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Dedicated to the Cause of Students

FOREWORD
Geotechnical Engineering: Principles and Practices of Soil Mechanics and Foundation
Engineering i s a long title befitting a major work. I am pleased t o introduce this superb volume
destined for a readership o f students, professors, an d consultants. What makes thi s text differen t
from other books on these subjects that appear each year and why am I recommending it to you? I
have been workin g and teaching in the area of geotechnical engineering for 25 years. I have read
and use d score s o f textbook s i n m y classe s an d practice . Dr . Murthy' s text i s b y fa r th e mos t
comprehensive tex t I have found. You will find that his organization of the subject matter follows
a logical progression. His example problems are numerous and, like the text, start from fundamenta l
principles an d progressivel y develo p int o mor e challengin g material . The y ar e th e bes t se t of
example problems I have seen in a textbook. Dr. Murthy has included ample homework problem s
with a rang e o f difficult y mean t t o hel p th e studen t ne w t o th e subjec t t o develo p his/he r
confidence an d t o assis t th e experience d enginee r i n his/he r revie w o f th e subjec t an d i n
professional development .
As the technical editor I have read the entire manuscript three times. I have been impressed by
the coverage, th e clarity of the presentation, and the insights into the hows and whys of soil and
foundation behavior. Often I have been astonished at Dr. Murthy's near-conversational approac h to
sharing helpfu l insights . You get th e impressio n he' s righ t ther e wit h yo u guidin g yo u along ,
anticipating your questions, and providing instruction and necessary information as the next steps
in the learning process. I believe you will enjoy this book and that it will receive a warm welcom e
wherever it is used.
I thank Dr. Murthy for his commitment to write this textbook and for sharing his professional
experience with us. I thank him for his patience in making corrections and considering suggestions.
I thank Mr. B. J. Clark, Senior Acquisitions Editor at Marcel Dekker Inc., for the opportunity to be
associated with such a good book. I likewise express my appreciation to Professor Pierre Foray of
1'Ecole National e Superieur e d'Hydrauliqu e e t d e Mecaniqu e d e Grenoble , Institu t Nationa l
Polytechnique de Grenoble, Franc e for his enthusiastic and unflagging support while I edited the
manuscript.
MarkT. Bowers, Ph.D., P. E.
Associate Professo r o f Civil Engineering
University of Cincinnati

FOREWORD
It give s m e grea t pleasur e t o writ e a forewor d fo r Geotechnical Engineering: Principles an d
Practices of Soil Mechanics an d Foundation Engineering. This comprehensive, pertinen t an d up-
to-date volum e i s wel l suite d fo r us e a s a textboo k fo r undergraduat e student s a s wel l a s a
reference boo k fo r consultin g geotechnica l engineers an d contractors. Thi s book is well writte n
with numerous examples on applications o f basic principles to solve practical problems.
The early history of geotechnical engineering and the pioneering work of Karl Terzaghi in
the beginning of the last century are described in Chapter 1 . Chapters 2 and 3 discuss methods of
classification of soil and rock, the chemical and the mechanical weathering of rock, and soil phase
relationships an d consistenc y limit s fo r clay s an d silts . Numerou s example s illustrat e th e
relationship between th e different parameters . Soi l permeability and seepage ar e investigated in
Chapter 4 . Th e constructio n o f flo w net s an d method s t o determin e th e permeabilit y i n th e
laboratory and in the field ar e also explained.
The concept o f effective stres s and the effect o f pore water pressure o n effective stress are
discussed in Chapter 5. Chapter 6 is concerned with stress increase in soil caused by surface load
and methods to calculate stress increase caused by spread footings, rafts, and pile groups. Several
examples are given in Chapter 6. Consolidation of soils and the evaluation of compressibility in
the laborator y b y oedomete r test s ar e investigate d in Chapte r 7 . Determinatio n o f draine d an d
undrained shea r strengt h by unconfine d compression, direc t shea r o r triaxial test s i s treated i n
Chapter 8.
The importan t subject of soi l exploratio n i s discussed i n Chapter 9 , includin g the us e of
penetration tests such as SPT and CPT in different countries. The stability of slopes is investigated
in Chapter 10 . Methods usin g plain and circular slip surfaces to evaluate stability are describe d
such a s th e method s propose d b y Bishop , Fellenius , Morgenstern , an d Spencer . Chapte r 1 1
discusses method s to determine activ e and passive earth pressures actin g on retaining and sheet
pile walls.
Bearing capacity and settlement of foundation an d the evaluation of compressibility in the
laboratory by oedometer test s are discussed in Chapters 12 , 13, and 14 . The effect o f inclination
and eccentricity of the load on bearing capacity is also examined. Chapter 1 5 describes differen t
pile types , th e concep t o f critica l depth , method s t o evaluat e th e bearin g capacit y o f pile s i n
cohesive and cohesionless soils , and pile-driving formulae. The behavior of laterally loaded pile s
is investigated in Chapter 16 for piles in sand and in clay. The behavior of drilled pier foundations
VII

viii Forewor d
and the effect of the installation method on bearing capacity and uplift ar e analyzed in Chapter 17.
Foundations on swelling and collapsible soils are treated i n Chapter 1 8 as are methods that can be
used t o reduc e heave . Thi s i s a n importan t subject, seldom treate d i n textbooks . Th e desig n o f
retaining wall s i s covere d i n Chapte r 19 , as wel l as th e differen t factor s tha t affec t activ e an d
passive eart h pressures. Differen t applications of geotextiles are covered in this chapter as well as
the topic of reinforced earth. Cantilever, anchored, and strutted sheet pil e walls are investigated in
Chapter 20 , a s ar e method s t o evaluat e stabilit y an d th e momen t distribution . Different soi l
improvement methods , suc h a s compactio n o f granula r soils , san d compactio n piles ,
vibroflotation, preloading , an d ston e columns , ar e describe d i n Chapte r 21 . Th e chapte r als o
discusses lim e and cemen t stabilization. Appendix A provides a list of S I units , and Appendi x B
compares methods tha t have been proposed .
This textbook b y Prof . V. N. S. Murthy is highly recommended fo r student s specializing i n
geotechnical engineerin g an d for practicing civil engineers i n the United States an d Europe . Th e
book include s recen t development s suc h a s soi l improvemen t an d stabilizatio n method s an d
applications o f geotextiles t o control settlements an d lateral earth pressure. Numerou s graph s an d
examples illustrat e th e mos t importan t concept s i n geotechnica l engineering . Thi s textboo k
should serve as a valuable reference book fo r many years to come.
BengtB.Broms, Ph.D.
Nanyang Technical University , Singapore (retired) .

PREFACE
This book has the following objectives:
1. T o explain the fundamentals of the subject from theor y to practice in a logical wa y
2. T o be comprehensive and meet the requirements of undergraduate students
3. T o serve as a foundation course for graduate students pursuing advanced knowledge in the
subject
There ar e 21 chapters i n this book. The first chapter traces the historical background o f the
subject and the second deal s with the formation and mineralogical composition o f soils. Chapter 3
covers th e index properties an d classification of soil. Chapters 4 and 5 explain soi l permeability,
seepage, an d th e effec t o f wate r o n stres s condition s i n soil . Stresse s develope d i n soi l du e t o
imposed surfac e loads , compressibilit y an d consolidatio n characteristics , an d shea r strengt h
characteristics o f soil ar e dealt with i n Chapters 6,7 , an d 8 respectively. The firs t eigh t chapter s
develop the necessary tool s for computing compressibility and strength characteristics o f soils.
Chapter 9 deals with methods for obtainig soil samples in the field for laboratory tests and for
determining soi l parameter s directl y by us e o f fiel d tests . Chapter s 1 0 to 2 0 dea l wit h stability
problems pertaining to earth embankments, retaining walls, and foundations. Chapter 2 1 explains
the various methods by which soil in situ can be improved. Many geotechnical engineer s hav e not
appreciated th e importanc e o f thi s subject . N o amoun t of sophisticatio n in th e developmen t of
theories will help the designers if the soil parameters used in the theory are not properly evaluated
to simulate field conditions . Professors wh o teach this subject should stress this topic.
The chapter s i n this book are arranged i n a logical wa y for the development o f the subject
matter. There is a smooth transition from one chapter to the next and the continuity of the material
is maintained. Each chapter starts with an introduction to the subject matter, develops th e theory,
and explain s it s applicatio n t o practica l problems . Sufficien t example s ar e wo r1
:ed ou t t o hel p
students understand the significance of the theories. Man y homework problem s ar e given a t the
end of each chapter .
The subjec t matte r deal t wit h i n eac h chapte r i s restricte d t o th e requirement s o f
undergraduate students. Half-baked theories an d unconfirmed test results are not developed in this
book. Chapter s ar e up-to-dat e a s pe r engineerin g standards . Th e informatio n provide d i n
Chapter 1 7 on drilled pier foundations is the latest available at the time of this writing. The design

Preface
of mechanically stabilized earth retaining walls is also current. A new method for predicting the
nonlinear behavior of laterally loaded vertica l and batter piles is described in Chapter 16.
The boo k i s comprehensive , rational, an d pertinen t to th e requirement s o f undergraduate
students. It serves as a foundation course for graduate students, and is useful as a reference book for
designers an d contractors in the field o f geotechnical engineering .
ACKNOWLEDGEMENTS
It is my pleasure t o thank Marcel Dekker, Inc., for accepting me as a single author for the
publication of my book. The man who was responsible for this was Mr. B.J. Clark, the Executive
Acquisition Editor . I t wa s m y pleasur e t o wor k unde r hi s guidance . Mr . Clar k i s a refine d
gentleman personified , polished , an d clea r sighted . I thank hi m cordiall y fo r the courtesie s an d
help extended to me during the course of writing the manuscript. I remain ever grateful to him.
Writing a book fo r American Universities by a nonresident o f America is not an easy task.
I neede d a n America n professo r t o edi t m y manuscrip t an d guid e m e wit h regard s t o th e
requirements of undergraduate students in America. Dr. Mark T. Bowers, Associate Professor o f
Civil Engineering, Universit y of Cincinnati, accepte d t o become m y consultant an d chief editor .
Dr. Bowers i s a man of honest y and integrity. He is dedicated t o the cause of his profession. He
worked hard for over a year in editing my book and helped me to streamline to make it acceptable
to the undergraduate student s o f American Universities. I thank Dr. Bowers for the help extended
to me.
There ar e man y i n Indi a wh o helpe d m e durin g th e cours e o f writin g thi s book . Som e
provided m e usefu l suggestion s an d other s wit h references . I acknowledg e thei r service s wit h
thanks. The members are :
Mr. S. Pranesh Managin g Directo r
Prism Books Pvt Ltd
Bangalore
Dr. K.S.Subba Rao Professo r of Civil Engineering
Indian Institute of Science Bangalor e
Dr. T.S. Nagaraj Professo r of Civil Engineering
(Emeritus), Indian Institute o f Science,
Bangalore
Professor of Civil Engineering
Dr. C. Subba Rao India n Institute of Technology
Kharagpur
Chaitanya Graphics , Bangalore , provide d th e artwor k fo r th e book . I than k M r S.K .
Vijayasimha, the designer, for the excellent job don e by him.
My so n Prakas h wa s associate d wit h th e boo k sinc e it s inception . H e carrie d o n
correspondence wit h the publishers o n m y behalf and sen t reference books a s needed. M y wif e
Sharadamani wa s mainl y responsibl e fo r keepin g m y spiri t hig h durin g th e year s I spen t i n
writing the book. I remain grateful to my son and my wife for all they did.
I sincerely thank Mr. Brian Black for his continuous effort s i n the production of this book. I
immensely thank Mr. Janardhan and Mr. Rajeshwar, compute r engineers of Aicra Info Mates Pvt
Ltd., Hyderabad, for their excellent typesetting work on this book.
V.N.S. Murthy

