correlates best with the product of the energy per drop times
‘the toll energy applied per unit of surface are.

‘Teron ae esc ton oan 30 mel. Vaste

5.8 FIELD COMPACTION CONTROL
AND SPECIFICATIONS,

Since the objective of compaction isto stabilize soils and improve
their engineering behavior it is important to keep in mind the desired
engineering properties of the Gl, not just ts dey density and water content
“This point is often los in earthwork construction control, Major emphasis

sn Compacto

is usually placed on achieving he specified dry density, and litle consider
“tion is given to the engineering properties desired of the compacted fil
ry density and water content correlate well with the engineering prope
ties (See. $4), and thus they are convenient construction control parame:

‘The usual design-construt procedure is as follows. Laboratory tests
are conducted on samples ofthe proposed borrow materials o define the
properties required for design. After the earth structure is designed, the
‘Compaction specifications are written. Field compaction conto! tests are
Specified, and the results of these become the standard for controlling the
project. Construction control inspectors then conduct these test 0 see that
{he specifications are met by the contractor

"There are basicaly two categories of earthwork specifications: (1)
endprodut specifications and (2) method specications. With the first pe, à
certain relaie compaction, or percent compaction, is specified. Relative
‘compaction is defined as the ratio of the field dry density a a 0 the
laboratory maximum dry density Pgo. according 10 some specified stan-
ard test, for example, the standard Proctor or the modified Proctor tes:

relative compaction (R.C) = Get 100(%) (3)

You should note the difference between relative compaction and relative
density D, or density index Ip, defined in Chapter 4. Relative density of
course, applies only to granular soils. If some fines are present, itis
diet 10 decide which type of test is applicable as à standard test.
ASTM (1980), Designation D 2049, suggests that the relative density is
applicable if the soil contains less than 12% fines (passing the No. 200
se the compaction test should be used. A relationship

(density and relative compaction is shown in Fig. 522. A
cal study of published data on 47 diferent granular soils indicated

‘erst index Ip of relative density O, Ds) 90

Fa. 522 Retawe deratyand rate compaction concept (eter
Lee ad Sing. Tor

Brut Compecton Conte and Spectator vn
(hat the relative compaction corresponding to zero relative deasiy is about

om

With endproduet specications, which are used for most highways
“and building foundations, as long as the contactor is able to oblain the
Specified relative compaction, how he obtains it doesn't matter, nor does
the equipment he uses. The economics of the project supposedly ensure
that the contactor will utlize the most efficent compaction procedures.
‘The most economical compaction conditions are illustrated in Fig. 523,
showing tree hypothetical field compaction curves ofthe same sil but at
ülferent compacive efforts. Assume that cure 1 represents a compactive
“fon that can easily be obtained by existing compaction equipment Then

Fp. 523 Dr deny verse water content nating the mon
fen consten tr Hid compacto her Sant 1388)

ss compaction

to achieve, say, 90% relative compaction, the placement water content of
the compacted fil must be greater than water content a and less than
water content e. These points are found where the 90% R.C. line imersets
‘compaction curve I. If the placement water content is ouside of the range
210 6. then it wil be difficult f not impossible, to achieve the required
percentage of relative compaction called for, no mater how much the
‘Contractor compact that Me. This is why it may be necessary at times 10
‘wet oF dey (rework) the soil prior to rolling inthe fel.

‘Now that we have established the range of placement water contents,
the contractor might ask: "What i the best placement water content 19
use?” From a purely economical viewpoint, the most efficient water
Content would be at 6, where the contractor provides the minimum com.
pactive effort to attain the required 90% relative compaction. To con.
Sstenty achieve the minimum relative compaction for the projet, the
contractor will usally use a slightly higher compactve effort as shown by
turve 2 of Fig. 523. Thue the most efficient placement water contents exis,
between the optimum water content and b

‘However what may be best from the contractor's viewpoint may not
provide fil with the desired engineering properties. Compacting a soil on
the wet side generally results in a lower shear strength than compacting the
Soi on the dy ide of the optimum water content (Figs. 57 and 58). Other
properties such as permeability and shrink-swell potential wil also be
different. Thus a range of placement water contents should also be speci-
Fied by the designer in addition to the percentage of relative compaction
‘This point illustrates why the desired engineering performance of the fil
rather than just the percentage of compaction must be kept in mind when
ring compaction specifications and designing field control procedures

