Lime Stabilization on Expansive Soils for Pavements

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LIME STABILIZATION ON EXPANSIVE SOILS FOR PAVEMENTS

A THESIS

submitted in partial fulfillment of the requirements

for the award of the degree of

MASTER OF TECHNOLOGY

in

CIVIL ENGINEERING

CONSTRUCTION TECHNOLOGY AND MANAGEMENT

by

VIGNESWARAN R

(CE08M174)

BUILDING TECHNOLOGY AND CONSTRUCTION MANAGEMENT DIVISION

DEPARTMENT OF CIVIL ENGINEERING

INDIAN INSTITUTE OF TECHNOLOGY, MADRAS.

MAY 2010


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CERTIFICATE

This is to certify that the thesis entitled LIME STABILIZATION ON EXPANSIVE

SOILS FOR PAVEMENTSsubmitted by VIGNESWARAN R, CE08M174, to Indian

Institute of Technology, Madras, in partial fulfillment of the requirements for the award

of the degree of Master of Technology in CONSTRUCTION TECHNOLOGY AND

MANAGEMENT, is a bonafide record of work carried out by his under our supervision.

The content of this thesis, in full or in parts, have not been submitted to any other institute

or University for the award of any degree or diploma.

Chennai600 036

Date: 03-05-2010

Dr. R. G. Robinson

Associate Professor and Guide

Geotech division

Department of Civil Engineering

IIT Madras

Dr. T. Thyagaraj

Assistant Professor and Co-guide

Geotech division


IIT Madras

Dr.K.Rajagopal

Professor & Head


IIT Madras


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ACKNOWLEDGEMENT

I wish to express my sincere thanks to my guides Dr. R. G. Robinson and Dr. T.

Thyagarajfor sparing their valuable time and guidance that has rendered throughout the

course of my project work. The knowledge and the values that I have learnt from them

would continue to guide me through the course of my entire lifetime. I also thank them for

giving me a lot of freedom during the course of project work that has led to improve my

creativity and self confidence.

I am also highly grateful to Prof. Koshy Varghese, Coordinator, UOP Program,

Department of Civil Engineering not only for providing necessary support for my project

work but also for providing guidance, direction and valuable feedback regarding my

performance. He has been a constant source of motivation for completing the project on

time.

I feel highly indebted to my L&T ECC guide Mr. S. N Rajan, (Manager, R&D) for

providing necessary support for my project work.

I would also like to thank Ms. Bhuvaneshwari, Research scholar, Geotechnical

Engineering Division, her invaluable suggestions, encouragement and support throughout

the project duration which helped me to complete my project in time. I am also very

grateful to my friends and lab colleagues in geotechnical department for their advice and

support. I also thank the lab staffs for their assistant and needful help during experiments.

I also take this opportunity to thank all my friends in CTAM XI batchand Tamiraparani

Hostelfor making my stay in IIT Madras a memorable one.

I would also like to express my sincere thanks and gratitude to the Management of Larsen

& Toubro Limited ECC Division for providing me the opportunity to undergo the


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course Construction Technology and Management at Indian Institute of Technology

Madras.

I also thank my parents for having tremendous faith in me and for being highly

supportive and encouraging.

Last but not the least, I express my humble gratitude to the Almighty for His constant

presence at every juncture of my life till date.

R.Vigneswaran

April 27, 2010


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ABSTRACT

KEYWORDS:Expansive soil, Lime Stabilization, Pavements, Resilient Modulus (MR),

Unconfined Compressive Strength (UCC), Cost Economics, Kenlayer.

Expansive soils are widespread all over the world. They are highly problematic due to

their swell-shrink behaviour caused by the seasonal fluctuation in moisture content. They

cause severe distress to lightly loaded structures founded on them, such as the single-

storey dwellings, pavements, canal linings and railway tracks. The volume change

problems posed by these soils can be mitigated by adopting numerous stabilization

techniques. Chemical alteration, specifically lime stabilization is the most viable choice

adopted globally for treating expansive soils. Lime addition renders the soil non plastic

and gradually imparts strength and stiffness to the soil due to immediate flocculation

reactions and long term pozzolonic reactions.

This study mainly focuses on the suitability of the lime treated soil for pavement subgrade

stabilization. Four problematic soils were selected for this study, from the places Siruseri,

Karaikudi, Paramakudi and Tuticorin situated in southern part of the TamilNadu state. The

basic tests carried out to characterize these soils revealed high expansivity. Eades and

Grim test was used to find the optimum lime content required for stabilization. The lime

treated soils were tested for three moisture content levels-dry, wet and optimum states for

different curing periods -3, 14 and 28 days. UCC, CBR, Suction tests and resilient

modulus test based on the AASHTO T-307 protocol were carried out. Main focus was

made to study the resilient behavior of the treated soil under cyclic loading conditions

which simulates the traffic loading in the real pavements.


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The permanent strains sufficiently reduced and resilient modulus radically increased for

the treated soils. Model studies to simulate the stress dependent behavior of the resilient

modulus values and correlation between the UCC, suction and resilient modulus were also

attempted.

With increase in the subgrade strength due to lime stabilization the thickness of the upper

layer in the flexible pavements can be reduced considerably. Further lime stabilization also

increases the pavement life to a much greater extent. KENLAYER is used for the analysis

purpose. Cost economics was done for different methods such as ordinary design, buffer

layer, blanket course and increased thickness usually carried out for expansive soils. Of

all these methods lime stabilization incurred minimum cost thereby saving 40% of the

cost.


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TABLE OF CONTENTS

Title Page

Certificate ii

Acknowledgement iii

Abstract v

Table of Contents vii

List of Tables xii

List of Figures xiii

Abbreviations xv

1. INTRODUCTION

1.1. Historical Background..... 1

1.2. Overview. ... 3

1.3. Objective of the Study.... 4

1.4. Scope of the Project.... 4

1.5 Methodology ... 4

1.5. Thesis Organization........ 6

2. LITERATURE REVIEW

2.1. Introduction.... 7

2.2. Expansive Soils...... 7

2.3. Identification of Expansive soils.... 8

2.2.1. Surface Examination..... 8

2.2.2. Subsurface Examination........ 8

2.4. Classification of Expansive Soils... 9

2.5. Solutions for the Problems in Expansive Soil........ 10

2.5.1. Removal and Replacement........ 11


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2.5.2. Remoulding and Compaction........... 11

2.2.3. Surcharge Loading........ 11

2.5.4. Prewetting...... 11

2.5.5. Sand Cushion..... 12

2.5.6Cohesive Non-Swelling Soil Cushion..... 12

2.5.7. Moisture Control....... 12

2.5.8. Chemical Admixture..... 13

2.5.9. Under Reamed Piles...... 13

2.5.10 Granular Piles...... 13

2.6. Lime Stabilization.. 13

2.6.1. Stabilization Mechanism....... 14

2.7. Resilient Modulus...... 15

2.7.1. Permanent Strain.. 16

2.7.2. Resilient Modulus of Lime Treated Soil.. 17

2.7.1. Regression Models.... 17

2.8. Suction... 20

2.8.1. Matric Suction....... 21

2.8.2. Osmotic Suction.... 21

2.8.3. Dewpoint Potentiameter.... 22

2.9. Review of Literature... 23

3. SOIL PROPERTIES AND EXPERIMENTAL METHODOLOGY

3.1. Introduction........ 24

3.2. Soil Characteristics .... 24

3.2.1. Micro Scale Factors.. ............. 24

3.2.2. Macro Scale Factors...... 24

3.3. Sampling Location.. 25

3.4. Soil Properties.. ..... 25


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3.4.1. Atterberg Limits... 26

3.4.2. Particle Size Distribution......... 26

3.4.3 Diffrential Free Swell Index.......... 26

3.4.4. X-Ray Diffraction............................................................. 27

3.4.5. Initial Consumption of Lime 27

3.4.6. OMC and Mdd... 28

3.5. Summary of Basic Properties......... 34

3.6. Sample Preperation........ 35

3.6.1. Testing Conditions........ 35

3.5.2 Soaked Sample Preparation .......... 36

3.7. Unconfined Compressive Strength........ 36

3.8. California Bearing Ratio............ 37

3.9 Resilient Modulus 38

3.9.1. Resilient Modulus Equipment...... 38

3.9.2. Test Procedure ...... 40

3.9.3. Sample Preperation ...... 42

3.9.4. Regression Analysis.......... 43

3.8. Total Suction.......... 39

4. TEST RESULTS AND ANALYSIS

4.1. Introduction .... 45

4.2. Unconfined Compressive Strength. 45

4.2.1. Untreated Samples.. 45

4.2.2. Treated Samples.... 46

4.2.3. Karaikudi, Paramakudi and Tuticorin Soil................ 49

4.2.4. Effect of Soaking....... 50

4.3. California Bearing Ratio. .... 51

4.4. Resilient Modulus... 52


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4.4.1. Effect of Confining Pressure..... 53