CONTENTS
Foreword Mar k T . Bowers v
Foreword Beng t B. Broms vi i
Preface i x
CHAPTER 1 INTRODUCTIO N 1
1.1 Genera l Remark s 1
1.2 A Brief Historica l Developmen t 2
1.3 Soi l Mechanic s an d Foundation Engineerin g 3
CHAPTER 2 SOI L FORMATION AND CHARACTERIZATION 5
2.1 Introductio n 5
2.2 Roc k Classificatio n 5
2.3 Formatio n o f Soil s 7
2.4 Genera l Type s o f Soil s 7
2.5 Soi l Particl e Siz e an d Shape 9
2.6 Compositio n o f Cla y Mineral s 1 1
2.7 Structur e of Clay Minerals 1 1
2.8 Cla y Particle-Wate r Relation s 1 4
2.9 Soi l Mass Structur e 1 7
XI

xii Content s
CHAPTER 3 SOI L PHASE RELATIONSHIPS, INDEX PROPERTIES
AND CLASSIFICATION 1 9
3.1 Soi l Phas e Relationship s 1 9
3.2 Mass-Volum e Relationships 2 0
3.3 Weight-Volum e Relationship s 2 4
3.4 Comment s o n Soi l Phas e Relationship s 2 5
3.5 Inde x Propertie s of Soils 3 1
3.6 Th e Shap e an d Siz e o f Particles 3 2
3.7 Siev e Analysi s 3 3
3.8 Th e Hydromete r Metho d o f Analysis 3 5
3.9 Grai n Siz e Distributio n Curves 4 3
3.10 Relativ e Densit y o f Cohesionless Soil s 4 4
3.11 Consistenc y o f Cla y Soi l 4 5
3.12 Determinatio n of Atterberg Limit s 4 7
3.13 Discussio n o n Limits an d Indices 5 2
3.14 Plasticit y Char t 5 9
3.15 Genera l Consideration s fo r Classification o f Soil s 6 7
3.16 Fiel d Identificatio n of Soil s 6 8
3.17 Classificatio n o f Soil s 6 9
3.18 Textura l Soi l Classificatio n 6 9
3.19 AASHT O Soi l Classificatio n System 7 0
3.20 Unifie d Soi l Classificatio n Syste m (USCS ) 7 3
3.21 Comment s o n th e System s o f Soi l Classificatio n 7 6
3.22 Problem s 8 0
CHAPTER 4 SOI L PERMEABILITY AND SEEPAGE 8 7
4.1 Soi l Permeabilit y 8 7
4.2 Darcy' s La w 8 9
4.3 Discharg e an d Seepag e Velocitie s 9 0
4.4 Method s o f Determinatio n of Hydrauli c Conductivity of Soil s 9 1
4.5 Constan t Hea d Permeabilit y Tes t 92
4.6 Fallin g Hea d Permeabilit y Tes t 9 3
4.7 Direc t Determinatio n of k o f Soil s i n Plac e b y Pumpin g Test 9 7
4.8 Borehol e Permeabilit y Test s 10 1
4.9 Approximat e Value s o f th e Hydrauli c Conductivity of Soil s 10 2
4.10 Hydrauli c Conductivit y in Stratifie d Layer s o f Soil s 10 2
4.11 Empirica l Correlation s fo r Hydrauli c Conductivity 10 3
4.12 Hydrauli c Conductivity of Rock s b y Packe r Metho d 11 2
4.13 Seepag e 11 4
4.14 Laplac e Equatio n 11 4

Contents xii i
4.15 Flo w Ne t Constructio n 11 6
4.16 Determinatio n o f Quantit y of Seepag e 12 0
4.17 Determinatio n o f Seepag e Pressur e 12 2
4.18 Determinatio n o f Uplif t Pressure s 12 3
4.19 Seepag e Flo w Throug h Homogeneou s Eart h Dam s 12 6
4.20 Flo w Ne t Consistin g o f Conjugat e Confocal Parabola s 12 7
4.21 Pipin g Failur e 13 1
4.22 Problem s 13 8
CHAPTER 5 EFFECTIV E STRESS AND PORE WATER PRESSURE 14 3
5.1 Introductio n 14 3
5.2 Stresse s whe n No Flo w Take s Plac e Through th e
Saturated Soi l Mas s 14 5
5.3 Stresse s Whe n Flo w Take s Plac e Through the Soi l
from To p to Botto m 14 6
5.4 Stresse s Whe n Flo w Take s Plac e Throug h th e Soi l
from Botto m t o Top 14 7
5.5 Effectiv e Pressur e Du e to Capillary Wate r Ris e i n Soi l 14 9
5.6 Problem s 17 0
CHAPTER 6 STRES S DISTRIBUTIO N IN SOILS
DUE TO SURFACE LOADS 17 3
6.2 Boussinesq' s Formul a fo r Poin t Load s 17 4
6.3 Westergaard' s Formul a fo r Point Load s 17 5
6.4 Lin e Load s 17 8
6.5 Stri p Load s 17 9
6.6 Stresse s Beneat h th e Corne r o f a Rectangular Foundation 18 1
6.7 Stresse s Unde r Uniformly Loade d Circula r Footin g 18 6
6.8 Vertica l Stress Beneat h Loade d Area s o f Irregula r Shap e 18 8
6.9 Embankmen t Loading s 19 1
6.10 Approximat e Method s fo r Computin g c r 19 7
6.11 Pressur e Isobar s 19 8
6.12 Problem s 20 3
CHAPTER 7 COMPRESSIBILIT Y AN D CONSOLIDATION 20 7
7.2 Consolidatio n 20 8
7.3 Consolidomete r 21 2

xiv Content s
7.4 Th e Standar d One-Dimensiona l Consolidatio n Tes t 21 3
7.5 Pressure-Voi d Rati o Curve s 21 4
7.6 Determinatio n of Preconsolidatio n Pressur e 21 8
7.7 e-logp Fiel d Curves for Normally Consolidate d and
Overconsolidated Clay s of Low to Medium Sensitivit y 21 9
7.8 Computatio n of Consolidatio n Settlemen t 21 9
7.9 Settlemen t Du e t o Secondar y Compressio n 22 4
7.10 Rat e o f One-dimensiona l Consolidation Theory o f Terzaghi 23 3
7.11 Determinatio n of th e Coefficien t o f Consolidatio n 24 0
7.12 Rat e o f Settlemen t Du e to Consolidatio n 24 2
7.13 Two - and Three-dimensional Consolidatio n Problems 24 3
7.14 Problem s 24 7
CHAPTERS SHEA R STRENGTH O F SOIL 25 3
8.2 Basi c Concep t o f Shearin g Resistanc e an d Shearin g Strengt h 25 3
8.3 Th e Coulom b Equatio n 25 4
8.4 Method s o f Determinin g Shea r Strengt h Parameters 25 5
8.5 Shea r Tes t Apparatu s 25 6
8.6 Stres s Conditio n at a Point in a Soil Mas s 26 0
8.7 Stres s Condition s in Soi l Durin g Triaxial Compressio n Tes t 26 2
8.8 Relationshi p Between th e Principal Stresse s an d Cohesion c 26 3
8.9 Moh r Circl e o f Stress 26 4
8.10 Moh r Circl e of Stres s When a Prismatic Elemen t i s Subjecte d to
Normal an d Shear Stresse s 26 5
8.11 Moh r Circl e o f Stres s fo r a Cylindrical Specime n
Compression Tes t 26 6
8.12 Mohr-Coulom b Failur e Theor y 26 8
8.13 Moh r Diagra m fo r Triaxial Compressio n Tes t a t Failure 26 9
8.14 Moh r Diagra m fo r a Direct Shea r Test a t Failure 27 0
8.15 Effectiv e Stresse s 27 4
8.16 Shea r Strengt h Equatio n i n Terms o f Effective Principa l Stresse s 27 5
8.17 Stress-Controlle d an d Strain-Controlled Test s 27 6
8.18 Type s o f Laborator y Tests 27 6
8.19 Shearin g Strengt h Tests o n San d 27 8
8.20 Unconsolidated-Undraine d Test 28 4
8.21 Unconfine d Compression Test s 28 6
8.22 Consolidated-Undraine d Tes t o n Saturate d Cla y 29 4
8.23 Consolidated-Draine d Shear Strengt h Tes t 29 6
8.24 Por e Pressur e Parameter s Unde r Undraine d Loadin g 29 8
8.25 Van e Shea r Tests 30 0

Contents x v
8.26 Othe r Method s fo r Determinin g Undraine d Shea r Strengt h
of Cohesiv e Soil s 30 2
8.27 Th e Relationshi p Between Undraine d Shear Strengt h an d
Effective Overburde n Pressure 30 4
8.28 Genera l Comment s 31 0
8.29 Question s and Problems 31 1
CHAPTERS SOI L EXPLORATIO
N 31 7
9.2 Borin g of Hole s 31 8
9.3 Samplin g in Soil 32 2
9.4 Roc k Cor e Samplin g 32 5
9.5 Standar d Penetration Test 32 7
9.6 SP T Values Related t o Relative Density of Cohesionless Soil s 33 0
9.7 SP T Values Related t o Consistency of Clay Soi l 33 0
9.8 Stati c Con e Penetratio n Test (CPT ) 33 2
9.9 Pressuremete r 34 3
9.10 Th e Flat Dilatomete r Test 34 9
9.11 Fiel d Vane Shear Test (VST) 35 1
9.12 Fiel d Plat e Load Test (PUT ) 3 51
9.13 Geophysica l Exploratio n 35 2
9.14 Plannin g of Soi l Exploratio n 35 8
9.15 Executio n of Soi l Exploratio n Progra m 35 9
9.16 Repor t 36 1
9.17 Problem s 36 2
CHAPTER 1 0 STABILIT Y O F SLOPES 36 5
10.2 Genera l Consideration s an d Assumptions in th e Analysis 36 7
10.3 Facto r o f Safet y 36 8
10.4 Stabilit y Analysi s of Infinit e Slope s i n Sand 37 1
10.5 Stabilit y Analysis of Infinit e Slope s i n Clay 37 2
10.6 Method s o f Stabilit y Analysis of Slopes o f Finite Heigh t 37 6
10.7 Plan e Surfac e of Failur e 37 6
10.8 Circula r Surface s of Failure 37 8
10.9 Failur e Unde r Undrained Condition s((f> u = 0 ) 38 0
10.10 Friction-Circl e Metho d 38 2
10.11 Taylor' s Stabilit y Number 38 9
10.12 Tensio n Crack s 39 3
10.13 Stabilit y Analysis by Method o f Slice s fo r Stead y Seepag e 39 3

xvi Content s
10.14 Bishop' s Simplifie d Metho d o f Slice s 40 0
10.15 Bisho p an d Morgenster n Metho d fo r Slop e Analysi s 40 3
10.16 Morgenster n Metho d o f Analysis for Rapi d Drawdow n Conditio n 40 5
10.17 Spence r Metho d o f Analysis 40 8
10.18 Problem s 41 1
CHAPTER 1 1 LATERA L EARTH PRESSURE 41 9
11.2 Latera l Eart h Pressur e Theor y 42 0
11.3 Latera l Eart h Pressur e fo r a t Rest Conditio n 42 1
11.4 Rankine' s State s o f Plasti c Equilibriu m for Cohesionles s Soil s 42 5
11.5 Rankine' s Eart h Pressur e Agains t Smoot h Vertica l Wall with
Cohesionless Backfil l 42 8
11.6 Rankine' s Activ e Earth Pressur e wit h Cohesiv e Backfil l 44 0
11.7 Rankine' s Passiv e Eart h Pressur e wit h Cohesiv e Backfil l 44 9
11.8 Coulomb' s Eart h Pressur e Theor y fo r San d fo r Active Stat e 45 2
11.9 Coulomb' s Eart h Pressur e Theor y fo r San d fo r Passiv e Stat e 45 5
11.10 Activ e Pressur e by Culmann' s Metho d fo r Cohesionles s Soil s 45 6
11.11 Latera l Pressure s b y Theor y o f Elasticit y fo r Surcharg e Load s
on th e Surfac e of Backfil l 45 8
11.12 Curve d Surface s o f Failur e fo r Computin g Passiv e Eart h Pressur e 46 2
11.13 Coefficient s of Passiv e Eart h Pressur e Table s an d Graph s 46 4
11.14 Latera l Eart h Pressur e o n Retainin g Walls Durin g Earthquake s 46 7
CHAPTER 1 2 SHALLO W FOUNDATION I:
ULTIMATE BEARING CAPACITY 48 1
12.2 Th e Ultimat e Bearing Capacit y o f Soi l 48 3
12.3 Som e o f th e Terms Define d 48 3
12.4 Type s o f Failur e in Soi l 48 5
12.5 A n Overvie w o f Bearin g Capacit y Theorie s 48 7
12.6 Terzaghi' s Bearin g Capacit y Theor y 48 8
12.7 Skempton' s Bearin g Capacit y Facto r N C 49 3
12.8 Effec t o f Water Tabl e o n Bearin g Capacit y 49 4
12.9 Th e Genera l Bearin g Capacit y Equatio n 50 3
12.10 Effec t o f Soi l Compressibilit y o n Bearin g Capacit y o f Soi l 50 9
12.11 Bearin g Capacit y o f Foundation s Subjecte d t o Eccentri c Load s 51 5
12.12 Ultimat e Bearin g Capacit y o f Footing s Base d o n SP T Value s (N) 51 8
12.13 Th e CP T Metho d o f Determinin g Ultimat e Bearin g Capacit y 51 8

