Factors affecting the strength characteristicsof calcium-carbonate - cemented soils.

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Authors Al-Ghanem, Abdulhakim M. F.

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Factors affecting the strength characteristics of calcium carbonate-cemented soils

AI-Ghanem, Abdulhakim M. F., Ph.D.

The University of Arizona, 1989

U·M·I 300 N. Zeeb Rd. Ann Arbor, MI 48106

FACTORS AFFECTING THE STRENGTH CHARACTERISTICS

OF CALCIUM CARBONATE-CEMENTED SOILS

by

Abdulhakim M.F. AI-Ghanem

A Dissertation Submitted to the Faculty of the

DEPARTMENT OF CIVIL ENGINEERING AND ENGINEERING MECHANICS

In Partial Fulfillment of the Requirements For the Degree of

DOCTOR OF PHILOSOPHY WITH A MAJOR IN CIVIL ENGINEERING

In the Graduate College

THE UNIVERSITY OF ARIZONA

198 9

THE UNIVERSiTY OF ARIZONA GRADUATE COLLEGE

2

As members of the Final Examination Committee, we certify that we have read

the dissertation prepared by __ ~A~bd~u~l~h~ak~im~~M~.~F~.~A~I-_G=h~a=n_e_m~ ______________ ___

entitled Factors Affecting the Strength Characteristics of

Calcium Carbonate-Cemented Soils

and recommend that it be accepted as fulfilling the dissertation requirement

Doctor of Philosophy for the Degree of ---------------------------------------------------------d~ tf -( J - J> J>

Date

v}>/I~g Date

C,j;3/ rg Date

G/ 131 ~g Date

Date

Final approval and acceptance of this dissertation is contingent upon the candidate's submission of the final copy of the dissertation to the Graduate College.

I hereby certify that I have read this dissertation prepared under my direction and recommend that it be accepted as fulfilling the dissertation requirement.

Date I

3

STATEMENT BY AUTHOR

This dissertation has been submitted in partial fulfillment of requirements for an advanced degree at The University of Arizona and is deposited in the University Library to be made available to borrowers under rules of the Library.

Brief quotations from this dissertation are allowable without special permission, provided that accurate acknowledgment of source is made. Requests for permission for extended quotation from or reproduction of this manuscript in whole or in part may be granted by the head of the major department or the Dean of the Graduate College when in his or her judgment the proposed use of the material is in the interests of scholarship. In all other instances, however, permission must be obtained from the author.

SIGNED: ________ + ________ _

4

ACKNOWLEOOMENT

I would like first and foremost to extend my deepest appreciation to my dissertation

director and academic advisor, Prof. Edward A. Nowatzki. Without his valuable assistance

and very capable guidance throughout my entire graduate program, and particularly with

this dissertation, it would not have been possible for the completion of this study. He has

been and always will be a source of inspiration not only in my graduate work but also in

my professional career.

To Prof. Jay S. DeNatale, I extend grateful appreciation for his invaluable support

and encouragement during the past several years with my studies and research. lowe him

a depth of gratitude for his personal consultation and his technical expertise which I wiII

not be able to repay.

I also want to thank the other members of my committee, including Prof. Ralph M.

Richard for his review of the manuscript and his many helpful suggestions. I am greatly

indebted to Prof. Jaak Daemen for his words of wisdom. And last, but not least, I extend

sincere appreciation to Prof. Ian Farmer for giving me the opportunity and honor of his

invaluable time by sitting on the committee.

I also express sincere thanks to Linda Harper for her meticulous care and excellent

work in preparing this manuscript.

5

TABLE OF CONTENTS

Page

LIST OF ILLUSTRATIONS 9

LIST OF TABLES ..... . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 15

ABSfRACT . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 18

1. INTRODUCTION ............................ : . . . . . . . . .. 20

1.1 Background .•................................... 20 1.2 Nature of the Problem .............................. 22 1.3 Purpose of the Research ............................. 25 1.4 Scope of Research ................................. 26

2. LITERATURE REVIEW . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 28

2.1 Cementation ..................................... 28 2.1.1 Cemented Soils ............................ 28 2.1.2 Cementation in Rocks . . . . . . . . . . . . . . . . . . . . . . .. 43

2.2 Calcareous Soils in Arizona ........................... 44 2.3 Determination of Calcium Carbonate Content

in Sediments ................................... " 52 2.3.1 Soil Calcium Determination using .

Ca++ Ion Concentration . . . . . . . . . . . . . . . . . . . . . .. S4 2.3.2 Soil Calcium Determination using

a CO;2 Concentration ...................... " S6 2.4 Phase Re]ation in Soils Whose Pore Water Con-

tains a "High" Percentage of Disso]ved Salts ................. S7

3. EQUIPMENT AND MATERIALS ............................ 61

3.1 Equipment ... . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 61 3.1.] The GDS Triaxia] Testing System ................ 62 3.1.2 A Control1ed Environment Curing

Room (Moisture Room) . . . . . . . . . . . . . . . . . . . . . .. 71 3.1.3 Modified Compaction Mo]d and Hammer ........... 71

. 3.1.4 Automatic Valving Vacuum Evaporator ............ 71 3.1.5 Hammer Sputter Coater . . . . . . . . . . . . . . . . . . . . . .. 73 3.1.6 Scanning E]ectron Microscope (SEM) .............. 73 3.1.7 Polaroid Positive/Negative 4 x S

Land Film Type S5 •••..••.••.••.••.....•.•. 76 3.1.8 Apparatus and Supplies for Particle

Size Ana]ysis of Soils ........................ 76

TABLE OF CONTENTS--continued

3.1.9 Apparatus and Supplies for Specific Gravity Test . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

3.1.10 Apparatus and Supplies for Atterberg Limits ................................. .

3.1.1 1 Apparatus and Supplies for Standard Proctor Compaction Test .............•........

3.1.12 Apparatus and Supplies for Modified'

3.2 Materials 3.2.1 3.2.2 3.2.3 3.2.4

Proctor Compaction Test ..................... .

Characteristics of Type A Soil ................. . Characteristics of Sierrita Soil .................. . Calcium Carbonate (CaC03) ••••••••••••••••••••

Water ................................. .

6

Page

76

77

77

77 77 77 82 85 88

4. DESCRIPTION OF RESEARCH. . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 91

4.1 Introduction ..................................... 91 4.2 . Approach . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 91 4.3 Mixing and Compaction of Artificially

Cemented Soils ................................... 94 4.3.1 The Preparation of Artificially

Cemented Specimens. . . . . . . . . . . . . . . . . . . . . . . .. 94 4.3.2 The Density and Water Content of

the Mix . . . • . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 95 4.4 Triaxial Compression Test Procedure ..................... 102

4.4.1 Laboratory Testing Program ... . . . . . . . . . . . . . . . .. 103 4.4.2 Specimen Preparation ........................ 103 4.4.3 Triaxial Testing Procedure ............. . . . . . . .. 105 4.4.4 Confining Pressure . . . . . . . . . . . . . . . . . . . . . . . . .. 107 4.4.5 Loading Method and Rate ..................... 108 4.4.6 Computations Related to Triaxial

Tests. . . . . . . . . . . . . . • . . . . . . . . . . . . . . . . . . .. 108 4.5 Electron Microscope Studies ................... . . . . . . .. 115

5. PRESENT A nON AND DISCUSSION OF THE TRIAXIAL COMPRESSION TEST RESULTS ............................. 119

5.1 Introduction ..................................... 119 5.2 Computation . . . . . • . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 123

5.2.1 Area Correction . . . . . . . . . . . . . . . . . . . . . . . . . . .. 123 5.2.2 Rubber Membrane Correction . . . . . . . . . . . . . . . . . .. 123

5.3 Unconsolidated Undrained Test Results . . . . . . . . . . . . . . . . . . .. 123

7

TABLE OF CONTENTS--continued

Page

S.3.1 Uncemented Specimens of Type A Soil . . . . . . . . . . . .. 124 S.3.2 Artificially Cemented Specimens of

Type A Soil ....................•......... 124 S.3.3 Reconstituted Specimens ...................... 129

S.4 Strength Parameters Obtained from Triaxial Compression Tests ..............•.................. 132

S.S Factors Influencing the Soil Strength ......•.............. 138 S.5.1 Confining Pressure, 03 ••••••••••••••••••••••• 138 S.S.2 Cement Content. . . . . . . . . . . . . . . . . . . . . . . . . . .. 138 S.S.3 Compaction Moisture Content . . . . . . . . . . . . . . . . . .. 144 S.5.4 Curing Period ................. . . . . . . . . . . .. 149

6. SOIL MICROSTRUCTURE AND COMPACTION CHARACTERISTICS OBSERVED BY THE SCANNING ELECTRON MICROSCOPE ......... 152

6.1 Introduction ..................................... 152 6.2 Scanning Electron Microscope Study on

Uncemented Type A Soil . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 153 6.3 Scanning Electron Microscope Study on

Artificially Cemented Type A Soil . . . . . . . . . . . . . . . . . . . . . .. ISS 6.3.1 Type A Soil Artificially Cemented

with IS% Calcium Carbonate ................... 158 6.3.2 Type A Soil Artificially Cemented

with 30% Calcium Carbonate ................... 161 6.4 Scanning Electron Microscope Study on

Naturally Cemented Sierrita Soil ........................ 164 6.5 Scanning Electron Microscope Study of

Calcium Carbonate Distribution with Artificially Cemented Soil ............................ 166

7. STABILITY ANAL YSIS OF CUT SLOPES IN CALCIUM CARBONATE CEMENTED SOILS . . . . . . . . . . . . . . . . . . . . . . . . . . .. 169

7.1 Introduction ..................................... 169 7.2 Field Observations of Slope Failures in Soil

Slopes in the Twin Buttes Open Pit Mine .................. 170 7.3 Choice of Slope Stability Analysis ....................... 170 7.4 The Shear Strength Parameters in Naturally

Cemented Sierrita Soil- . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 172 7.5 Slope Stability Analysis in Reconstituted

and Artificially Calcium Carbonate Cemented Soils ....... _. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 175

8

TABLE OF CONTENTS--continued

Page

8. SUMMARY, CONCLUSIONS AND RECOMMENDATIONS ........... 179

8.1 Summary ................................. . . . . .. 179 8.2 Conclusions ..................................... 180 8.3 Recommendations ..................•.............. 184

APPENDIX A: PHASE RELATION IN SOILS WHOSE PORE. WATER CONTAINS A HIGH PERCENTAGE OF DISSOLVED SALTS. . . . . . . . . . . . . . . . . . . . . . . . . .. 186

APPENDIX B: DETAILED EXPERIMENTAL PROCEDURE .......... 191

APPENDIX C: SUMMARY OF TEST DATA ..................... 197

APPENDIX D: STRESS-DEFORMATION CHARACTERISTICS FOR TRIAXIAL COMPRESSION TESTS ON UNCEMENTED, ARTIFICIALLY CEMENTED, AND RECONSTITUTED SOILS .................................... 208

APPENDIX E: MOHR CIRCLE DIAGRAMS FOR TRIAXIAL COMPRES­SION TESTS ON UNCEMENTED, ARTIFICIALLY CEMENTED, AND RECONSTITUTED SOILS .......... 218

REFERENCES ......................................... 230

9

LISr OF ILLUSTRATIONS

Figure Page

1.1 Vertical banks of the Santa Cruz River 21

1.2 An overview of the Twin Buttes Open Pit Mine .............. 23

1.3 Vertical slope of the Twin Buttes Mine . . . . . . . . . . . . . . . . . . .. 24

1.4 In situ appearance of the alluvial fanglomerate materials ....................................... 24

2.1 Matrix structure (Sowers and Sowers, 1979) ................. 30

2.2 Skeletal structure (Sowers and Sowers, 1979) 31

2.3 Behavior of collapsing soil structure upon wetting (Jennings and Knight, 1957) .•................... 38

2.4 Typical collapsible soil structure formed by capillary tension (Dudley, 1970; Barden et aI., 1973; Clemence and Finbarr, 1981) ...................... 39

2.5 Typical collapsing soil structure, formed by cementing agent (Dudley, 1970; Barden et al., (1973; Clemence and Finbarr, 1981) .... . . . . . . . . . . . . . . . . .. 41

2.6 Distribution of calcareous soils in Arizona (Beckwith and Hansen, 1982) .......................... 45

2.7 Phase diagram showing relationship of weights, masses, and volumes of soil, salt, water, and air in soil or rock ................................. 60

3.1 Diagrammatic layout of the GDS triaxial testing system. 1 - Bishop/Wesley Triaxial Cell 2 - Cell and lower chamber digital pressure controllers 3 - Sample pore water digital pressure controller 4 - Hewlett Packard HP 85B computer 5 - Hewlett Packard 7470A graphic plotter ................. 63

3.2 Bishop/Wesley stress path apparatus ...................... 64

3.3 Photograph of Bishop/Wesley Triaxial Apparatus . . . . . . . . . . . . .. 6S

10

LIST OF ILLUSTRATIONS--continued

Page

3.4 Diagrammatic layout of the digital pressure controller .......... 67

3.5 Photograph of the digital pressure controller . . . . . . . . . . . . . . . .. 68

3.6a Photograph of HP85B computer ........................ 70

3.6b Photograph of HP7470A graphic plotter ................... 70

3.7 Compaction mold and hammer for specimen preparation . . . . . . . .. 72

3.8 Mikros VE-I0 Vacuum Evaporator ...................... 74

3.9 Hummer sputter coater .............................. 74

3.10 I.s.I. DS-130 Scanning Electron Microscope ................. 75

3.11 Charts for visual estimation of roundness and sphericity of soil grains . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 79

3.12 Thin section photomicrograph of Type A soil 80

3.13 Grain size distribution curve of Type A soil 81

3.14 Dry density-water content curves of Type A soil . . . . . . . . . . . . .. 83

3.15

3.16

Thin section photomicrograph of Sierrita soil

Grain size distribution curves of Sierrita soil

84

86

3.1 7 Dry density-water content curves of Sierrita soil . . . . . . . . . . . . .. 87

3.18 Thin section of electron photomicrograph of calcium carbonate. a. Magnification 501X. b. Boxed area in (a) magnified at 50 1 OX ••••••••••••..•. • • • . • . . • . • • . •• 89

4.1 Stress-strain relationships for ideal and real soils ... . . . . . . . . . .. 93

4.2 Dry density and water content curves for uncemented and calcium carbonate artificially cemented Type A soil . . . . . . . . . . .. 97

4.3 Dry density and moisture content curves of the three groups. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 100

11

LIST OF ILLUSTRA TIONS--continued

Page

5.1 Strength and stress deformation characteristics of cemented soils (Means and Parcher, 1963) .................. 121

5.2 Mohr failure envelopes for peak strength from triaxial compression tests on uncemented and artificially cemented Type A soil .......•............ : . . . . . . . . .. 134

5.3 Mohr failure envelopes for residual strength from triaxial compression tests on uncemented and artificially cemented Type A soil . . . . . . . . . . . . . . . . . . . . . . .. 135

5.4 Mohr failure envelopes for peak and residual strength from triaxial compression tests on reconstituted naturally cemented soil (Sierrita soil) ..................... 136

5.5 Stress-deformation characteristics of reconstituted fanglomerate material (Sierrita soil) ...................... 137

5.6 Typical triaxial stress-strain curves for Type A uncemented soil. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 139

5.7 Typical triaxial stress-strain curves for Type A artificially cemented soil with 15% calcium carbonate .. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 140

5.8 Typical triaxial stress-strain curves for artificially cemented Type A soil with 30% calcium carbonate

5.9 Difference between cemented and uncemented Type A soil stress-strain response for specimens compacted at dry

141

side of OMC .......•..........•................. 143

5.1 0 Typical stress-strain curves for reconstituted Sierrita soil under 100 kPa confining pressure . . . . . . . . . . . . . . . . . . . .. 145

5.11 Typical triaxial stress-strain curves for Type A uncemented soil (Points I and 4) . . . . . . . . . . . . . . . . . . . . . . .. 146

5.12 Typical triaxial stress-strain curves for artificially cemented Type A soil with 15% calcium carbonate (Points 2 and 5) . . . . . . . • . . . . . . . . . . . . . . . . . . . . . . . . . .. 147

LIST OF ll..LUSTRA TIONS--continued

5.13 . Typical triaxial stress-strain curves for artificially cemented Type A soil with 30% calcium carbonate

12

Page

(Points 3 and 6) . . . . . . . . • . • • . . . . . • . . • . . . . . . . . . . . . .. 148

5.14 Typical triaxial stress-strain curves for artificially cemented Type A soil with 15% calcium carbonate

6.1 Electron photomicrograph of Type A soil compacted

150

dry of OMC ................................... " 154

6.2 Electron photomicrograph of Type A soil compacted wet of OMC . . . . . . • . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 156

6.3 Electron photomicrograph of calcium carbonate .............. 157

6.4 Electron photomicrograph of Type A soil artificially cemented with 15% calcium carbonate and compacted dry of OMC ..... : ............................. " 159

6.5 Electron photomicrograph of Type A soil artificially cemented with 15% calcium carbonate and compacted wet of OMC . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 160

6.6 Electron photomicrograph of Type A soil artificially cemented with 30% calcium carbonate and compacted dry of OMC . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 162

6.7 Electron photomicrograph of Type A soil artificially cemented with 30% calcium carbonate and compacted wet of OMC . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 163

6.8 Electron photomicrograph of naturally cemented Sierrita soil . . . . . . . . . . . . . . . . . . . • . . . . . . . . . . . . . . . . .. 165

6.9 Mosaic of photomicrographs of artificially cemented Type A soil compacted dry of OMC ..................... 167

7.1 Typical slope failures in cemented soil slopes in Twin Buttes Open Pit Mine ........................... 171

7.2 The excavated tunnel at the slope side, 120 feet below the ground surface . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 174

13

LIST OF ILLUSTRATIONS--continued

Page

7.3 Slope stability chart for calcium carbonate cemented soil ....•....•.......................... 177

D.I Stress-deformation characteristics for uncemented Type A soil compacted at dry side of OMC . . . . . . . . . . . . . . . .. 209

D.2 Stress-deformation characteristics of uncemented Type A soil compacted at wet side of OMC . . . . . . . . . . . . . . . .. 210

D.3 Stress-deformation characteristics of Type A soil . artificially cemented with 15% CaC03 and compacted at dry side of OMC ................................ 211

D.4 Stress-deformation characteristics of Type A soil artificially cemented with 15% CaC03 and compacted at wet side of OMC ................................ 212

D.S Stress-deformation characteristics of Type A soil artificially cemented with 30% CaC03 and compacted at dry side of OMC ..........•..................... 213

D.6 Stress deformation characteristics of Type A soil artificially cemented with 30% CaC03 and compacted at wet side of OMC ................................ 214

D.7 Stress-deformation characteristics of Type A soil artificially cemented with 15% CaC03 , compacted at dry side of OMC, and 7 days curing ..................... 215