Figures 523 and 51 also lustre that specified densities can be
“achieved at higher water contents if more compacte effort is applied,
her by using heavier rollers or more passes of the same roller. But, as
Shown in Fig, 8, at higher water contents the strength measured by the
CBR test curves cross, and a lower strength wil be obtained with higher
‘compaction energies wet of optimum. This effect is known as overcompac-
tion: Overcompaction can occur in the field when wet of optimum soils are
Dprosfrled with very heavy, smooth wheeled rollers (Fig. S.1a) or an
‘excessive number of passes are applied to the lift Mills and DeSalvo,
1978). Otherwise even good matenal can become weaker. You can also
detect overcompaction in the feld by careful observation of the behavior
of the soil immediately under the compactor or the wheel of a heavily
Toaded scraper Ifthe sits 100 wet and the energy applied is 100 great,
‘pumping or weaving ofthe fill will result as the whee! shoves the wet weaker
fill ahead of sl, Also, sheepsfoot rollers won't be able to "walk out.”

2 ruta Compaction Conta and Spectators us

Im method specifications, the second general category, the type and
weight of roller, the number of passes of that roller, as well as the lit
thicknesses are specified by the engineer. A maximum allowable size of
‘material may also be specified. In contrast 10 the end-product specfia-
ons, where the contractor is responsible for proper compaction. with
method specifications the responsibility rests with the owner or owe
Engineer s lo the quality of the earthwork. If compaction control tests
performed by the engineer fail (0 meet a certain standard, then the
Eonttactor will be paid extra for additional rolling, This specification
requires prior knowledge ofthe borrow soils so as to be able to predict in
dance how many passes of, for example, a certain type of roller will
produce adequate compaction performance, This means that during de
Sign. test fil must be constructed with different equipment, compactive
Fons ete, in order to determine which equipment and procedures will be
the most efficient Since tes fill programs are expensive, method speifca-
tions can only be just for very large compaction projects such as earth
ams, However, considerable savings in earthwork construction unit costs
fre possible because a major part of the uncertainty associated with
‘compaction wil be eliminated forthe contractor. He can estimate quie
wel in advance just how much construction will cost. The contactor also
knows that if extra rolling is required he will be adequately compensated.

How i relative compaction determined? First, the test site is selected
Ik should be representative or typical of the compacted lift and borrow
materal. Typical specifications call for a new field test for every 1000 10
3000 mor so. or when the borrow material changes significantly. I is also
{advisable to make the field tet atleast one or maybe two compacted lifts
below the already compacted ground surface, especially when sheepsfoot
rollers are wed or in granular soils

‘Field contol ets can ether be desrctce or nondestructive, Destruc-
tive tes involve excavation and removal of some of the fill material,
‘whereas nondestructive tests determine the density and water content of
the fill indice. The steps required for the common destructive field tests

1. Excavate a hole in the compacted fil at the desired sampling
ration (he sie wil depend on the maximum sizeof material in
the fill, Determine the mass of the excavated material

2. Take a water content sample and determine the water content,

3. Measure the volume of the excavated material. Techniques com
‘monly employed for this include the sand cone, the balloon
method, or pouring water or ol of known density into the hole
(Fir. 528), In the sand cone method, dry sand of known dry

(Oi ornate mato
Fi. 524 Some methods fr determining ana ote fel

68 Pld Compaction Cont and Spione

density is allowed to Now through a cone-pouring device into the
hole. The volume ofthe hole can then easly be determined from.
the weight of sand in the hole and its dry density. dt is necessary
‘hat the contractor stop earth-moving equipment From vibra
and densfying the sand in the hole during the sand cone
otherwise the measured percent relative compaction wil be lower
than actual) In the balloon method, the volume is determined
dire by the expansion ofa balloon direct in the bole.

4. Compute the total density p. Knowing M, the total mass of the
material excavated from the hole, and the Volume of the hole, we
can compute p. Since we also know the water content, we can
obtain the dry density of the fil, an

5. Compare ss hPa ma and calcite relative compaction (EQ,
53).

EXAMPLE 5.3

Gwen:

A Field density testis performed by the balloon method (Fig. 524).
‘The following data were obtained from the tes

Mass of soil removed + pan = 1590,

Mass of pan = 125m
Balloon readings:
Final = 1288 em?
Tita 2 Sem

Water content information:
Mass of wet soil + pan = 40498
Mass of dry soil + pan = 365.98
Mass of pan 1208

Requires:

2. Compute the dry density and water content ol he soil
D. Using curve 2 of Fig. 5. asthe laboratory standard, compute-the
relative compact

sn ‘compaction
Solution:

M,
2. Compute the wet density = DE

ORNS LISE 1 95 geen? = 195 Mg/m
CRETE)
Water content determination:

1. Mass of wet soil + pan = 4049 g
2. Mass of dry oil + pan = 3659 8
3. Mass of water M (I~ 2) = 3908
4. Mass of pan = 1320 g

5. Mass of dry soil M, (2 — 4) = 439 8

6. Water content (M./M,)% 100 3 + 9) = 16%
For caleultion of dry density use Eq. 2-14:
ESA

Tie" "Tr016
. For calulaion of relative compaction, use Ea. $3:

Paras 1 99 =
Rc u mar

‘There are several problems associated with the common destructive
Field density test. Fist the laboratory maximum density may not be
known exactly is not uncommon. especialy in highway construction, for
teres of laboratory compaction tests o be conducted on “representative”
samples of the borrow materials forthe highway. Then, when the field test
is conducted, is results compared with the results of one or more of these
Job “standard” sis If the sols atthe site are highly variable, this i a poor
procedure, Another alternative isto determine the complete compaction
Curve for etch fiel test—a time-consuming and expensive proposition,

A second alternative is to perform a field check point, or 3 point
Proctor test. When the field engineer knows in advance thatthe so in
Which he is performing a field density test does not exact visually match
one of the borrow sols, an extra amount of sol s removed from the
compacted fil during the test. The total amount of soil removed should be
Sullicien to perform a singe laboratory compaction test The only reste.
tions necessary for the performance of the field check point are that:

1. During compaction, the mold must be placed on a smooth solid
mass of atleast 100 kg, a requirement which may be dificult to
achieve in the field. Asphalt pavement or compacted sol should
not be used

52. Mais Compaction Conto! and Spacititions ve

2. The soil to be compacted must be dey of optimum for the
compactive effort used, and to know when the soil is dry of
‘optimum takes some field experience

“The reason for this second requirement may be apparent from Fig.
525. Three compaction curves are shown for sos A, B, and C from a
iven construction job borrow area. The soil just tested for density, as
identified by the field engineer, does not match any soils for which curves
‘exist. The field check point is plotted as point X on the graph. By drawing
à line parallel to the dry side of optimum of eurves A, B, and C and
Teaching a maximum at the “line of optimus,” a reasonable approxima
tion of the maximum dry density may be obtained. Ifthe sol was not
adequately dried out before the compaction es, a point such as Y would
bbe obtained. Then it would be difficult to distinguish which laboratory
‘curve the soil belonged to, and therefore an estimate of the maximum dry
‘density would be imposible. Some experience is required to “feel” when
the sol is dried out enough for the field check point water content 10 be
less than the OMC.

On émis
i

Water cote 06)

Fig 28 Princip ofthe ene pot ist.

se compact

“The second major problem withthe common destructive density test
procedure l that the determination of the water content takes time (several
Fours or overnight according to ASTM, 1980). Time is often of the utmost
value on a compaction job, and if it takes a day or even several hours
before the results are available, several lifts of fil may have been placed
Tod compacted over the “bad” or “Tiling” test area. Then the engineer has.
3 uifieult decision to make: should the contractor be required to tear out a
Tot of possibly good il just 10 improve the relative compaction of that one
pad RIO Contractors understandably are very hesitant 10 do that, and
Jet how many zones of “bad” compaction are allowable in an embank-
ment? Of couse, the problem is statistical and again, on a typical job, itis
‘ifficlt and expensive to conduct sufficient tess for a statistical analysis
ol the compaction results.

‘Since determining the water content takes the most time, several
methods have been proposed 10 obtain a more rapid water content. Pan
ing or "Ting" the sample over an open flame is commonly used, but
Since it is difficult to control the temperature, it gives poor results,
Epeciaty for fa clay (CH) soils. The “speedy” moisture meter, in which
{he water in the soll reacts with carbide to produce acetylene gas, is
another altemative. The gas pressure shown on a calibrated gage is
proportional to the water content, Burning with methanol and the special
icohobhydrometer method are also sometimes used. The correlation with
Standard oven drying for these methods is approximate—generally sais
Factory for sills and lean clays but poor for organic soils and fat clays