Contents xvi i
12.14 Ultimat e Bearin g Capacit y o f Footings Restin g o n Stratifie d
Deposits o f Soi l 52 1
12.15 Bearin g Capacit y o f Foundations o n Top of a Slop e 52 9
12.16 Foundation s o n Roc k 53 2
12.17 Cas e Histor y of Failure o f the Transcona Grai n Elevato r 53 3
CHAPTER 13 SHALLO W FOUNDATION II:
SAFE BEARING PRESSURE AND SETTLEMENT CALCULATION 54 5
13.2 Fiel d Plat e Loa d Test s 54 8
13.3 Effec t o f Siz e o f Footings o n Settlemen t 55 4
13.4 Desig n Chart s fro m SP T Values for Footings o n San d 55 5
13.5 Empirica l Equation s Base d o n SP T Values for Footing s o n
Cohesionless Soil s 55 8
13.6 Saf e Bearing Pressur e fro m Empirica l Equation s Based o n
CPT Values for Footings o n Cohesionless Soi l 55 9
13.7 Foundatio n Settlemen t 56 1
13.8 Evaluatio n of Modulu s of Elasticit y 56 2
13.9 Method s o f Computing Settlements 56 4
13.10 Elasti c Settlemen t Beneat h the Corner o f a Uniformly Loade d
Flexible Are a Based o n the Theory o f Elasticity 56 5
13.11 Janbu , Bjerrum an d Kjaernsli' s Metho d o f Determinin g
Elastic Settlemen t Unde r Undrained Conditions 56 8
13.12 Schmertmann' s Metho d o f Calculatin g Settlemen t i n Granular
Soils b y Using CPT Values 56 9
13.13 Estimatio n o f Consolidatio n Settlemen t b y Usin g Oedometer
Test Dat a 57 5
13.14 Skempton-Bjerru m Metho d o f Calculatin g Consolidatio n
Settlement (1957 ) 57 6
CHAPTER 14 SHALLO W FOUNDATION III:
COMBINED FOOTINGS AND MAT FOUNDATIONS 58 5
14.2 Saf e Bearin g Pressure s fo r Ma t Foundation s on San d an d Clay 58 7
14.3 Eccentri c Loadin g 58 8
14.4 Th e Coefficien t of Subgrad e Reactio n 58 8
14.5 Proportionin g o f Cantileve r Footin g 59 1

xviii Content s
14.6 Desig n o f Combine d Footing s b y Rigi d Metho d (Conventiona l
Method) 59 2
14.7 Desig n o f Ma t Foundatio n b y Rigi d Metho d 59 3
14.8 Desig n o f Combined Footing s b y Elasti c Lin e Metho d 59 4
14.9 Desig n o f Mat Foundation s by Elasti c Plat e Metho d 59 5
14.10 Floatin g Foundatio n 59 5
CHAPTER 15 DEE P FOUNDATION I :
PILE FOUNDATION 60 5
15.2 Classificatio n of Piles 605
15.3 Type s o f Piles Accordin g to the Metho d o f Installation 60 6
15.4 Use s o f Piles 60 8
15.5 Selectio n o f Pile 60 9
15.6 Installatio n of Piles 61 0
PART A-VERTICAL LOAD BEARING CAPACITY OF ASINGLE VERTICAL PILE 61 3
15.7 Genera l Consideration s 61 3
15.8 Method s o f Determinin g Ultimat e Load Bearin g Capacit y o f a
Single Vertical Pile 61 7
15.9 Genera l Theor y fo r Ultimat e Bearing Capacit y 61 8
15.10 Ultimat e Bearin g Capacit y i n Cohesionless Soil s 62 0
15.11 Critica l Dept h 62 1
15.12 Tomlinson' s Solutio n fo r Qbin Sand 62 2
15.13 Meyerhof' s Metho d o f Determining Q bfor Pile s i n San d 62 4
15.14 Vesic' s Metho d o f Determinin g Q b 62 5
15.15 Janbu' s Metho d o f Determining Qb 62 8
15.16 Coyl e an d Castello's Metho d o f Estimating Qbin Sand 62 8
15.17 Th e Ultimat e Skin Resistanc e of a Single Pile i n Cohesionless Soi l 62 9
15.18 Ski n Resistanc e Q fby Coyl e an d Castell o Metho d (1981 ) 63 1
15.19 Stati c Bearin g Capacity of Piles i n Clay Soi l 63 1
15.20 Bearin g Capacit y of Piles i n Granular Soil s Base d o n SP T Value 63 5
15.21 Bearin g Capacit y o f Piles Base d o n Stati c Con e Penetratio n
Tests (CPT ) 65 2
15.22 Bearin g Capacit y o f a Singl e Pile b y Loa d Tes t 66 3
15.23 Pil e Bearing Capacity fro m Dynamic Pile Driving Formulas 66 6
15.24 Bearin g Capacit y o f Piles Founde d o n a Rock y Be d 67 0
15.25 Uplif t Resistanc e o f Pile s 67 1

Contents xi x
PART B-PILE GROUP 67 4
15.26 Numbe r an d Spacin g o f Piles i n a Group 67 4
15.27 Pil e Grou p Efficienc y 67 6
15.28 Vertica l Bearin g Capacity o f Pile Group s Embedded i n
Sands an d Gravels 67 8
15.29 Settlemen t o f Piles an d Pile Group s i n Sands an d Gravels 68 1
15.30 Settlemen t of Pile Group s in Cohesive Soil s 68 9
15.31 Allowabl e Loads o n Groups o f Piles 69 0
15.32 Negativ e Frictio n 69 2
15.33 Uplif t Capacit y o f a Pile Grou p 69 4
CHAPTER 16 DEE P FOUNDATION II :
BEHAVIOR OF LATERALLY LOADED VERTICAL AND
BATTER PILES 69 9
16.2 Winkler' s Hypothesi s 70 0
16.3 Th e Differential Equatio n 70 1
16.4 Non-dimensiona l Solution s fo r Vertical Piles Subjecte d t o
Lateral Load s 70 4
16.5 p- y Curve s for the Solutio n o f Laterally Loade d Pile s 70 6
16.6 Broms ' Solution s fo r Laterally Loade d Pile s 70 9
16.7 A Direct Metho d fo r Solvin g th e Non-linear Behavio r of
Laterally Loade d Flexibl e Pil e Problem s 71 6
16.8 Cas e Studies fo r Laterally Loade d Vertical Pile s in San d 72 2
16.9 Cas e Studie s for Laterally Loade d Vertica l Piles in Clay 72 5
16.10 Behavio r o f Laterally Loade d Batte r Pile s i n Sand 73 1
CHAPTER 17 DEE P FOUNDATION III :
DRILLED PIER FOUNDATIONS 74 1
17.2 Type s o f Drilled Pier s 7 4
1
17.3 Advantage s and Disadvantage s o f Drilled Pie r Foundation s 74 3
17.4 Method s o f Constructio n 74 3
17.5 Desig n Consideration s 75 1
17.6 Loa d Transfe r Mechanis m 75 2
17.7 Vertica l Bearing Capacit y o f Drilled Pier s 75 4
17.8 Th e Genera l Bearin g Capacit y Equatio n fo r the Bas e Resistanc e
= 75 5
"

xx Content s
17.9 Bearin g Capacit y Equation s fo r the Bas e i n Cohesiv e Soi l 75 6
17.10 Bearin g Capacit y Equatio n fo r the Bas e i n Granula r Soi l 75 6
17.11 Bearin g Capacit y Equation s fo r th e Base i n Cohesive IG M o r Rock 75 9
17.12 Th e Ultimat e Ski n Resistanc e o f Cohesiv e and
Intermediate Material s 76 0
17.13 Ultimat e Ski n Resistanc e i n Cohesionles s Soi l an d Gravell y Sand s 76 3
17.14 Ultimat e Side an d Tota l Resistanc e i n Roc k 76 4
17.15 Estimatio n o f Settlement s of Drille d Pier s a t Working Load s 76 5
17.16 Uplif t Capacit y o f Drille d Pier s 77 7
17.17 Latera l Bearin g Capacit y o f Drille d Pier s 77 9
17.18 Cas e Stud y of a Drille d Pier Subjecte d t o Lateral Load s 78 7
CHAPTER 18 FOUNDATION S ON COLLAPSIBLE AND
EXPANSIVE SOIL S 79 1
PART A-COLLAPSIBLE SOILS 79 3
18.2 Genera l Observation s 79 3
18.3 Collaps e Potentia l an d Settlemen t 79 5
18.4 Computatio n o f Collaps e Settlemen t 79 6
18.5 Foundatio n Desig n 79 9
18.6 Treatmen t Method s fo r Collapsibl e Soil s 80 0
PART B-EXPANSIVE SOILS 80 0
18.7 Distributio n of Expansiv e Soil s 80 0
18.8 Genera l Characteristic s of Swellin g Soil s 80 1
18.9 Cla y Mineralog y an d Mechanis m o f Swellin g 80 3
18.10 Definitio n o f Som e Parameter s 80 4
18.11 Evaluatio n o f th e Swellin g Potentia l o f Expansiv e Soil s b y Singl e
Index Metho d 80 4
18.12 Classificatio n o f Swellin g Soil s b y Indirec t Measuremen t 80 6
18.13 Swellin g Pressure b y Direc t Measuremen t 81 2
18.14 Effec t o f Initia l Moistur e Conten t an d Initia l Dry Densit y o n
Swelling Pressur e 81 3
18.15 Estimatin g the Magnitud e of Swellin g 81 4
18.16 Desig n o f Foundation s i n Swellin g Soil s 81 7
18.17 Drille d Pie r Foundation s 81 7
18.18 Eliminatio n of Swellin g 82 7

Contents xx i
CHAPTER 19 CONCRET E AND MECHANICALLY STABILIZED
EARTH RETAINING WALLS 83 3
PART A-CONCRETE RETAINING WALL S 83 3
19.2 Condition s Unde r Which Rankin e an d Coulomb Formula s Ar e
Applicable t o Retainin g Walls Unde r th e Active Stat e 83 3
19.3 Proportionin g o f Retainin g Walls 83 5
19.4 Eart h Pressur e Chart s fo r Retainin g Walls 83 6
19.5 Stabilit y of Retainin g Walls 83 9
PART B-MECHANICALLY STABILIZED EART H RETAINING WALL S 84 9
19.7 Backfil l an d Reinforcing Material s 85 1
19.8 Constructio n Detail s 85 5
19.9 Desig n Consideration s fo r a Mechanically Stabilize d Eart h Wal l 85 7
19.10 Desig n Metho d 85 9
19.11 Externa l Stabilit y 86 3
19.12 Example s o f Measured Latera l Eart h Pressure s 87 5
CHAPTER 20 SHEE T PILE WALLS AND BRACED CUTS 88 1
20.2 Shee t Pil e Structure s 88 3
20.3 Fre e Cantileve r Shee t Pil e Walls 88 3
20.4 Dept h o f Embedmen t o f Cantileve r Walls i n Sand y Soil s 88 5
20.5 Dept h o f Embedmen t o f Cantileve r Walls in Cohesiv e Soil s 89 6
20.6 Anchore d Bulkhead : Free-Eart h Suppor t Method—Dept h o f
Embedment o f Anchored Shee t Pile s i n Granula r Soil s 90 8
20.7 Desig n Chart s fo r Anchored Bulkhead s in San d 91 3
20.8 Momen t Reductio n fo r Anchored Shee t Pil e Walls 91 6
20.9 Anchorag e o f Bulkhead s 92 5
20.10 Brace d Cut s 93 1
20.11 Latera l Eart h Pressur e Distributio n on Braced-Cuts 93 5
20.12 Stabilit y o f Brace d Cut s i n Saturate d Clay 93 8
20.13 Bjerru m an d Eid e Metho d o f Analysis 94 0
20.14 Pipin g Failure s i n Sand Cut s 94 5

X X I I Contents
CHAPTER 21 SOI L IMPROVEMENT
21.1 Introductio n
21.2 Mechanica l Compaction
21.3 Laborator y Test s o n Compaction
21.4 Effec t o f Compactio n o n Engineerin g Behavio r
21.5 Fiel d Compactio n an d Contro l
21.6 Compactio n fo r Deepe r Layer s o f Soi l
21.7 Preloadin g
21.8 San d Compactio n Pile s an d Ston e Column s
21.9 Soi l Stabilizatio n by th e Us e o f Admixtures
21.10 Soi l Stabilizatio n by Injectio n of Suitabl e Grouts
21.11 Problem s
951
951
952
953
959
962
973
974
980
981
983
983
APPENDIX A S I UNITS IN GEOTECHNICAL ENGINEERING 987
APPENDIX B SLOP E STABILITY CHART S AND TABLES 993
REFERENCES 1007
INDEX 1025