4.4.2. Effect of curing.. 54

4.4.3. Effect of Moisture Content....... 54

4.4.4. Effect of Soaking .. 55

4.4.5. Effect of Permanent Strain with Curing.... 55

4.4.6. MRfor Karaikudi, Paramakudi and Tuticorin Soils...... 56

4.4.7. Regression Model.......... 57

4.4.8. Comparison of Model Study....... 62

4.5. Total Suction...... 62

4.5.1. Effect of Suction with Curing....... 62

4.5.2. Correlation of Suction with UCC and MR.... 63

4.5.3. Correlation of UCC with MR.... 64

5 COST ECONOMICS AND OPTIMIZATION

5.1. Introduction.... 66

5.2. Pavement on Expansive Soil.. 66

5.2.1. Buffer Layer...... 66

5.2.2. Blanket Course...... 66

5.2.3. Increased Thickness for BC and DBM.. 66

5.2.4. Lime Stabilization..... 66

5.3. Distress Model in Pavement... 67

5.3.1. Vertical Compressive Strain . 67

5.3.2. Critical Tensile Strain... 67

5.4. Distress Model in KENPAVE.... 68

5.4.1. Application of KENPAVE.... 68

5.4.2. Input Parameters in KENPAVE........ 69

5.4.3. Design Parameters..... 69

5.5. Cost Economics.. 72


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5.6. Results.... 74

6 SUMMARY AND CONCLUSION

6.1. Summary . 75

6.2. Conclusion.. 76

7 REFERENCE

7.1. Reference 77

APPENDIX AKENPAVE RESULTS

A1 Lime Stabilization. .... 82

A2 Natural Subgrade .. 85

A3 Natural Subgrade Increased Thickness.. 88


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LIST OF TABLES

Table. No. Title Page

2.1 Degree of Expansiveness and Free Swell 10

3.1 Physical Properties of Soil.. 29

3.2 Sequence of Testing.... 40

4.1 UCC strength for untreated soil... 46

4.2 UCC strength for different moisture content and curing days................... 48

4.3 UCC strength for all soils with % of fines.. 50

4.4 CBR Values. 52

4.5 MRstrength for all soil with % of fines... 57

4.6 Regression coefficients for K- Model...... 57

4.7 Regression coefficients for Power Model... 58

4.8 Regression coefficients for Octahedral Stress Model..... 59

4.9 Regression coefficients for Uzan Model..... 59

4.10 Regression coefficients for Pezo Model...... 60

4.11 MRprediction from Thompson equation. 64

5.1 Subgrade Modulus in Different Period.... 70

5.2 Lime Stabilized Subgrade. ... 73

5.3 Natural Subgrade..... 73

5.4 Buffer Layer. ... 73

5.5 Blanket Course.... 74

5.6 Increased BC and DBM...... 74


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LIST OF FIGURES

Fig. No. Title Page

1.1 Expansive soil problems in pavements 2

2.1 Chart for potential expansiveness of soil . 9

2.2 Plasticity Vs clay content.. 10

2.3 Solubility of SiO2and Al2O3with pH.. 15

2.4 Dewpoint potentiameter 23

3.1 Soil source 25

3.2 Eades and Grim pH test.... 28

3.3 Mini compaction mould 28

3.4 Xrd for Siruseri treated and untreated samples 30

3.5 Xrd for Karaikudi, Paramakudi and Tuticorin samples 31

3.6 Lime fixation point for all soil samples... 32

3.7 OMC and Mdd curves of all soil samples 33

3.8 Different testing condition for Siruseri soil.. 35

3.9 Soaked sample preparation... 36

3.10 UCC samplepreparation... 37

3.11 CBR testing... 37

3.12 Loading setup 39

3.13 Experimental set up.. 39

3.14 Haversine loading form 41

3.14 Load pulse in computer 41

3.15 Resilient modulus setting. 42


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3.16 Samplepreparation... 42

3.17 Samples covered with cling film.. 43

3.18 Dewpoint potentiameter suction measurement..... 43

4.1 UCC test results for untreated Siruseri soil ..... 45

4.2 UCC test results for treated soil at different curing period at optimummoisture content

46

4.3 UCC test results for treated soil at different curing period at dry sidemoisture content

47

4.4 UCC test results for treated soil at different curing period at wet sidemoisture content 47

4.5 UCC strength for Siruseri soil with curing days at different

moisture content .....48

4.6 UCC test results for treated and untreated Karaikudi soil sample...... 49

4.7 UCC test results for treated and untreated Paramakudi soil sample... 49

4.8 UCC test results for treated and untreated Tuticorin soil sample... 50

4.9 UCC for all soils with curing... 51

4.10 CBR versus penetration curve for untreated soil 51

4.11 CBR versus penetration curve for treated soil 52

4.12 MRfor untreated Siruseri sample.. 53

4.13 MRfor 28 days treated Siruseri samples...... 53

4.14 Effect of MRwith curing... 54

4.15 Effect of curing with MRfor different placement condition.. 54

4.16 Effect of MRwith soaking.... 55

4.17 Effect of permanent strain with curing. 56

4.18 Mr for all soil samples.. 56

4.19 Octahedral model.. 61


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4.20 Uzan model... 61

4.21 Pezo model 61

4.22 Power model. 61

4.23 K-theta model... 62

4.24 Total suction with curing.. 63

4.25 UCC Vs total suction 63

4.26 MRVs total suction...... 63

4.27 Actual MRversus predicted MR.... 65

5.1 Pavement composition.. 67

5.2 Pavement failure... 68

5.3 Kenpave software package... 69

5.4 Cross section used in analysis... 70

5.5 General information of layers... 70

5.6 Layer thickness and Poissonsratio. 71

5.7 Layer modulus for each period. 71

5.8 Damage analysis... 71

5.9 Damage analysis graph. 72


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ABBREVIATIONS

OMC Optimal Moisture Content

Mdd Maximum Dry Density

XRD X-Ray Diffraction

MR Resilient Modulus

UCC UnConfined Compressive Strength

CBR California Bearing Ratio

BC Bituminous Macadam

DBM Dense Bituminous Macadam


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CHAPTER 1

INTRODUCTION

1.1 HISTORICAL BACKGROUND

Soil is one of the natures most abundant construction material. Almost all constructions are built

with or upon soil. When unsuitable construction condition are encountered, a constructor has

four options:

1. Find a new construction site2. Redesign the structure so it can be constructed on the poor soil3.

Remove the poor soil and replace it with good soil

4. Improve the engineering properties of the in-situ soilIn general, options 1 and 2 tend to be impractical today, while in the past, option 3 has been the

most commonly used method. However, due to improvement in technology coupled with

increased transportation costs, option 4 is being used more often today and is expected to

dramatically increase in future.

Expansive soils are soils that swell enough to cause pavement problems and generally fall into

the AASHTO A-6 or A-7 group. Expansive soils swell on absorption of water during wet season

and shrink during dry season. Expansive soils can expand to as much as 10 times its original

size, thus causing severe damage. If the moisture content and or soil type differs at various

locations under the foundation, localized or non-uniform movement may occur in the structure.

This isolated movement of sections can cause damage to the foundation and pavement. Due to

their expansive potential to provide non-uniform support at the base of a pavement structure,

expansive soils must be properly addressed during the design and construction phase, to support

the pavement and traffic loads. Fig. 1.1 shows the failure of pavement in expansive soils.


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Fig. 1.1 Expansive Soil Problems in Pavements

(Ref. Texas Department of Transportation)Improving an on-site soils engineeringproperties is referred to as either Soil modification or

Soil stabilization. The term stabilization means that the engineering properties of the soil have

been changed enough to allow field construction to take place.

There are two primary methods of soil stabilization used today:

1. Mechanical stabilization and2. Chemical or additive stabilization

Nearly every road construction project will utilize one or both of these stabilization techniques.

The most common form of mechanical soil stabilization is compaction of the soil, while the

addition of cement, lime, bituminous or other agents is referred to as a chemical method of soil

stabilization. There are two types of additives used during chemical soil stabilization: mechanical

additives and chemical additives.

Mechanical additives, such as soil, cement mechanically alter the soil by adding a quantity of a

material that has engineering characteristics to upgrade the load-bearing capacity of the existing

soil.

Chemical additives, such as lime chemically alter the soil itself, thereby improving the load-

bearing capacity of the soil. There are the two primary mechanisms by which chemicals alter the

soil into a stable subgrade:


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1. General increase in particle size by cementation, reduction in plasticity index,hydraulic conductivity, and shrink/swell potential.

2. Absorption and chemical binding of moisture that will facilitate compaction.Essentially soil stabilization allows engineers to distribute a larger load with less material over a

longer life cycle. Soil stabilization is used in roads, parking lots, airport runways, building sites,

and landfills.