“Another method for quickly and efficiently determining the relative
compaction of cohesive sols was developed in the 1950's by the US.
Bureau of Reclamation (1974, and Hilf, 1961). The procedure makes it
possible to determine accurately the relative compaction ofa fill as well as
ven close approximation of the difference between the optimum water
Content andthe fill water content without oven drying the sample. Samples
of the fil materials are compacted according to the desired laboratory
Slandard atthe fill water content and, depending on an estimate of how
“lose the fill sto optimum, water is ether added or subtracted from the
‘ample (Fig 526). With a litle experience itis relatively easy to estimate

the fill material is about optimum, slightly wet, or slightly dry of
Splimum. From the wet density curve, the exact percent relaive compac.
‘don based on dry density may be obtained. Only one water content, the fill
Fate content. need be determined and that only for record purposes. The
main advantage of the rapid” method i thatthe contactor has the results
In very short time, Experience has shown that itis possible to obtain the
Values required for contro of construction in about Ih from the time the
Field density tests performed

8. ats Compaction Control aná Spinne 18

a fd

mitre comes umole; ra of come tle dente of compacted te

ern ot conpuevon ttt ==

Fig. 526 Procede or rapid manos of determina degree of
pac sanas Sana 1950)

Other problems with destructive field tests are associated with the
determination of the volume of the excavated material. The sand cone,
often taken as the “standard,” is subject to errors. For example, vibration
from nearby working equipment wil increase the density ofthe sand in the
ole, which gives a lager hole volume than should have; this results in a
lower field density. All of the common volumetric methods are subject o
error ifthe compacted fl is gravel or contains large gavel particles. Any

om

Proton paths
9, 527 clear dere and water conten catenin: a)

(ct vacamieor ()buokcate ca uo (oh Tor Ee”
None Laboratori, nc, Resour Tangle Pus, Not Carte.

$7 Eaumating Parormence o Compactos Sle 1

kind of unevenness in the wall of he Bole causes a significant error inthe
balloon method. If the sol is coarse sand or gravel, none of the liquid
methods works well, ales the hole is very large and a polyethylene sheet
is used to contain the water or ol

Because of some of the problems with destructive field tests, nonde-
structive density and water content testing using radioactive isotopes has
increased in popularity during the past few years. Nuclear methods have
several advantages over the traditional techniques, The tests can be con-
‘ducted rapidly and results obtained within minutes. Therefore the contrac-
tor and engineer know the results quickly, and corrective action can be
taken before too much additional il has been placed. Since more tests can
be conducted, a better statistical control of the il is provided. An average
value of the density and water content is obtained over a significant
volume of fil, and therefore the natural variability of compacted soils can
be considered. Disadvantages of nuclear methods include their relatively
igh initial cost and the potential danger of radioactive exposure to feld
personnel. Strict radiation safety standards must be enforced when nuclear
devices are used

Basically, evo types of sources or emiters are necessary to determine
both the density andthe water content. Gamma radiation, as provided by
radium ora radioactive isotope of cesium, Scattered by the soi particles:
the amount of seater i proportional tothe total density ofthe material.
‘The spacing between the source and pickup, usually a scintillation or
Geiger counter, is constant, Hydrogen atoms in water scatter neutrons, and.
this provides a means whereby water content can be determined. Typical
neutton sources are americium-berylium isotopes. Calibration’ against
‘compacted materials of known density is necessary, and for instruments
‘operating on the surface the presence of an uncontrolled air gap can.
significantly affect the measurements

“Three nuclear techniques are in common use. The direct transmission
‘method is iNustrated schematically in Fig. S272, and the backscatter
technique is shown in Fig, 5270, The less common airgap method (Fig.
15270) is sometimes used when the composition of the near-surface materias
‘adversely afecis the density measurement

5.7 ESTIMATING PERFORMANCE
OF COMPACTED SOILS

How will a given soil behave in a fil, supporting a foundation,
holding back water, or under a pavement? Will frost action be a critical
factor? For future reference, we present the experience of the US. Army

a Compact

(Corps ol Engineers on compaction characteristics applicable 1 roads and
sleds (Table 54) and the experince of the U.S. Department ol the
Interior. Bureau of Reclamation for several types of earth structures (Table
ss)

In Table 5-4, the terms hase, subhase, and subgrade (columns 7, 8,
And 9) refer to components of a pavement system, and they are defined in
Fig. 328. In column 16, the term CBR represents the California bearing
ratio, The CBR is used by the Corps of Engineers forthe design of flexible
pavements, The modulus of subgrade reaction (column 1) is used by them
for rigid pavement design. Though the difference is rather arbitrary, the
upper layers of flexible pavements usualy are constructed of asphaltic
concrete, whereas rigid pavements are made of Portland cement concrete.
A good reference for the design of pavements is Ihe book by Yoder and
Witezak (1975).