CHAPTER 1
INTRODUCTION
1.1 GENERA L REMARK S
Karl Terzaghi writing in 1951 (Bjerrum, et. al., 1960), on 'The Influence of Modern Soil Studies on
the Design and Construction of Foundations' commente d on foundations as follows:
Foundations can appropriately be described as a necessary evil. If a building is to be
constructed on an outcrop of sound rock, no foundationis required. Hence, in contrast to the
building itself which satisfies specific needs, appeals to the aesthetic sense, and fills its
matters with pride, the foundationsmerely serve as a remedy for the deficiencies of whatever
whimsical nature has provided for the support of the structure at the site which has been
selected. On account of the fact that there is no glory attached to the foundations, and that
the sources of success or failures are hidden deep in the ground, building foundations have
always been treated as step children; and their acts of revenge forthe lack of attention can be
very embarrassing.
The comment s mad e by Terzaghi ar e very significan t an d shoul d be take n note of by all
practicing Architects and Engineers. Architects or Engineers who do not wish to make use of the
growing knowledge of foundation design are not rendering true service to their profession. Sinc e
substructures are as important as superstructures, persons who are well qualified in the design of
substructures shoul d alway s b e consulted an d the old proverb that a 'stitc h in time saves nine'
should always be kept in mind.
The design of foundations is a branch of Civil Engineering. Experience has shown that most
of these branches have passed in succession through two stages, the empirical an d the scientific,
before they reached th e present one which may be called the stage of maturity.
The stage of scientific reasoning in the design of foundations started with the publication of
the book Erdbaumechanik (means Soil Mechanics) by Karl Terzaghi in 1925. This book represents
the first attempt to treat Soil Mechanics on the basis of the physical properties o f soils. Terzaghi's

Chapter 1
contribution for the development of Soil Mechanics and Foundation Engineering is so vast that he
may truly be called the Father o f Soil Mechanics, Hi s activity extended over a period of about 50
years starting from th e year 1913. He was born on October 2, 188 3 in Prague and died on October
25, 196 3 i n Winchester, Massachusetts, USA. His amazing career is well documented in the book
'From Theory t o Practice in Soil Mechanics' (Bjerrum , L., et. al., 1960) .
Many investigator s in the field of Soil Mechanics were inspired by Terzaghi. Som e o f th e
notable personalitie s wh o followe d hi s footstep s ar e Ralp h B . Peck , Arthu r Casagrande ,
A. W. Skempton, etc. Because of the unceasing efforts of these and other innumerable investigators,
Soil Mechanics and Foundation Engineering ha s come to stay as a very important par t of the Civil
Engineering profession.
The transitio n of foundation engineering fro m th e empirica l stag e t o tha t of th e scientific
stage started almos t a t the commencement o f the 20th century. The design o f foundations during
the empirical stage was based mostly on intuition and experience. There use d to be many failures
since the procedure of design was only by trial and error.
However, in the present scientific age, the design of foundations based on scientific analysis
has received a much impetus. Theories hav e been develope d base d o n fundamental properties of
soils. Still one can witness unsatisfactory performance of structures constructed even on scientific
principles. The reasons for such poor performance are many. The soil mass on which a structure is to
be buil t i s heterogeneou s i n characte r an d n o theor y ca n simulat e fiel d conditions . Th e
fundamental propertie s o f soi l whic h w e determin e i n laboratorie s ma y no t reflec t trul y th e
properties o f th e soi l in-situ. A judicial combination o f theor y an d experienc e i s essentia l fo r
successful performance of any structure built on earth. Another method that is gaining popularity is
the observational approach. Thi s procedur e consist s i n makin g appropriat e observation s soo n
enough during construction to detect signs of departure of the real conditions from those assume d
by th e designe r an d i n modifying either the design o r the method o f construction in accordanc e
with the findings.
1.2 A BRIE F HISTORICA L DEVELOPMEN T
Many structure s that were buil t centurie s ago ar e monuments of curiosity eve n today . Egyptia n
temples buil t three or four thousand years ago still exist though the design of the foundations were
not based o n any presently known principles. Romans built notable engineering structures such as
harbors, breakwaters, aqueducts, bridges, large public buildings and a vast network of durable and
excellent roads . Th e leaning tower o f Pisa i n Italy completed durin g the 14t h centur y is stil l a
center of tourist attraction. Many bridges were also built during the 15t h to 17th centuries. Timber
piles were used for many of the foundations.
Another marvel of engineering achievement is the construction o f the famed mausoleum Taj
Mahal outsid e the city of Agra. This was constructed in the 17t h century by the Mogul Emperor of
Delhi, Shahjahan, to commemorate his favorite wife Mumtaz Mahal. The mausoleum is built on the
bank of the river Jamuna. The proximity of the river required special attention in the building of the
foundations. I t is reported tha t masonry cylindrical wells have been use d fo r the foundations . It
goes to the credit of the engineers who designed and constructed this grand structure which is still
quite sound even afte r a lapse of about three centuries.
The firs t rationa l approach fo r th e computation of eart h pressure s o n retainin g wall s wa s
formulated by Coulomb (1776), a famous French scientist. He proposed a theory in 1776 called the
"Classical Eart h Pressur e Theory" . Poncele t (1840 ) extende d Coulomb' s theor y b y givin g a n
elegant graphica l metho d fo r findin g th e magnitud e of eart h pressur e o n walls . Later, Culmann
(1875) gave th e Coulomb-Poncelet theor y a geometrical formulation , thus supplying the metho d
with a broad scientifi c basis. Rankine (1857) a Professor of Civil Engineering in the University of

Introduction
Glasgow, proposed a new earth pressur e theory, which is also called a Classical Earth Pressure
Theory.
Darcy (1856), on the basis of his experiments on filter sands, proposed a law for the flow of
water in permeable materials and in the same year Stokes (1856) gave an equation for determining
the terminal velocity of solid particles falling in liquids. The rupture theory of Mohr (1900) Stres s
Circles ar e extensivel y used i n the stud y of shea r strengt h of soils . On e o f the mos t important
contributions to engineering science was made by Boussinesq (1885) wh o proposed a theory for
determining stres s distributio n under loaded area s i n a semi-infinite, elastic, homogeneous, an d
isotropic medium .
Atterberg (1911), a Swedish scientist, proposed simpl e tests for determining the consistency
limits o f cohesiv e soils . Felleniu s (1927 ) heade d a Swedis h Geotechnica l Commissio n fo r
determining the causes of failure of many railway and canal embankments. The so-called Swedish
Circle method or otherwise termed as the Slip Circle method was the outcome of his investigation
which was published in 1927 .
The developmen t o f th e scienc e o f Soil Mechanic s an d Foundation Engineerin g fro m th e
year 1925 onwards was phenomenal. Terzaghi laid down definite procedures in his book published
in 192 5 for determinin g propertie s and the strengt h characteristic s of soils . The moder n soi l
mechanics was born in 1925 . Th e present stage of knowledge in Soil Mechanics an d the design
procedures o f foundation s ar e mostl y du e t o th e work s o f Terzagh i an d hi s ban d o f devote d
collaborators.
1.3 SOI L MECHANIC S AND FOUNDATIO N ENGINEERIN G
Terzaghi defined Soil Mechanics a s follows:
Soil Mechanics is the application of the laws of mechanics and hydraulics to engineering
problems dealing with sediments and other unconsolidated accumulations of solid particles
produced by the mechanical and chemical disintegration of rocks regardless of whether or
not they contain an admixture of organic constituents.
The ter m Soil Mechanics i s no w accepte d quit e generall y to designat e tha t disciplin e of
engineering science which deals with the properties an d behavior of soil as a structural material.
All structures have to be built on soils. Our main objective in the study of soil mechanics is
to lay down certain principles, theories and procedures for the design of a safe and sound structure.
The subjec t of Foundation Engineering deal s wit h the desig n o f variou s types o f substructures
under different soi l an d environmental conditions.
During th e design , th e designe r ha s t o mak e us e o f th e propertie s o f soils , th e theorie s
pertaining t o th e desig n an d hi s ow n practica l experienc e t o adjus t th e desig n t o sui t fiel d
conditions. He has to deal wit h natural soil deposits whic h perform th e engineering functio n o f
supporting th e foundatio n an d th e superstructur e abov e it . Soi l deposit s i n natur e exis t i n a n
extremely errati c manne r producing thereby a n infinite variet y o f possible combination s which
would affect th e choice and design of foundations. The foundation engineer must have the ability
to interpret the principles of soil mechanics to suit the field conditions. The success or failure of his
design depends upon how much in tune he is with Nature.

CHAPTER 2
SOIL FORMATION AND CHARACTERIZATION
2.1 INTRODUCTIO N
The word 'soil' has different meanings for different professions. To the agriculturist, soil is the top
thin layer of earth withi n which organic forces ar e predominant and which is responsible fo r the
support of plant life. To the geologist, soi l is the material in the top thin zone within which roots
occur. Fro m th e poin t o f vie w o f a n engineer , soi l include s al l eart h materials , organi c an d
inorganic, occurring in the zone overlying the rock crust.
The behavior of a structure depends upon the properties o f the soil materials o n which the
structure rests. The properties o f the soil materials depend upon the properties o f the rocks fro m
which they are derived. A brief discussion of the parent rocks is, therefore, quite essential in order
to understand the properties of soil materials.
2.2 ROC K CLASSIFICATIO N
Rock can be defined as a compact, semi-hard to hard mass of natural material composed of one or
more minerals. The rocks that are encountered at the surface of the earth or beneath, are commonly
classified into three groups according to their modes of origin. They are igneous, sedimentary and
metamorphic rocks.
Igneous rock s ar e considere d t o b e th e primar y rock s forme d b y th e coolin g o f molten
magmas, or by the recrystallization of older rocks under heat and pressure great enough to render
them fluid. They have been formed on or at various depths below the earth surface. There are two
main classes of igneous rocks. They are:
1. Extrusiv e (poured out at the surface), and
2. Intrusiv e (large rock masses which have not been formed in contact with the atmosphere) .

6 Chapte r 2
Initially both classes of rocks were in a molten state. Their present state results directly from
the way in which they solidified. Due to violent volcanic eruptions in the past, some of the molten
materials wer e emitte d int o the atmospher e wit h gaseous extrusions . These cooled quickl y and
eventually fell on the earth's surface as volcanic ash and dust. Extrusive rocks are distinguished, in
general, by their glass-like structure.
Intrusive rocks , coolin g an d solidifyin g a t grea t depth s an d unde r pressur e containin g
entrapped gases, are wholly crystalline in texture. Such rocks occur in masses of great extent, often
going to unknown depths. Some of the important rocks that belong to the igneous group are granite
and basalt. Granite i s primarily composed of feldspar, quartz and mica an d possesses a massive
structure. Basalt i s a dark-colored fine-graine d rock. I t is characterized b y the predominance o f
plagioclase, th e presence of considerable amounts of pyroxene and some olivine and the absence of
quartz. The colo r varie s fro m dark-gre y t o black. Bot h granit e an d basal t ar e use d a s building
stones.
When th e product s o f th e disintegratio n an d decompositio n o f an y roc k typ e ar e
transported, redeposited, an d partly or fully consolidate d o r cemented int o a new rock type , the
resulting materia l i s classifie d a s a sedimentary rock. Th e sedimentar y rock s generall y ar e
formed in quite definitely arrange d beds, o r strata, which can be seen to have been horizontal at
one time although sometimes displace d through angles up to 90 degrees. Sedimentary rocks are
generally classified on the basis of grain size, texture and structure. From an engineering point of
view, the most important rocks tha t belong to the group are sandstones, limestones, and shales.
Rocks forme d b y th e complet e o r incomplete recrystallizatio n o f igneou s o r sedimentar y
rocks by high temperatures, high pressures, and/or high shearing stresse s ar e metamorphic rocks.
The rock s s o produce d ma y displa y feature s varying from complet e an d distinc t foliatio n o f a
crystalline structur e t o a fine fragmentary partially crystallin e stat e caused b y direct compressiv e
stress, including also the cementation of sediment particles by siliceous matter. Metamorphic rocks
formed withou t intense shea r action have a massive structure . Some o f the important rock s tha t
belong to this group are gneiss, schist, slate an d marble. Th e characteristic feature of gneiss is its
structure, the minera l grain s are elongated, o r platy, and banding prevails. Generally gneis s i s a
good engineerin g material. Schist is a finely foliate d rock containin g a high percentage o f mica .
Depending upon the amount of pressure applied by the metamorphic forces, schis t may be a very
good buildin g material. Slat e i s a dark colored, plat y rock wit h extremely fin e textur e and eas y
cleavage. Becaus e o f this easy cleavage, slat e i s split into very thin sheets an d used a s a roofing
material. Marble is the end product of the metamorphism of limestone and other sedimentary rock s
composed o f calciu m o r magnesium carbonate. I t is ver y dens e an d exhibit s a wid e variet y of
colors. I n construction, marble is used for facing concrete o r masonry exterior an d interior walls
and floors.
Rock Mineral s
It is essential t o examine th e properties o f the rock formin g minerals sinc e al l soils ar e derive d
through the disintegration or decomposition o f some parent rock. A 'mineral' is a natural inorganic
substance of a definite structure and chemical composition. Some of the very important physical
properties o f mineral s ar e crysta l form , color , hardness , cleavage , luster , fracture , an d specifi c
gravity. Out of these only two, specific gravity and hardness, are of foundation engineering interest.
The specifi c gravity of the mineral s affect s th e specifi c gravity of soils derive d fro m them. Th e
specific gravity of most rock and soil forming minerals varies from 2.50 (some feldspars) and 2.65
(quartz) to 3.5 (augite or olivine). Gypsum has a smaller value of 2.3 and salt (NaCl) has 2.1. Some
iron minerals may have higher values, for instance, magnetite has 5.2.
It is reported tha t about 95 percent of the known part of the lithosphere consist s of igneous
rocks and only 5 percent of sedimentary rocks. Soil formation is mostly due to the disintegration of
igneous rock which may be termed as a parent rock.