When selecting a stabilizer additive, the following factors must be considered

1. Type of soil to be stabilized,2. Type of soil quality improvement desired,3. Required strength and durability of the stabilized layer and4. Cost and environmental conditions.

1.2 OVERVIEW

The performance of any construction project depends on the soundness of the underlying soils.

Unstable soils can create significant problems for pavements or structures. Expansive soil is fine-

grained clay which occurs naturally and is generally found in areas that historically were a flood

plain or lake area and highly unstable. The swelling and shrinkage potential of expansive soil

vary in proportion to the amount of clay minerals present in the soil.

Large areas of our country are covered with expansive soils such as black cotton soil. These

clays have caused persistent difficulties in road construction. Specific problem associated with

road construction over expansive soils is commonly the seasonal volumetric change rather than

its low bearing strength. Expansive soils shrink and crack when they dry out and swell when they

get wet. The cracks allow water to penetrate deep into the soil, hence causing considerable

expansion. This results in deformation of road surfaces, since the expansion and the subsequent

heave are never uniform. Excessive drying and wetting of the soil will progressively deteriorate

the pavement over the years.

To mitigate expansive soil problems several alternative solutions can be applied and stabilization

is one among them. Soil stabilization significantly changes the characteristics of a soil to produce


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long-term permanent strength and stability. There are various types of soil stabilization and lime

is one among them. Lime is extensively used to stabilize expansive soils.

Resilient modulus is a dynamic test response defined as the ratio of repeated axial load to the

recoverable deformation. Resilient modulus (MR) has become a well-known parameter to

characterize unbound pavement materials because the elastic (resilient) pavement deflection

possesses a better correlation to field performance than the total pavement deflection. Resilient

modulus is more realistic to characterize moving wheel loads.

Soils are typically considered to be either dry, or a fully saturated mixture of soil and water. But

in real world they exist in the form of partially saturated soil. These soils exert a potential

negative pressure over moisture in its vicinity. This is known as suction, and it is responsible for

drawing water into a soils structure. As suction increases, the possibility of substantial volume

change increases. This can be reduced by addition of lime to soil. However, information about

Resilience modulus and suction properties of lime stabilized soils are scarce in the literature.

1.3 OBJECTIVE OF THE STUDY

The main objective of the project is to study the effect of lime stabilizer on expansive soil

through various tests such as resilient modulus, UCC, CBR and suction characteristics and to

find the suitability of the soil for pavement subgrade stabilization.

1.4 SCOPE OF THE PROJECT

The scope of the project is limited to use of lime as a stabilizing material

1. Identification of different expansive soils through basic properties.2. Resilient Modulus of natural and lime treated stabilized soil.3. Develop an empirical correlation for determining resilient modulus.4. Cost economics of lime stabilized soil.

1.5 METHODOLOGY

The methodology followed in the project is represented in the flowchart shown in Fig. 1.2


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Expansive Soil

Identification of Expansive

soil

Other Soil typesDetailed study

TuticorinParamakudi KaraikudiSiruseri

1. Index Properties (LL, PL, Sl)2. Diffrential Free swell Index3. OMC & MDD for Untreated Soil4. Lime Requirement based on Eades & Grimm pH

Test

5. Treated OMC & MDD6. X-Ray Diffraction Analysis7. Unconfined Compression Strength ( 0, 14 Days)Soaked

& Unsoaked

8. Resilient Modulus (0,14, Days) Soaked & Unsoaked

1. Index Properties2. Diffrential Free swell3. OMC & MDD4. Lime Requirement5. Treated OMC & MDD6. X-Ray Diffraction7. Unconfined Compression Strength

( 0,3,7,14,28 Days)

8. Resilient Modulus (0, 3,14,28Days)

Regression Model & Correlation development

Economics and Cost analysis

Lime Stabilization

METHODOLOGY:


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1.6 THESIS ORGANISATION

The thesis is organized into six chapters. Chapter one gives the brief description of historical

background, outline, and objective of the project, scope and methodology adopted.

Chapter two gives the summary of identification, Classification and problems in expansive soil,

Lime stabilization and stabilization mechanisms, resilient modulus and its various models and

the suction characteristics.

Chapter three provides the soil characteristics in micro and macro scale level, sampling location

and its basic properties. It also presents the sample preparation and laboratory procedure of UCC,

CBR, Resilient Modulus, and total suction.

Chapter four presents the test results and analysis, done with the various tests is explained in the

form of tables and graphs. Also the correlation with the different tests is also stated.

Chapter five deals with the cost economics of natural and lime treated subgrade soil and its

influence on above layers such as sub-base, base and asphalt layer. Cost economics of different

methods such as buffer layer, blanket course, increased thickness and lime stabilized subgrade is

discussed with the help of Kenpave.

Chapter Six provides the summary, findings and conclusion of the project.


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CHAPTER 2

LITERATURE REVIEW

2.1 INTRODUCTION

Expansive soils are present throughout the world. Every year they cause billions of dollars in

damage. Even though expansive soils cause enormous amounts of damage most people have

never heard of them. This is because their damage is done slowly and cannot be attributed to a

specific event. The damage done by expansive soils is then attributed to poor construction

practices or a misconception that all buildings experience this type of damage as they age.

2.2 EXPANSIVE SOILS

Expansive soil is a term used for soils which exhibit moderate to high plasticity, low to moderate

strength, and high swell and shrinkage characteristics (Holtz and Gibbs 1956). They show

evidence of large volume changes under varying moisture conditions from seasonal changes

(Nelson and Miller 1992). Such soils are commonly found in many arid and semi-arid areas of

the world such as Australia, Canada, China, India, Israel, Italy, South Africa, UK, and USA.

Expansive soils cover nearly 20% of the land area in India and include almost the entire Deccan

plateau, Western Madhya Pradesh, parts of Gujarat, Andhra Pradesh, Uttar Pradesh, Karnataka,

and Maharashtra (Ranjan and Rao 1991). In our country the typical example of expansive soils

are black cotton soil, mar and kabar.

Three factors play important role in the heave and swell properties of soils: (i) soil properties

such as compaction, natural moisture content variation, dry density, and plasticity index (ii)

environmental conditions, which include temperature and humidity and (iii) natural overburden

pressure and foundation loading conditions. The degree of saturation in a typical expansive soil

increases in stages from 40% to 100%, when the soil starts to heave due to soaking and wetting

conditions. Hence, it can be inferred that swell magnitudes depend on the natural and compacted

moisture content. Swelling characteristics are associated with the wetting of soil particle surface

area and the void distribution between them.


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2.3 IDENTIFICATION OF EXPANSIVE SOIL

A major concern in geotechnical engineering is identification of expansive soils and estimation

of their swelling magnitudes when subjected to changes in environment (Rao and Satyadas 1987;

Day 1994; Al-Homoud et al. 1995).

The field study is used to determine the presence, extent, and nature of expansive soil and ground

water conditions. The two major phases of field exploration are surface examination and

subsurface exploration. The surface examination is conducted first since the results help to

determine the extent of the subsurface exploration. In situ tests may also be helpful, particularly

if a deep foundation, such as drilled shafts, is to be used.

2.3.1 SURFACE EXAMINATION

A study of the site history may reveal considerable qualitative data on the probable future

behaviour of the foundation soils. Maps of the proposed construction site should be examined to

obtain information on wooded areas, ponds and depressions, water-courses, and existence of

earlier buildings. Surface features, such as wooded areas, bushes, and other deep-rooted

vegetation in expansive soil areas, indicate potential heave from accumulation of moisture

following elimination of these sources of evapo-transpiration.

A thorough visual examination of the site by the geotechnical engineer is necessary. The

appearance of cracking in nearby structures should be especially noted. The surface soil at the

site should be examined. Local experience is very helpful in indicating possible design and

construction problems and soil and groundwater conditions at the site.

2.3.2 SUBSURFACE EXAMINATION

Subsurface exploration provides representative samples for visual classification and laboratory

tests. Classification tests are used to determine the lateral and vertical distribution and types offoundation soils. Soil swell, consolidation, and strength tests are needed to evaluate the

load/displacement behaviour and bearing capacity of the foundation in swelling soil.


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2.4 CLASSIFICATION OF EXPANSIVE SOIL

The swell pressure of a soil is the external pressure that needs to be placed over a swelling soil to

prevent volume increase, while the swell potential of an expansive soil is the magnitude of heave

of a soil for a given final moisture content and loading condition. These expansive soil

parameters can be directly estimated in the laboratory from special oedometer tests or indirectly

from the index properties of the soils and the differential free swell test.