D.8 Stress-deformation characteristics of Type A soil artificially cemented with 15% CaC03 , compacted at dry side of OMC, and 14 days curing. . . . . . . . . . . . . . . . . . . .. 216

D.9 Stress-deformation characteristics of Type A soil artificially cemented with 15% CaC03, compacted at dry side of OMC, and 28 days curing . • . . . . . . . . . . . . . . . . . .. 217

E.I Mohr diagrams for triaxial compression tests on uncemented Type A soil compacted at dry side of OMC . . . . . . . .. 219

E.2 Mohr diagrams for triaxial compression tests on uncemented Type A soil compacted at wet side of OMC . . . . . . . .. 220

LISf OF ILLUSTRA TIONS--continued

E.3 Mohr diagrams for compression tests on Type A soil artificially cemented with 15% Caco3 and compacted

14

Page

at dry side of OMC ......•......................... 221

E.4 Mohr diagrams for compression tests on Type A soil artificially cemented with 15% Caco3 and compacted . at wet side of OMC .......................... . . . . .. 222

E.5 Mohr diagrams for compression tests on Type A soil artificially cemented with 30% CaC03 and compacted at dry side of OMC ................................ 223

E.6 Mohr diagrams for compression tests on Type A soil artificially cemented with 30% CaC03 and compacted at wet side of OMC ................................ 224

E.7 Mohr diagrams for compression tests on Type A soil artificially cemented with 15% CaC03, compacted at dry side of OMC, and 7 days curing ..................... 225

E.8 Mohr diagrams for compression tests on Type A soil artificially cemented with 15% CaC03, compacted at dry side of OMC, and 14 days curing. . . . . . . . . . . . . . . . . . . .. 226

E.9 Mohr diagrams for compression tests on Type A soil artificially cemented with 15% CaC03, compacted at dry side of OMC, and 28 days curing . . . . . . . . . . . . . . . . . . . .. 227

E.10 Mohr diagrams for peak strength of triaxial compression tests on fanglomerate assemblage soils (Sierrita site) .....................•........... 228

E.11 Mohr diagrams for residual strength of triaxial compression tests on fanglomerate assemblage soils (Sierrita site) ..............•.................. 229

15

LISr OF TABLES

Table Page

2.1 Summary of Available Information on Cemented Sands (Sitar, 1979) •• ;;............................. 34

2.2 Engineering Classification of Calcareous Soils of the Southwestern United States (Beckwith and Hansen, 1982) •...•.••.••..•................... 48

2.3 Engineering Properties of Representative Calcareous Soils of Arizona (Beckwith and Hansen, 1982) • . . . . . • • . • . . • . . • . . . . . . . . . . . . . . . . . . .. 50

2.4 Proposed Classification System for Cemented Soils (Rad and Clough, 1985) ..•..•.......•.....•...... 53

2.5 Methods of Determining Calcium or Calcium Carbonate in Soils (Chaney, et at, 1982) ................... 58

3.1 Properties of Calcium Carbonate ........................ 90

4.1 Summary of Maximum Dry Density and Optimum Water Contents of the Compaction Test Carried Out on Type A Soil ................................ 98

4.2 Summary of the Dry Density and Moisture Content of the Chosen Research Point Values ..................... 101

4.3 Summary of the Laboratory Testing Program ................ 104

4.4 Summary of the Statistical Parameters for the Dry Density of the Triaxial Testing Specimens

4.5 The Correction Measured on Compression Strength Due to the Effect of the Rubber Membrane (Henkel

106

and Gilbert, 1952) •.•.....•..•..•.......•...••...•. 116

5.1 Summary of Triaxial Compression Test Results on Uncemented Type A Soil . . . . . . . . . . . . . . • . . . . . . . . . . . . .. 125

5.2 Summary of Triaxial Compression Test Results on Type A Soil Cemented with 15% CaC03 and Tested Without Curing ................................... 127

LIST OF T ABLES--continued

5.3 Summary of Triaxial Compression Test Results on Type A Soil Cemented with 30% Caco, and Tested

16

Page

Without Curing ..........•........................ 128

5.4 Summary of Triaxial Compression Test Results on Type A Soil Cemented with 15% CaCO, and Cured for 7, 14, or 28 Days . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 130

5.5 Summary of Triaxial Compression Test Results on Reconstituted Fanglomerate Material (Sierrita Soil) . . . . . . . . . . . .. 131

5.6 Strength Characteristics of Uncemented, ArtificiaIIy Cemented, and Reconstituted Soils . . . . . . . . . . . . . . . . . . . . . .. 133

5.7 Influence of Confining Pressure and Cement Content on Initial Tangent Modulus, Ei ......................... 142

5.8 Influence of Curing Period on the Strength Parameters, C and r/J • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • •• 151

7. I The Summary of the Previous Back Analysis Determination of the Cohesion in the Vicinity of the Sierrita Site ............ 173

7.2 Summary of Slope Stability Analyses ..................... 176

A.I Comparison Between the Values Reprp.senting Pelagic Clays Phase Diagram Computed from Equation Derived by Noorany (1984) and Those Computed from the Conventional Equations .. . . . . . . . . . . . . . . . . . . . . . . . . . . .. 190

C.I Summary of Triaxial Compression Test Results for Type A Soil Without CaC03 and Dry Side of Optimum Moisture Content . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 198

C.2 Summary of Triaxial Compression Test Results for Type A Soil Without CaC03 and Wet Side of Optimum Moisture Content . . . . . • . . . . . . . . . . . . . . . . . . . . . . . . . . .. 199

C.3 Summary of Triaxial Compression Test Results for Type A Soil With 15% Caco3 and Dry Side of Optimum Moisture Content . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 200

17

LIST OF TABLES--continued

Page

C.4 Summary of Triaxial Compression Test Results for Type A Soil With 15% CaC03 and Wet Side of Optimum Moisture Content ..•..•.•.........•.............. 0 201

C.s Summary of Triaxial Compression Test Results for Type A Soil With 30% CaC03 and Dry Side of Optimum Moisture Content 0 0 0 0 0 0 • 0 0 • 0 0 0 0 0 0 0 0 • 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 202

Co6 Summary of Triaxial Compression Test Results for Type A Soil With 30% CaC03 and Wet Side of Optimum Moisture Content 0 0 0 0 0 0 0 0 0 0 0 • 0 0 0 0 • 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 203

Co7 Summary of Triaxial Compression Test Results for Type A Soil With 15% CaC03• Dry Side of Optimum Moisture Content and 7 Days Curing 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 o. 204

e.8 Summary of Triaxial Compression Test Results for Type A Soil With 15% CaC03• Dry Side of Optimum Moisture Content and 14 Days Curing 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 205

Co9 Summary of Triaxial Compression Test Results for 0

Type A Soil With 15% CaC03• Dry Side of Optimum Moisture Content and 28 Days Curing 0 0 0 0 • 0 • 0 • 0 0 0 0 0 0 0 0 0 0 0 206

C.l 0 Summary of Triaxial Compression Test Results for Fanglomerate Assemblage Soils (Sierrita Site) . 0 • 0 0 0 0 0 0 0 0 0 0 0 0 0 207

18

ABSTRACf

The factors which affect the engineering properties of calcium carbonate cemented

soil are examined. The influence of calcium carbonate content, molding moisture content,

and confining pressure on the strength characteristics of two types of soil is investigated in

two distinct phases of the research.

Type A soil, obtained from the University of Arizona Campbell Avenue Farm in

Tucson, was used for the artificially cemented specimen stage. It is composed of sand and

silt-size particles with some clay and is virtually free of calcium carbonate in its natural

state. Sierrita soil, obtained from the Twin Buttes Open Pit Mine south of Tucson, was

used for the reconstituted sample stage. It is naturally cemented with calcium carbonate

and is composed mainly of sand, gravel, a small amount of silt, and occasional large-sized

(boulder and cobble) particles. Specimens for triaxial compression testing were compacted

for each phase of the study under carefully controlled conditions. Three test series were

carried out on Type A soil artificially cemented with calcium carbonate. Three

percentages (0%, 15%, and 30%) on a dry weight basis of the soil were used. Two molding

water contents, one dry and one wet of optimum moisture content, were established for

each test series. Unconsolidated undrained triaxial compression tests were carried out on

oven-dried specimens at three different confining pressures to obtain shear strength

parameters. The fabric characteristics of selected specimens were then defined by viewing

them under a scanning electron microscope.

The results indicate that the strength of the calcium carbonate cemented soil

depends on the distribution and not necessarily the content of the cementing agent within

the soil mass. Visual examination of the various microstructures of the artificially

cemented soil confirmed the hypothesis that strength gain occurs when the calcium

carbonate particles are concentrated at the points of contact between soil grains.

19

Visual examination of the fabric of the naturally cemented Sierrita soil showed the

microstructure to be highly compressed with weathered calcium carbonate particles

dominating the soil structure. The calcium carbonate content was found to range from 14

to 23%.

Because of sampling difficulties, an in situ cohesion value for the Sierrita soil could

not be obtained from conventional laboratory tests. Therefore, the value was obtained by

back analysis of the stability of actual slopes existing at Twin Buttes Mine.. Slope stability

analyses using Bishop's Modified Method with a search routine based on the Simplex

Method of NeIder and Mead were performed. Stability analyses were also performed using

strength properties of artificially cemented Type A soil. These analyses showed the

relationships among cohesion, friction angle, safety factor, and calcium carbonate content

for a specified slope geometry.

20

CHAPTER 1

INTRODUCTION

1.1 Background

Cemented soils are widely distributed in various parts of the earth, especiaIly where

arid to semi-arid climatic conditions exist. The cementation in soil is generaIly formed by

either chemical or physical (mechanical) processes, or a combination of both. Calcareous

soils, which are formed by precipitation of calcium carbonate, are an example of the

chemical cementation. Cementation-like effects due to mechanical interlocking of

particles, dense packing of sand grains, or capillary tension, on the other hand, are

examples of physical or mechanical cementation. One common characteristic of cemented

soils is that they are able to stand in high, nearly vertical slopes. This characteristic is also

common to rocks, however, unlike a rock, a smaIl piece of cemented soil can usuaIly be

smashed by the fingers.

Steep slopes in cemented soils may be divided into two broad categories, natural and

man-made. Natural steep slopes are formed mainly by active erosion process. They are

generally found along stream beds or along beaches. Figure 1.1 shows the banks of the

Santa Cruz River, Tucson, Arizona. The strength exhibited by these slopes, which is

generally attributed to cementation effects, depends on the degree of cementation. The

common cementing agents that are found in these slopes are: calcium carbonate, clay,

silica, silt and iron-bearing minerals.

Natural steep slopes in cemented soils are found throughout the world. For

example, natural vertical slopes in loess deposits of China exceed 90 meters (300 ft) in

height (Lutton, 1969). The vertical and near vertical slopes in weakly cemented soils in

21

Figure 1.1 Vertical banks of the Santa Cruz River.

22

the coastal cliffs of California and Oregon are up to 180 meters (600 ft) in height (Sitar,

1979). The steep slopes in the Shirasu deposits on the shores of Southern Kyushu Island in

Japan reach up to 250 meters (833 ft) in height (yamanouchi et aI., 1981). Near vertical

slopes exceeding 100 meters (333 ft) in height can be found in volcanic ash deposits in

Guatemala (Sitar, 1979).

Man-made slopes in cemented soils can also be found throughout the world, most

frequently in highway cuts. Cut slopes of the Interstate highway system around Vicksburg,

Mississippi, are steeper than 500 and exceed 18 meters (60 ft) in height. Slopes over 24

meters (80 ft) high were cut at a slope angle of 530 in loess deposits in Nebraska (Lutton,

1969). Highway cuts steeper than 800 and often exceeding 30 meters (100 ft) in height

were excavated in tephra deposits in Guatemala (Sitar and Clough, 1983). Also, highway

cuts with slopes up to 900 and exceeding 200 meters (667 ft) in height were excavated in

Shirasu deposits in Japan (Yamanouchi et al., 1973, 1981).

A special example of man-made slopes in cemented soils related to this investigation

is the system of near-vertical slopes in alluvial fanglomerate materials at the Twin Buttes

Open Pit Mine, 30 miles south of Tucson (Figure 1.2). As shown in Figure 1.3, these

slopes are typically about 150 feet high, benched vertical walls, which have been stable

since they were excavated 10 to 20 years ago. The soils are composed mainly of sand,

gravel, small amounts of silt, and occasionally boulder and cobble-sized particles, as shown

in Figure 104. They derive their strength from calcium carbonate cementation and particle

interlocking.

1.2 Nature of the Problem

Although the behavior of slopes in cemented soil indicates that the shear strength is

high, the factors influencing the strength of such soils have not yet been fully explained.

23

24

Figure 1.3 Vertical slopes of the Twin Buttes Mine.

Figure 1.4 In situ appearance of the alluvial fanglomerate materials.

2S

The shortage of information on the strength characteristics of cemented soils is due, to a

large extent, to the difficulty of obtaining good quality undisturbed samples for lab testing.

The susceptibility of the cemented soil to crumble when subjected to sampling disturbance

is one of the main problems encountered during sampling. Another problem is that the

degree and strength of cementation within cemented soils are highly variable. Variation in

cementation occurs not only on a micro-scale as part of the soil's fabric, but also on a

macro-scale over the structure of the entire mass. This variability is attributed to unequal

precipitation of calcium carbonate and to partial leaching of the calcium carbonate within

the soil mass. Hence, it is difficult to obtain representative samples for laboratory testing

even if expensive, highly sophisticated sampling techniques are used. Consequently, unique

definition of the strength characteristics of these materials is extremely difficult.

Most of the published data on the engineering behavior of cemented soils pertains

to soils artificially-cemented with portland cement (Sitar, ]979, 1981, 1983; Mitchell, ]976;

Dupas and Pecker, 1979; Sherwood, ]968; etc.). The results of these studies show that the

compressive strength of cemented soils is directly proportional to the amount of portland

cement in the mixture. These results are expected because the portland cement itself

enters into a chemica] reaction with water as it does in concrete. In the case of portland

cement stabilized soils, the soil is just the "aggregate". However, these results would not be

applicable to the type of naturally cemented soils which are the subject of this research,

because of differences in the properties and distribution of the cementing agents.

1.3 Purpose of the Research

The primary objective of this research was to study the behavior of calcium

carbonate cemented soils, in particular to determine the factors that affect the strength

characteristics of such soils. The study was designed to meet the following objectives:

26

1. Investigate the effects of calcium carbonate content on the engineering properties of

soils by sample preparation under carefully controlled conditions,

2. Develop a testing procedure to provide consistent results,

3. Define the effect that soil structure and calcium carbonate distribution have on the

strength characteristics of artificially cemented specimens,

4. Examine the effect of compaction variables on the composite structure of artificially

cemented specimens,

5. Evaluate the effect of confining pressure on the strength characteristics of artificially

cemented soil,

6. Evaluate the effect of curing time on the strength of artificially cemented soil,

7. Study the stress-deformation characteristics of a reconstituted, naturally cemented soil,

8. Examine the microstructure of the naturally cemented soil,

9. Study the effect of calcium carbonate content and distribution on the stability of

slopes by using data obtained from laboratory tests.

1.4 Scope of Research

This investigation was conducted in two phases. One phase was intend.ed to

determine the strength characteristics of artificially cemented specimens and was conducted

in the laboratory using the GDS triaxial apparatus, an advanced, accurate, and com­

puterized triaxial cell system. . The second phase was intended to define the fabric of

selected specimens from the first phase by viewing them under a scanning electron

microscope in order to gain insight into the mechanisms responsible for the macro

properties observed as part of phase one.

Slope stability analyses were used in the back calculation of the in situ cohesion for

the naturally cemented Sierrita soil. Slope stability analyses using strength properties of

27

artificially cemented specimens were also used to show the relationships among cohesion,

friction angle, safety factor, and calcium carbonate content for specified slope geometry.

28

CHAPTER 2

LITERATURE REVIEW

2.1 Cementation

Cemented materials are herein defined as soils composed of sand or gravel-sized

particles or fragments of rocks bonded together by a cementing agent to form a larger

composite structure having distinctive geological and geotechnical properties. The binding

is the result of cementation action which occurs either chemically, physically, or through a

combination of both. The degree of cementation within the deposit is variable, and

generally depends on many factors, such as the amount and type of cementing agent,

groundwater movement and weathering. The cementing agents, on the other hand, may be

present in the soil at the time of deposition, precipitate from percolating of either

infiltrated surface water or groundwater, or form by weathering of minerals present in the

soil mass. Typically, the common cementing agents that are naturally found are: silica,

calcium carbonate, clay, silt and iron-bearing minerals.

In the following discussions, background information is given on cementation of

soils and rock in general, together with summaries of state-of-the-art descriptions of the

behavior of specific cemented materials.

2.1.1 Cemented Soils

The cementation process depends on a number of factors including the type,

amount and spatial distribution of the cementing agent, the degree of packing, the density

and characteristics of the soil particles, and the method of deposition. Therefore, a wide

variety of cemented soil structures exists. Sowers and Sowers (1979) classified the structure

of cemented soils into the following two main categories based on the relative amount of

. cementing agent, binder, and bulky-grained soil particles:

29

1. Matrix Structure: This structure develops when the volume of the bulky grains is

less than about twice that of the binder, and little if any contact occurs among the

bulky grains (Figure 2.1). The physical properties of this type of structure depend

on the strength of either the binder or the bulky grains, whichever is weaker. As an

example, if the binder is clay and the bulky grains are sand, then the physical

properties of the structure are those of the clay matrix and they· tend to be cohesive.

If the opposite is the case, then the properties are controlled by the bulky grain.

2. Skeletal Structure: This structure develops when the volume of bulky grains is more

than about twice the volume of the binder. This type of structure can be subdivided

into either contact-bond structure or a void-bond structure.

a. Contact-bond structure: In this structure, the individual particles are mainly

cemented at the points of contact (Figure 2.2a). This structure can be formed

in soils with predominating particle sizes of sands or greater. The contact­

bond structures are relatively rigid and incompressible. However, a sudden

loss of strength of bonding material can occur as groundwater contacts it. The

material can also be leached from the points of contact by groundwater. In

either case, this loss of bond causes the structural arrangements to move into

denser configurations.

b. Void-bond structure: In this structure, the individual particles are in contact

with each other and the voids are filled by the binder (Figure 2.2b). This

structure develops when the soil particles are deposited and the cementation

action takes place subsequently. Binders, such as calcium carbonate, iron

. . . . . . . '. .'

. . . . . .. .... . . . . . . . . . ... . . ". . ' . . . ..' .. : .' I' ,,', •. .... . .

. . . . .' . . . · · . .. , .,

. . . . . ... . . .

• . I' • .' . : . .. ' .. • • • •

. " . . . . . . .. . . '. ...

. . ...

· . . . .

· '. . . . . . . · . .. . . · . . . . ..

. .. . . . . . . .. '. " . . . . . Binder

.. . . . . . . . . . . . . . . . . . . . . .. . , '. . . . .. . . . . . .