Soil Formation and Characterization 7
Table 2. 1 Minera l compositio n of igneou s rock s
Mineral Percen t
Quartz 12-2 0
Feldspar 50-6 0
Ca, Fe and Mg, Silicates 14-1 7
Micas 4- 8
Others 7- 8
The average mineral composition of igneous rocks is given in Table 2.1. Feldspars ar e the most
common rock minerals, which account for the abundance of clays derived from the feldspars on the
earth's surface. Quartz comes next in order of frequency. Most sands are composed o f quartz.
2.3 FORMATIO N O F SOILS
Soil is defined as a natural aggregate o f mineral grains, with or without organic constituents, that
can b e separate d b y gentl e mechanica l mean s suc h a s agitatio n i n water . B y contras t roc k i s
considered to be a natural aggregate of mineral grains connected by strong and permanent cohesive
forces. The process o f weathering of the rock decrease s th e cohesive force s binding the mineral
grains and leads to the disintegration of bigger masses to smaller an d smaller particles . Soil s are
formed by the process of weathering of the parent rock. The weathering of the rocks might be by
mechanical disintegration, and/or chemical decomposition .
Mechanical Weatherin g
Mechanical weatherin g of rock s t o smalle r particles i s due t o th e actio n o f suc h agent s a s th e
expansive forces of freezing water in fissures, due to sudden changes of temperature or due to the
abrasion o f rock b y movin g water or glaciers. Temperature change s o f sufficien t amplitud e an d
frequency brin g abou t changes i n the volume of the rocks i n the superficial layers of the earth' s
crust in terms of expansion and contraction. Such a volume change sets up tensile and shear stresse s
in the rock ultimately leading to the fracture of even large rocks. This type of rock weathering takes
place in a very significant manner in arid climates where free, extreme atmospheric radiation brings
about considerable variatio n in temperature at sunrise and sunset.
Erosion by wind and rain is a very important factor and a continuing event. Cracking forces
by growing plants and roots in voids and crevasses of rock can force fragments apart.
Chemical Weatherin g
Chemical weatherin g (decomposition) ca n transform hard rock minerals into soft, easily erodable
matter. The principal type s o f decomposition ar e hydmtion, oxidation, carbonation, desilication
and leaching. Oxygen and carbon dioxide which are always present in the air readily combine with
the elements of rock in the presence of water.
2.4 GENERA L TYPES OF SOILS
It ha s bee n discusse d earlie r tha t soi l i s forme d b y th e proces s o f physica l an d chemica l
weathering. The individua l size of the constituent parts of even the weathered roc k migh t range
from th e smalles t stat e (colloidal ) t o th e larges t possibl e (boulders) . This implie s tha t al l th e
weathered constituent s of a parent rock cannot be termed soil . According to their grain size, soil

8 Chapte r 2
particles are classified as cobbles, gravel, sand, silt and clay. Grains having diameters i n the range
of 4.75 t o 76.2 mm are called gravel . If the grains are visible to the naked eye, bu t are less than
about 4.75 m m in size the soil is described a s sand. The lower limit of visibility of grains for the
naked eyes is about 0.075 mm. Soil grains ranging from 0.075 to 0.002 mm are termed a s silt and
those tha t are finer than 0.002 mm as clay. This classification is purely based o n size which does
not indicat e the properties o f fine grained materials .
Residual an d Transporte d Soil s
On the basis of origin of their constituents, soils can be divided into two large groups :
1. Residua l soils , an d
2. Transporte d soils .
Residual soils ar e thos e tha t remai n a t th e plac e o f thei r formatio n a s a resul t o f th e
weathering of parent rocks. The depth of residual soil s depend s primaril y o n climatic condition s
and th e tim e o f exposure . I n som e areas , thi s depth migh t be considerable . I n temperate zone s
residual soils are commonly stiff an d stable. An important characteristic o f residual soil is that the
sizes of grains are indefinite. For example, whe n a residual sample is sieved, the amount passin g
any given sieve size depends greatly on the time and energy expended i n shaking, because o f the
partially disintegrated condition.
Transported soils ar e soil s tha t ar e foun d a t location s fa r remove d fro m thei r plac e o f
formation. The transporting agencies of such soils are glaciers, wind and water. The soils are named
according t o th e mod e o f transportation . Alluvial soil s ar e those tha t have bee n transporte d b y
running water. The soils that have been deposited i n quiet lakes, are lacustrine soils . Marine soils
are those deposite d i n sea water. The soils transporte d an d deposited b y wind are aeolian soils .
Those deposited primaril y through the action of gravitational force, as in land slides, are colluvial
soils. Glacial soil s are those deposited b y glaciers. Man y of these transported soil s are loose and
soft to a depth of several hundre d feet. Therefore, difficultie s wit h foundations and other types of
construction are generally associated wit h transported soils .
Organic an d Inorgani c Soil s
Soils in general ar e further classifie d as organic o r inorganic. Soil s of organic origi n ar e chiefly
formed eithe r by growth and subsequent decay of plants such as peat, o r by the accumulation of
fragments o f the inorganic skeletons or shells of organisms. Hence a soil of organic origin can be
either organic or inorganic. The term organic soil ordinarily refers to a transported soil consisting of
the products of rock weathering with a more or less conspicuous admixture of decayed vegetabl e
matter.
Names o f Som e Soil s that ar e Generall y Use d i n Practice
Bentonite i s a cla y forme d b y th e decompositio n o f volcani c as h wit h a hig h conten t o f
montmorillonite. It exhibits the properties of clay to an extreme degree .
Varved Clay s consist of thin alternating layers of silt and fat clays of glacial origin. They posses s
the undesirable properties o f both silt and clay. The constituents of varved clays were transported
into fresh wate r lakes b y the melted ice at the close o f the ice age .
Kaolin, Chin a Cla y are very pure forms of white clay used in the ceramic industry.
Boulder Cla y i s a mixtur e o f a n unstratifie d sedimente d deposi t o f glacia l clay , containin g
unsorted rock fragments of all sizes ranging from boulders, cobbles, and gravel to finely pulverize d
clay material.

Soil Formation and Characterization 9
Calcareous Soi l i s a soil containing calcium carbonate. Such soil effervesces when tested wit h
weak hydrochloric acid.
Marl consists of a mixture of calcareous sands, clays, or loam.
Hardpan is a relatively hard, densely cemented soil layer, like rock which does not soften when
wet. Boulder clays or glacial till is also sometimes named as hardpan.
Caliche is an admixture of clay, sand, and gravel cemented by calcium carbonate deposited fro m
ground water.
Peat i s a fibrou s aggregat e o f fine r fragment s o f decaye d vegetabl e matter . Pea t i s ver y
compressible and one should be cautious when using it for supporting foundations of structures.
Loam is a mixture of sand, silt and clay.
Loess is a fine-grained, air-borne deposit characterized by a very uniform grain size, and high void
ratio. The size of particles ranges between about 0.01 to 0.05 mm. The soil can stand deep vertical
cuts because of slight cementation between particles. It is formed in dry continental regions and its
color is yellowish light brown.
Shale is a material in the state of transition from clay to slate. Shale itself is sometimes considered
a rock but, when it is exposed to the air or has a chance to take in water it may rapidly decompose .
2.5 SOI L PARTICL E SIZ E AND SHAP E
The size of particles a s explained earlier, may range from gravel to the finest siz e possible. Their
characteristics vary with the size. Soil particles coarser than 0.075 mm are visible to the naked eye
or may be examined by means of a hand lens. They constitute the coarser fraction s of the soils.
Grains finer than 0.075 mm constitute the finer fraction s o f soils. It is possible to distinguish the
grains lying between 0.075 mm and 2 JL (1 [i = 1 micron = 0.001 mm ) under a microscope. Grain s
having a size between 2 ji and 0.1JLA can be observed under a microscope but their shapes cannot be
made out . Th e shap e o f grain s smalle r tha n 1 ja ca n b e determine d b y mean s o f a n electro n
microscope. The molecular structure of particles can be investigated by means of X-ray analysis.
The coarser fractions of soils consist of gravel and sand. The individual particles of gravel,
which are nothing but fragments of rock, ar e composed o f one or more minerals , wherea s sand
grains contain mostly one mineral which is quartz. The individual grains of gravel and sand may be
angular, subangular , sub-rounded , rounded o r well-rounde d a s show n i n Fig . 2.1. Grave l ma y
contain grains which may be flat. Some sands contain a fairly high percentage of mica flakes that
give them the property of elasticity.
Silt and clay constitute the finer fractions of the soil. Any one grain of this fraction generally
consists of only one mineral. The particles may be angular, flake-shaped or sometimes needle-like .
Table 2. 2 give s th e particl e siz e classificatio n system s a s adopte d b y som e o f th e
organizations i n th e USA . Th e Unifie d Soi l Classificatio n Syste m i s no w almos t universally
accepted and has been adopted by the American Society for Testing and Materials (ASTM).
Specific Surfac e
Soil is essentially a paniculate system, that is, a system in which the particles are in a fine state of
subdivision or dispersion. In soils, the dispersed or the solid phase predominates and th e dispersion
medium, soil water, only helps to fill the pores between the solid particles. The significance of the
concept of dispersion becomes mor e apparent when the relationship of surface to particle size is
considered. In the case of silt, sand and larger size particles the ratio of the area of surface of the
particles to the volume of the sample is relatively small. This ratio becomes increasingly large as

Chapter 2
Angular Subangular Subrounded
Rounded Wel l rounded
Figure 2.1 Shape s of coarse r fractions o f soil s
size decreases from 2 JL which is the upper limit for clay-sized particles. A useful index of relative
importance of surface effects i s the specific surface o f grain. The specific surface is defined as the
total are a o f th e surfac e o f th e grain s expresse d i n squar e centimeter s pe r gra m o r pe r cubi c
centimeter of the dispersed phase.
The shap e o f the clay particles is an important property fro m a physical point of view. The
amount of surface pe r uni t mass o r volume varies with the shape of the particles. Moreover , th e
amount of contact area per unit surface changes with shape. It is a fact that a sphere has the smallest
surface are a pe r uni t volum e wherea s a plat e exhibit s th e maximum . Ostwal d (1919 ) ha s
emphasized the importance of shape in determining the specific surface of colloidal systems. Since
disc-shaped particle s ca n b e brought more i n intimate contact wit h each other , thi s shape ha s a
pronounced effect upo n the mechanical properties of the system. The interparticle forces between
the surfaces of particles have a significant effect on the properties of the soil mass if the particles in
the media belong to the clay fraction. The surface activity depends not only on the specific surface
but also on the chemical and mineralogical composition of the solid particles. Since clay particles
Table 2. 2 Particl e siz e classification b y various system s
Name o f the organizatio n
Massachusetts Institut e of
Technology (MIT )
US Department o f Agriculture (USDA)
American Associatio n of State
Highway an d Transportatio n
Officials (AASHTO )
Unified Soi l Classificatio n System ,
US Bureau o f Reclamation, US Army
Corps of Engineers an d American
Society fo r Testing an d Material s
Particle size (mm)
Gravel San d Sil t Cla y
> 2 2 to 0.06 0.0 6 t o 0.002 <
> 2 2 to 0.05 0.0 5 t o 0.002 <
76.2 t o 2 2 to 0.075 0.07 5 to 0.002 <
76.2 t o 4.75 4.7 5 t o 0.075 Fine s (silt s and clays)
< 0.075
0.002
0.002
0.002