Besides direct quantification of swell potentials from the oedometer tests, it is also possible to

indirectly estimate the degree of expansivity of clay soils from their index properties or from the

differential free swell test. The Atterberg limits and swell potentials of clays depend on the

quantity of water that clay can imbibe. The higher the plasticity index, the greater the quantum of

water that can be imbibed by the soil and hence greater would be its swell potential. The colloid

content (


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Fig. 2.2 Plasticity Vs Clay content (Ref. Williams 1957)

Table 2.1 Degree of Expansiveness and Free Swell

(Ref. Seed et.al. 1962)

Degree of Expansiveness DFS (%)

Low 50

2.5 SOLUTIONS FOR THE PROBLEMS IN EXPANSIVE SOILSThe various solutions for the problem in expansive soil suitable for any construction activity is

listed below (Nelson and Miller 1991)

1. Removal and Replacement2. Remoulding and Compaction3. Surcharge loading4. Prewetting5. Sand cushion6. Cohesive non-swelling soil cushion7. Moisture Control8. Chemical AdmixturesLime Stabilization9. Under reamed piles10.Granular pile anchor


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2.5.5 SAND CUSHION

One of the oldest practices used, is the sand cushion technique (Satyanarayana 1969). In this

technique, either the entire depth of the expansive soil stratum or a part of it may be removed and

replaced with a sand cushion compacted to a low density. The cushion is placed directly beneath

the footing. The principle of sand cushion is that while the expansive clay bed swells due to the

percolation of water during monsoon, the sand cushion settles. During summer, as the expansive

soil shrinks, the sand undergoes bulking due to partial saturation. As a result, there will be

minimum volume change in the soil system beneath the footing. It is difficult to arrive at the

exact thickness and the density of the sand cushion. Foundation engineers often suggest some

arbitrary thickness without considering the depth of the active zone, which is the zone within

which potential volume changes occur. If the thickness is inadequate, the problem aggravates as

the high permeability of sand facilitates easy ingress of moisture from the surface run-off and the

swelling process accelerates. This is the main drawback of the sand cushion.

2.5.6 COHESIVE NON-SWELLING SOIL CUSHION

From large-scale laboratory studies and field investigations (Katti 1979) it was found that, in an

expansive soil stratum, development of cohesive bonds takes place upon saturation which helps

to inhibit heave in the soil below a depth of 1.0 m to 1.2 m. However, the soil in the top 1.0 m to

1.2 m does swell. It was felt that if an environment similar to the one which exists over this

thickness is produced and the soil is not allowed to swell, it should be possible to arrest heave in

the expansive soil. By replacing the soil in the top 1.0 1.2 m with a cohesive non-swelling soil

(CNS), this kind of environment can be produced. The specifications for CNS material,

placement conditions and thickness requirements have been standardized by the Bureau of Indian

Standards. However, later studies (Rao 2000) revealed that the swell-shrink behaviour of a CNS

cushioned expansive clay is effective only in the first cycle and that it becomes less effective

during subsequent cycles.

2.5.7 MOISTURE CONTROL

Soil expansion problems are primarily the result of fluctuations in water content. Non uniform

heave will result from either non uniform water content changes, non-uniform soil conditions, or


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both. If fluctuations in water content over time can be minimized and if the water content in the

subsoil can be made uniform, a major part of the expansion problem can be mitigated.

2.5.8 CHEMICAL ADMIXTURES

Soil stabilization has been long recognized as the art of improving the behaviour of foundation

materials through careful selection of moisture control and compaction. Various organic and

inorganic fractions of different soil types undergo modification when a catalyst agent is

introduced into the soil. In turn, the chemical reaction converts inferior and formerly

unsuitable materials to highly satisfactory roadbed materials.

2.5.9 UNDER REAMED PILES

Under-reamed piles are piles which are provided with enlarged bulbs near the bottom. The bulbs

provide larger resistance to the pile both in compression and uplift. These are very popular in

India. However, when the piles are to be anchored in sand underlying the expansive clay bed,

this is not useful because formation of bulb in sandy soils is difficult as sands cannot take

negative slope.

2.5.10 GRANULAR PILE ANCHOR

Based on the investigations carried out on large-scale laboratory models (Srirama et al. 2007), it

was found that heave of expansive clay beds can be reduced significantly by reinforcing them

with granular pile-anchors, which are granular columns with an anchor rod placed centrally in it

connecting the foundation at the top and an anchor plate at the bottom. The frictional resistance

at the interface between the granular pile and the soil is instrumental in inhibiting the upward

movement of the soil (heave) up to some distance around the granular pile.

2.6 LIME STABILIZATION

Stabilization as applied to highway construction can be defined as a means of permanently

consolidating soils and base materials by markedly increasing their strength and bearing capacity

and decreasing their water sensitivity and volume change during wet/dry cycles. To achieve

stability an additive can be incorporated with the soil. This additive is particularly effective with


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clay-bearing soils and aggregates, with which it reacts both chemically and physically to yield

quality road building materials.

2.6.1 STABILIZATION MECHANISM

Laboratory testing indicates that lime reacts with medium, moderately fine, and fine-grained

soils to produce decreased plasticity, increased workability, and increased strength (Little 1995).

Strength gain is primarily due to the chemical reactions that occur between the lime and soil

particles. These chemical reactions occur in two phases, with both immediate and long-term

benefits.

The first phase of the chemical reaction involves immediate changes in soil texture and soil

properties caused by cation exchange. The free calcium of the lime exchanges with the adsorbed

cations of the clay mineral, resulting in reduction in size of the diffused water layer surrounding

the clay particles. This reduction in the diffused water layer allows the clay particles to come into

closer contact with one another, causing flocculation/agglomeration of the clay particles, which

transforms the clay into a more silt-like or sand-like material. Overall, the flocculation and

agglomeration phase of lime stabilization results in a soil that is more readily mixable, workable,

and, ultimately, compactable. According to Eades and Grim 1960 practically all 4 fine-grained

soils undergo this rapid cation exchange and flocculation/agglomeration reactions when treated

with lime in the presence of water.

The second phase of the chemical reaction involves pozzolanic reactions within the lime-soil

mixture, resulting in strength gain over time. When lime is mixed with clay soil, the pH of the

pore water increases. When the pH reaches 12.4, the silica and alumina from the clay become

soluble and are released from the clay mineral. In turn, the released silica and alumina react with

the calcium from the lime to form cement, which strengthens in a gradual process that continues

for several years (Eades and Grim 1960). As long as there is sufficient calcium from the lime to

combine with the soluble silica and alumina, the pozzolanic reaction will continue as long as the

pH remains high enough to maintain the solubility of the silica and alumina (Little 1995).

Strength gain also largely depends on the amount of silica and alumina available from the clay


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itself thus it has been found that lime stabilization is more effective for montmorillonitic soils

than for kaolinitic soils (Lees et. al.1982).

Fig. 2.3 Solubility of SiO2and Al2O3with pH

(Ref. Berger 2005)

In addition to pozzolanic reactions, carbonation can also lead to long-term strength increases for

soils stabilized with lime. Carbonation occurs when lime reacts with carbon dioxide from the

atmosphere to produce a relatively insoluble calcium carbonate. This can be advantageous since

after mixing, the slow process of carbonation and formation of cementitious products can lead tolong-term strength increases (Arman and Munfakh 1970).

2.7 RESILIENT MODULUS

Over many past decades, the California Bearing Ratio (CBR) has been used for the

characterization of subgrade soils. The CBR value is similar to the undrained shear strength of

soil which is independent of confining stress conditions, and is different from the stiffness of

soil.

In a road structure subjected to repeated traffic loadings, subgrade soils play an important role in

supporting the asphalt and base layers and traffic loadings. Due to this important role, the

subgrade should have enough bearing capacity to perform its function appropriately. If the


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subgrade soils respond primarily in an elastic mode, the rutting problem typical in weak

subgrades will not occur.

However, rutting problems are observed in many roads, resulting in expensive rehabilitation

efforts. Therefore, the assumption that subgrade soils are purely elastic is not consistent with

most observation mode in practice. It is more realistic to treat the subgrade soils as elasto-plastic

materials (Kim 2006). In reality, subgrade soils subjected to repeated traffic loadings exhibit

nonlinear resilient and permanent behaviour even at small strains, before reaching their yield

strengths.

MRis a dynamic response of materials defined as the ratio of the repeated axial deviator stress to

the recoverable axial strain. MR could be determined in the laboratory by means of a cyclic

triaxial test at different confining and deviator stresses. The magnitude and sequence of these

stresses are different depending on whether the material is granular or fine-grained soil.

AASHTO T-307 test classifies soil as type I and type II for granular and fine-grained soils,

respectively.

2.7.1 PERMANENT STRAIN

The major function of subgrade soils is to provide support to pavement structures. Under heavy

traffic loads, subgrade soils may deform and contribute to distress in the overlying pavementstructure. In asphalt pavements this distress normally takes the form of cracking and rutting. It

has been well documented that the subgrade soil plays a critical role in the initiation and

propagation of permanent deformation of pavement structures and directly influences pavement

performance (Huang 1993).