· • · . . .

Figure 2.1 Matrix structure (Sowers and Sowers, 1979).

30

'.:lIfo"' Dense ••.•• : Loose ~;jii1:1 Binder :.:.::; Binder

a. Contact-bond structure.

:i.:~ (./:':.\:'.: ::.: : ~'. ",": ~ '::':::">~:",\ '; :~: ~: ::'.:':"},:~ ....

:.:.':': Binder .... . . .. b. Void-bond structure.

Figure 2.2 Skeletal structure (Sowers and Sowers, 1979).

31

32

oxides and silica, are carried by the groundwater and precipitated to form a

cemented sand or gravel. The structures of void-bond materials are more

stable than those of contact-bond soils.

2.1.1.1 Cementation in Sands

Cemented sands are found in various locations throughout world, and in many

different geological environments. Sitar (1979) defined weakly cemented sands as naturally

occuring cemented deposits of loess, volcanic ash, dune sands, and marine beach sands

with measurable strength. The cementation process of cemented sand is generally

attributed to the effects of the binding together of individual grains by a cementing agent.

This process can take place either at the time of deposition by precipitation of the

cementing agent from percolating groundwater, or after deposition by weathering effects in

the existing soil minerals. The most common cementing agents found in cemented sand

are silica, clay, iron oxides and carbonate.

The degree of cementation of cemented sands generally depends on the charac­

teristics of the sand such as the grain size distribution, texture, shape and mineralogy

(Mitchell, 1976), as well as on the factors discussed in Section 2.1.1. However, cementa­

tion-like effects in sand can be produced by either mechanical interlocking of grains,

dense packing of sand grains, or capillary tension (Dusseault and Morgenstern, 1978; Sitar,

1979).

Chemically treated soils have been used for a long time and are well recognized in

the literature. Chemical additives, including lime, lime-fly ash, and calcium and sodium

chloride have been used in various parts of the world to stabilize collapsing soils. Soil

stabilization by portland cement was reported by Baker (1954), Felt (1955), Lambe, et at.

(1957, 1959), Norling and Packard (1958), Larsen (1967), Mitchell (1979), Portland Cement

33

Association (1954, 1956, 1979), and Sherwood (1968). Stabilimtion by use of bituminous

materials was reported by the American Road Builders Association (1953), Asphalt Institute

(1947, 1954), Johnson (1957), Michaels and Puzinauskas (1956). The use of chemicals for

stabilimtion was reported by Lambe (1951), Calcium Chloride Institute (1953), Anday

(1963), Transportation Research Board (1976), Terrel et aI. (1984), Thompson (1966, 1970),

Yamanouchi et al. (1982) and Youder and Witcmk (1975).

Table 2.1 shows a summary of data from the late 1970's regarding the engineering

characteristics and mechanical behavior of naturally cemented sands. The availability of

such data is limited. The remainder of this section presents a review of the geotechnical

characteristics of naturally and artifically cemented sands.

Sitar (1979) carried out a comprehensive study of the engineering characteristics of

weakly cemented sands that exist in California, along the Pacific coast between San

Francisco and Santa Cruz, and in Guatemala. The soils in California are medium-to-fine

grained sands which are naturally cemented with clay, iron oxides, and silica. The soils in

Guatemala are mainly a combination of sand and silt-size volcanic ash. The cementation

effect is produced by the interlocking of highly angular volcanic glass fragments.

Because of difficulties encountered during field sampling and the variability of the

degree of cementation within the deposits, Sitar conducted his study with artifically

cemented sands that were designed to simulate the field conditions. The testing program

included static and dynamic triaxial compression tests, simple shear tests, and the Brazilian

tension test. Specimens were prepared with 2% and 4% portland cement by weight. The

strengths were obtained for curing periods ranging from about 3 to 28 days.

The study concluded that cemented sands were brittle at low confining pressures,

and that ductility increased substantially as the confining pressure increased. While the

34

Table 2.1 Summary of Available Information on Cemented Sands (Sitar, 1979)

Korbin& Salamone Saxena &

Alfi Bachus Brekke Mitchell & <>them Lutrico

(1978) (1918) (1916) (1916) (1978) (1978)

SoU Naturally Naturally Artificially Artificially Naturally Naturally

Teated cemented cemented cemented cemented cemented cemented

IIaJId land IIaJId ADd And land

Cementing Carbonate Carbonate Shaping Portland Carbonate Carbonate

Agent and clay and clay wax cement

Sample Hand Hand Compacted Compacted 76mm Deni- 76mm Deni-

Type trimmed trinuned in molds in mold a BOn Sampler BOn Sampler

Type of Drained Drained .tatic Unconfmed Iaotropically Iaotropically

Teata .tatic .tatic triaxial, compreaaion cODllolidated coll801ldated

triaxial triaxial, indirect .tatic triaxial, cycle undrained

indirect tension indirect ten- triaxial .tatic

tension mon flexure

Streaa-Strain Yea Yea Yea Partial No Yea

Curves

Preaented

~,degreea 48 39-42 11.6-36 30-46 87-39 37-39

Dry Density, 17.8 16.-17.1 16.7 Not 11.8-15.7 11.8-15.7

kN/m3 aVailable

Water 10.6 8.8-18.5 N/A Not 20-40 20-40

Content, % available

Unconfined 2700 60 SS7 1000-15000 Not Not

Compreaaion available available

kN/mz

Approximate 1.6 .6 .6 .36-.8.0 Not 2-23.6

Strain at available

Failure, % Conunents Dynamic Dynamic Dynamic Data II moetly StrelB-.train Streaa-atrain

teats not teats teats not in reneralized curves not curves unla-

donej high not done donej BOU formj no dy- presentedj un- labeledj uncon-

.tatic haa time- namlc dataj confined com- rUled comprea-

.trength dependent pelt failure preaive mve Itrength

reapoll8e o-felata not .trength un- un1mOWDj

available knownj effect effect

of lample ofaample

cliaturbance cliaturbance

unknown un1moWD

3S

dynamic compression strength of cemented sand is about 16% higher than the static

strength, the dynamic tensile strengths were found to decrease as the number of loading

cycles (stress reversals) increased. This finding has great significance in the study of the

stability of cemented soil slopes since the principal mode of failure in such slopes is

believed to be tension.

Furthermore, a comparison of the results of the study conducted by Clough et at.

(1981) on four naturally cemented sands in the San Francisco Bay area with those of the

study on artifically cemented sands by Sitar yields the following results:

1. The similarity between data representing the strength behavior of naturally cemented

soil and that of artifically cemented sand leads to the conclusion that experimental

results obtained from tests on artificially cemented sands is valid for natural soils.

2. The angle of internal friction of cemented sand is basically the same as that of

uncemented sand. Therefore, the strength of cemented saud is attributed to two

components: friction and the cement itself.

3. Dilatancy of cemented sands during shear occurs at a smaller strain than that of

uncemented sands.

4. Density, grain size distribution, grain shape and grain arrangement have a significant

effect on the behavior of cemented sands.

S. Some degree of residual strength due to cohesion was detected in all of the cemented

sands investigated, yet the residual strength of cemented sands is close to that of the

uncemented sands.

36

2.1.1.2 Cementation in Collapsing Soils

Some soils at their natural water content have substantial strength, but they

experience an appreciable loss of volume upon wetting, load application, or both (Sultan,

1969; Clemence and Finbarr, 1981). This phenomenon is known as collapse, and is

described in the literature under a variety of topics including: collapsing soils, metastable

soil, near-surface subsidence, subsidence, hydrocompaction, and hydroconsolidation. The

collapsing soil structure may develop when fine sand or cohesionless silt particles are

bonded together at their contact points by cementing agents or capillary tension. A

honeycomb structure, which has a high void ratio and consequently low density is created.

Collapsing soils are found in many parts of the world. They can be formed in

many different depositional environments: loessial, colluvial, alluvial, subaerial, and aeolian.

They can also be found in mud flow deposits, volcanic tuffs, and man-made fills (Dudley,

1970). They can even be present in residual soils. Regardless of origin, however, they are

generally porous in fabric, and geologically young. Thus, in general, they vary in origin,

have porous fabrics, and are geologically young.

Although the shear strength of collapsing soil is mainly due to friction, a significant

amount of apparent cohesion also appears when the soil becomes dry or damp. In

Casagrande's (1932) work on collapsing soil, he defined such a soil as one having a

structure of sand grains bonded in loose silty sand. He concluded that a portion of the

fine fraction that exists in small gaps between adjacent grains of the soils that undergo

local compression bonded the larger grains.

Jennings and Knight (1957) provided a graphical demonstration of the collapse

mechanism based on Casagrande's concept. They discovered that a collapse-susceptible soil

at its natural water content could support an applied loading with negligible compression.

37

The soil structure remained reasonably unchanged and the fine particles between the larger

sand particles were locally compressed as a result of the loading. At low water contents,

the micro-shear forces of the bonded soil at the sand particle interfaces prevented the

grains from undergoing appreciable movement (Figure 2.3). However, when the loaded

soil was wetted and a certain critical water content was exceeded, the bonds became

weakened either because of softening of the fine silt or clay bridges or because of their

removal from the structure. This reduction in strength resulted in a reduction in volume,

and an increase in density, as shown in Figure 2.3b.

Barden et al. (1969) identified the major characteristics of the collapse mechanism

as: (1) an open, potentially unstable, and partially saturated soil structure; (2) a high

applied-load used to increase the instability; and (3) temporary bonding strength, such as

that resulting from high suction, a cementing agent, or both, which could be reduced upon

wetting to produce collapse. In addition, the collapse process could also be controlled by

the following factors: soil type, water content, plasticity, mineralogy, fabric, and the nature

of grain-to-grain contact (Sultan, 1971).

The work of Dudley (1970), Barden et aI. (1973), and Clemence and Finbarr (1981)

on the collapsing mechanism provides the various possible structural types of collapsing soil

shown in Figure 2.4. Their work confirmed the basic phenomenon of the collapsing

mechanism and the role of water in the process. A brief summary of their studies follows.

Dudley (1970) discussed the common case of the collapsing structure. His study

indicated that a temporary bond can exist due to capillary tension. The sand grains are

held in place by water menisci that remain after the soil is dried below its shrinkage limit

(Figure 2.4a). Since the air-water interfaces in these menisci are under tension, the actual

effective stress becomes greater than the total stress applied by the load. However, if

Consolidated Flocculated Clay Particles

Unconsolidated -+-----.;-.Flocculated

Clay Particles

a. Loaded soil structure before inundation.

Consolidated Flocculated Clay Particles

b. Loaded soil structure after inundation.

Fjgure 2.3 Behavior of coUapsing soil structure upon wetting (Jennings and Knight, 1957).

38

39

Meniscus

a. Capillary tension.

Silt grains

b. Fine silt bond.

Figure 2.4 Typical collapsible soil structures formed by capillary tension (Dudley, 1970; Barden et aI., 1973; Clemence and Finbarr, 1981).

40

water is added, the capillary tension is destroyed and, if the soil is porous, a new

arrangement in the soil structure occurs that causes rapid reduction in volume.

Dudley (1970) and Barden et aI. (1973) concluded that the capillary forces can also

exist in a collapsing material consisting of sand with a fine silt binder, as shown in Figure

2.4b. Hence, capillary tension can exist between silt-to-silt and silt-to-sand contact as well

as between sand-to-sand contact.

Clay is another potential bonding agent between the bulky sand and silt grains. A

number of structural arrangements of clay plates can be found, based on the geologic

origins and history of the soil (Barden et aI., 1973).

When the clay particles are depressed within the fluid in the pores, they cluster

around the junction in a random flocculated arrangement giving a buttress support to the

bulky grains, Figure 2.5a. Similarly, the clustering of clay particles usually found in mud

flow type of separation is shown in Figure 2.5b.

In the case where the clay is formed in place by authigenesis, a clay onion-skin

bond can develop as shown in Figure 2.Sc. The difference between this condition and

those shown in Figures 2.5a and 2.5b is the near parallel arrangement of clay particles.

Figure 2.5d shows a clay bridge structure where the sand particles are connected by a clay

bridge to form a honeycomb structure. This structure is similar to that shown in Figure

2.5a. It is also similar to Figure 2.Sb with the exception that the clay infilling is not

complete.

In the previous cases, the cementation that exists to support the bulky grains can be

destroyed with the addition of water. Water can leach out the clay and/or reduce its

strength. In either case, the addition of water ultimately causes the soil structure to

undergo a tremendous rearrangement that results in significant (instantaneous) volume

changes.

41

~~>-~~t~~- Clay buttress

a. Flocculated clay buttress.