Soil Formatio n and Characterization 1 1
are th e activ e portion s o f a soi l becaus e o f thei r hig h specifi c surfac e an d thei r chemica l
constitution, a discussion on the chemical composition and structure of minerals is essential.
2.6 COMPOSITIO N O F CLAY MINERAL S
The word 'clay' is generally understood to refer to a material composed of a mass of small mineral
particles which, in association wit h certain quantities of water, exhibits the property of plasticity.
According to the clay mineral concept, clay materials are essentially composed of extremely small
crystalline particles o f one o r more member s of a small grou p of minerals tha t are commonly
known a s cla y minerals . Thes e mineral s ar e essentiall y hydrou s aluminu m silicates , wit h
magnesium or iron replacing wholl y or in part for the aluminum, in some minerals . Many clay
materials may contain organic material and water-soluble salts. Organi c materials occur either as
discrete particles of wood, leaf matter, spores, etc., or they may be present a s organic molecule s
adsorbed on the surface of the clay mineral particles. The water-soluble salts that are present in clay
materials must have been entrapped in the clay at the time of accumulation or may have developed
subsequently as a consequence of ground water movement and weathering or alteration processes.
Clays can be divided into three general groups on the basis of their crystalline arrangement
and i t i s observe d tha t roughl y simila r engineerin g properties ar e connecte d wit h al l th e cla y
minerals belonging to the same group. An initial study of the crystal structure of clay minerals leads
to a better understanding of the behavior of clays under different condition s of loading. Table 2.3
gives the groups of minerals and some of the important minerals under each group.
2.7 STRUCTUR E O F CLAY MINERAL S
Clay mineral s ar e essentiall y crystallin e i n natur e thoug h som e cla y mineral s d o contai n
material which is non-crystalline (for example allophane). Two fundamental building blocks
are involved in the formation of clay mineral structures. They are :
1. Tetrahedra l unit.
2. Octahedra l unit.
The tetrahedral unit consists o f four oxygen atoms (or hydroxyls, if needed t o balance
the structure) placed at the apices of a tetrahedron enclosing a silicon atom which combines
together t o form a shell-like structur e with all the tips pointin g in the sam e direction . Th e
oxygen at the bases of all the units lie in a common plane .
Each of the oxygen ions at the base is common to two units. The arrangement is shown in
Fig. 2.2. The oxygen atoms are negatively charged with two negative charges each and the silicon
with four positiv e charges. Eac h of the three oxygen ions at the base shares its charges wit h the
Table 2.3 Cla y mineral s
Name of minera l Structura l formula
I. Kaoli n group
1. Kaolinite Al 4Si4O10(OH)g
2. Halloysite Al 4Si4O6(OH)16
II. Montmorillonit e grou p
Montmorillonite Al 4Si8O20(OH)4nH2O
III. Illit e group
Illite K y(Al4Fe2.Mg4.Mg6)Si8_y
Aly(OH)4020

1 2 Chapter 2
adjacent tetrahedra l unit . The sharin g of charge s leave s thre e negativ e charge s a t th e bas e per
tetrahedral unit and this along with two negative charges at the apex makes a total of 5 negative
charges to balance the 4 positive charges of the silicon ion. The process of sharing the oxygen ions
at the base with neighboring units leaves a net charge of -1 per unit.
The second building block is an octahedral unit with six hydroxyl ions at apices of an octahedral
enclosing an aluminum ion at the center. Iron or magnesium ions may replace aluminum ions in some
units. These octahedral units are bound together in a sheet structure with each hydroxyl ion common to
three octahedral units. This sheet is sometimes called as gibbsitesheet. The Al ion has 3 positive charges
and each hydroxyl ion divides its -1 charg e with two other neighboring units. This sharing of negative
charge with other units leaves a total of 2 negative charges per unit [(1/3) x 6]. The net charge of a unit
with a n aluminu m ion a t th e cente r is +1 . Fig. 2. 3 give s th e structura l arrangements o f the units.
Sometimes, magnesiu m replaces th e aluminu m atoms i n th e octahedra l unit s in thi s case , th e
octahedral sheet is called a brucite sheet.
Formation o f Mineral s
The combination of two sheets of silica and gibbsite in different arrangement s and conditions lead
to the formation of different clay minerals as given in Table 2.3. In the actual formation of the sheet
silicate minerals , the phenomenon of isomorphous substitution frequentl y occurs. Isomorphou s
(meaning same form) substitution consists of the substitution of one kind of atom for another.
Kaoiinite Minera l
This i s th e mos t commo n minera l o f th e kaoli n group . The buildin g blocks o f gibbsit e an d
silica sheets ar e arranged a s shown in Fig. 2.4 to give the structure of the kaolinite layer . The
structure i s compose d o f a singl e tetrahedra l shee t an d a singl e alumin a octahedra l shee t
combined i n unit s s o tha t th e tip s o f th e silic a tetrahedron s an d on e o f th e layer s o f th e
octahedral sheet form a common layer. All the tips of the silica tetrahedrons point in the same
direction and towards the center of the unit made of the silica and octahedral sheets. This gives
rise to strong ionic bonds between the silica and gibbsite sheets. The thickness of the layer is
about 7 A (on e angstro m = 10~ 8
cm) thick . The kaolinit e minera l i s formed b y stackin g th e
layers one above the other with the base of the silica sheet bonding to hydroxyls of the gibbsite
sheet b y hydroge n bonding . Sinc e hydroge n bond s ar e comparativel y strong , th e kaolinit e
(a) Tetrahedral unit (b) Silica sheet
Silicons
Oxygen
]_ Symbolic representation
of a silica sheet
Figure 2.2 Basi c structural unit s in the silico n shee t (Grim , 1959 )

Soil Formatio n and Characterizatio n 13
(a) Octahedral uni t (b) Octahedral shee t
0 Hydroxyl s
I Symboli c representatio n
of a octahedral shee t
Aluminums,
magnesium or iron
Figure 2.3 Basi c structural unit s in octahedral sheet (Grim , 1959 )
crystals consist of many sheet stackings that are difficult t o dislodge. The mineral is therefore,
stable, an d wate r canno t ente r betwee n th e sheet s t o expan d th e uni t cells . Th e latera l
dimensions of kaolinite particles range from 100 0 t o 20,000 A and the thickness varie s fro m
100 to 100 0 A . In the kaolinite mineral there is a very small amount of isomorphous substitution.
Halloysite Minera l
Halloysite minerals are made up of successive layers with the same structural composition as those
composing kaolinite. In this case, however, the successive units are randomly packed and may be
separated by a single molecular layer of water. The dehydration of the interlayers by the removal of
the wate r molecules lead s t o change s in the properties o f the mineral. An importan t structural
feature of halloysite is that the particles appear to take tubular forms as opposed to the platy shape
of kaolinite.
Ionic bond
Hydrogen bon d
Gibbsite sheet
Silica shee t
T
7A
7A
7A
Figure 2.4 Structur e o f kaolinit e laye r

14 Chapter 2
Montmorillonite Minera l
Montmorillonite i s th e mos t commo n minera l o f th e montmorillonit e group . Th e structura l
arrangement o f thi s minera l i s compose d o f tw o silic a tetrahedra l sheet s wit h a centra l alumin a
octahedral sheet . All the tips of the tetrahedra point in the same direction and toward the center of the
unit. The silica and gibbsite sheets are combined in such a way that the tips of the tetrahedrons of each
silica sheet and one of the hydroxyl layers of the octahedral sheet form a common layer . The atom s
common t o both the silica and gibbsite layer become oxyge n instead of hydroxyls. The thickness of
the silica-gibbsite-silica unit is about 10 A(Fig. 2.5). In stacking these combined units one above the
other, oxyge n layer s o f eac h uni t ar e adjacen t t o oxyge n o f th e neighborin g unit s wit h a
consequence tha t there i s a very weak bon d an d an excellent cleavage betwee n them . Wate r ca n
enter between the sheets, causing them to expand significantly and thus the structure can break into
10 A thic k structural units. Soils containin g a considerable amoun t o f montmorillonite mineral s
will exhibit high swelling and shrinkage characteristics. The lateral dimensions of montmorillonite
particles rang e fro m 100 0 t o 500 0 A wit h thicknes s varying from 1 0 to 5 0 A. Bentonit e cla y
belongs t o th e montmorillonit e group. I n montmorillonite , there i s isomorphou s substitutio n of
magnesium and iron for aluminum.
Illite
The basi c structura l uni t o f illit e is simila r t o tha t o f montmorillonit e excep t tha t som e o f th e
silicons are always replaced b y aluminum atoms and the resultant charge deficienc y is balanced by
potassium ions . Th e potassiu m ion s occu r betwee n uni t layers . Th e bond s wit h th e
nonexchangeable K +
ions are weaker than the hydrogen bonds, but stronger tha n the water bond of
montmorillonite. Illite , therefore , doe s no t swel l a s muc h i n th e presenc e o f wate r a s doe s
montmorillonite. Th e latera l dimension s o f illit e clay particle s ar e abou t th e sam e a s thos e o f
montmorillonite, 100 0 t o 500 0 A , bu t th e thicknes s o f illit e particle s i s greate r tha n tha t o f
montmorillonite particles, 50 to 500 A. The arrangement of silica and gibbsite sheets are as shown
in Fig. 2.6 .
2.8 CLA Y PARTICLE-WATE R RELATIONS
The behavior of a soil mass depends upon the behavior of the discrete particles composing th e mass
and th e patter n o f particl e arrangement . I n al l thes e case s wate r play s a n importan t part . Th e
Figure 2. 5 Structur e o f montmorillonit e laye r

Soil Formatio n an d Characterization 15
10A
T I I I I
T
loA
I I I I I I I I I I I I I I I I H T M — Potassium molecules
II I Mil I I I I I I III II I

1 1 1 1 1 1 1 1 1 1 1 1 I I 1 1 1 1 1 V«— Fairly strong bond
Silica sheet
Gibbsite sheet
Figure 2.6 Structur e o f illit e layer
behavior o f th e soi l mas s i s profoundly influence d by th e inter-particle-wate r relationships , th e
ability of the soil particles to adsorb exchangeable cations and the amount of water present.
Adsorbed Wate r j
The cla y particle s carr y a ne t negativ e charg e ^ n thei r surface . Thi s i s th e resul t o f bot h
isomorphous substitution and of a break in the continuity of the structure at its edges. The intensity
of the charge depend s t o a considerable exten t on tljie mineralogical characte r o f the particle. Th e
physical an d chemical manifestation s of the surfac e charge constitut e the surfac e activit y of the
mineral. Minerals ar e said to have high or low surface activity , depending on the intensity of the
surface charge. As pointed out earlier, the surface activity depends no t only on the specific surfac e
but also on the chemical and mineralogical composition of the solid particle. The surface activity of
sand, therefore, will not acquire all the properties of ^ true clay, even if it is ground to a fine powder.
The presenc e o f wate r doe s no t alte r it s properti e
changing it s unit weight. However, th e behavior o l
of coarse r fraction s considerabl y exceptin g
' a saturated soi l mas s consistin g o f fine san d
might chang e unde r dynamic loadings . Thi s aspec t o f the problem i s not considere d here . Thi s
article deals only with clay particle-water relations.
In nature every soil particle is surrounded by ^ater. Since the centers of positive and negative
charges of water molecules d o not coincide, the molecules behave like dipoles. The negative charge
on th e surfac e o f th e soi l particle , therefore , attract s th e positiv e (hydrogen ) en d o f th e wate r
molecules. The wate r molecules ar e arranged i n a definite pattern in the immediate vicinit y of the
boundary between solid and water. More than one layer of water molecules sticks on the surface with
considerable force and this attractive force decreases wit h the increase i n the distance o f the water
molecule from the surface. The electrically attracted water that surrounds the clay particle is known as
the diffused double-layer of water. The water located within the zone of influence is known as the
adsorbed layer as shown in Fig. 2.7. Within the zone of influence the physical properties of the water
are very different fro m those of free or normal water at the same temperature. Near the surface of the
particle the water has the property of a solid. At the middle of the layer it resembles a very viscous
liquid and beyond the zone of influence, the propenles of the water become normal. The adsorbe d
water affects the behavior of clay particles when subjected to external stresses, since it comes between
the particle surfaces. To drive off the adsorbed water , the clay particle mus t be heated to more than
200 °C, whic h woul d indicat e tha t th e bon d betwee n th e wate r molecule s an d th e surfac e i s
considerably greater than that between normal water molecules.