Deformation of subgrade soils can be divided into two parts: recoverable elastic deformation that

is a measure of the resilient behaviour and non-recoverable plastic deformation that indicates the

absorbing behaviour. Current pavement design procedures consider soil support characteristics in

terms of its resilient behaviour. These procedures ignore permanent deformation behaviour even

though it may be a very important component in pavement performance.


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The Mr values are stress dependent and strongly rely on the material tested. Fine grained soils

and granular soils differ in their response to the stress conditions. AASHTO test method

recommends the use of bulk stress model for mathematical modelling of granular soil. There are

several other universal models that can be used for both the soils.

The lime treated soil differs from the typical soil types, due to the cementitious reactions

developed during curing which eventually hardens the material, and hence the model

characterising this composite material should be able to incorporate the hardening behaviour as

well. Various models are compared based on their ability to replicate the experimental M rresults.

The resilient modulus of granular soils increases with increasing confining stresses (Witczak and

Uzan 1988). Several relationships have been used to describe the non-linear stress- strain

behaviour of granular materials. AASHTO 294-92I test method uses bulk stress (q) to model MR

as follows:

2

1

K

RM K

(1)

Where, K1, K2are model constants and is the bulk stress (1+ 2+ 3)

Another form of this equation is used by most pavement engineers (Hicks and Monismith 1971;

Shook et al. 1982; Santha 1994) and can be obtained by dividing both bulk stress and resilientmodulus by the atmospheric pressure to make the resulting regression constants dimensionless.

The equation is as follows:

2

1

K

R

atm atm

MK

(2)

Where, atmis atmospheric pressure, in units same as those for MRand is the bulk stress.

The main disadvantage of the bulk stress is that it does not account for shear stresses and shear

strains developed during loading (Louay et al. 1999; Uzan 1985; Witczak and Uzan 1988). This

model does not properly handle volumetric strains of soils (Brown and Pappin 1981). Moreover,

it cannot adequately explain the non-linear behaviour of granular soils (Uzan 1985).


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The most basic model used in conjunction with the MRtesting of fine-grained soils is a power

model:

R dn

M K (3)

Where K, n = model constants

However, the power model cannot represent the bilinear relationship between the resilient

modulus and deviatoric stress. The power model can be extended by dividing it by atmospheric

pressure. The modified equation is given as

2

1

K

dR

atm atm

MK

(4)

Another model using octahedral stress was proposed by Louay et al. (1999). The model can be

used for various soil types without altering model attributes, octahedral normal and shear

stresses. It gives results in octahedral stress environments, which are assumed to represent

realistic stress states occurring in the field (Houston et al. 1992). They stated that octahedral

normal and shear stresses, on which MRproperties depend, provide a better explanation for stress

states of a material in which stresses change during loading. The octahedral model is as follows:

2 3

1

K K

oct oct R

atm atm atm

MK

(5)

Where atmis atmospheric pressure, K1, K2, K3are regression constants

oct= octahedral normal stress 1 3 31 1

2 33 3

d

oct = octahedral shear stress

1 1

2 2

1 3

2 2

3 3 d

d = deviatoric stress

A universal model as proposed in 1985 by Uzan takes the following form after modification by

dividing MRand stresses by the standard atmospheric pressure:

2 3

1

K K

dR

atm atm atm

MK

(6)


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Rafael Pezo (1993) suggested a pavement engineer-oriented model that contains separate terms

for both deviator stress and confining stress. It is a general model that suits both granular and

fine-grained soils. The suggested model was as follows:

32

1 3

KK

R dM K (7)

The model can be modified by dividing MR, dand 3by the standard atmospheric pressure, atm,

which equals 101.3 kPa. In this form of the model the resulting constants will be dimensionless,

especially, K1. The modified model takes the following form:

2 3

3

1

K K

dR

atm atm atm

MK

(8)

2.8 SUCTION

Soils are three phase system consisting of water, air and soil solids. For many situations, soils are

considered to be fully saturated. While this is a convenient model for many purposes, it does not

accurately represent the real condition in the field.

Clays, and other soils in a natural state, commonly display a water table that has dropped belowthe grounds surface. If this soil pore-water was only under the influence of gravity, the soil

above the water table level would be dry. However, physical forces act on the boundary between

soil and water, causing the water to be drawn into and held inside the empty pores in the soil

fabric. The pore-water pressure in the ground above the water table level becomes negative with

respect to atmospheric pressurethis being referred to as suction. De-saturation of a soil can be

caused either by environmental changes, or by physical changes such as compaction.

As suction increases, the possibility of substantial volume change increases. This process can be

retarded by the addition of lime, due to reactions occurring at different scales within the clay

fabric.


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2.8.1 MATRIC SUCTION

At the air-water interface of an unsaturated soil, the pore-air pressure (ua) is greater than the

pore-water pressure (uw). The difference (ua - uw) is referred to as the soil matric suction

(Rahardjo et al. 1995).

Matric suction can be defined as a measure of the energy required to remove a water molecule

from the soil matrix without the water changing state. Matric suction is the result of two

mechanisms, capillarity and adsorption. In terms of the capillarity, the suction is governed by the

size of the soils pores: The smaller the void, the harder it is to remove water from the soil.

Hence, suction will increase as water content decreases, as initially, water is easily removed from

the larger pores.

2.8.2 OSMOTIC SUCTION

Fredlund and Rahardjo (1993) defined osmotic potential as a measure of the additional stress

necessary to remove a water molecule from the water phase, due to the presence of dissolved

salts. An increasing level of dissolved salts in the pore-water will lead to a lower relative

humidity at the air-water interface. The effect of this is to reduce the osmotic potential aiding the

transfer of water molecules. This will seemingly raise the value of suction above that provided

by the soil matrix. The combination of matric suction and osmotic suction is referred to as total

suction.

The resilient modulus of cohesive soils is not a constant stiffness property, but highly dependent

upon factors such as the state of stress, soil structure, and water content (George 2004). The

resilient modulus values changes with respect to parameters such as confining stress, bulk stress,

deviator stress, soil physical properties and moisture content.

The importance of the water content in affecting the resilient modulus of soils has been well

documented by past researchers. For example, Drumm et al. (1997) showed a significant

reduction of resilient modulus of A-4, A-6, and A-7 soils as the moisture content was increased

above the optimum moisture content. Pezo et al. (1992) have observed significant influences


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exerted by the water content on the measured resilient modulus of cohesive soils. The moisture

content of the subgrade soils underneath the pavement is usually varied over time.

According to Uzan (1998), the clayey soils underneath the pavement exhibit an increase in

moisture content to about 2030% higher than the plastic limit of the soil. This occurs during the

first 35 years of pavement service. Similarly, Elfino and Davidson (1989), Thadkamalla and

George (1995), and Uzan (1998) indicated that the moisture content of the subgrade soils would

vary with season until reaching an equilibrium moisture content. The various methods for

measuring suction are

1. Filter paper method2. Pressure plate apparatus3. Tensiometer4. Dewpoint potentiameter

2.8.3 DEWPOINT POTENTIAMETER

WP4 uses the chilled-mirror dewpoint technique to measure the water potential of a sample

(Leong et al. 2003). The sample is equilibrated with the headspace of a sealed chamber that

contains a mirror and a means of detecting condensation on the mirror. At equilibrium, the waterpotential of the air in the chamber is the same as the water potential of the sample. In the WP4,

the mirror temperature is precisely controlled by a thermoelectric cooler. Detection of the exact

point at which condensation first appears on the mirror is observed with a photoelectric cell. A

beam of light is directed onto the mirror and reflected into a photodetector cell. The

photodetector senses the change in reflectance when condensation occurs on the mirror. A

thermocouple attached to the mirror then records the temperature at which condensation occurs.

WP4 then signals the user by flashing a green LED and/or beeping. The final water potential and

temperature of the sample is then displayed (Fig. 2.4).

WP4 uses an internal fan that circulates the air within the sample chamber to reduce time to

equilibrium. Since both dewpoint and sample surface temperatures are simultaneously measured,


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the need for complete thermal equilibrium is eliminated, which reduces measurement times to

less than five minutes.

Fig. 2.4 Dew point potentiameter

2.9 SUMMARY OF LITERATURE

1. Expansive soil causes a lot of problems to pavements and other structures and it can beidentified by simple tests.

2. Expansive soil can be classified as very high, high, moderate and low according to itsdifferential free swell index.

3. Solutions for expansive soil include remoulding, surcharge loading, prewetting, sandcushion, cohesive non-swelling cushion, piles etc. Of these lime stabilization is best

suited for pavements.

4. A pH of 12.4 is required in the sample for the pozzolanic reaction to occur and to gain therequired strength. Lime treatment will result in increase in Wpand decrease in WLand PI.