Clustered -clay

~~~~~ particles

Sand

b. Mud flow type of separation.

Sand grains~--------~~

d. Clay bridge bond.

Sand 4-:1lI-----i~,., grains

Clay particles

c .. Clay onion-skin bond.

Figure 2.5 Typical colJapsing soil structures, fonned by cementing agent (Dudley, 1970; Barden et aI., 1973; Clemence and Finbarr, 1981).

42

Finally, chemical cementation can exist in some soils where inorganic materials,

such as iron oxides and calcium carbonate or the welding of the grain contact, produce

strength for many potentially collapsing soils (Barden et al., 1973; Clemence and Finbarr,

1981).

Loessial soils, on the other hand, are a typical example of wind-borne, naturally

cemented collapsing soils. Terzaghi and Peck (1967) defined loess as a uniform cohesive

wind-blown sediment in which the cohesion is predominantly provided by cementing of

the grains with calcareous material or clay. According to Sowers and Sowers (1979), loess

deposits consist of angular and subangular quartz and feldspar particles which are slightly

cemented with calcium carbonate or iron oxide. One of their characteristics, which is

related to this research, is their ability to stand in nearly vertical slopes. Generally, loessial

soils at low water content are able to support heavy loads without substantial settlement.

Upon wetting, their inter-particle bonds tend to soften, inducing collapse to their structure

and consequently causing large deformations (Clevenger, 1956).

The characteristics of the bond between loessial soil particles can be influenced by

both the liquid and the solid components. Thus, the structure of loess can be altered by

local weathering conditions. For example, in humid climates, loess structures tend to be

relatively dense and slightly plastic, forming loess loam.

The pronounced behavior of loess and its susceptibility to subsidence deformation is

determined by the action of internal and external factors (Larionov, 1965). Among the

former is the chemico-mineralogical peculiarities of the loess structure. The external

factors, on the other hand, are the intensity of the load applied to the loess mass, including

its own weight, and the character of wetting (duration, quantity, pressure, chemicals

contained in water).

43

Natural, undisturbed, in situ "dry" unit weights of true loess range from 75 to 85

pef. However, upon wetting, the loess consolidates and the natural unit weight is

increased. In some cases, the natural unit weight of wet loess reaches as much as 100 pcf

or more.

In conclusion, all collapsing soils are weakened by the addition of water, regardless

of their structural type. The water destroys the negative water pressure (capillary tension)

in the meniscus of the interparticle water (Figures 2.4a,b) and causes the effective stress to

decrease. The ion concentration is also affected by the amount of water present, since the

ion concentrations tend to decrease with the increase of water. Finally, in the collapsing

soil types that are cemented by the binder, the bonds are weakened by either leaching out

of the binders or by softening of them.

2.1.2 Cementation in Rocks

When fragments of any rock type are bonded firmly together with a cementing

agent to form a new rock type, the resulting material is classified as a cemented rock. The

cementation process of rocks can take place either from the infiltration of water carrying

various chemicals or the dissolution of certain minerals in the mass to form new bonding

materials.

Sedimentary rocks are formed mainly from the consolidation and cementation of

sediments, which are the end products of the weathering process (Farmer, 1983).

According to Krynine and Judd (1957), the most common cements found in sedimentary

rocks are: silica or siliceous cement, calcium carbonate or calcarious cement, clay or

argillaceous cement, and iron-bearing minerals or ferruginous cement. Calcium carbonate,

silica and iron-bearing minerals precipitate in the voids to bind the sediments. Clay

cement, on the other hand, is formed in dry climates as desiccation bonds.

44

Each of the cementing agents is susceptible to weathering just as they are in soils.

Siliceous cement is the most resistant to water action. while clay is the least resistant.

Calcareous cement is easily leached by water containing carbon dioxide or acids.

Limestone or dolostone are other examples of cemented rocks. They are composed

of calcium and magnesium carbonates. and are found mainly in marine deposits. They are

formed from soluble bicarbonate by bio-chemical and physico-chemical processes. One of

their distinguishable characteristics is their solubility in water that induces the formation of

large cavities. Secondary porosity or cracks may also occur in the limestone structure upon

hardening. However. the limestone may be indurated either from consolidation by

accumulating formations above or cementation due to the additional precipitation of

carbonates that bond the grains together (Sowers. 1975).

The cementing materials in rocks are the most influential factor controlling their

strength. The highest compressive strength is obtained when the cementing medium is

quartz, while the lowest compressive strength generally occurs in rocks that are cemented

entirely or partially with clay.

2.2 Calcareous Soils in Arizona

Calcareous soils are found in many parts of Arizona where predominantly arid to

semi-arid climatic conditions exist. They may be defined as those soils that have been

cemented and/or replaced by calcium carbonate. Machette (1985) defined calcic soils as

those soils that contain significant amounts of secondary calci~m carbonate. The

distribution of calcareous or calcic soils in Arizona is shown in Figure 2.6. These soils

have distinguishable geotechnical characteristics quite different from those of typical soils

found in other parts of the State or the country.

~ t..:.:.:J

D

Soft to nodular (non-continuous)

Relatively strong cementation (generally continuous)

Not present

Figure 2.6 Distribution of calcareous soils in Arizona (Beckwith and Hansen, 1982).

45

46

Calcareous soils of Arizona are formed by the accumulation of calcium carbonate.

Such a formation can take place by a wide variety of processes. Goudie (1973) discussed

the most common model of duricrust formation. In the following discussion, a brief

review of the major processes involved in calcium carbonate accumulation, as reported by

Goudie, and their validity to the actual formations that exist in Arizona are illustrated.

It is believed that calcium carbonate precipitation can take place in upward moving

capillary flow of calcareous water. The height of capillary rise is inversely proportional to

the capillary radius. Therefore, the capillary process occurs most efficiently in silty soils

with a near surface water table. Generally, these conditions are not satisfied in Arizona

where cemented sediment is found.

Carbonate is also accumulated from in situ weathering. Calcium carbonate

precipitation occurs during in situ weathering of calcium rich rocks by infiltrating water.

The atmosphere is the source of the CO2; rock, such as basalt, is the source of the calcium

cations (Ca++), and the water is the source of oxygen. However, weathering of rocks by

water is not likely to take place in arid to semi-arid environments. Therefore, this process

is not the primary source of the calcareous soil of Arizona.

Finally, calcium carbonate accumulation can be developed as a result of the supply

of calcareous material from an outside source. The carbonates in aerosolic dust, silt and

aeolean sand, are dissolved in rainwater to form Ca++ cations. These cations are carried

downward by percolation of the water from the surface, and subsequently precipitate to

form the cemented horizons.

Machette (1985) concluded that the calcareous soils of the southwestern United

States are formed mainly by subaerial precipitation of calcareous material that is supplied

by airborne carbonate and Ca++ dissolved in rainwater over thousands to millions of years.

47

However, the observation of carbonate formation in gravelly sediments shows

different morphological sequences with continual accumulation of carbonate (Gile et aI.,

1966). Gile et al. (1966) and Gardner (1972) described four stages in which calcareous

horizons develop in granular sediments. These four stages are:

Stage I - the development of thin discontinuous particle coatings.

Stage II - the continuous coating of particles by carbonate, with some of the voids

being filled. A weakly cemented matrix is formed.

Stage m - further coating of carbonate until all grains are coated and most of the

voids are filled. A strongly cemented horizon is formed.

Stage IV - induration of the carbonate formation. This 'results in a relatively

strong, petroca\cic horizon.

The stages of development of calcareous horizons in clay-type sediments are

essentially the same, with the exception of the varying nodal occurrence in Stages II and

m.

Furthermore, the development of any previous horizon is greatly influenced by a

variety of factors including, but not limited to, climate, type of soil, rate of erosion or

deposition, amount and chemical characteristics of airborne materials, and chemistry of

rain and surface waters. However, among all of the above, the climate factor has the most

pronounced influence in controlling the development of calcareous soils.

Consequently, a classification system associated with the stages of calcareous soils

formation was developed by Beckwith and reported by Beckwith and Hansen (1982). Five

classes of increasing strength were established according to matrix strength, structure, and

geotechnical properties. These classes are summarized in Table 2.2.

48

Table 2.2 Engineering Classification of Calcareous Soils of the Southwestern United States (Beckwith and Hansen, 1982).

elaas Typical Properties Description

1 dry properties; Holocene "coDaplini" loila. Gile et aI. Stage I of dllVe1op-a~ = lSOdeg ment. Weakly cemented with filaments and particle grain be = 200 Ib/Ct2 coatings

cEs = 1-6 bi dN = <16

2 Ea = 6-10 kei moderately cemented. Moderately weakened by moisture

~ = 33-37 deg increases. Gile et aI., Stage n, often nodular structure with

e = 1.0-3.0 kef continuoully cemented matrix. P1eilltocene

N = 6-26

3 Ea = 8-16 kel strongly cemented, only Ilightly affected by moillrure in-, = 36-42 deg creaeea. Gile et aI., Stage In, orten hili! laminated

e = 3.0-6.0 ksf or stratified structure. Pleistocene

N = 26-60

Ea = 16-60 kei very strongly cemented with essentially the properties of equ = 10-20 kef 110ft rock. Not IigniflCllJltly affected by moisture increases,

N = 60-200+ often haa .tratifled IItructure. Gile et aI., Stage IV.

Pleistocene or older

6 Ea = 60-600 kei moderately hard rock. Rock mechanice approachee neceulll'Y

qu = 1.6-6.0 kei for inveetigation and analYlie. Gile et a!., Stage IV.

N = 200+ Pleistocene or older

a Friction angle b Cohesion intercept c Deformation modulus from seismic surveys d Standard penetration test, blow count in blows per foot of penetration e Unconfined compressive strength

49

Beckwith and Hansen (1982) reached the following conclusions:

1. The calcareous soils of Arizona were developed primarily by infiltration of rainwater

and precipitation in the arid and semi-arid environments over the past several million

years.

2. The deposited materials of Stage I are silty sands, sandy silts, and clay-like sands of

low plasticity possessing high moisture sensitivity and having a distinct behavior which

places them in the category of collapsing soils.

3. Some of the clays of Class 2 soils and a few of Class 3 soils are potentially expansive

and should be evaluated by the expansive soil methods.

4. Standard geotechnical sampling techniques are usually not adequate to obtain

"undisturbed" specimens for lab testing because of the presence of nodules,

stratification, and relatively large gravel particles.

S. Many of the calcareous soils that exist in Arizona are relatively strong in the support

requirement of small-to-medium size structures. Therefore, a simple method of soil

investigation can be performed, i.e., standard penetration tests, soil classification and

determination of the index properties.

6. Large projects, which involve heavy structural loads, deep excavations, embankments

and dynamic loads, require more advanced methods of investigation. The examination

of large exposures in open pits, trenches, or large-diameter borings is also essential.

7. The engineering properties of calcareous soils are continuous over wide areas and are

easily mapped.

Table 2.3 gives a summary of typical engineering properties of the five classes of

calcareous soils in Arizona.

Table 2.3 Engineering Properties of Representative Calcareous Soils of Arizona (Beckwith and Hansen, 1982).

W, PIlII'. UnIW waa.r N £pad ~. r..' Ea'

lioii DIpth, CIMII- CMI- eon"", PI,- "Ub 81o .. /nc 1000 1000 1000 1000 ttgh

,.. c'J PI" Sot No. o.atpeIoa (n.) IIcalIen rlcaUon f") (") (") w w br br W dec W w W

lbIa.v.u."AI 0-1 1 11M 1-2 1-10 21·SS 2·1 O.l-U J.S.4JI --.,~

2 ... v.u."AI 1-2 S SM-ML 1-2 1-15 25-40 28 ... U-S.I U-1U 1I1DIIII'...., 10 lbandr_ted

• McCanaIdIIlMIdt, AZ 1-2 1 Mr.-a. 2 8-0 22-2t 8 !.I-U --- s.o (cS..t),.." _ted

• McCanaIdIIlMIdt, AI 1-2 2 Mr.-a. s T-I 2t-21 2O-!IO u·s..s --- s.o (fII).~ _ted

I W. ........ t.AS 0-1 2 GC 2 H u-u --- u-u ---(0I'UItII). -'b _ted

• ............... AI 1-2 • 1 85-1110 u-u --- u (' ...... " 1Uan." --.ted

f ....... 8...,.., 0-1 J se-a. 2-8 10-15 !IO-SI 25-!IO U-S.I --- S.8-8.0 ---AS"....Jdp1o ~_ted

• a.. a-., AI 1-1 J CL-CR I-T 20-50 21-70 2O-SS u-u T.8·u

• ........ AJ( .... B). .... .,arJWIted 0-1' 2 CL-al 8-U 2O.!IO to-50 10-25 O.2-U 1..3- 40 0.1- 10-25 O.T-S.I 10.8 2.0

Ibal." _ted ll-!IO S CL-CR 10-20 20-45 !IO-50 to-200 0.8-S.4 32-15 S.I-I2.o

VI 0

Soil No.

10

11

12

Table 2.3 Engineering Properties of Representative Calcareous Soils of Arizona (Beckwith and Hansen, 1982) --continued

W, Encr. UniCIecI Water N Eli ~. ~f Egc

Depth, CIuII- CIuII- Cmtent PI.a Wu.b BIa_/nc 1000 1000 1000 1000 'luh

'" ci Pl· sa'-DeDaipIIoIl (R.) fleaUon fleaUon ('" ('" ('" kif kif kif kif be dq kif bl kif

T.".,., AZ (de C) IDI:ICIaUaIJ __ ted 0-10 3 a.-CH 11-10 1&-60' 30-70 15-35 0.2-0.7 sg 0.5- 10-38 s.o-e..o

2..0

~ ... 10-23 3-C SO lC-30 20-60 010-75 26-65 O.5-U SO-eo 7..0-11..0 IIra'IIIT __ ted

Tompe. AZ (de A) wakIr C8llWlted 0-7 2 a. I-IS 10-20 26-35 5-20 2.\1-7.2 0.3-2.0 C2 0.2- 13-38 1.D-U

O~

IIIDd..teIr to 7-12 3 CR-Se 1-1& 1&-26 35-60 26-50 0.3-t.S 23-51 3.5-10..0 IIra'IIIT __ ted

T-..,AZ __ ., __ ted 0-& 2 a. I-IS 10-26 25-45 10-35 2 .. 0.51 10-30

IIDCIeraWr ... 1-%5 3-" a. 10-20 40-200 IIlrGnIlT mmmted

aP1Mt1cit)-IDdc:It bUqu1d1lmil

C Standard pcIIIttdIon tat, 111_ CIMlt In bIawa per foot 01 penetratIart

d Deformaticln IIIDCIulul fram plate load tat ·Olll~ moduJ .. 'Mill ~ moter tab

f OlllanMlloD moduJ .. fram MiImic "'"8JII COIII--'loa moduJ .. boock-calculated fram Mtu-t _ hlltorial

"UDCaII"-I a.nprain .tnnath I FrictIan anal. JCGhiolGa InWclpt

'kLialil ~,.. fram pre.IN IDIler t.d '-S'-"'alIa ~ fram a.,.-- __ tat VI .....

52

These results and others of various studies (Bissell and Chilingar, 1967; Fookes and

Higginbottom, 1975; Ham, 1962; etc.) that produced a large number of schemes for

engineering classification of carbonate sediments were largely derived from variables such

as the origin of constituent particles, texture, grain size, and mineral composition.

Consequently, none of those published schemes present an overall classification of the

whole range of materials.

The work by Rad and Clough (J 985) presents the only classification scheme that is

based on unconfined compressive strength of the cemented soil. This scheme is presented

in Table 2.4, which classifies the cemented soil into five classes, ranging from very weakly

cemented to very strongly cemented. According to Rad and Clough, this classification

system provides both simplicity and versatility. They suggest that their system can be used

for all cemented soils regardless of the type of cementation agent(s).

2.3 Determination of Calcium Carbonate Content in Sediments

In addition to calcareous soils, calcium carbonate is found in the form of dolomitic

limestones, marl or shells. Since calcium carbonate distribution within these materials is

not uniform, all soil samples that required analysis should be finely ground to eliminate

subsampling errors.

Many methods of determination of calcium carbonate content in soils have been

developed. The diversity of these methods are due to numerous factors, including

accuracy required, the nature of the sample being tested, testing time, testing cost, skill

required, and evironmental conditions.

53

Table 2.4 Proposed Classification System for Cemented Granular Soils (Rad and Clough, 1985)

Classification UCSa Description (kPa)

Very weakly cemented <100 cementation almost unap-parent to touch

Weakly cemented 100 - 300 breaks down under slight fin-ger pressure; can be scratched with the finger tip

Moderately cemented 300 - 1000 hardly breaks under finger pressure; can be easily scratched with the fingernail

Strongly cemented 1000 - 3000 difficult to trim, can be hardly scratched with the fingernail

Very strongly cemented >3000 very low strength soft rock (rock type)

a USC = Unconfined Compressive Strength

54

However, two basic methods of determination are available. In the first method the

calcium ion (Ca++) concentration is determined, while in the second method, the carbonate

anion (COi-) concentration is measured. Both methods are based on the assumption that

both Ca++ ions and CO;- ions are naturallly combined as calcium carbonate. The

requirements for accuracy of this assumption are acceptable for calcareous soil, since their

formation is based on this assumption also (Section 2.2). A discussion of the most common

methods for determination of Ca++ and COi- ion concentrations follows.

2.3.1 Soil Calcium Determination using Ca++ Ion Concentration

1. Calcium Specific Ion Electrode:

Woolson et al. (I970) proposed that the calcium content in calcareous soils could be

determined by using calcium specific ion electrodes with the calcium from soils extracted

by sodium acetate. The method is to add 50 ml of 0.5 N sodium acetate, NaC~H30~

(pH 8.2), to 4.00 gm of air-dried soil and place the mixture in a 250 ml polyethylene

centrifuge bottle for 2 hours. After the materials are centrifuged, 10 ml of the supernatant

solution is diluted with 100 ml of distilled water. The calcium content is determined by

use of a calcium-specific ion electrode.

2. Atomic Absorption Spectrometry (AAS):

The process involved in this method is to measure the amount of light energy

absorbed at specific wavelengths. The amount of light energy absorbed at a given

wavelength increases as the number of the atoms of a specific element in the light path is

increased. Hence, the atomic concentration of selected elements can be determined by

correlation of the amount of light they absorb to that of analyte present in known

standards.

55

The method requires the following instruments: a light source (either a hallow

cathode lamp or an electrodeless discharge lamp) an atom source generally obtained by heat

from a graphite furnace; a monochrometer to isolate specific wavelengths of the used light;

a detector to measure the wavelengths of the light accurately; electronics to treat the signa~

and a data collection device to show the results.

By using this method, separate determination of Ca and Mg can be made from the

same solution (Siesser and Rogers, 1971). For more information on the technique used in

this method, see Perkin-Elmer (1968).

3. Ethylenediamine Tetraacetic Acid (EDT A) Titration:

Details of this method are described in Bisque (1961), Black et aI. (1965), and

Glover (1961). A summary of the procedure along with the main features of this method

follow.

In this method, an organic acid, ethylenediamine denitril otatracetic acid (EDT A), is

used as a complexing agent for calcium. The experimental procedure is summarized by

Chaney et aI. (1982) as follows:

I. Acquire an aliquot of the soil water extract

2. Add sodium hydroxide (NaOH) with murexide indicator

3. Titrate solution with EDT A.

The amount of calcium present can be calculated using the following relation:

where

F = 1000 (A • B) v

F '" miUiequivalents of calcium/liter

v =: volume of specimen (mI)

A = volume of EDT A (mI)

B = normality of EDTA.

The method has the following features:

1. Use of standard laboratory equipment and chemicals