16
Particle surfac e
Chapter 2
Adsorbed
water
Distance
Figure 2. 7 Adsorbe d wate r laye r surrounding a soil particl e
The adsorbed film of water on coarse particles is thin in comparison wit h the diameter o f the
particles. In fine grained soils, however, this layer of adsorbed water is relatively much thicker and
might even exceed th e size of the grain. The forces associate d wit h the adsorbed layer s therefor e
play an important part in determining the physical properties of the very fine-grained soils, but have
little effect o n the coarser soils .
Soils in which the adsorbed film is thick compared to the grain size have properties quite different
from othe r soil s havin g th e sam e grai n size s bu t smalle r adsorbe d films . Th e mos t pronounce d
characteristic o f the forme r is their ability to deform plasticall y without cracking whe n mixed wit h
varying amounts of water. This is due to the grains moving across one another supported by the viscous
interlayers of the films. Such soils are called cohesive soils, for they do not disintegrate with pressure but
can be rolled into threads with ease. Here the cohesion is not due to direct molecular interaction between
soil particles at the points of contact but to the shearing strength of the adsorbed layers that separate the
grains at these points.
Base Exchang e
Electrolytes dissociat e whe n dissolve d i n wate r int o positivel y charge d cation s an d negativel y
charged anions . Acids break up into cations of hydrogen and anions such as Cl or SO4. Salts and
bases split into metallic cations such as Na, K or Mg, and nonmetallic anions. Even water itself is an
electrolyte, because a very small fraction of its molecules always dissociates into hydrogen ions H+
and hydroxyl ions OH". These positively charged H+
ions migrate to the surface of the negatively
charged particle s and form what is known as the adsorbed layer . These H+
ions can be replaced by
other cations such as Na, K or Mg. These cation s enter the adsorbed layer s and constitute what is
termed a s an adsorption complex. The process of replacing cations of one kind by those of another
in an adsorption comple x is known as base exchange. B y base exchange is meant the capacity of

Soil Formation and Characterization 1 7
Table 2. 4 Exchang e capacity o f som e clay mineral s
Mineral group Exchang e capacity (meq per 10 0 g)
Kaolinites 3. 8
Illites 4 0
Montmorillonites 8 0
Table 2.5 Cation s arranged in the orde r of decreasing shear strength of clay
NH/ > H+
> K+
> Fe+++
>A1+++
> Mg+
> Ba++
> Ca++
> Na+
> Li+
colloidal particle s to change the cations adsorbed o n their surface. Thus a hydrogen clay (colloi d
with adsorbed H cations) can be changed to sodium clay (colloid wit h adsorbed N a cations) by a
constant percolation of water containing dissolved Na salts. Such changes can be used to decrease
the permeability of a soil. Not all adsorbed cations are exchangeable. The quantity of exchangeable
cations in a soil is termed exchange capacity.
The base exchange capacity is generally defined in terms of the mass of a cation which may
be held on the surface of 100 gm dry mass of mineral. It is generally more convenient to employ a
definition o f base exchange capacity in milli-equivalents (meq) per 10 0 gm dry soil. One meq is
one milligra m o f hydroge n o r th e portio n o f an y io n whic h wil l combin e wit h o r displac e
1 milligram of hydrogen.
The relative exchange capacity of some of the clay minerals is given in Table 2.4.
If one element, suc h as H, Ca, or Na prevails over the other in the adsorption comple x o f a
clay, the clay i s sometimes give n the name of this element, fo r example H-cla y or Ca-clay. The
thickness and the physical properties of the adsorbed film surrounding a given particle, depend to a
large extent on the character of the adsorption complex. These films are relatively thick in the case
of strongly water-adsorbent cations such as Li+
and Na+
cations but very thin for H+
. The films of
other cations have intermediate values. Soils with adsorbed Li+
and Na+
cations are relatively more
plastic at low water contents and possess smaller shear strength because the particles are separated
by a thicker viscous film. The cations in Table 2.5 are arranged in the order o f decreasing shea r
strength of clay.
Sodium clays in nature are a product either of the deposition of clays in sea water or of their
saturation by saltwater flooding or capillary action. Calcium clays are formed essentially by fres h
water sediments. Hydroge n clay s are a result of prolonged leachin g o f a clay by pur e or acidi c
water, with the resulting removal of all other exchangeable bases.
2.9 SOI L MASS STRUCTURE
The orientation of particles in a mass depends on the size and shape of the grains as well as upon
the mineral s o f whic h th e grain s ar e formed . Th e structur e of soil s tha t i s forme d b y natural
deposition ca n b e altere d b y externa l forces . Figur e 2.8 gives the variou s type s o f structure s of
soil. Fig. 2.8(a) is a single grained structure whic h is formed by the settlement of coarse grained
soils in suspension in water. Fig. 2.8(b ) is a flocculentstructure forme d by th e deposition o f the
fine soi l fractio n i n water . Fig . 2.8(c ) i s a honeycomb structure whic h i s forme d b y th e
disintegration o f a flocculen t structur e unde r a superimpose d load . Th e particle s oriente d i n a
flocculent structur e wil l hav e edge-to-fac e contac t a s show n i n Fig . 2.8(d) wherea s i n a

Chapter 2
(a) Single grain structure (b) Flocculent structure (c) Honeycomb structure
(d) Flocculated typ e structure
(edge to face contact)
(e) Dispersed structure
(face to face contact)
(f) Undisturbed salt water deposit (g ) Undisturbed fresh wate r deposit
Figure 2. 8 Schemati c diagram s o f various type s of structures (Lambe , 1 958a)
honeycomb structure , the particles will have face-to-face contac t as shown i n Fig. 2.8(e). Natural
clay sediment s wil l hav e mor e o r les s flocculate d particl e orientations . Marine clay s generall y
have a more open structur e than fresh water clays. Figs. 2.8(f) an d (g) show th e schematic views
of salt water and fres h water deposits.

CHAPTER 3
SOIL PHASE RELATIONSHIPS, INDEX
PROPERTIES AND CLASSIFICATION
3.1 SOI L PHAS E RELATIONSHIP S
Soil mass i s generally a three phase system . It consists of solid particles, liqui d and gas. For all
practical purposes, the liquid may be considered to be water (although in some cases, the water may
contain some dissolve d salts ) and the gas as air. The phase system may be expressed i n SI units
either i n term s o f mass-volum e o r weight-volum e relationships . Th e inte r relationship s o f th e
different phases are important since they help to define the condition or the physical make-up of the
soil.
Mass-Volume Relationshi p
In SI units, the mass M, i s normally expressed i n kg and the density p i n kg/m3
. Sometimes, th e
mass and densities are also expressed i n g and g/cm3
or Mg and Mg/m3
respectively. The density of
water po a t 4 °C is exactly 1.0 0 g/cm3
(= 1000 kg/m3
= 1 Mg/m3
). Since the variation in density is
relatively small over the range of temperatures encountered in ordinary engineering practice, th e
density of water pw a t other temperature s ma y be taken the same a s that at 4 °C. The volum e is
expressed eithe r in cm3
or m3
.
Weight-Volume Relationshi p
Unit weigh t o r weigh t pe r uni t volum e i s stil l th e commo n measuremen t i n geotechnica l
engineering practice. The density p, may be converted to unit weight, 7by using the relationship
Y=pg (3.la )
The 'standard ' value of g is 9.807 m/s2
(= 9.81 m/s2
for all practical purposes) .
19

20 Chapter 3
Conversion o f Densit y o f Water pw t o Uni t Weight
From Eq. (3.la)
•W ~ ^VV °
Substituting pw = 1000 kg/m3
and g = 9.81 m/s2
, we have
r= 1000^9.81^1=9810^
m3
s 2
/ m 3
s2
1 kg-m
Since I N (newton) = — , w e have,
rrr nr
cm-
I S 1
or 7 , = lx—s — x 9.81 =9.81 kN/m3
In general, the unit weight of a soil mass may be obtained from the equation
y=9.81pkN/m3
(3.If )
where in Eq. (3. If), p is in g/cm3
. For example, if a soil mass has a dry density, pd = 1.7 g/cm3
, the
dry unit weight of the soil is
7^=9.81 x 1.7 = 16.6 8 kN/m3
(3.1g )
3.2 MASS-VOLUM E RELATIONSHIP S
The phase-relationships in terms of mass-volume and weight-volume for a soil mass are shown by a block
diagram in Fig. 3.1. A block of unit sectional area is considered. The volumes of the different constituents
are shown on the right side and the corresponding mass/weights on the right and left sides of the block. The
mass/weight of air may be assumed as zero.
Volumetric Ratio s
There are three volumetric ratios that are very useful i n geotechnical engineering and these can be
determined directly from the phase diagram, Fig. 3.1.
Weight Volume
W
Air
Water
Solids
Mass
Mu
M
Figure 3.1 Bloc k diagram—three phase s of a soil elemen t

Soil Phas e Relationships, Inde x Propertie s and Soil Classificatio n 2 1
(3.2)
1. Th e void ratio, e, is defined as
«=^
S
where, V v = volume of voids, and Vs = volume of the solids .
The void ratio e is always expressed a s a decimal.
2. Th e porosity n is defined as
Vv
v__ - I (CG1 / O O
n — x luu /o {->•->)
where, V -tota l volume of the soil sample.
The porosity n is always expressed a s a percentage.
3. Th e degree of saturation S is defined as
5 =
^LX100% (34 )
v
where, V w = volume of water
It is always expressed a s a percentage.When S = 0%, the soil is completely dry , and when
S = 100%, th e soil is fully saturated .
Mass-Volume Relationships
The othe r aspect s o f th e phas e diagra m connecte d wit h mass o r weigh t ca n b e explaine d with
reference to Fig. 3.1.
Water Content , w
The water content, w, of a soil mass is defined as the ratio of the mass of water, Mw, in the voids to
the mass of solids, Ms, as
M
The water content, which is usually expressed as a percentage, can range from zero (dry soil) to
several hundred percent. The natural water content for most soils is well under 100%, but for the soils of
volcanic origin (for example bentonite) it can range up to 500% or more.
Density
Another ver y usefu l concep t i n geotechnical engineerin g i s density (or , uni t weight ) whic h i s
expressed a s mas s pe r uni t volume. Ther e ar e several commonl y use d densities . Thes e ma y be
defined as the total (or bulk), or moist density, pr; the dry density, pd; the saturated density, psat; the
density of the particles, solid density, ps; and density of water pw. Each of these densities is defined
as follows with respect t o Fig. 3.1.
M
Total density, p t = — (3.6 )

22 Chapte r 3
s
Dry density, p d = -y
- (3.7 )
M
Saturated density, /? sat = — (3.8 )
forS= 100 %
M?
Density of solids, p s = — -
(3.9 )
Mw
Density of water, P w
=
~77L
(3.10 )
w
Specific Gravit y
The specific gravity of a substance is defined as the ratio of its mass in air to the mass of an equal
volume of water at reference temperature, 4 °C. The specific gravity of a mass of soil (including air,
water and solids) is termed as bulk specific gravity Gm. It is expressed a s
r -?< - M
™
The specific gravity of solids, Gs, (excluding air and water) is expressed b y
_ P, _ M
, (3J2)
Interrelationships o f Differen t Parameter s
We can establish relationships between the different parameters defined by equations from (3.2) through
(3.12). In order to develop the relationships, the block diagram Fig. 3.2 is made use of. Since the sectional
area perpendicular to the plane of the paper is assumed as unity, the heights of the blocks will represent
the volumes. The volum e of solids may be represented as V s = 1 . When the soil is fully saturated , the
voids are completely filled with water.
Relationship Betwee n e an d n (Fig . 3.2 )
1-n
l + e
(3.13)
Relationship Betwee n e, G s and S
Case 1: When partially saturated (S < 100%)
p

Soil Phas e Relationships , Inde x Propertie s an d Soil Classificatio n 23
wG wG
Therefore, 5 = - o r e=- (3.14a)
Case 2: When saturated (S = 100%)
From Eq. (3.14a), we have (for 5=1)
e = wG. (3.14b)
Relationships Betwee n Densit y p an d Other Parameter s
The density of soil can be expressed in terms of other parameters for cases of soil (1) partially
saturated (5 < 100%); (2) fully saturate d (S = 100%); (3) Fully dry (S = 0); and (4) submerged.
Case 1 : For S < 100%
=
Pt
~
V l + el + e
From Eq. (3.1 4a) w = eS/Gs; substitutin g for w in Eq. (3.15), we have
p
'=
1 «
Case 2: For S=100%
From Eq. (3.16)
Case 3: For S = 0%
FromEq. (3.16)
l + e
(3.15)
(3.16)
(3.17)
(3.18)
Weight
W
Air
Water
Volume
Solids
I
V
V=e
-V= l+e
Mass
M
Figure 3.2 Bloc k diagram—three phases of a soil elemen t