5. Resilient modulus simulates the site condition and it is extensively used in modernpavement design.

6. The various regression models provide a powerful tools to conduct pavement analysis ina more realistic manner

7. Suction characteristics will be a useful in understanding the stabilization effect onexpansive soils.


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CHAPTER 3

SOIL PROPERTIES AND EXPERIMENTAL METHODOLOGY

3.1 INTRODUCTION

Expansive soils are found in arid and semi-arid regions. Tamilnadu is one of the places in India,

where large areas are covered by expansive soil. For the present study four types of expansive

soils are collected from different regions of Tamilnadu. The sources and the initial properties are

presented in this chapter.

3.2 SOIL CHARACTERISTICS

Soil characteristics may be considered either as microscale or macroscale factors. Microscalefactors include the mineralogical and chemical properties of the soil. Macroscale factors include

the engineering properties of the soil, which in turn are dictated by the microscale factors.

3.2.1 MICROSCALE FACTORS

Microstructure is more important in understanding the soil behaviour. The microstructure of clay

is the complete geological history of that deposit, including both the stress changes and

environmental conditions during deposition. These geological imprints tend to affect the

engineering response of the clay very considerably.

Clay minerals of different types typically exhibit different swelling potentials because of

variations in the electrical field associated with each mineral. The swelling capacity of an entire

soil mass depends on the amount and type of clay minerals in the soil, the arrangement and

specific surface area of the clay particles, and the chemistry of the soil water surrounding those

particles.

3.2.2 MACROSCALE FACTORS

Macrostructure of fine-grained soil has an important influence on soil behaviour in engineering

practice. Macroscale soil properties reflect the microscale nature of the soil. Because they are

more conveniently measured in engineering work than microscale factors, macroscale


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characteristics are primary indicators of swelling behaviour. Commonly determined properties

such as soil plasticity and density can provide a great deal of insight regarding the expansive

potential of soils.

3.3 SAMPLING LOCATION

The soil for testing is collected from four different areas. They are listed below

1. Siruseri in Chennai2. Karaikudi3. Paramakudi4. Tuticorin

These samples are selected because they are fundamentally posing a lot of problems to the

structures and pavements in that area.

Fig. 3.1 Soil Source (Ref. Tamilnadu-online website)

3.4 SOIL PROPERTIES

Lime stabilization is most suitable for use in clayey soil. The basic soil properties of all soils are

tested according to Indian Standards. A brief procedure of the tests is given below.

Siruseri, Chennai

Karaikudi

Paramakudi

Tuticorin


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3.4.1 ATTERBERG LIMITS

The atterberg tests such as Liquid Limit (LL), Plastic Limit (PL) and Shrinkage Limit (SL) are

useful in understanding the basic properties of the soils. These tests are carried according to

Indian Standards code of practice.

The liquid limit of fine-grained soil is the water content at which soil behaves practically like a

liquid. The test is done according to IS: 2720 (Part 5). Casagrandes apparatus is used for this.

The plastic limit of fine-grained soil is the water content of the soil below which it ceases to be

plastic. It begins to crumble when rolled into threads of 3 mm dia. The test is done according to

IS: 2720 (Part 5). The shrinkage limit of fine grained soil is the moisture content of a soil below

which a decrease in moisture content will not cause a decrease in volume, but above which an

increase in moisture will cause an increase in volume.

3.4.2 PARTICLE SIZE DISTRIBUTION

Wet sieve analysis is carried out for the sail by taking 500gram of air dried sample and passing

through a set of sieves. The amount of soil retained in each sieve is weighed separately. A graph

is drawn between the samples retained in each sieve to the cumulative passing.

The samples passed through 75 micron sieve were subjected to hydrometer analysis. In this

approximately 50 grams of dry soil was treated with a dispersing agent for 18 hours. A

hydrometer analysis was then performed to measure the amount of silt and clay size particles.

Grain size distribution curve is drawn for the sample size and percentage passing. Fig. 3.3 shows

the Grain size distribution (GSD) for all the samples.

3.4.3 DIFFERENTIAL FREE SWELL INDEX

The differential free swell index is done according to IS: 2720 (Part XL). Samples passing

through 425 micron sieve are taken and 10 g of oven dried sample is placed into a 100 ml jar.

One jar is filled with water and the other with kerosene. After 48 hours the swell in the 100 ml


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jar with water and kerosene are noted and used to find the free swell index. The free swell index

is defined as

*100d k

k

V VDFS

V

Vdand Vkare the reading in the jar containing water and kerosene respectively.

3.4.4 X-RAY DIFFRACTION

Mineralogical analysis of each soil consisted of X-ray diffraction (XRD) on the clay fraction (


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Fig. 3.2 Eades and Grim pH test

3.4.6 OMC AND MDD

Mini compaction test was performed on all the untreated and treated samples according to

Sridharan and Sivapullaiah (2005). For treated samples the percentage of lime is added to the soil

and mixed thoroughly before the experiment is done. The maximum dry density and the

optimum moisture are got from the curves and it is used for sample preparation and compaction.

The compaction curves for all the soil samples are plotted in Fig.3.4. The values of optimum

moisture content and maximum dry density are given in Table 3.1.

Fig.3.3 Mini compaction mould


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Table 3.1 Physical properties of soils

Physical Soil Properties of the samples

S.No. Soil Property Karaikudi Paramakudi Tuticorin Siruseri

1 % passing 75 micron Sieve 82.84 64.15 64.96 93.5

2 % Gravel 4.5 3.0 4.5 0.5

3 % Sand 15.5 32.0 30.5 7.0

4 % Silt 22.0 23.0 29.0 24.0

5 % Clay 58.0 42.0 36.0 69.0

6 Liquid limit, wL(%) 76 78 60 78

7 Plastic limit, wP (%) 37 37 35 30

8 Plasticity index, ip (%) 39 41 25 48

9 Shrinkage limit, wS(%) 8 7 9 9

10 Shrinkage ratio 2.09 2.06 2.15 2

11 Differential free swell index (%) 144 211 100 100

12 Optimal Moisture Content (%) 24 27 24 28

13Lime Requirement, Initial

consumption of lime (%)3 4 3 4

14Optimal Moisture Content of

treated soil (%)27 32 26 31

15 Maximum Dry Density, (g/cc) 1.51 1.53 1.56 1.45

116Maximum Dry Density of Lime

Treated Soil, (g/cc)1.45 1.43 1.44 1.33


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Fig. 3.4 XRD for Siruseri treated and untreated samples

0

2000

4000

6000

8000

10000

12000

14000

16000

18000

20000

10 15 20 25 30 35 40 45 50 55 60

XRD for treated and Untreated Siruseri Soil

Siruseri

Siruseri Treated 28 Days


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Fig.3.5 XRD for Karaikudi, Paramakudi and Tuticorin soil samples

2000

4000

6000

8000

10000

12000

10 15 20 25 30 35 40 45 50 55 60

XRD for Karaikudi, Paramakudi and Tuticorin Samples

Karaikudi

Paramakudi

Tuticorin


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Lime Fixation point

Fig.3.6 Lime fixation point for all soil samples

10.5

11

11.5

12

12.5

13

1 2 3 4 5

pH

Lime Content (%)

Siruseri

10.5

11

11.5

12

12.5

13

1 2 3 4 5

pH

Lime Content (%)

Karaikudi

10.5

11

11.5

12

12.5

13

1 2 3 4 5

pH

Lime Content (%)

Paramakudi

10.5

11

11.5

12

12.5

13

1 2 3 4 5

pH

Lime Content (%)

Tuticorin


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OMC and MddCurves

Fig. 3.7 OMC and MDD curves for all soil samples

1.26

1.31

1.36

1.41

1.46

15 20 25 30 35 40

Dry

density(g/cc)

Water content (%)

SiruseriUntreated Soil

Treated 4% lime

1.35

1.40

1.45

1.50

1.55

15 20 25 30 35

Dry

density(g/cc)

Water Content (%)

KaraikudiUntreated

Treated

1.34

1.39

1.44

1.49

1.54

15 20 25 30 35

Dryde

nsity(g/cc)

Water Content (%)

Paramakudi Untreated

Treated

1.42

1.47

1.52

1.57

15 20 25 30 35

Drydensity(g/cc)

Water content (%)

Tuticorin Untreated

Treated


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3.5 SUMMARY OF BASIC PROPERTIES

1. All the soils show a liquid limit of greater than 60 and plasticity index greater than 25.The shrinkage limit of the soil is less than 9 for all samples.

2. The differential free swell index of all the soil is greater than 100%.3. Based on the previous literature on the classification of expansive soil it is visible that the

four soils are highly expansive.