2. Separate determination for Ca and Mg can be made from the same solution

3. The method is relatively accurate

4. The initial outlay is low.

2.3.2 Soil Calcium Determination using a CO;-! Concentration

The following methods fall in this category of soil calcium determination:

1. Vacuum-distiUation and titration.

2. Gravimetric.

3. Acid-neutralization.

4. Gravimetric method for loss of carbon dioxide.

5. Volumetric calcimeter.

6. Pressure-calcimeter.

7. Acid-soluble weight loss.

S6

Methods 1-6 have been described in detail by Black et al. (1965). Method 7 has

been described in detail by Twenhofel and Tyler (1941).

Since several methods of carbonate analysis exist, the method best suited to the

requirements of accuracy and precision desired, time, operator skill, equipment cost,

57

reagents utilized, and laboratory equipment available should be selected. These require-

ments are compared for the abovementioned methods in Table 2.5.

2.4 Phase Relation in Soils Whose Pore Water Contains a "High" Percentage of Dissolved Salts

A typical phase diagram for conventional soil, schematically shown in Figure 2.7a,

consists of three phases (solid, water, air). The solid phase is defined as the small grains of

different non-soluble minerals. However, when soils saturated with a high percentage

(3-4% by weight) of dissolved salts are dried, the dissolved salts remain with the soil solids,

as shown schematically in Figure 2.7b. Hence, soil physical properties such as void ratio,

moisture content, degree of saturation, specific gravity of solids, porosity, dry density, etc.,

that are computed using the conventional phase relation of Figure 2.7a and given by Holtz

and Kovacs (1981) are not accurate (Noorany, 1984). Noorany's (1984) study presented

correct definitions and accurate phase relations for such soils by taking into account

dissolved salt in the pore water, as shown in Figure 2.7b. Appendix A illustrates these

definitions along with their complete derivation.

58

Table 2.5 Methods of Determining Calcium or Calcium Carbonate in Soils (Chaney, et al. 1982).

Analytical Initial

Relative Speedb Equipment SkJlloC

Method Accuracya Specimenl/day Coat Operator

Calcium-specific 10 low Some chemical experl;iee

ion electrode required

Atomic abeOl'ption accurate 20 high Skill and expertise re-

spectrophotometry quired Cor letup and

calibration

EDTA titration accurate 6-10 low Some chemical expertiee

required

Vacuum-distillation 8 moderate Some chemical expertiee

and titration method required

Gravimetric method good 10 low Some chemical expertiee

required

Acid-lOluble weight rough 60 minimal Minimal .kill

lou methods

Acid -neutralization 20 minimal Some chemical expertiee

method required

Gravimetric method low Minimal skill

Cor 1018 oC CO2

Volume calcimeter 10 low Some chemical expertiee

method required

Pressure Guometric accurate 10 low Some chemical expertiee

calcimeter Methods

method . Karbonat 50 low Minimal.kill

Bomba

a Claases oC accuracy balled on the Collowing: l--accurate, generally leu than ±1%i 2--good, generally leas than ±6%i

and S--rough, generally over ±6%.

b E'.etimatea baaed on 8-h day with one apparatus and one technician.

59

Table 2.5 Methods of Determining Calcium or Calcium Carbonate in Soils (Chaney, et aI., 1982)--continued.

Method

Calclum-lpecific

ion electrode

Atomic abaorption

spectrophotometry

EDTA titration

Vacuum-distillation

and titration method

Gravimetric method

Acid-soluble weight

10ea methods

Acid-neutralization

method

Gravimetric method

tor lou of CO2

Volume calcimeter

method

Preuure

calcimeter

method

Gaaometric

Methods

Karbonat

Bomba

cyanide

ammonia

Ba(OHh HCL.SnCI2

HCL

HCL

NaOH

HCL

HCL

HCL

HCL

Comments

1. Determines Ca+2

2. 0.6 N IIOdium acetate (Na~HS02) having a pH of

8.2 mUlt be UJed to limit tree CaCOS

1. Accurate at low concentrationa

2. Separate determinations a Ca ++ and Mg++ can be made

from the same solution

Separate determinations a Ca++ and Mg++ can be made

from the lame solution by an ~itional titration

Foaming is frequently excessive. especially with soils high

in carbonate

Accuracy of this method is dependent on the accuracy

of the weighings and the ability of the absorbent

to retain all the CO2

Accuracy and precision decrease markedly for specimen

weights 1_ than 2.0 g

Estimate of carbonate will usually be IIOmewhat high due

to other constituents reacting to some degree

with the acid

Accuracy of this method is dependent on the accuracy of

weighings and upon the degree to which CO2 retained

in solution i. compensated for by water vapor 10_

Accuracy dependent on (1) vigoroua Ihaking of reaclion

f1uk. (2) uniform temperature of environment.

and (8) standardised input a HCL

1. Hi normally employed in apparatua preBIure 'Yltem

2. Range a calibration from S to 110%

Figure 2.7

Weight

Va Air War:4 0

vvT n Vw Water Ww

:~:~:·;:it~:·:::::·~:"::~l·\:·.:S::.~:~g!:.:.: .... ·::::: W V

Vs 'll~iiir'i Ws ...&.. ___ -L-_

a. Typical soil.

b. Soil.containing a "high" percentage of dissolved salts.

Phase diagram showing relationship of weights, masses, and volumes of soil, salt, water, and air in soil or rock.

60

CHAPTER 3

EQUIPMENT AND MATERIALS

61

A variety of equipment was used at different stages of this study. Soil was

obtained from two locations in and around Tucson, Arizona. However, one main soil type

was used throughout this research. The description of the equipment and materials used .

are presented in this chapter; Specimen preparation, instrumentation, testing procedures and

associated computations are discussed in the following chapters.

3.1 Equipment

A description of the following equipment is presented in this section:

I. The GDS Triaxial Testing System

2. A Controlled Environment Curing Room (Moisture Room)

3. Modified Compaction Mold and Hammer

4. Automatic Valving Vacuum Evaporator Model VE-IO

5. Hammer Sputter Coater

6. Scanning Electron Microscope (SEM)

7. Polaroid Positive/Negative 4 x 5 Land Film, Type 55

8. Apparatus and Supplies for Particle Size Analysis of Soils

9. Apparatus and Supplies for Specific Gravity Test

10. Apparatus and Supplies for Atterberg Limits

11. Apparatus and Supplies for Standard Proctor Compaction Test

12. Apparatus and Supplies for Modified Proctor Compaction Test

62

3.1.1 The GDS Triaxial Testing System

The shear strength testing equipment used for this research was a GDS Triaxial

Testing System developed by GDS Instruments Ltd. of Surrey. England. The system.

shown schematically in Figure 3.1. consists of:

(1) One Bishop/Wesley Triaxial Cell.

(2) Two GDS digital pressure controllers with a capacity of 2000 kPa (1000 cc) each.

(3) One GDS digital pressure controller with a capacity of 1000 kPa (200 cc).

(4) A Hewlett Packard HP85B computer.

(5) A Hewlett Packard 7470A graphic plotter.

Detailed descriptions of each of the system's elements can be obtained from the

manufacturer's brochure; a brief description of each is given in the following sections.

3.1.1.1 Bishop/Wesley Triaxial Cell

The Bishop/Wesley (1975) Triaxial Cell or Hydraulic Triaxial Apparatus is shown

diagrammatically in Figure 3.2 and photographically in Figure 3.3. The changing of fluid

energy into mechanical energy is the principle by which the apparatus works.

The upper part of the cell is similar to a conventional triaxial cell except that it is

stationary during the testing operation. The load cell is brought to contact with the top

loading disk before the test is begun by .the adjusting nut on top of the cell.

The lower section of the cell. the bottom pressure chamber, is the moveable section.

It consists of an aluminum cylindrical chamber containing a moveable aluminum piston

which can be controlled by the fluid pressure of the chamber.

The axial load is applied by increasing the pressure in the bottom pressure chamber

which pushes the loading ram upwards. The sample is placed on a pedestal at the top of

@) ,r== I I!-. ®

I

{} @ r:Ii]aR'.;fD ..... :. III ~

I ~

@L;flSNi$\ ® I

Figure 3.1 Diagrammatic layout of the GDS triaxial testing system. I - Bishop/Wesley Triaxial CeU 2 - Cell and lower chamber digital pressure controllers 3 - Sample pore water digital pressure controller 4 - Hewlett Packard HP 8SB computer S - Hewlett Packard 7470A graphic plotter

CD

0'\ W

64

- ,..... College

ee"

::: C1ll11der • " - pre.llre line S .. ~

~ Porous .ample

Upper (,r/olliol

pore pre • ..".e tran.tlucer

Bellofram .eol

D .e

I D

oS ,"oodlng

gauge ~ ,"Ineor • CD Dial gauge

~

! Cross

i;~ Spacer block B.llofram 1001

.",Q .. litE -.~ Bottom In/.t to apply 'a.~ pressure to lOading

ram

Figure 3.2 Bishop!Wesley stress path apparatus.

65

Figure 3.3 Photograph of Bishop/Wesley Triaxial Apparatus.

66

the loading ram. The piston and pressure chamber are located beneath the load ram. Pore

pressure leads from both ends of the sample pedestal are taken down the center of the

equipment and out through the slots in the base for connection to a controller and pore

pressure and/or volume change measuring devices.

Two identical Bellofram roDing seals are used in the apparatus to retain the cell

fluid and the bottom pressure chamber fluid while allowing the loading ram to move up

and down. The use of the two seals has the following advantages:

(I) Strain measurement can be made externally either by means of the dial gauges

placed on the cross arm attached to the loading ram (as shown in Figure 3.2) or by

means of measuring the volume of fluid entering the load chamber. Both

measurements were used throughout this research.

(2) Extension tests (tests in which radial stress is greater than axial stress) can be

performed by making the pressure in the bottom pressure chamber less than the

cell pressure.

(3) The linear bearing in the bearing housing is not submerged in either the cell or

loading chamber fluids. Therefore, the use of oil to protect the bearing is not

needed.

The worst thing that can happen to a bellofram seal is that it be turned inside out.

Although this apparatus is designed to minimize the probability of this happening, care

should be taken not to push the loading ram up or down manually or not to depressurize

the bottom pressure chamber excessively.

3.1.1.2 Pressure Controllers

The GDS Digital Pressure Controller is shown diagrammatically in Figure 3.4 and

photographically in Figure 3.5. It provides the essential link between the computer and the

OfgIraf con'ro' clrcul'

S'~per mo'or and ,ear bo.

'fsrep$

1 Linear bearing

Ball!er ..

Analo, 'eedbock

PresSUre cylinder

Air

Pis'on

Oeafred wa'.,.

Figure 3.4 Diagrammatic layout or the digital pressure controller.

Pressure outl ••

'\. Press .... 'ranSduce,

0\ -J

68

Figure 3.S Photograph of the digital pressure controller.

69

test cell. This microcompressor controlled, hydraulic servo-mechanism generates and

measures water pressure and volume change and digitally displays the value "real time"

during the test. It has the following features:

(I) A constant or varying water pressure source that can be controlled to an accuracy

of I kPa. The pressure magnitude is digitally displayed.

(2) A constant-volume pore pressure measuring system.

(3) A digital volume-change gauge that displays volume-change to I mm3•

Details of the components are contained in the manufacturer's brochure.

3.1.1.3 Hewlett Packard Computer and Graphic Plotter

The computer system used as part of the triaxial system in this research was a

Hewlett Packard HP85B computer with a 7470A graphic plotter. Figures 3.6a and 3.6b

show a photograph of this computer and plotter.

The HP85B computer has the following significant features:

(1) The computer has a built-in drive that enables it to load and store programs and

data on a magnetic tape cartridge. The data tapes can be played back after the test

is complete.

(2) The computer itself has the high-speed storage capacity of a built-in "hard" disc.

(3) The computer can list programs and data by a built-in thermal printer.

(4) The computer has graphics capabilities if provided with appropriate software.

The HP7470A Graphics Plotter is a vector plotter which produces high quality,

multi-color graphics. Plotting occurs with approximately 2g acceleration and a maximum

velocity of 38.1 cm/s.

70

Figure 3.6a Photograph of HP8SB computer.

Figure 3.6b Photograph of HP7470A graphic plotter.

71

3.1.2 A Controlled Environment Curing Room (Moisture Room)

The room is located in the Civil Engineering Building at the University of Arizona.

The environment is controlled by a thermometer and a hygrometer to obtain the desired

curing conditions. Normal curing conditions, 700F and 100% relative humidity, were used

for this study.

3.1.3 Modified Compaction Mold and Hammer

A specially-built cylindrical, aluminum mold consisting of three split sections and a

small drop hammer (Figure 3.7) were used for triaxial specimen preparation. The mold

consists of a 50 mm internal diameter and a 100 mm high cylinder with a base and collar.

During compaction, the base plate is firmly fixed to the mold's bottom with three wing

nuts. The mold collar, on the other hand, is held to the mold's top by three pins.

3.1.4 Automatic Valving Vacuum Evaporator

To prepare specimens for viewing under an electron microscope, an automatic

valving vacuum evaporator, Model VE-IO (Mikros Inc., Portland, Oregon) was used for

drying the specimens prior to their initial coating with a gold-paUadium coating. This

equipment is located in Room 103 of the Agricultural Sciences Building and is maintained

by the College of Agriculture at the University of Arizona. The vacuum evaporator,

shown photographically in Figure 3.8, has automatic pre-programmed circuitry to the

vacuum system and is controlled by OPERATE, CHANGE and STOP push buttons. The

vacuum level is indicated on a meter in millimeters of mercury (Torr) as measured by a

Pirani gauge in the vacuum manifold.

72

· '.'

Figure 3.7 Compaction mold and hammer for specimen preparation.

73

3.1.5 Hummer Sputter Coater

Since natural soils are not generally electrically conductive, they cannot be imaged

using the Scanning Electron Microscope (SEM) unless they are coated with a conductive

material. A Hummer I (Technics Company, Alexandria, Virginia) was used for specimen

coating. This device is also located in Room 103 of the Agricultural Sciences Building and

is maintained by the College of Agriculture at the University of Arizona.

The Hummer I (shown in Figure 3.9) is a d-c sputtering system. A negative

potential is applied to the cathode, in which a gold-palladium coating is used, and enclosed

in the process chamber at a pressure of 50- I 000 miUitorr. The cathode material is

subsequently deposited on the specimen, which is placed on a standard specimen holder

(aluminum disc). A process cycle of 2-3 minutes for 7S to 200 Jl. coatings is favored and

was used in this research.

3.1 .6 Scanning Electron Microscope (SEM)

An I.s.I. DS-130 scanning electron microscope (International Scientific Instruments,

Inc., Santa Clara, California) was used to observe the microfabric of the soils. This

instrument is located in Room 103 of the Agricultural Sciences Building and is maintained

by the College of Agriculture at the University of Arizona. The SEM (Figure 3.10) is a

sophisticated imaging system enabling the surface topography of very fine-grained soils to

be studied with a high resolution. However, it differs radically from conventional trans­

mission and reflection electron microscopes in producing a magnified image without inter­

position of lenses of any sort between the specimen and the screen upon which the image

is displayed. The image is obtained by detecting low energy electrons produced by

secondary emission. To produce this secondary emission from the sample surface, an

electron beam is demagnified by passing it through a five-lens system to produce a

74

Figure 3.8 Mikros VE-IO Vacuum Evaporator .

• .. I).

Figure 3.9 Hummer Sputter Coater.

75

Figure 3.10 I.S.I. DS-130 Scanning Electron Microscope.

76

focused image. This focused beam, upon impinging the surface of the specimen, causes the

emission of low energy secondary electrons from the area being irradiated. The detected

electrons are sent to a cathode ray tube for imaging. For every point on the scanned

position of the specimen, there is a corresponding point on the face of the cathode ray

tube. Differential emissions from various areas of the specimen surface produce contrast,

and an image of the specimen is seen.

An lSI DS-130 is a dual-stage scanning electron microscope. The five-lens system

makes it possible to examine large (up to S in. diameter) specimens on the bottom stage at

low resolution in order to focus the instrument. Ultra-high resolution can be obtained on

the top stage. The acceleration voltage ranges from 1 to 40 kV (l-kV steps). The

magnification is controlled by varying the amount of deflection of the electron beam and

ranges from 10 to 300,000 times. Working distances change from 8 to S3 mm. The second

stage resolution can reach 60 ~ while the first stage reaches 30 X.

3.1.7 Polaroid Positive/Negative 4 x S Land Film Type SS

A Polaroid camera loaded with Positive/Negative, 4 x 5 Land Type 55 Film

(Polaroid Corporation, Cambridge, Massachusetts) was used in the SEM-mount to photo­

graph the specimens being viewed. The typical process time was between 20-25 seconds.

For best results, the temperature at the time of processing was kept between 70-80oF.

3.1.8 Apparatus and Supplies for Particle Size Analysis of Soils

As specified by ASTM D 422 [Particle-Size Analysis of Soils].

3.1.9 Apparatus and Supplies for Specific Gravity Test

As specified by ASTM D 854 [Specific Gravity of Soils].

77

3.1.10 Apparatus and Supplies for Atterberg Limits

As specified by ASTM D 423-24 [Liquid Limit, Plastic Limit, and Plasticity Index

of Soils].

3.1.11 Apparatus and Supplies for Standard Proctor Compaction Test

As specified by ASTM D 698 [Moisture-Density Relations of Soils and Soil­

Aggregate Mixtures using S.S-16 (2.49 kg) Rammer and 12-in. (30S-mm) Drop].

3.1.12 Apparatus and Supplies for Modified Proctor Compaction Test

As specified by ASfM D ISS7 [Moisture-Density Relations of Soils and Soil­

Aggregate Mixtures using IO-Ib. (4.S4 kg) Rammer and 18-in. (457 mm) Drop].

3.2 Materials

Two types of soils were used in this research. Only one soil type (Type A) was

used throughout the study. Type A soil was coUected from the University of Arizona

CampbeU Avenue Farm, located at 4101 N. Campbell Avenue, Tucson, Arizona. The other

soil type (Sierrita), used at a later stage of the study, was collected from the Twin Buttes

open pit mine, located 30 miles south of Tucson. Discussions of the engineering

characteristics of these materials are presented in the following sections.

3.2.1 Characteristics of Type A Soil

3.2.1.1 General

Type A Soil was used to prepare artificially cemented specimens for the following

reasons:

(I) The soil contains no calcium carbonate or other soluble minerals

(2) The soil's geotechnical characteristics were suitable for the study

78

(3) The Campbell A venue Fann was readily accessible for obtaining samples.

3.2.1.2 Grain Shape

The shape of a soil particle is defined by the particle's sphericity and roundness

(Krumbein and Sloss, 1955). Sphericity is related to the degree of acquiescence of the

shape of the particle to that of a sphere. Roundness, on the other hand, is related to the

sharpness of the edges and corners. Two approaches have been developed to classify grain

shape. The first approach, developed by Russell and Taylor (1937), Krumbein (1941),

Powers (1953), and Krumbein and Sloss (1955), was concerned with either photographic or

visual comparison of the grains. The second approach, developed by Wadell (1932, 1933,

1935) and Krumbein and Sloss (1955), was used to describe grain shape.

A visual classification was used in this study. In a visual comparison of the

photomicrograph, shown in Figure 3.12, to the charts of Powers (1953), Figure 3.1 la, and

Krumbein and Sloss (1955), Figure 3.11 b, the grain shape of Soil Type A is considered

angular to subangular with a high degree of sphericity. The estimated ranges of the

particles' sphericity and roundness are 0.6 to 0.8 and 0.3 to 0.4, respectively. A perfectly

spherical particle would have sphericity and roundness values of 1.0

3.2.1.3 Grain Size Distribution

Grain size distributions (gradations) for the soil were obtained by means of sieve

and hydrometer analyses. A typical grain size distribution curve is shown in Figure 3.13.