24 Chapte r 3
Case 4: When the soil is submerged
If the soil is submerged, th e density of the submerged soi l pb, is equal to the density of the
saturated soil reduced b y the density of water, that is
p (G + e)p
EsJ
-- £s
Relative Densit y
The looseness or denseness of sandy soil s can be expressed numericall y b y relative density D r,
defined by the equation
D
r= e
e
maX
~l * 10Q
(3.20 )
max mi n
in which
emax= voi d ratio of sand in its loosest state having a dry density of p dm
e
mm =VO
^ ra
ti° m
its
densest stat e having a dry density of pdM
e
= voi d ratio under in-situ condition having a dry density of p d
From Eq. (3.18), a general equation for e may be written as
Pd
Now substituting the corresponding dry densities for emax, em-m and e in Eq. (3.20) and simplifying,
we have
n _ PdM v Pd ~Pdmi m
U — A A 1 JJ/" 5 O 1
r
o o - o U-^ 1
)
rd VdM ^dm
The loosest state for a granular material can usually be created by allowing the dry material to
fall into a container from a funnel hel d in such a way that the free fall is about one centimeter. The
densest state can be established by a combination of static pressure and vibration of soil packed in
a container.
ASTM Test Designation D-2049 (1991) provides a procedure fo r determining the minimum
and maximu m dry uni t weight s (o r densities) o f granular soils. Thi s procedur e ca n b e use d fo r
determining Dr in Eq. (3.21).
3.3 WEIGHT-VOLUM E RELATIONSHIP S
The weight-volume relationships can be established from the earlier equations by substituting yfor
p and W for M. The various equations are tabulated below.
W
1. Wate r content w = -j^L
xlOO (3.5 a)
s
W
2. Tota l unit weight ^ =
17 (3.6a )
Ws
3. Dr y unit weight y d
= —j- (3.7a )

Soil Phas e Relationships , Inde x Propertie s and Soil Classification 2 5
W
4. Saturate d unit weight y sal = —(3.8a )
W
s
5. Uni t weight of solids y f
s
=
~y~ (3.9a )
w
6. Uni t weight of water YW =
~V~~ (3.10a )
w
W
1. Mas s specific gravity G = -
(3. 1 la)
' w
W
si _ S
8. Specifi c gravity of solids s
~Vv (3.12a )
s'w
G Y ( 1 +w)
9. Tota l unit weight for 5< 10
0 y =-£^z -
(3.15a )
or 1 +e
Y (G +e)
10. Saturate d unit weight Y^
= — —- -
(3.17a )
1 +e
Y G
11. Dr y uni t weight y d = -!K
—*- (3 . 18a)
1 + e
Y ( G -1 )
12. Submerge d unit weight Yh
= — —- -
(3.19a )
l + e
n _ Y dM „ Yd ~ Y dm
13. Relativ e density r
~T~ v T ^ (3.21a )
'd idM f dm
3.4 COMMENT S O N SOIL PHAS E RELATIONSHIP S
The void ratios of natural sand deposits depend upon the shape of the grains, the uniformity of
grain size, and the conditions of sedimentation. The void ratios of clay soils range from less than
unity to 5 or more. The soils with higher void ratios have a loose structure and generally belong
to the montmorillonite group. The specific gravity of solid particles of most soils varies from 2.5
to 2.9. For most of the calculations, G ca n be assumed as 2.65 for cohesionless soils and 2.70 for
5
clay soils. The dr y unit weights (yd) o f granular soils range from 1 4 to 1 8 kN/m3
, whereas, th e
saturated unit weights of fine grained soils can range from 12.5 to 22.7 kN/m 3
. Table 3.1 gives
typical values of porosity, void ratio, water content (when saturated) and unit weights of various
types of soils.

26 Chapter 3
Table 3. 1 Porosity , voi d ratio, water content , and unit weights of typical soils i n
natural stat e
Soil
no.
1
1
2
3
4
5
6
7
8
9
10
Description o f soi l
2
Uniform sand , loos e
Uniform sand , loos e
Mixed-grained sand , loos e
Mixed-grained sand , dens e
Glacial till , mixed grained
Soft glacia l clay
Soft glacia l clay
Soft slightl y organic clay
Soft highl y organic clay
Soft bentonit e
Porosity
n
%
3
46
34
40
30
20
55
37
66
75
84
Void
ratio
e
4
0.85
0.51
0.67
0.43
0.25
1.20
0.60
1.90
3.00
5.20
Water
content
w%
5
32
19
25
16
9
45
22
70
110
194
Unit weight
kN/m3
rd
6
14.0
17.0
15.6
18.2
20.8
11.9
16.7
9.1
6.8
4.2
'sat
7
18.5
20.5
19.5
21.2
22.7
17.3
20.3
15.5
14.0
12.4
Example 3. 1
A sampl e o f we t silt y clay soi l ha s a mas s o f 12 6 kg. Th e followin g data wer e obtaine d fro m
laboratory test s on the sample: Wet density, pt = 2.1 g/cm3
, G = 2.7, water content, w - 15% .
Determine (i ) dry density, pd, (ii ) porosity, (iii) void ratio, and (iv) degree of saturation.
Solution
Mass of sample M = 126 kg.
Volume V =
126
= 0.06 m
2.1 xlO3
Now, M s + Mw = M, o r M y + wMy = M?(l + w) = M
Therefore, M. = -^—= -— = 109.57 kg ; M ,= M
^ l + w 1.1 5H s= 16.43 k g
Volume Mass
Air
Water
Solids-
M,.
M,
M
Figure Ex . 3. 1

Soil Phas e Relationships , Inde x Propertie s an d Soil Classification 2 7
Now, V == = 0.01643 m 3
;
w
p w 100 0
= 0.04058
Gspw 2.7x100 0
= V-V=0.06000 -0.04058 =0.01942 m 3
.
(i) Dr y density, /?.= —* - =
= 1826.2 kg/m 3
j ^ ^ y 0.0 6
(ii) Porosity , n^xlOO~ ft01942xl0
° = 32.37%
V 0.0 6
(iii) Voi d ratio, e = ^-
=Q
-01942
=0.4786
V; 0.0405 8
(i v) Degre e of saturation, S = -*
- x1 00 = °'01 43
x 1 00 = 84.6%
V. 0.0194 2
Example 3. 2
Earth is required to be excavated from borrow pits for building an embankment. The wet unit weight
of undisturbed soil is 1 8 kN/m3
and its water content is 8%. In order to build a 4 m high embankment
with top width 2 m and side slopes 1:1 , estimate the quantity of earth required to be excavated per
meter length of embankment. Th e dry unit weight required in the embankment i s 15 kN/m3
with a
moisture content of 10% . Assume the specific gravity of solids a s 2.67. Also determin e th e void
ratios and the degree o f saturation of the soil in both the undisturbed and remolded states .
Solution
The dry unit weight of soil in the borrow pit is
7, = -£
- =— = 16.7 kN/m 3
d
l + w1.0 8
Volume of embankment per meter length Ve
2
The dry unit weight of soil in the embankment is 15 kN/m3
2m — |
Figure Ex. 3. 2

28 Chapte r 3
Volume of earth required to be excavated V pe r meter
V= 24 x
— = 21.55m3
16.7
Undisturbed state
V = -^- = — x— = 0.64 m 3
; V = 1-0.6 4 = 0.36 m 3
5
Gj w 2.6 7 9.8 1
n^^>
e = —-=0.56, W = 18.0-16. 7 = 1.3 kN
0.64
V
Degree of saturation, S = — —x 100 , wher e
V
= 0.133 m3
9.8i
Now, £ = -9^x100 =36.9%
0.36
Remolded state
V = -^ - = -
- -
=0.57 m3
s
Gy w 2.67x9.8 1
yv= 1-0.57 = 0.43 m 3
0.43
e = = 0.75; 7 , = yd (1 +w) = 15 x 1.1 = 16.5 kN/m 3
0.57
Therefore, W = 16.5-15. 0 = 1.5 kN
Vw = —= 0.153 m3
w
9.8 1
0.43
Example 3. 3
The moistur e conten t of a n undisturbed sample o f clay belonging t o a volcanic region i s 265%
under 100 % saturation. The specifi c gravity of the solids is 2.5. The dr y unit weight is 21 Ib/ft 3
.
Determine (i ) the saturated unit weight, (ii) the submerged unit weight, and (iii) void ratio.
Solution
(i) Saturated unit weight, ysat = y
W=W + W = w W + W = W ( l + w)
w s a s s ^ '
W W
From Fig. Ex. 3.3, Yt= — = —=W. Henc e

Soil Phas e Relationships, Inde x Propertie s and Soil Classificatio n 29
V = l
Water
W=Y,
Figure Ex. 3. 3
Yt = 21(1 +2.65) = 21 x3.65 = 76.65 lb/ft 3
(ii) Submerged unit weight, yb
Yb = ^sat -Yw = 76.65 - 62.4 = 14.25 lb/ft 3
(iii) Void ratio, e
V = -^
- =
= 0.135 ft 3
5
G trw 2.5x62. 4
Since 5 =100%
v =v = W X s
= 2.65x— =0.89 ft 3
Y
• V
K 0.8 9
62.4
V 0.13 5
= 6.59
Example 3. 4
A sample of saturated clay from a consolidometer test has a total weight of 3.36 Ib and a dry weight
of 2.3 2 Ib: the specific gravity of the solid particles i s 2.7. For this sample, determin e the water
content, void ratio, porosity and total unit weight.
Solution
W 336-23 2
w = —a-x100% =
= 44.9% = 45%
W. 2.3 2
0.45 x 2.7
e —
n =
1
1.215
= 1.215
= 0.548 o r 54.8 %
l + e 1 + 1.215
Yw(Gs+e) 62.4(2. 7 + 1.215)
l + e 1 +1.215
= 110.3 lb/ft 3

30 Chapte r 3
Example 3. 5
A sample of silty clay has a volume of 14.88cm3
, a total mass of 28.81 g, a dry mass of 24.83 g, and
a specific gravity of solids 2.7. Determine the void ratio and the degree o f saturation.
Solution
Void rati o
Ms 24.8 3 „ „ ,
y _ -
5_
_ -
= 9
2 cm 3
J
G spw 2.7(1 )
V = V- V = 14.88-9.2 = 5.68 cm3
V5 9. 2
Degree of saturation
Mw 28.81-24.8 3
w =— — = -
=0.16
M 24.8 3
0.618
= 0 - 7 0 o r 7 0 %
Example 3. 6
A soil sample in its natural state has a weight of 5.05 Ib and a volume of 0.041 ft3
. In an oven-dried
state, the dry weight of the sample is 4.49 Ib. The specific gravity of the solids is 2.68. Determine
the total unit weight, water content, void ratio, porosity, and degree o f saturation.
Solution
V 0.04 1
5 05 - 4 49
3
-U3
** y
W 4.4 9
or 12.5 %
V W 44 9
= ^,V= -
"—=
= 0.026 8 ft 3
Vs
G 2.6 8 x 62.4
V = V-V= 0.041-0.0268 =0.0142 ft 3
0.0268
r £^'~)
n=— = — :
-
-0.3464 o r 34.64%
+e 1 + 0.53
0125X168
0.53

Soil Phas e Relationships, Inde x Propertie s an d Soil Classificatio n 3 1
Example 3. 7
A soil sample has a total unit weight of 16.97 kN/m3
and a void ratio of 0.84. The specific gravity
of solids is 2.70. Determine the moisture content, dry unit weight and degree o f saturation of the
sample.
Solution
Degree of saturation [from Eq . (3.16a)]
= o r 1=
=
' l + e1 + 0.84
Dry unit weight (Eq. 3.18a)
d
l + e1 + 0.84
Water content (Eq. 3.14a1
Se 0.58x0.8 4 n i o
w- —= -
= 0.18 or 18 %
G 2. 7
Example 3. 8
A soil sample in its natural state has, when fully saturated, a water content of 32.5%. Determine the
void ratio, dry and total unit weights. Calculate the total weight of water required to saturate a soil
mass of volume 10 m3
. Assume G^ = 2.69.
Solution
Void ratio (Eq. 3.14a)
= ^
= 32.5 x2.69
S (l)xlO O
Total unit weight (Eq. 3.15a)
= . ) =
2*9 (9-81)0 +0323) = ,
' l + e1 + 0.874
Dry unit weight (Eq. 3.18a)
L&___ 2.69x9.8 1 = 14Q8kN/m3
d
l + e1 + 0.874
FromEq. (3.6a), W=ytV= 18.6 6 x10= 186.6 kN
From Eq . (3.7a), Ws = ydV= 14.0 8 x1 0 =140.8 kN
Weight of water =W-WS= 186. 6 - 140. 8 =45.8 kN
3.5 INDE X PROPERTIE S OF SOILS
The various properties of soils which would be considered as index properties are:
1 .Th e size and shape of particles.
2. Th e relative density or consistency of soil.

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