‘The use of these tables in engineering practice is best shown by an
example. They are very helpful for preliminary design purposes, choosing
{he most suitable compaction equipment, and for rapid checking of field
and laboratory test result.

202 om Parlament 2 Bem ha cone

10m spice Ten né pod Men

OP

© BR ce

er may bn omite: 1630 om sna ae

199.520 Datntions et ter ring o parement aten, wth
‘plc! imensons ana mat lor Sach compra

uv pur spray 1 JU sms +5 SAVE

ss

porno rs anava

TABLE S4 Continued

Notes
tuna dios of GM and SM poops it ibis of and var forex a
retry Soon à où ao Alar ms sl (eq, OM wil be wed
‘Men he lu tn ov wane pet ide of the sev wl Be
deca D, de cnipa ed wil way rc ied tn à à
LR fe nce co ner peso que! are ted eee wae so
a ‘nite 3 pve al peop may e diet equpmeet a some
FRE conan otro Open ay be ec
À race fave merit onder angler mater. Seed and rubber
Re nd coc ele mar et dead
ng. Ruther rs eme esominnde fr vlg Suing o) ia
“pets fr on und poe mates
SEE uta e see Oe he
ips watt meh cos a 3060 1 (4001)
ters quen whe! od ns of 18000 1 ODA) whe od
{hgh 08 8 0D kg ma be necessary o ob the rege denn
{erate eae und sam pee aprem 6 1150 poe
‘Sota ia xs
‘Step eu rete on 61 12 io 401 D om? foo 1 Dein
‘Sec pe cso sy and pee a hgh 2 60 pa (OPA) may
Scag cba he eure! d forse mera Te we of de
Te ad De a ne 2 lo tol pepe ren of De drum. eg de
3 1 clus Hand 1S, den ae for compels at epi wat come fr
did AASHTO compaction fr.
ctm 1, msimem vals ac be ue di of is im sms een
Used by ras sd play vequremens.

EXAMPLE 5.4

Given:

A soil, clasiied as a CL according to the USCS, is proposed for a
‘compacted fill

Requires

Consider the soi 10 be used as:
a. Subgrade
D. Earth dam
© Foundation support or a structure
se Tables 54 and 3-5 and comment on:
1. The overat suitability ofthe soil
2. Potential problems of Frost,
3. Significant engineering properties
4. Appropriate compaction equipment to use

‘solution:
Prepare a table for soil ype CL.
Ten Im Sana Haren Sr Fortis
To Apia LT] Te compacted
‘ “taie fou and not
2 Fron pots Meint Landes Medan higher ome
‘i yen "wae y temperate aad
Sees Ser
ee
Den Meum LRD Potent for poor strength
Fer comprends Toma andern poor
Ma vpn poto
CCR TS
oe
4 Aprcprite compacto. Sepucot18/ Step and] Shape
rent "craertied caen or ber ed
lke E ‘ie

Note: Once you have finished with this book and a course in foundation
eoginecring you could readily expand the information inthis table.

PROBLEMS

5:1. For the data in Fig 5:

(Estimate the maximum dry density and optimum water content
for both the standard curve and the modified Proctor cur.

(6) What is the placement water content range for 90% relative
compaction for the modified Proctor curve and 95% relative
‘compaction forthe standard Proctor curve?

(6) For both curves, estimate the maximum placement water content
for the minimum compactive effort to achieve the percent rel
tive compaction in part (0)

$522. The natural water content of a borrow material is known to be 10%.

‘Assuming 6000 g of mer soil is used for laboratory compaction test

points, compute how much water is to be added to other 6000 8

Samples to bring their water contents up to 13, 17,20, 24, and 28%

$2. For the soil shown in Fig. 5 a field density test provided the

Following information:

Water content = 14%
Wei density = 1.89 Mg/m? (118 161/10)
Compute the percent relative compaction based on the modified
Proctor and the standard Proctor curves
5.4. For the data given below (9, = 264 Mg/m?):

(a) Plot the compaction curves.

(0) Estblish the maximum dry density and optimum water content
for exch test.

(© Compute the degree of saturation atthe optimum pont for data
in column À.

(8) Plot the 100% saturation (zero air vos) curve. Als plot Ihe 70,
90, and 90% saturation curves. Plo the ine of optimums.

(modes dard tow se)
A o OT EE OL
Tea 93 53 IE 109
iio na eS
tims FH 1
im OU ma Es]
ven a 2 2

An introduction to geotechnical engineering (holtz and kovacs)

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An introduction to geotechnical engineering (holtz and kovacs)

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