The effective particle diameter, D1O' is 0.031 mm, and the material has a Coefficient of

Uniformity of Cu = 5.57 and a Coefficient of Concavity of Cc = 1.39. According to

American Association of State Highway and Transportation Officials (AASHTO) and the

Unified Soil Classification System (uses) criteria, the soil would be classified as an A-2-6

and SM, respectively.

YEll'!' allOULa"

0.9

~ 0.7 o it IIJ :z: 5; 0.5

0.3

• -.. ..

0.1

MOULAII lue-" "

AllClUL .... II.e-" "

IIOUNDeO IIOUllOED

a. Roundness scale (Powers, 1953) .

• • • • ~ .-. • ~ • .. • -... .. ~ .. 0.3 0.5 0.7 0.9

ROUNDNESS

"" "EU.-; ROUIID£D

b. Roundness and sphericity scale (Krumbein and Sloss, J 955).

Fjgure 3.11 Charts for visual estimation of roundness and sphericity of soil grains.

79

80

Figure 3.12 Thin section photomicrograph of type A soil.

100

80

g'so --en en o 0. ~40

20

010=0.031 030=0.087 060=0.174

Cu= 5.57 CC = 1.39

.. ~ 0"-..0'

w

D-o QOI

1,.00 10-1-

J V~

I/O

I J .0

7 IU

IU

~

0:1 . I Particle Size (mm)

Figure 3.13 Grain size distribution curve of type A soil.

-

10

00

82

3.2.1.4 Compaction Tests

Standard and Modified Proctor Tests were performed to obtain the material's

compaction characteristics. The maximum dry density obtained from the Standard Proctor

Compaction Test (ASTM D-698) was 1.77 gm/em3 (110.5 Ib/ft3 ) and the optimum water

content was 14.75%. The Modified Proctor Compaction Test (ASTM D-1557), on the

other hand, yielded a maximum dry density of 1.90 gm/em3 (118.6 Ib/ft3) and an optimum

water content of 11.5%. The specific gravity of the soil solids is 2.67. The compaction

curves and the zero air voids curve are shown in Figure 3.14.

3.2.2 Characteristics of Sierrita Soil

3.2.2.1 General

Samples were collected at the Twin Buttes open pit mine from approximate depths

of 120 and 240 feet below the original ground surface. The samples were manually

collected in the form of blocks approximately I cubic foot in volume. Attempts failed to

obtain undisturbed samples for triaxial and direct shear testing by sculpting the blocks in

the laboratory. Therefore, the blocks were thoroughly broken up with a mortar and pestle.

All particles larger than 4 mm were removed from the broken sample. A representative

sample was then obtained by dividing the soil using a sample splitter.

32.2.2 Grain Shape

The grain shape of Sierrita soils, shown in Figure 3.15, was considered subangular

with some subrounded particles with relatively high sphericity. The particle sphericity was

between 0.3-1.0, while the roundness ranged from about 0.5-0.6.

-rt')e 1.85

~ e 0' -~ ---en c:: (1)

0 ~ o 1.75

A

£ \ £

•

10.00 0/0 Water Content

\ 0

£ MOD • STO o ZAV

\ 0

\ 0

\

20.00

Figure 3.14 Dry densjty-water content curves of Type A Soil,

83

84

Figure 3.15 Thin section photomicrograph of Sierrita soil.

85

3.2.2.3 Grain Size Distribution

Grain size distributions for the Sierrita samples were obtained by means of sieve

and hydrometer analyses. A typical gradation curve for each sampling depth is shown in

Figure 3.16. For Location I (120 foot depth level), 0 10 is 0.134 mm, Coefficient of

Uniformity of Cu = 11.18, and the Coefficient of Concavity of Cc = 1.19. At Location II

(240 foot depth level), 0 10 is 0.115 mm, Coefficient of Uniformity of Cu = 9.86, and the

Coefficient of Concavity of Cc = 1.35. According to uses criteria, the soil is classified as

SW. It is classified as A-I-a, according to the AASHTO system. The two grain size

distribution curves shown in Fig. 3.16 have the same shape and are approximately

coincident. This indicates that the distribution is consistent with depth.

3.2.2.4 Compaction Tests

Standard and Modified Proctor Tests were performed to obtain the deaggregated

material's compaction characteristics. The maximum dry density obtained from the

Standard Proctor Compaction Test (ASTM 0-698) was 2.04 gm/cm3 (127.3 Ib/ft3) and the

optimum water content was 9.8%. The Modified Proctor Compaction Test (ASTM 0-1557)

yielded a maximum dry density of 2.12 gm/cm3 (132.3 Ib/ft3) and an optimum water

content of 8.3%. The specific gravity of the soil solids is 2.69. The compaction curves

and the zero air void curves are shown in Figure 3.17.

3.2.3 Calcium Carbonate (CaC03 )

A commercially available reagent grade calcium carbonate Caco3 , meeting

American Chemical Society (A.CS.) specifications, was used as an additive to artificially

cement specimens. The pure calcium carbonate, in powder form, was manufactured by

J.T. Baker Chemical Co., Phillipsburg, New Jersey. An electron photomicrograph of a thin

100 Location I (.) Location 11 (0)

80

at .~ 60 en en

~ ~40

20

010=0.134 030=0.489 060= 1.498

Cu= 11.18 Cc=1.I9

o 0.01

010=0.115 030=0.420 / 060= 1.137

/' l,'/ Cu=9.86

//'~ Cc= 1.35

IJV 1/ II

J

II I .. J j

)~ '':' •

_n~ ~.,

• ",.. 0.1 I Particle Size (rrim)

~ /

Figure 3.16 Grain sim distribution curves of Sierrita soil.

~D ", ..

10

co 0\

-I"')E 2.05

~ E 0' ->----CJ) C CIJ c >-C 1.95 II

II

~

\ .r, 0

~

\ A

\ II

A MOO II STO

o ZAV

0

\ 0

II

1.85 1-...L-'-""-..I~-'-.L...IL.-L.-'-...a.-.IL.-L.-'---"""""'---2-0.00 0.00 10.00

0/0 Water Content

Fjgure 3.1 7 Dry densjty-water content curves of Sierrita Soil.

87

88

section of the calcium carbonate is shown in Figures 3.18a,b. The chemical and physical

properties of the calcium carbonate. as reported by the manufacturer. are shown in

Table 3.1.

3.2.4 Water

De-aired and distilled water was used throughout the study for specimen

preparation and during the triaxial testing phase. The pH of the water was between 6.5

and 7.

89

a.

Figure 3.18 Thin section of electron photomicrograph of calcium carbonate. a. Magni­fication SOIX. b. Boxed area in (a) magnified at SOIOX.

Table 3.1 Properties of Calcium Carbonate t

Chemical Analysis

Assay (CaCo3 ) (by EDT A titrm) Insoluble in Dilute HCl Ammonium Hydroxide Precipitate Chloride (Cl) Fluoride (F) Sulfate (So 4) Barium (Ba) Heavy Metals (as Pb) Iron (Fe) Magnesium (Mg) Potassium (K) (by AAS) Sodium (Na) (By AAS) Strontium (Sr)

Physical Analysis

A verage particle diameter ("') Surface area (mz/gm) Bulk density (gm/cm3)

Specific gravity

Sieve Analysis

% passing No. 70 sieve % passing No. 100 sieve % passing No. 140 sieve % passing No. 200 sieve % passing No. 325 sieve

tAs given by the manufacturer, J.T. Baker Chemical Co.

Value

99.4 0.002 0.002

< 0.001 0.0004

< 0.005 < 0.01

0.0005 < 0.001

0.002 0.0004 0.005 0.002

24 0.3 3.1 2.72

100 100 99 97 88

90

91

CHAPTER 4

DESCRIPTION OF RESEARCH

In this chapter,· the laboratory testing program is described. This includes a

description of the methodology used for each type of test, specimen preparation,

instrumentation, testing procedures, and associated computations.

4.1 Introduction

Several problems were encountered with sampling the cemented soils at the Sierrita

site. It is technically difficult to obtain undisturbed samples of the ~turally cemented soil

that are directly suited for strength testing unless expensive, highly sophisticated sampling

techniques are used. It was found that the degree and strength of cementation within the

soil deposits at the Sierrita site were highly variable. In addition, the presence of larger

particles (boulder size) within the soil mass made sculpturing of specimens for strength

testing virtually impossible.

Given the above-mentioned problems, it was difficult to conduct an experimental

investigation on the naturally cemented soils from the Sierrita site. Hence, specimens were

prepared by artificially cementing the Type A Soil with calcium carbonate to suit the

natural cementation condition that exists in the field. The reasons for selecting Type A

Soil in conducting the artificially cementing phase are given in Section 3.2.1.1. The use of

the artificially cemented specimens provided the investigation with uniform test specimens,

consistency in the procedures, and reproducibility of results.

4.2 Approach

The first approach for solving soil mechanics problems involving effects of stress

distribution and deformation is to assume the soil to be an ideal elastic medium

92

(Figure 4.1a) where stress-strain properties are defined by the deformation modulus, E,

and Poisson's ratio, II (Terzaghi, 1936). For stability problems, classical solutions are

obtained by assuming the soil to be rigid-plastic (Figure 4.Jb) or elastic-plastic (Figure

4.1c) where properties are defined by a single value of strength. However, real soils depart

from the elastic-plastic idealization, shown in Figure 4.1c, in one important aspect real

soils generally do not continue to yield at a constant stress after the point of failure, F, is

reached. Strain softening usually occurs as shown in Figure 4.ld. Furthermore, the stress­

strain relationship of soil is non-linear, therefore the relationship shown in Figure 4.1 e

usually applies. In reality, the constitutive relationships depend upon a number of factors

including type of soil, density, water content, structure, stress history, number of loading­

unloading cycles, confining pressure, loading rate and load duration. Therefore, the

modulus of elasticity and Poisson's ratio are generally not constant for a given soil and may

fluctuate as a function of one or more of the above-mentioned factors. The effect of each

of these factors on the stress-strain characteristics of soil can be best observed in a triaxial

test.

Although this research is primarily intended to define the macro strength properties

of cemented soils, other factors such as the effect on strength of the distribution of the

cementing agent within soil specimens will also be investigated. As indicated in Table 3.1,

the size of CaC03 particles is in the range of silt and clay. Hence, the Scanning Electron

Microscope (SEM) is used to determine the distribution of the cementing particles by

visual observation.

The procedures followed in this research to evaluate the effect of

cementation/CaC03 content on the strength particles of cemented soils consisted of the

following:

ITiESS

STRESS

STIESS

STRAIN

a) Elastic

STRAIN

c) Elastic-Plastic

STRAIN

e) Real Soil

STiESS

STiUS

F

STRAIN

b) Rigid Plastic

F

STiAIN

d) Elastic-Plastic Softening

F Denotes Failure

R Denotes Residual Value

Figure 4.1 Stress-strain relationships for ideal and real soils.

93

J. Mixing and compaction of artificially cemented soil

2. Triaxial compression test procedures

These are discussed in detail in the following sections.

4.3 Mixing and Compaction of Artificially Cemented Soils

94

The soil used in the experimental study was artificially cemented by the addition of

CaC03 to meet the following objectives:

1. To evaluate the effect of the calcium carbonate content on the strength characteristics

of the cemented materials.

2. To evaluate the effect of soil structure and cement distribution on strength at

different values of calcium carbonate content.

3. To develop a specimen preparation process that was reproducible.

4. To develop a testing procedure that yielded consistent results.

The experimental study conducted in order to attain the above-mentioned objectives

had the following critical aspects:

1. The preparation of artificially cemented specimens by a reproducible process.

2. Control of the density and water content of the mix.

These are discussed in detail in the following sections.

4.3.1 The Preparation of Artificially Cemented Specimens

Calcium carbonate was chosen as the cementing agent because it is the predominant

binder that naturally exists in the cemented soils at the Sierrita site. The reagent grade,

dry, calcium caibonate was added in powdered form to the soil in a predetermined

95

percentage quantity. The percentages used were 0%, 15% and 30%. These percentages are

on a dry weight basis of calcium carbonate to soil (i.e., 15% calcium carbonate content

means 15 parts of calcium carbonate to 100 parts of soil by weight). The Type A soil was

used for preparing artificially cemented specimens because it contained little or no CaC03

as determined by laboratory tests.

4.3.2 The Density and Water Content of the Mix

All triaxial test specimens were prepared using the specially built cylindrical

aluminum mold described in Chapter 3.

The Standard Proctor Compaction effort (Section 3.2.1.4) was used to prepare all

specimens. The soils were compacted in the mold in ten layers of equal weight. The drop

hammer used weighed 830 gm and was dropped from a height of 30 cm. In order to

obtain the Standard Proctor Compaction energy (592.7 kJm3/12375 ft-lbf/ft3), the number

of blows on each layer was computed as follows:

where

C.E. = M·g·H·L·B v

C.E. = compactive effort (kJ/m3, Ibft/ft3)

M = mass of the hammer (kg,lb)

g = acceleration of gravity (9.8/m/secz, 32.2 ft/secZ)

H = height of the hammer ram (m, ft)

L = number of layers

B = number of blows per layer

v = volume of compaction mold (m3, ft3)

(4.1)

96

Compaction tests using this specialized equipment were performed on Soil Type A

for the following conditions: Three tests without calcium carbonate, two tests with 15%

calcium carbonate content, and two tests with 30% calcium carbonate content. The

resulting compaction curves are shown in Figure 4.2. One test was performed on soil

without calcium carbonate using the Standard (ASTM 0-698) sample mold, hammer and

procedures. Table 4.1 gives a summary of the maximum dry density and optimum water

contents for all the tests performed.

The maximum dry densities of the group of soils without calcium carbonate

compacted in the special mold (1.694, 1.712, 1.723 gm/cm3) were less than that obtained

by using the Standard (ASTM 0-698) procedures as reported in Section 3.2.1.4, even

though the amount of compaction energy per unit volume was the same for aU tests.

These differences were due to one or more of the following factors:

1. The size and the shape of the mold (Johnson and Sallberg, 1962);

2. The H/D (height/diameter) ratio (Bishop and Henkel, 1962);

3. The mold support (Ray and Chapman, 1954);

4. Type and dimension of rammer and rammer guide (Proctor, 1933, 1948);

5. Weight, velocity, energy and momentum of the rammer (Proctor, 1948; Maclean and

Williams, 1948; Soil Mechanics for Engineers, 1952; Sowers and Kennedy, 1954);

6. Diameter of the rammer (Sowers and Kennedy, 1954; Hveem, 1957; Jackson, 1961);

7. Percent of total compaction energy applied in each tamp (Sowers and Kennedy, 1954).

Although the maximum dry-densities were different, the optimum moisture contents for all

these tests were similar.

-ft)e ~ e 0\ -~ ---en C (I)

0 ~

1.75

30% CoCO! o 30% CoCO! + 15% CoCO! x 15% CoCO! A w/oCoCO! • w/o CoCO! • w/o CoCO!

C 1.65

1.55 u-.a...a..."-'-......... .I...J,..I-L...a.....a....I....L...t...a.~~...a...Iu...I~1-'-1..J 0.00 10.00 20.00 30.00

0/0 Wafer Content

97

Figure 4.2 Dry density and water content curves for uncemented and calcium carbonate artificially cemented Type A soil.

98

Table 4.1 Summary of the Maximum Dry Density and Optimum Water Contents of the Compaction Test Carried Out on Type A Soil

Calcium No. of Volume Dry Water Carbonate No. of Blows per of the

Density Content Content Layers Layer Mold Comments (gm/cm3) (%) (%) (cm3)

1.694 13.00 0 10 5 196.35 Special Mold

1.712 15.00 0 10 5 196.35 Special Mold

1.723 14.70 0 10 5 196.35 Special Mold

1.760 14.75 15 10 5 196.35 . Special Mold

1.770 13.20 15 10 5 196.35 Special Mold

1.8IO 10.89 30 10 5 196.35 Special Mold

1.820 13.60 30 10 5 196.35 Special Mold

1.770 14.75 0 3 25 944.00 ASTM D-698

99

It was also noticed that the maximum dry density increased as the calcium

carbonate content increased. This increase was primarily due to:

I. The addition of very fine-grained material (calcium carbonate) increases the dry

density of the entire mass by filling the air voids.

2. The specific gravity of the calcium carbonate (2.72) is higher than that of the soil

(2.67).

In order to obtain a representative value for each condition, the families of curves

shown in Figure 4.2, were combined into three main groups. Each group was reported by

a single compaction curve to represent the average of the group. These "average" curves

are shown in Figure 4.3. Subsequently, six points were chosen from the curves to achieve

the objectives of this research. The locations of these points were chosen to minimize the

initial variation of the dry density and water content factors for test result comparison

purposes. The values of these points are presented in Table 4.2.

Hence, the variable factors affecting the strength of the mixture were accounted for

as follows:

I. The effect of calcium carbonate content (0%, 15%) at a constant compaction moisture

content 11.0%) dry of optimum was studied by specimens compacted under conditions

described by Points 1 and 2.

2. The effect of calcium carbonate content (0%, 30%) at a constant compaction moisture

content (-16.8%) wet of optimum was studied by testing specimens compacted under

conditions described by Points 4 and 6.

-rt') 1.75 E ~ E Ol -~

;t: en c: cv C ~ o 1.65

e 30% CaC03 • 15°/0 CoC03 o w/o CaC03

10.00 20.00 30.00 % Water Content

Figure 4.3 Dry density and moisture content curves of the three groups.

100

101

Table 4.2 Summary of the Dry Density and Moisture Content of the Chosen Research Point Values

Calcium Compaction Point Dry Water Carbonate Moisture

Number Density Content Content Content3 (gm/cm3) (%) (%)

1 1.69 11.00 0 Dry

2 1.75 11.00 15 Dry

3 1.75 6.71 30 Dry

4 1.69 16.60 0 Wet

5 1.75 14.85 15 Wet

6 1.75 17.00 30 Wet

a Relative to Optimum Moisture Content

102

3. The effect of calcium carbonate content (15%, 30%) at constant dry density

(1.75 gm/cm3) for compaction at moisture contents dry of optimum was studied by

testing specimens compacted under conditions described by Points 2 and 3.

4. The effect of calcium carbonate content (15%, 30%) at constant dry density

(1. 75 gm/cm3) for compaction at moisture contents wet of optimum was studied by

testing specimens compacted under conditions described by Points 5 and 6.

5. The effect of variable moisture contents wet (16.6%) and dry (11.0%) of optimum at

constant dry density (1.69 gm/cm3) and constant calcium carbonate content (0%) was

studied by testing specimens compacted under conditions described by Points 1 and 4.

6. The effect of variable moisture contents wet (14.85%) and dry (11.0%) of optimum at

constant dry density (1.75 gm/cm3) and constant calcium carbonate content (15%) was

studied by testing specimens compacted under conditions described by Points 2 and 5.

7. The effect of variable moisture contents wet (17.0%) and dry (6.71%) of optimum at

constant dry density (1.75 gm/cm3) and constant calcium carbonate content (30%) was

studied by testing specimens compacted under conditions described by Points 3 and 6.

In addition to studying the effect of the variables listed above, the effect of curing

time on the strength of CaC03 cemented soil samples was also investigated. Specimens

compacted under conditions described by Point 2 were tested after 7, 14, and 28 days of

curing in a controlled environment room.

4.4 Triaxial Compression Test Procedure

In this section, details of the laboratory procedures followed in performing triaxial

compression tests are presented. Included are descriptions of the laboratory testing

program, specimen preparation, triaxial testing procedure, loading method and rate as well

as the computational procedures followed in reducing the data.

103

4.4.1 Laboratory Testing Program

A laboratory testing program was designed to meet the objectives discussed in

Section 4.3. A summary of the test program is presented in Table 4.3. Untreated

specimens and specimens cemented with 15% and 30% percent calcium carbonate were

used to study the effect of CaCO:s content on strength. A few tests were also carried out

on (reconstituted) fanglomerate materials from the Sierrita site. In addition, a group of

specimens compacted at a constant CaC03 content, moisture content and dry density were

tested after being allowed to cure in a moisture room for 7, 14, and 28 days to examine

the effect of the curing time on strength.

4.4.2 Specimen Preparation

All specimens were prepared by placing ten layers of soil of equal weight into the

specially designed compaction mold described in Section 3.1.3. Prior to specimen

preparation, nine aliquots of material, each composed of an amount of over-dried material

equal to 1/10 of the desired specimen dry weight and an amount of distilled water equal to

1/10 of the weight of water required for the desired molding water content were

thoroughly mixed and tempered. These would be used for the first nine layers in the