4. Some of the minerals present in these expansive soils were Quartz, kaolinite, feldspar,Montmorillonite, Chlorite Vermiculite etc.,

5. Eades and Grim test shows the percentage of lime required varies from 3 to 4%.6. The addition of lime brings about identical changes in the XRD patterns. The treated soil

does not cause any disappearance of the existing mineral peaks present, rather causes

only some suppression of the mineral peaks, specifically the quartz peak.

7. The maximum dry density of the lime treated soil is less than the untreated soil, but theoptimal moisture content increases with treatment.


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3.6 SAMPLE PREPERATION

The samples were prepared by static compaction. The amount of sample required for the

particular test is found from the volume of the mould and the dry density of the soil. The required

sample is taken and mixed with the lime thoroughly. After through mixing the water is sprayed

uniformly and mixed to achieve the required moisture content. The compacted sample is then

wrapped with cling film and kept in the moisture control room for curing.

3.6.1 TESTING CONDITIONS

The samples are tested in both treated and untreated condition. To check the effect of moisture

content in the curing and subsequent strength the testing is done in all three condition dry,

optimum and wet condition. Also the testing is done at various curing period such as 0, 3, 7, 14

and 28 days (Fig. 3.). For optimum the maximum Mdd is selected. For dry side and wet side 95%

of the optimum is taken for untreated soil and 98% of the maximum Mdd for treated soil.

Fig. 3.8 Different testing condition for Siruseri Soil

1.37

1.38

1.43

1.45

1.40

1.38

1.301.30

1.32

1.33

1.32

1.29

1.25

1.30

1.35

1.40

1.45

1.50

15 20 25 30 35 40

Drydensity(g/cc)

Water Content (%)

Siruseri Soil

Untreated

Treated 4% Lime


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3.6.2 SOAKED SAMPLE PREPERATION

To check the effect of soaking on the strength the 14 days cured samples were soaked in a sand

bath for a period of 24 hours. Before soaking the treated samples were first rolled with filter

paper and then covered with cloth (Fig. 3.9). This prevents loss of fines from the sample. Soaked

samples were prepared for both the UCC and MRtest.

Fig. 3.9 Soaked sample preparation

3.7 UNCONFINED COMPRESSIVE STRENGTH

The unconfined compression test is a special form of a triaxial test in which the confining pressure is

zero. The test can be conducted only on clayey soils which can withstand without confinement. The

test is generally performed on intact, saturated clay specimens. The test is used to find the

unconfined strength of the soil. It is also used to find the shear strength of the soil. The test is

done according to IS 2720 part 10.

The test is done on all three moisture condition and curing days. The sample is prepared as

stipulated in IS code and covered with cling film to avoid any moisture loss. The covered sample

is kept in desiccators. The tests were carried at deformation of 0.5mm/min.

Also the testing is done at various curing periods such as 0, 3, 7, 14 and 28 days (Fig. 3.10).


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Fig. 3.10 UCC sample preparation

3.8 CALIFORNIA BEARING RATIO

The California bearing ratio test is penetration test meant for the evaluation of subgrade strength

of roads and pavements. These results obtained by these tests are used with the empirical curves

to determine the thickness of pavement and its component layers. This is the most widely used

method for the design of flexible pavement. Soaked CBR was performed for the treated and

untreated sample to study the effect of soaking.

The test is done according to IS 2720(part 16)-1979. The schematic diagram of the setup is

shown in Fig. 3.11.

Fig. 3.11 CBR Testing


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t

s

PCBR

P (10)

Where,

Pt is load corresponding to chosen penetration of 2.5mm or 5mm.

Ps is the standard load for corresponding penetration.

3.9 RESILIENT MODULS

From 1986, AASHTO required the use of the subgrade resilient modulus for the design of

flexible pavements. Resilient modulus is an important material property, similar in concept to the

modulus of elasticity. It differs from the modulus of elasticity in that it is obtained by a repeated-load triaxial test and is based only on the recoverable strains. Resilient modulus is defined as:

d

R

r

M

(11)

Where MR is the resilient modulus; d is the repeated deviator stress; and r is the recoverable

axial strain.

The current standard test method to determine the resilient modulus is described by AASHTO T

307-99 which has recently been upgraded from AASHTO T 294-94 and AASHTO T 274. In

AASHTO T 307-99, traffic conditions are simulated by applying a series of repeated deviator

stresses, separated by rest periods and field conditions are simulated by conditioning and post

conditioning.

3.9.1 RESILIENT MODULUS EQUIPMENT

The equipment for resilient modulus consists of a triaxial cell, an actuator, two sensitive LVDT

(Linear Variable Differential Transducers), a CDAS (Continuous Data Acquisition System) and a

computer.

The apparatus used for resilient modulus testing is shown in Fig. 3.12. Fig.3.13 shows the whole

equipment; in this the confining pressure used is air which is supplied by a compressor.


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Fig. 3.12 Loading setup

Fig. 3.13 Experimental set up


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The first sequence is a conditioning cycle. Haversine load pulse is used for loading. In this load is

applied for a period of 0.1 s and rest is given for 0.9 s. A contact load of 10% of the cyclic load is

maintained throughout the testing condition (Fig. 3.14)

Fig. 3.14 Haversine loading form

The entire test is visible in the screen and the resilient modulus values along with resilient strain,

permanent strain are visible in the screen. In addition to this shear test can also be performed on

the samples with zero confining pressure. The screenshot of the screen is shown in the Fig. 3.15

and Fig. 3.16.

Fig.3.15 Load pulse in computer


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Fig. 3.16 Resilient modulus setting

3.9.3 SAMPLE PREPERATION

The sample is prepared for all the three moisture condition. The required amount of soil is taken

and it is mixed with lime. Water is then added to the mixture to attain the moisture content

needed for the test. The mould for the test is fully cleaned and oiled (3.17).

Fig. 3.17 Sample preperation


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The sample is separated into five equal parts and it is placed into the mould one above the other.

After each part of soil is placed it is lightly compacted with hammer and the top portion is

scratched. Similarly all the layers are placed into the mould. The mould is now covered with the

top and bottom plates and compacted using static compaction to achieve uniform density

throughout the sample. The compacted specimen is covered with cling film and placed in a mist

room for curing (Fig.3.18).

Fig. 3.18 Samples covered with cling film

3.9.4 REGRESSION ANALYSIS

There are several models that were developed for the estimation of resilient modulus of subgrade

soils and base/sub base materials. In this the power model, K- model, Octahedral stress model,

Uzan model and Rafael pezo model are intensively used to find the best suitable model for

finding the relationship between resilient modulus and stress level for the experiments carried out

in this investigation.

3.10 TOTAL SUCTION

The dew point potentiameter (WP4) measures total suction in the range of 0 to 300MPa. WP4employs chilled mirror technique (Leong et al., 2003) and relative humidity principle for

measuring wide range of suction .

The time taken for measuring the sample is about 5 minutes and the temperature can be varied

between 15 to 50 degree Celsius.

The samples are made in the same manner as UCC and MR. The sample for measuring total

suction is cut from the UCC sample or from the MR. The sample is placed in the measuring cup

and the lid is closed (Fig.3.19). The variation in temperature between the sample and the


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instrument is maintained below one degree Celsius to get accurate readings. The WP4 waits until

temperature becomes constant. Then it gives the values for total suction in MPa.

Fig. 3.19 Dewpoint potentiameter suction measurement

CHAPTER 4


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TEST RESULTS AND ANALYSIS

4.1 INTRODUCTION

The following section presents the results of laboratory tests performed for the four soils thathave caused extensive problems to foundations and pavements. This section presents the results

of Unconfined compressive strength, California bearing ratio, Resilient modulus and Total

suction measurement. The strength gain with curing is discussed and it is compared with

untreated soil for the Siruseri. Also the relationships between various tests were explored.

4.2 UNCONFINED COMPRESSIVE STRENGTH

The laboratory results of unconfined compression test on the Siruseri soil was carried out for

three moisture content levels. The conditions were chosen on the dry side, optimum content and

wet side respectively as discussed in the previous chapter. Further the effect of different curing

period for the above moisture content levels were also investigated.

4.2.1 UNTREATED SAMPLES

Fig. 4.1 shows the UCC test results of the untreated Siruseri soil for different moisture

conditions. The stress strain behaviour shows the typical softening behaviour, characteristic of

clay soils. The sample at optimum moisture content shows higher strength compared to the dry

side and wet side. The soil sample gives UCC strength of 200 kPa, 140 and 135 kPa for the

optimum, dry side and wet respectively (Table 4.1). The failure strains are more than 10%.