mold. For the last layer, the amount of soil and water prepared was slightly increased by a

known weight, to cover any shortage of compacted material that might occur due to

preparation losses. The mold was covered with a piece of wet linen to reduce moisture

evaporation during the compaction procedure. Leftover material from specimen

preparation was collected, oven-dried, weighed and subtracted from the initial dry weight

of the tenth layer to determine the actual weight of the last lift of the specimen.

Table 4.3 Summary of the Laboratory Testing Program

Triaxial Compaction Cement Test No. of Curing Confininga Moisture Content Type Tests Time Pressure Contentc

(%) (days) (kPa)

0 UUb 9 0 0,150,300 Dry

IS UU 9 0 0,150,300 Dry

30 UU 9 0 0,150,300 Dry

0 UU 9 0 0,150,300 Wet

IS UU 9 0 0,150,300 Wet

30 UU 9 0 0,150,300 Wet

IS UU 9 7 0,150,300 Dry

IS UU 9 14 0,150,300 Dry

IS UU 9 28 0,150,300 Dry

Rd UU 3 0 0 Dry

R UU 3 0 SO Dry

R UU 3 0 100 Dry

R UU 1 0 200 Dry

R UU 2 0 300 Dry

aThree tests were performed for each confining pressure level during the artificially cemented specimens stage

b Unconsolidated-Undrained cRelative to Optimum Moisture Content d Reconstituted specimens of naturally cemented Sierrita Soil.

104

105

The water content of the compacted specimen, however, was found not to be equal

to that of the batch of soil from which it was prepared, particularly for specimens

compacted on the wet-side of optimum water content. This error may have resulted from

evaporation of the water during the specimen preparation. Therefore, the water content

was determined from measurements made after the specimens were completely dried. The

corrected water content was calculated from the difference between the weights of the

specimens measured before and after drying in the oven.

Following their preparation, the specimens were weighed and oven-dried, except for

those used to study the effect of cure time. They later were placed in the moisture room

to cure prior to testing. Reproducibility was found to be excellent as witnessed by the fact

that the weight of specimens prepared in this way had a maximum variation of only 2 gms

in a total weight of 355 gm, i.e., a maximum variation of less than 0.6%. Table 4.4

summarizes the statistical parameters for the dry densities of the specimens prepared for

this study. The statistical analysis shows that the method used for specimen preparation

was reliable in duplicating the dry density of compacted specimens.

4.4.3 Triaxial Testing Procedure

In prepration for each test, the lower chamber of the triaxial testing device was

f'llied with de-aired water (Figure 3.2). The test specimen was then positioned on the

pedestal. Once the specimen had been set up in the triaxial cell, the membrane was placed

on the sample. The thickness of the membranes was measured with a micrometer and

carefully inspected for local weaknesses and holes prior to each test. A suction membrane

stretcher and a split-cylindrical O-ring stretcher were used during the membrane

placement. These methods were discussed by Bishop and Henkel (1962) and Head (1982,

1986). The triaxial cell was then mounted on the bearing housing with the top cap ball

106

Table 4.4 Summary of the Statistical Parameters for the Dry Density of the Triaxial Testing Specimen

Dry Density

Cement No. or gm/em3 Standard Standard

Content SpecilJleIlll Mean Deviation Error (%) Minimum Maximum (m/em3 gm/em3 gm/em3

0 18 1.6868 1.6949 1.6902 0.0028 0.00065

15 45 1.7423 1.7691 1.7505 0.0032 0.00047

30 18 1.7427 1.7669 1.7492 0.0043 0.001

Ra 13 1.7092 1.8110 1.7681 0.0302 0.0084

a Reconstituted specimens of naturally cemented Sierrita Soil.

107

seated approximately 2 nun from the conical register fixed to the load cell. The triaxial

cell waS sealed shut and filled with de-aired distilled water.

Because the cementing agent (calcium carbonate) is water soluble, the tests were

carried out on dry specimens. Therefore, the specimen saturation phase of the triaxial test

was eliminated and an unsaturated undrained triaxial compression test was performed. The

test conditions (conf'ming pressure, displacement rate, etc.) discussed later were then read

into the HP computer. From that point on, the test was virtually run and completely

monitored by the computer. A program was written to direct the pressure controllers to

set the required confining pressures and make the required volume changes for the axial

deformation. Real time readings of pressure and volume changes were taken at preset

intervals under computer commands. The data collected by the computer was stored on

tape cassettes for future analysis and reduction. The results were also shown for real time

on the computer CRT according to specified analog formats, e.g., principal stress

difference versus strain. A detailed description of the equipment and procedures used for

these tests is presented in Appendix B.

4.4.4 Confining Pressure

Confining pressures of 0, 150, and 300 kPa were chosen to simulate the overburden

pressures at various levels in the pit slopes of the Twin Buttes mine. The 0 kPa confining

pressure was representative of the surface, 300 kPa represented the conditions in the

sidewall at the bottom of the pit, and 150 kPa was an intermediate value of the stresses.

108

4.4.5 Loading Method and Rate

The specimens were loaded at a constant rate of displacement under a constant

radial stress (confining pressure). Since dry specimens were used and the test performed

under unconsolidated-undrained conditions, no upper limit of the displacement rate was

required as is the case with saturated specimens. However, to provide an adequate time

for the pressure in the lower chamber and in the cell to be equalized, a 10 mm/hr dis­

placement rate was used throughout the testing program. The required axial displacement

. for the desired increment was then set. A computer program was written in BASIC to

calculate the lower chamber volume change required to obtain the specified displacement.

The program also monitored cell pressure until the required value was reached.

A detailed discussion of the displacement rate control on unconsolidated-undrained

tests are also presented in Appendix B.

4.4.6 Computations Related to Triaxial Tests

The following two sections contain a presentation of the equations involved in

evaluating the change in conditions that took place during operation of the hydraulic

triaxial apparatus.

4.4.6.1 Standard Calculations

The following parameters were measured during a test by the components indicated.

These parameters were used extensively in the computer program for controlling and

operating the equipment and calculating the results of the tests.

(1) Cell Controller:

(Jr = total radial stress

Pc = cell pressure

Il.vr = radial volume change

Il.vc = cell volume change, designated by cell controller = Il.vr

(2) Pore Pressure or Back Pressure Controller:

u = pore water pressure

Ppr = pore water pressure of the specimen, designated by the controller = u

Il.vu = volume change in the specimen

Il.vpr = volume change of the specimen, designated by the controller = Il.vu

(3) Lower Chamber Pressure Controller:

(Ja = P = axial pressure or pressure in the lower chamber

Pt '" pressure of the lower chamber, designated by the controller'" P

Il.vp = volume change in the lower chamber

Il.Vt = volume change in the lower chamber, designated by the controller = Il.vp

(4) Deviator stress, (Jd

(5) Original area of test specimen Ao

109

where Do = the mean original diameter of the specimen, due allowance being made

for the thickness of the rubber membrane.

110

(6) Original volume of the test specimen, Vo

where Lo = the original height of the test specimen.

The parameters described above were used to calculate the following values:

(1) Axial strain fa

(4.2)

where

a the effective area of the Bellofram seal

A.vl = volume change in the lower chamber.

(2) Current average area of test specimen A, assuming right circular cylindrical

deformation as per Bishop and Henkel (1962),

(4.3)

The derivation of this equation is as follows:

At any time after a change toL in length and to V in volume, the current average

volume of the specimen, V

V = Vo - to V = A (Lo - toL)

or

111

But A V = Apr> i.e.,

= [Vo-Apr ] A L - AL o

Multiplying the equation by LoiLo

A=

or

Ao - Ao Apr V A (I - A )/V A = 0 = 0 Dr 0

I - fa I - fa

[I - Apr v;] I - fa

However, Apr = 0 for the unconsolidated undrained triaxial test. Thus, the average

area of the UU test specimen A,

A A= __ 0_

I - fa (4.4)

112

(3) Total axial stress, ua

ePl .!..+U (I _.!.) _ W A r A A

(4.5)

where

W ::: weight of the loading ram

(4) Effective axial strr,ss, ua (4.6)

(5) Effective radial stress, u; U; = ur - u (4.7)

(6) Pressure in lower chamber, Pl

Given a target value of ua ' the desired pressure in the lower chamber is

calculated from Eq. (4.5) as follows:

A A W A P l ::: ua - - ur - + ur + - -a a A a

A W P l = (ua - ur ) - + ur + -a a (4.8)

(7) Principal effective stress ratio, K'

K' = ua/u; (4.9)

113

(8) Current average diameter, D

(4.10)

(9) Maximum shear stress, q

(4.1 I)

(10) Mean stress, p

(4.12)

(I I) Mean effective stress, p'

p' = (O'a + 0';)/2 (4.13)

(12) Axial deformation, 5

(4.14)

4.4.6.2 Calculations for Evaluating Loading Ram Friction

A certain amount of frictional force is developed in moving the linear bearing and

in rolling up amd unrolling the two Bellofram seals in the triaxial cell. Bishop and Wesley

(1975) found the frictional resistance to be equivalent to an axial stress difference of about

4 kPa. Since this would be significant for this study, the first step in all tests was to

calculate the value of the frictional resistance by measuring the lower chamber pressure

after having moved the ram up and after having moved the ram down. The frictional

resistance was then taken to be half the difference between the two readings. The

calculated value was then used to modify the pressure in the lower chamber.

In this research, the entire procedure was carried out automatically by the computer.

For more detail, see Appendix B.

114

4.4.6.3 Calculations for Accounting for the Rubber Membrane Effects

4.4.6.3.1 General. The cylindrical specimens in a triaxial device are sealed in a

water-tight rubber membrane before they are subjected to fluid pressure in the test cell.

Although there are many difficulties with installing the rubber membrane, and although its

presence may influence the test results, there are no practical alternatives. Investigations of

the problems associated with using rubber membranes have been made by many

researchers. Perhaps the most comprehensive of these is the study performed by Henkel

and Gilbert (I 952). An alternative to rubber membranes is the use of a cell fluid which is

not dissolvable, but de~ity and chemical effects on the soil eliminate this alternative.

Besides the effect of the rubber membrane on the soil strength and volume change

characteristics of the soil being tested, there may be membrane-related problems

encountered during testing due to leakage and the effect of dissolved gases and minerals in

the water on the elastic properties of the membrane. Testing membranes before their use

and using distilled and fully de-aired water usually overcomes these problems.

4.4.6.3.2 Membrane Thickness. The influence of the membrane on the strength of

the soil being tested is analogous to that of a reinforcing spiral on the strength of a

reinforced concrete column. Henkel and Gilbert (1952) showed that the strength

contributed by the rubber membrane is independent of the specimen strength, proportional

to the stiffness of the membrane, and independent of the cell pressure. The membranes

may increase the minor and intermediate principal stresses during specimen deformation if

they wrinkle or buckle under load. This is especially true in the case of loose cohesionless

soils during drained tests.

A method of membrane correction was derived by Henkel and Gilbert (1952) based

on the following assumptions: the rubber membrane and test specimen deform as a unit,

115

and the rubber membrane acts as a compression sheD. Hence, the total pressure on the

sample can be divided into two parts: the axial pressure (deviator pressure), and the

compression shell pressure (lateral pressure due to the rubber membrane).

The correction, Uno (psi), applied to the measured compressive strength due to the

effect of the rubber membrane, is given by the following expression:

where

0' 1rDMe 1rDMdl-d rm"---A Ao

D = initial diameter of the sample [inch]

E = axial strain

Ao = initial cross-sectional area of the specimen = A(I-E) [square inches]

A = the corrected area of the sample at axial strain E [square inches]

M = compression modulus of the membrane [lb. per inch].

(4.15)

Values for compression modulus can be assumed to be approximately the same as

those for extension, which can be easily measured. As has been shown by Henkel and

Gilbert (1952), the correction is approximately proportional to the sample strain for each

membrane. The corrections measured in the various tests that were carried out on the

common types of rubber membrane are summarized in Table 4.5. The computation of Eq.

(4.15) is carried out entirely by the computer throughout each experiment.

4.5 Electron Microscope Studies

The scanning electron microscope (SEM) was used to study the micromorphology

and microfabric of the cemented soils. Its use was intended to clarify on a submicroscopic

level the mechanisms that affect the macro-strength properties of cemented soils. Visual

observation of the amount and distribution of cementing agents in the artificially cemented

116

Table 4.5 The Correction Measured on Compression Strength Due to the Effect of the Rubber Membrane (Henkel and Gilbert, 1952)

Correction (psi/kPa) on Compression Strength (at 15% axial strain)

Test Type Thick Rubber Standard Rubber Thin Rubber (0.5 mm/0.020 in) (0.2 mm/O.OOS in) (0.1 mm/0.OO4 in)

Triaxial 1.4/9.65 0.6/4.14 0.3/2.07

Rubber Only 0.7/4.S3 0.25/1.72 0.1/0.69

117

specimens provides an explanation of the strength characteristics of the cemented soil

determined from the triaxial testing phase.

The SEM study was conducted on specimens obtained from the samples tested in

the triaxial device. A sizeable piece of the triaxial test specimen was obtained after the

test by manually breaking off a piece of the specimen away from the failure plane. Then,

pieces were chosen to represent the macro-structure of the material. The chosen pieces

were free of any fractures or molded surfaces (i.e., the pieces were obtained from the

center of the specimen). Each piece was then fractured horizontally and vertically so that

the fabric in both directions could be viewed under the SEM. The following specimen

preparation procedure was followed:

I. The fractured pieces were placed in a vacuum desiccator overnight for drying.

2. After the pieces were completely dried, each was coated with a thin film of gold­

palladium deposited in a Hummer I sputtering device. The coating was deposited

under pressures less than 100 millitorr at a current of 10 rnA and high voltage for 3

minutes. Specimens were mounted on a standard specimen holder (aluminum disc) by

using a double adhesive tape.

3. The gold-palladium coating of the specimen was then connected to the specimen

holder by forming a small strip of low-resistance silver contact cement to provide a

conductive coating over the specimen surface prior to its examination in the SEM.

4. The specimen and its holder were then placed in the second (lower) stage chamber of

the SEM, I's.I. Model DS-130. After the image was enhanced, an overall scanning of

the specimen was performed at low magnification (4S0X to SSOX).

S. A representative area of the specimen was selected to be examined at high magnifi­

cation. Photographs of the enhanced image were taken using Polaroid 4 x 5 Land

film Type SS/positive-negative at various magnifications.

118

The results of the triaxial tests and electron microscope study are presented in the

following chapters.

CHAPTER 5

PRESENTATION AND DISCUSSION OF TIlE TRIAXIAL COMPRESSION TESf RESULTS

119

In this chapter, the results of the unconsolidated undrained (UU) triaxial com-

pression tests are presented. Stress-strain curves and strength parameters obtained by using

specimens prepared by artificially cementing Type A soil and specimens of reconstituted

Sierrita soil are compared. The significance of selected variables, such as the cement and

water content, and confining pressure, is discussed.

5.1 Introduction

The triaxial compression test is widely used in geotechnical engineering to

determine the shear-strength parameters, the angle of internal friction (ifJ) and cohesion (c).

The most practical shear-strength testing of soil is based upon the Mohr-Coulomb failure

criterion, which expresses the shear strength (S) of soil as:

s = c + (un) tan ifJ (5.1)

where

ifJ = angle of internal friction

c = cohesion

Un = the is the normal stress acting on the failure surface.

It should be noted that c and ifJ are merely parameters defining the equation of

shear strength as a straight line (i.e., tan ifJ = the slope of the line, and c = the intercept on

the shear-strength axis). This straight line is called the "failure envelope" and represents

the limiting combinations of normal stress and shear stress that will result in failure in the

soil. Neither c nor ifJ is a physical property of the material, such as color, density,

120

odor, etc. The shear strength parameters can vary according to a variety of factors that

were discussed in Section 4.2. In addition, the shape of the failure envelope can also vary

depending upon a number of factors such as the type of soil, the testing conditions, etc.

In certain cases, it may be desireable to break the Mohr Coulomb failure envelope into two

straight line segments (Means and Parcher, 1963).

In their work on the failure mechanism of naturally-cemented granular soils, Means

and Parcher (1963) concluded that the cemented material undergoes two failures; one due

to the breaking of the cohesion bond of cementation (segment AB of Figure S.l a), and the

other when the internal shearing resistance of the granular component is exceeded (segment

BC of Figure S.la). In any case, the strain required to break the cementation is much less

than that required to develop the full shear resistance in the granular components. Hence,

they showed that the shear strength of naturally cemented soil can be represented by the

following:

(I) The strength due to the cementation

where

and

s = c + U tan tjl for U < ufB

tan q>' is the slope of the line ABO (Figure S.la)

ufB is the normal stress acting on the failure plane corresponding to point

B (Figure S.la) which is the point on the the Mohr failure circle where

both strength lines lines (AD and OC) are approximately tangent to the

circle

-C/) -.s:::. .... t:J) c: Q) ~ ....

C/) ~

0 Q)

.s:::. en

0 c oS '--en ~ 0

5

Figure S.J

121

c

A

I 0 0"3 0;8

Normal Stress (0")

a. Strength line of cemented soil.

Stress (Tf> Stress (Tf) Stress (Tf)

,-A 0 A 0 , c c \ oS e \ '-

\ - -en en C7'f=0;8 ~ ~ C7'f> 0', 8

0 0

5 5

(I) (2) (3)

b. Stress-deformation characteristics of cemented soil.

Strength and stress deformation characteristics of cemented soils (Means and Parcher, 1963).

122

(2) The strength due to the internal shear resistance

for CT> CTfB

where

tan tP is the slope of the line OBC (Figure 5.1a).

These two strength segments are admissible under mutually excfusive ranges of the

confining pressure and different magnitudes of strain.

Means and Parcher illustrated their findings by conducting a series of tests carried

out at different confining pressures and terminated after the development of the full shear

resistance, Figure 5.I b. Figure 5.1 b( I) shows the stress-strain curve for the case where the

confining stress CT3 is such that the normal stress on the failure plane, CTf is less than the

critical stress CTfB. In this case, the soil acts like a "loose" material. The cementation bonds

are broken at low strain (point A). Upon continuing strain, the shear strength (resistance)

stays approximately constant while the grains readjust to the altered conditions. Under low

confining pressure (Figure 5.I b(2», on the other hand, the readjustments of the shear

strength (resistance) decreases after the rupture of the cementation bond is reached. This

decrease corresponds to the difference in strength represented by lines AB and OB of

Figure 5.Ia. However, under high confining pressure, the readjustment of the shear