Fig 4.1 UCC test results of untreated Siruseri soil

Table 4.1 UCC strength for untreated soil

0

50

100

150

200

250

0 2 4 6 8 10 12 14 16 18

AxialStress(kPa)

Axial Strain (%)

Dry side

Opt side

Wet side


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Natural Untreated

Dry side Optimum Wet side

138.64 kPa 191.41 kPa 131.35 kPa

4.2.2 TREATED SAMPLES

For the treated soil the UCC tests were carried out for the three moisture conditions at 0, 3, 7, 14

and 28 days curing period. The stress strain characteristics of lime treated soil are completely

different from that of the untreated soil. The treated samples gradually become brittle with

increase in curing period. Fig. 4.2, 4.3 and 4.4 shows that the samples exhibit increased strength

and fails at lesser strain level compared to the untreated soil.

Fig. 4.2 UCC test results of lime treated Siruseri sample at different curing period at optimal

moisture content

The strength development in the lime treated soil depends on the moulding moisture content

levels, adopted to compact the soil. For all the three moisture content levels the strength at zero

days curing period is around 150 kPa but the failure strain levels differs. The samples compacted

at dry side shows strength of 150 kPa at zero days curing and increases to 270 kPa at 28 days of

curing.

0

100

200

300

400

500

600

700

0 2 4 6 8 10 12 14 16

Axi

alStress(kPa)

Axial Strain (%)

0 Days 3 Days

7 Days 14 Days

28 Days


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Fig. 4.3 UCC test results of lime treated Siruseri sample at different curing period at dry moisture

content

Fig. 4.4 UCC test results of lime treated Siruseri sample at different curing period at wetmoisture content

The strength development in the lime treated soil depends on the moulding moisture content

levels, adopted to compact the soil. For all the three moisture content levels the strength at zero

days curing period is around 150 kPa but the failure strain levels differs. The samples compacted

at dry side shows strength of 150 kPa at zero days curing and increases to 270 kPa at 28 days of

curing (Table 4.2). The failure strain also reduces from 6% at zero days curing to 2.5% at 28

0

50

100

150

200

250

300

0 2 4 6 8 10 12 14 16

AxialStress(kPa)

Axial Strain (%)

0 Days

3 Days

7 Days

14 Days

28 Days

0

100

200

300

400

500

600

700

800

900

0 2 4 6 8 10

AxialStre

ss(kPa)

Axial Strain (%)

0 Days

3 Days

7 Days

14 Days

28 Days


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days. Conversely the samples compacted at optimum moisture content depicts a radical increase

in strength of 600 kPa at 28 days curing. Whereas the samples compacted at wet side shows a

ductile behaviour with no prominent failure points at zero days but eventually the behaviour

changes to brittle and the strength escalates to 750 kPa at a failure strain of 3%. The higher

strength at wet side compacted samples is due to the availability of sufficient moisture content

for the progress of the lime reaction during the curing period and the decreased strength in dry

side is due to the under developed pozzolanic reaction at lesser water content. Fig.4.5 shows the

UCC strength increase with curing days.

Table 4.2 UCC strength for different moisture content and curing days

Condition Dry Opt Wet

0 Days 157.45 149.83 141.1

3 Days 184.35 255.92 379.55

7 Days 230.04 417.48 479.0018

14 Days 248.38 557.13 615.4528

28 Days 261.8223 590.3724 766.5896

Fig. 4.5 UCC strength for Siruseri soil with curing days at different moisture content

0

100

200

300

400

500

600

700

800

900

0 6 12 18 24 30

UCC(kPa)

Curing Days

Dry side Opt side

Wet side


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4.2.3 KARAIKUDI, PARAMAKUDI AND TUTICORIN SOIL SAMPLE

The UCC test results carried out for the other three soils are given in the Fig. 4.5, 4.6, and 4.7.

Similar results were observed. Increased UCC strength of 800, 700 and 1300 kPa at 14 days

curing, were observed for the treated karaikudi, Paramakudi and Tuticorin soil samples,

respectively. Typical brittle behaviour and failure at lesser strain of around 2.5% were observed.

All the four soils including the siruseri sample have fines content greater than 70% and a liquid

limit more than 75%. The stabilizing effect of lime is fully utilized by these soils due to the

highly compressible and expansive nature. Table 4.3 shows the UCC values for treated and

untreated samples.

Fig. 4.6 UCC test results for treated and untreated Karaikudi soil sample

.

Fig. 4.7 UCC test results for treated and untreated Paramakudi soil sample

0

100

200

300

400

500

600

700

800

0 2 4 6 8 10 12

Stressin(kPa)

Strain (%)

0 Days

14 Days

0

100

200

300

400

500

600

700

800

900

0 2 4 6 8 10 12

Stress

(kPa)

Strain (%)

Paramakudi

0 Days 14 Days


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Fig. 4.8 UCC test results for treated and untreated Tuticorin soil sample

Table 4.3 UCC strength for all soils with % of fines

SoilLime Content

%

UCC untreated

kPa

UCC treated

kPaClay % Silt %

Siruseri 4% 191.41 557.13 69 24

Karaikudi 3% 395.73 731.46 58 22

Paramakudi 3% 283.67 822.33 42 23

Tuticorin 4% 358.97 1311.87 36 29

4.2.4 EFFECT OF SOAKING

The UCC tests also were performed on these compacted samples after subjecting to sand bath

soaking for a period of 24 hrs. Fig. 4.9 compares the effect of soaking on the treated samplessubjected to 14 days of curing. The soaking effect reduces the UCC strength of the soil around 5

-20% depending upon the soil and the water content of the soaked sample increases from 31% to

40%. The soaking of Tuticorin samples does not show any decrease in strength due to high silt

and low clay content in the soil sample.

Testing for untreated soaked UCC samples were not performed, because the sample swells and

disintegrates before testing.

0

200

400

600

800

1000

1200

1400

0 2 4 6 8 10 12

Stress(kPa)

Strain (%)

Tuticorin0 Days

14 Days


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Fig. 4.9 UCC for all soils with curing

4.3 CALIFORNIA BEARING RATIO

California bearing ratio tests were conducted for both treated and untreated samples of Siruseri

samples. The load versus penetration curve for both the untreated and treated soil samples are

shown in Fig. 4.10 and 4.11, respectively. The CBR values are tabulated in Table 4.4.

Fig. 4.10 CBR versus penetration curve for untreated soil

0

200

400

600

800

1000

1200

1400

Siruseri Karaikudi Paramakudi Tuticorin

UCC(kPa)

Soil Source

UCC for all Soils with CuringUntreated

14 Days

14 Days Soaked

0

20

40

60

80

100

120

140

0 2 4 6 8 10 12 14

Loadkg

Peneteration (mm)

Soaked unsoaked


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Fig. 4.11 CBR versus penetration curve for untreated soil

The untreated soaked samples have a much lesser CBR value, which shows that the sample

losses strength drastically when immersed in water. This is due to the swelling of the soil. The

CBR values for treated samples were much higher than the untreated samples. The soaked treated

samples does not show much variation from unsoaked case, showing that the strength of the

subgrade remains same in the first cycle. Further, the failure of these samples occurs at much less

penetration than the untreated soil. This is because the sample becomes brittle with treatment.

Table 4.4 CBR Values (%)

Condition Unsoaked Soaked

Untreated 8.5 1

14 days treated 61 55

4.4 RESILIENT MODULUS

The resilient modulus result consists of resilient modulus, resilient strain, permanent strain,

deformation and load values for different deviatoric stress and confining pressure. For calculation

and design purpose the resilient modulus value corresponding to 41.4 kPa confining pressure and68.9 kPa axial stresses was taken as the resilient modulus of the sample (AASHTO T-307 2006).

0

200

400

600

800

1000

1200

1400

1600

0 2 4 6 8

Loadkg

Peneteration (mm)

CBR for Treated Soil 14 days

Soaked Unsoaked


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4.4.1 EFFECT OF CONFINING PRESSURE

Fig. 4.12 shows the behaviour of untreated Siruseri soil. With increasing confining pressure the

resilient modulus of the soil increases. But with increasing deviatoric stress the material softens

and shows a decreasing trend.

The behaviour of lime treated Siruseri soil shows an increasing trend with both deviatoric and

confining pressure. This depicts the hardening behaviour of the treated soil (Fig. 4.13).

Fig. 4.12 MRfor untreated Siruseri soil

Fig. 4.13 MRfor 28 days treated Siruseri soil

100

150

200

250

0 25 50 75 100

MR(MPa)

Deviatoric Stress (kPa)

41.4 kPa

27.6 kPa

13.8 kPa

60

70

80

90

0 20 40 60 80

M

R(MPa)

Deviatoric Stress (kPa)

41.4 kPa

27.6 kPa

13.8 kPa


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4.4.2 EFFECT OF CURING

Fig. 4.14 shows the effect of resilient modulus with curing. As the curing period increases the

response of the soil-lime composites for the cyclic loading transforms to a more responsive trend.

The effect of deviatoric stress at zero curing is not much pronounced but as the curing

Documents

Lime Stabilization on Expansive Soils for Pavements