resistance after the cementation bond is broken increases (5.Ib(3». This increase is

according to the difference in strength represented by lines BD and BC.

However, Sherwood (1968), Sitar (1979), Mitchell (1979) and Clough et at. (1981)

found that this phenomenon is not necessarily characteristic of artificially cemented soils.

Their observations were verified by this research.

123

5.2 Computation

5.2.1 Area Correction

Computations of the deviator stress during axial loading for undrained tests were

based on an area correction according to Eq. (4.4).

5.2.2 Rubber Membrane Correction

A correction to the deviator stress to account for the rubber membrane confinement

was proposed by Henkel and Gilbert (1952), (Eq. 4.14) as

(5.1 )

where

O'dc = corrected deviator stress

O'd = deviator stress before membrane correction.

By assuming the modulus of elasticity of the membrane to be 1.373 kPa (199 psi) as

used by Poulos (1964), the compression modulus M becomes 13.7 kN/m (0.78 Ib/in). The

calculated O'r value is 1.4 kPa (0.2 psi) for 5 mm (1.9685 in) diameter specimen at 15%

axial strain and 0.1 mm (0.004 in) membrane thickness. When this value is compared to

that of Henkel and Gilbert (1950), (refer to Table 4.5), it can be seen' that the same results

were obtained at the same strain level.

The computation of Eqs. (4.2) through (4.I5) as well as Eq. (5.l) are carried out

entirely by the computer throughout each experiment.

5.3 Unconsolidated Undrained Test Results

Over 90 triaxial compression tests were conducted as part of this study. All tests

were performed under strain-control conditions of loading. The test results are reported

according to individual groups for the purpose of studying the factors influencing strength.

124

The test data are summarized in Tables C.I through C.I0 in Appendix C. The stress­

defonnation curves are shown in Figures DJ through D.lO of Appendix D.

5.3.1 Uncemented Specimens of Type A Soil

Two series of tests were performed at different confining pressures (0, 150, 300

kPa) on untreated specimens of Type A soil compacted to identical densities (1.69

gm/cm3). One series was carried out on specimens compacted dry of optimum moisture

content (OMC), the other on specimens compacted wet of optimum. Table C.I (Appendix

C) presents a summary of results for tests conducted on specimens compacted dry of OMC

(w = 11%). Typical stress-strain curves corresponding to these tests are shown in Figure

D.l (Appendix D). Table C.2 (Appendix C) presents a summary of results for tests

perfonned on specimens compacted wet of OMC (w = 16.6%). The corresponding stress­

defonnation curves are shown in Figure D.2 (Appendix D).

Data consisting of effective confining pressure, average principal stress differences,

average axial strain, and average initial tangent modulus (Ei) for these two series of tests

are presented in Table 5.1.

5.3.2 Artificially Cemented Specimens of Type A Soil

Dry cementing agent (calcium carbonate in a powder form) was used in all

artificially cemented soils. The cementation quantity was accurately weighed. Two

percentages (I5% and 30%) were used on a dry weight basis of the soil.

The following three groups of specimens were tested:

1. Soil specimens cemented with 15% calcium carbonate and tested at zero curing age.

2. Soil specimens cemented with 30% calcium carbonate and tested at zero curing age.

125

Table 5.1 Summary of Triaxial Compression Test Results on Uncemented Type A Soil

No.

Compaction Confming of

Moisture Pressure, 113 T.te PointsD Contentb kPa

0 3

1 Dry 150 3

300 3

0 3

4 Wet 160 3

300 3

a The research point illustrated in Figure 4.3.

b Relative to Optimum Moisture Content

Average Peak Strength

Principal

sm. Difrerence Axial

( I1r I13) Strain

kPa 96

888 0.76

1671 1.78

2146 2.66

893 0.83

1706 1.93

2274 2.63

Average Residual Strength

Principal Initial

Stl'elll Tangent

Difference Axial Modulus

( I1r I13) Strain Ei kPa 96 kPa

84 10 133,383

723 10 136,000

1046 10 200,000

87 10 133,383

630 10 137,931

1107 10 200,000

126

3. Soil specimens cemented with 15% calcium carbonate an~ cured for 7, 14, and 28 days

prior to testing.

In the rest of this section, triaxial compression test results of these groups are

presented. Discussion of these results and factors influencing their strength characteristics

are presented in later sections of this chapter.

5.3.2.1 Type A Soil Cemented with 15% Calcium Carbonate and Tested at Zero

Curing Age. Two series of triaxial specimens were used in this group. Specimens in both

series were tested at confining pressures of 0, 150, and 300 kPa. Specimens in each series

were prepared at identical densities (1.75 gm/cm3). Specimens in the first series were

compacted dry of OMC (w = 11%); while specimens in the second series were compacted

wet of OMC (w = 14.85%). The results of the first and second series are presented in

Tables C.3 and C.4 of Appendix C, respectively. The cor!esponding stress-strain curves

are shown in Figures D.3 and D.4 of Appendix D.

Table 5.2 is a summary of the results in terms of confining pressure, average

principal stress difference for peak and residual strength, corresponding axial strains, and

initial tangent modulus for the individual test series.

5.3.2.2 Soil Cemented with 30% Calcium Carbonate and Tested at Zero Curing

Age. Specimens in this group were similar to those of the preceeding group with two

exceptions: 30% calcium carbonate was used, and the compaction water contents are

different. The first set of specimens was compacted dry of OMC at a water content of

approximately 6.71 %. The second set of specimens was compacted wet of OMC at a water

content of approximately 17%. Tables C.S and C.6 (Appendix C) and Figures D.5 and D.6

(Appendix D) present the results of these two sets, respectively. A summary of the

average data of both sets is presented in Table 5.3.

127

Table 5.2 Summary of Triaxial Compression Test Results on Type A Soil Cemented with 15% CaC03 and Tested Without Curing

No.

Compaction ConfIDing or

Moisture Pressure, as Teets Points! Contentb kPa

0 S

2 DIY 150 S

SOO 3

0 3

5 Wet 160 3

SOO 3

a The research point ilIU11trated in Figure 4.3.

b Relative to Optimwn Moisture Content

Average Peak Strength Average Residual Strength

Principal Principal InItial

Streae Streae Tangent

Dlrference Aldal Dirference Axial Modulus

(aI-aS) Strain (aI-aS) Strain Ei kPa % kPa % kPa

1065 0.83 96 10 145,455

1965 1.77 710 10 177,778

2549 2.20 1217 10 228,571

931 0.70 80 10 ISS,SSS

1744 1.73 650 10 160,000

2250 2.50 1100 10 213,SSS

128

Table 5.3 Summary of Triaxial Compression Test Results on Type A Soil Cemented with 30% CaC03 and Tested Without Curing

No. Compaction Conrming of

Moisture Pressure, as Teats

Points Contentb kPa

0 S

S Dry 160 S

300 3

0 3

6 Wet 160 3

300 8

a The research point ilIuatrated in Figure 4.8.

b Relative to Optimum Moilture Content

Average Peak Strength

Principal

Stras Difference Axial

(aI-aS) Strain

kPa 9Ii

869 0.68

1099 ·1.40

1475 1.74

303 0.80

709 2.92

960 6.20

Average Residual StlUlgth

Principal Initial

Stras Tangent

DirrelUlCe Axial Modulus

(aI-aS) Strain Ei kPa 9Ii kPa

80 10 66,667

690 10 12S,686

1018 10 147,692

124 10 66,667

. 680 10 102,400

900 10 184,646

129

5.3.2.3 Soil Cemented with 15% Calcium Carbonate and Cured for 7, 14, and 28

Days. All specimens described in this section were prepared in the same way as those of

the dry side series described in Section 5.3.2.1. However, they cured for 7, 14, and 28

days. ·The results of these tests are summarized in Tables C.7, C.8, and C.9 of Appendix

C, respectively. The corresponding stress-strain curves are shown in Figures 0.7, 0.8, and

D.9 of Appendix D. Table 5.4 presents a summary of the average triaxial test results of

these groups.

5.3.3 Reconstituted Specimens

As indicated previously, the naturally cemented soil of the Sierrita site could not be

sampled in an undisturbed condition. Therefore, deaggregated soil was reconstituted to the

same density as that of the artificially cemented soil (1.75 gm/cm3) and consequently tested

under confining pressures which represented the overburden pressure existing in the field.

The triaxial test results of these specimens are summarized in Table C.lO of Appendix C.

The stress-strain curves of the reconstituted Sierrita specimens were not as easily replicated

as those of the artificially cemented Type A soils. The differences in strength exhibited

by the reconstituted specimens are due to differences in the amount and distribution of

calcium carbonate in the specimens. The calcium carbonate content was found to be

between 14% and 23%. The stress-deformation characteristics of the reconstituted

specimens are shown in Figure 0.10.

Table 55 summarizes the average values of the principal stress difference, axial

strain at peak, residual strength, and initial tangent modulus, for the different confining

pressures of these tests.

Table S.4 Summary of Triaxial Compression Test Results on Type A Soil Cemented with 15% CaC03

and Cured for 7, 14, or 28 Days

Compaction Cure Conrllling

Moisture Period Pressure, D3 PointR! Contentb days kPa

0

2 Dry 7 150

300

0

2 Dry 14 160

300

0

2 Dry 28 150

300

a The research point i1hmtrated in Figure 4.3.

b Relative to Optimum Moisture Content

AYefllie Peak Strength

Principal

No. Stre.

or Difference AlOal

Testa (DrIJs) Strain

kPa %

3 1200 0.78

3 2032 1.48

3 2697 1.97

3 984 0.67

3 2094 1.39

3 2636 1.71

3 1112 0.63

3 2009 1.43

3 2676 1.85

A~ Residual Stnmgth

Principal Initial

Stre. Tangent Difference AlOal Modulus

(IJrIJs) Strain E1 kPa % kPa

40 10 150,943

710 10 168,421

i

1160 10 216,216

67 10 149,667

I

730 10 163,797 !

1347 10 213,333 I I

frl 10 145,456 I

710 10 160,000

1360 10 218,671

_._ .. -

.... w o

131

Table 5.5 Summary of Triaxial Compression Test Results on Reconstituted Fanglomerate Material (Sierrita Soil)

Average Peak Strength Average Residual Strength

Principal Principal Initial

No. Stl"ellll Streee Tangent

Confming or DiCCerence Axial Difference ~al Modulus

Preaaure, 173 Tests ( 171-173) Strain ( 171-178) Strain Ej kPa kPa % kPa % kPa

0 3 244 0.70 68.88 10 62,148

60 8 1201 1.86 396.67 10 101,818

100 3 1878.88 2.08 818.33 10 94,891

200 1 S468 3.20 1400 10 133,8SS

sao 2 1990 3.16 1426 10 111,688

132

5.4 Strength Parameters Obtained from Triaxial Compression Tests

The peak and residual strength parameters of uncemented and artificially cemented

sepcimens of Type A soil, and of Sierrita reconstituted specimens are summarized in

Table 5.6. Figure 5.2 shows plots of Mohr failure envelopes (peak strength) for the Type

A soil tested under various conditions. The residual strength failure envelopes are shown

in Figure 5.3. Peak and residual envelopes for the reconstituted Sierrita material are shown

in Figure 5.4.

The friction angle, ,p, of uncemented and artificially cemented Type A soil with

15% calcium carbonate are similar for both peak and residual. However, the peak

cohesion, c, of the artificially cemented soil is 16% higher than that of the uncemented

soil. A comparison of Type A specimens that were 15% and 30% artificially cemented

suggests that the strength is dramatically decreased with increase in CaC03 content. This

will be discussed in Chapters 6 and 7.

The reconstituted specimens, on the other hand, exhibit the same friction angle for

both residual and peak; the cohesion, however, is different. The residual cohesion, CR, is

an effect of the calcium carbonate cementation, a chemical process. The difference

between the peak, Cp, and residual, CR, cohesion, however, is due to interlocking, a

mechanical process. The peak strength that was obtained from different levels of

confining pressure demonstrates the cementation effect on its strength. The influence of

confining pressure is overshadowed by the cementation effects. For example, as shown in

Figure 5.5, different peaks occur from tests carried out under SO kPa confining pressure.

The axial stresses of these tests are 2169, 1037, and 548 kPa, which demonstrates the

cementation effect on the strength. The differences in strength exhibited by the tests are

due to differences in the amount and distribution of calcium carbonate in these specimens.

133

Table 5.6 Strength Characteristics of Uncemented, Artificially-Cemented, and Recon­stituted Soils

A verage Peak Average Residual Average Strength Parameters Strength Parameters

Unconfined Type of Soil Strength Cohesion rp Cohesion rp

kPa kPa Degrees . kPa Degrees

Uncemented 890 231 42.5 30 39.75 Type A Soil

Artificially Cemented Type A with 15% CaC03 998 268.75 42.63 43.75 38.25

Artificially Cemented Type A with 30% CaC03 336 131.25 32.75 26.5 35.75

Reconstituted Sierrita Soil 244 175 43.5 50 43.5

cvvv -C 0.. ..lC: -... en en Q) .... -en 1000 .... c Q)

.c: en

o[ 0

Figure S2

L' CaC03 Contents S'd f OMC Curing Time me (%) , eo (days)

CD 0 dry 0

® 15 dry 0

® 30 dry 0

@) 0 wet 0

® .5 wet 0

® 30 wet 0

0 15 dry 7

® .5 dry 14

® 15 dry 28

I I .000 2000

Normal Stress 0' (kPa) ,~-

Mohr railure envelopes ror peak strength rrom triaxial compression tests on uncemented and artificially cemented Type A soil.

-w ~

_2000'

[L -=c: -.... en en (J) '--CJ) 1000 '-c (J)

.c: CJ)

Figure 5,3

L' CaC03 Contents· S'd f OMC Curing Time me (%) leo (days)

(i) 0 dry 0

® 15 dry 0

® 30 dry 0

@) 0 wet 0

® 15 wet 0

® 30 wet 0

® 15 dry 7

® 15 dry 14

® 15 dry 28

I I 1000 2000

Normal Stress (j' (kPa)

Mohr failure envelopes for residual strength from triaxial compression tests on uncemented and artificially cemented Type A soil.

-w VI

_2000

~ ~ -... en en Q) ~ -en 1000 ~

o Q)

L:. en

Figure 5.4

P = Peak Strength R = Residual Strength

1000 2000 3000 4000 Normal Stress u (kPa)

Mohr failure envelopes for peak and· residual strength from triaxial compression tests on reconstituted naturally cemented soil (Sierrita soil). -\.I.)

0\

4000------~----~----~----~----~

3200 -c a.. =2400 V) V) Q) ... .... (f) 1600 c )(

<[

800

r,

" I I I

I ! , I I I

I .' '. , I .' '. I .;. . I ~, •• , "i /." •• 1' :."'.

Confining Pressure, CT3

--- OkPo ------ 50kPo .-.-._. 100 kPo

----- 200 kPo ......... 300kPo

1-, • ..... 1 ., •••••••••••••••••••••••••• I,./'!\ \'" ........................ .

~.. ,. ..._-------------:if ,.. . ..!l, :6J~.-.~·,.-.-.-.-.-.-.-.-.-. :.I~~'-\ \ " . ... "., "._:-....._._. _._._.-.-._.

, 7.1 , \ •• '1 \ ...

,- .. ~ \. -----------------------­, ..... ~----------------------,----------------------2 4 6 e 10

0/0 Axial Strain

137

Figure 5.S Stress-deformation characteristics of reconstituted fanglomerate material (Sierrita Soil).

138

The Mohr Circles for peak and residual strengths of all triaxial tests of this study

are shown in Figures E.I through E-ll.

5.5 Factors Influencing the Soil Strength

The following factors affected the strength:

1. Confining pressure

2. Cement content

3. Compacted moisture content

4. Curing period

These are discussed in detail in the following sections.

55.l Confining Pressure, C13

The influence of confining pressure on the stress-strain characteristics of Type A

Soil specimens is shown in Figures 5.6 through 5.8. AU specimens tested under zero

confining pressure exhibit dense sands behaviors, in which the stress-strain curve starts

with a steep slope, reaches its peak at less than approximately I % strain, and then rapidly

drops. As the confining pressure increases, the peaks gradually broaden.

The confining pressure clearly influences the initial tangent modulus, Ei. The

influence of the confining preSsure on Ei is presented in Table 5.7. As shown in the

figure, the initial tangent modulus increases as the confining pressure increases.

5.5.2 Cement Content

The differences in strength between cemented and uncemented Type A soil due to

basic cementation effects are shown in Figure 5.9. In this figure, the cementation effects

are presented by comparing stress-strain curves for un cemented and 15% and 30%

4000ri----,-----r----,~--~----,

3200 -c. oX

- 2400 lit lit ., ~ en o )(

<l

-.~ , ..... :~:~ ,. '. ~ l

Confining Pressure,lr3

--- OIlPo ----- 150llPo ._._.- 300llPo

l '#'-' '" ~ \ \'~~. ._._._._._.-" \ \\ .......... ~;.~:.::-:~~--.-~" I \\ .. ... "1 \ .......... __ ===:. __ ....... ,J \ ' ....... =::::= ______ _ A.. _ .... __

246 B 10 % Axial Strain

3. Compacted at dry side of OMC.

-~

4000~i----'-----r----'-----r----,

3200 Confining Pressure,lr,

---O"Po ----- 150 IIPo

oX -2400 en

,;.--:-. I//'-~ '. ~, !I _ i.

._._.- 300 "Po

en ., ~ -en

(~-... ~ 1600 [ .. ~ ,_31,.... :,.

It I \ ,. -::: .. -.-----..-.., .~ I,' 1\ \ .-._._._._._._._.

<l ., h\ 800 IIJt \~~~.!!!~

r ':' , 00 2 4 6 8 10

% Axial Strain

b. Compacted at wet side of OMC.

Figure 5.6 Typical triaxial stress-strain curves for Type A un cemented soil.

W \Q

~oo~,----~--~----~--~----~

3200

~ .~~ .-: // "1., - 2400 •• J . ::: I! ,. it ~ ~ I!II' I'

Confining Pressure,v3

--- OkPo ----- I~O kPO ._._.- 300 kPo

Q) :J~' .. \ - ., I···' (I) 1600 1\ .- .-.-._._.-.-._ ... .-.-._-_._--c; !1 ~ ·"::S\D'-···- ._._._._ ...

·x II I~ 4 800 l \_.-------------~

00 246 6 10

% Axial Strain

a. Compacted at dry side of OMC.

4000 r-, ---,.---r---,---.,,..----,

3200 -o Q..

~2400 In In ell ~

Ui 1600

.2 )(

<l 800

Confinino Pressure,v3 ---OkPo

----- 150 kPo ._._.- 300 kPo

". ... .:.~~, , ". ,. Ii .~~ I· " I~~ ,\. /f ~\ .~:~ .... ~'PII&.~ ..... _._ •• _.1.1

.' \'

; ~~------------00 2 4 6 8 10

% Axial Strain

b. Compacted at wet side of OMC.

Figure 5.7 Typical triaxial stress-strain curves for Type A artificially cemented soil with J 5% calcium carbonate.

-A o

4000r'----~----~----r_--~r_--~

3200 -~ ~2400 lit ." cu ~

Ui 1600 o 'K «

Confining Pressure,C7'3

---OkPo

----- 1!501lPo _._.- 300llPo

~" ..... " ,.. --._._ .. -._-_._._-_._.-i "'--.-:.':0:,:,...,_ "'" .. ,~~ ·f "-~-------------900

I ",~ '---..:::.;::---______ _

~ ~-~------,,/

00 246 9 10 % Axial Strain

a. Compacted at dry side of OMC.

4000ri-----r----~----~----~~--~

3200

~ ~2400 lit lit cu ~

00 1600 "0 )C

« 900

Confining PressYre,C7'3

---OIlPo

----- 1!50 kPo ._.-.- 300kPo

....:.-._._._._.-. ...... ~.-=.-= ....... ~ ......... ,.wI~ .. : ......... .~.

~==---------------~ ~' ~--~-~--~~~~

rSi 00 2 Ii 6 B 10

% Axial Strain

b. Compacted at wet side of OMC.

Figure S.8 Typicat triaxial stress-strain curves for artificially cemented Type A soil with 30% calcium carbonate.

-~

142

Table 5.7 Influence of Confining Pressure and Cement Content on Initial Tangent Modulus, Ei

A verage Initial Tangent Modulus, Ei kPa

Confining 15% Artificially 30% Artificially Pressure, 03 Uncemented Cemented Cemented Reconstituted

° 133,333 139,394 66,667 52,148

150 136,966 168,889 113,018 ---

300 200,000 220,952 141,119 111,538

~I~--~--~---r--~--~

3200 -./oCoCO, ··········I'"JI.CoCO, -- 30%CoCO,

4 II •

% Allal Sirain

a. «1,.0 kPa

Figure 5.9

10

4000rl----,-----r----,-----r--~

3200 -~ ~2400 .. .. .. .. in 1600

:2 • Cl

.::.:; .... .t., ".!

-./OCOCO, ··········15%CoCO, -.-- 50'll.CoCO,

OJ ; : ~ ~ ~ % Alial Strain

b. «1, - ISO kPa

40001r-----r-----r-----T-----T-----,

S200

-.IoCoCO, ··········15"J1.CoCO, _.- 30'll.Caco,

o I , , • , ,

OZ. I • 10 % Alial Sirain

C. «1,. 300 kPa

Difference between cemented and uncemenred Type A soil stress-strain response for specimens compacted at dry side of OMC.

-A W

144

artificially-cemented Type A soil (points I, 2 and 3; Figure 4.3) for three confining

pressures. Three phonomena are illustrated by these plots:

I. With respect to uncemented specimens, the peak strength increased for specimens

having 15% CaC03 content

2. With respect to uncemented specimens, the peak strength dramatically decreased for

specimens having 30% CaC03 content

3. Following the peak, a rapid decline (almost vertical) in strength was exhibited for

specimens having 15% CaCOa whereas the decline was more gradual for untreated and

30% CaC03 specimens.

The effects of cementation are also exhibited for reconstituted Sierrita material, as

shown in Figure 5.10. The stress-strain curves of specimens tested under 100 kPa

confining pressure is presented. One of the specimens was leached for over three weeks

with diluted hydrochloric acid (0.1 molar) at 20 em head. Unlike the other specimens, the

leached sample exhibited no pronounced peak on full mobilization of cementation bonds.

This is consistent with the work of Jackson (1974), who has shown that the strengh of soil­

cement is reduced with leaching.

The cementation content has' similar effects on the initial tangent modulus Ei

which, as shown in Table 5.7, increased for Type A soil cemented with 15% calcium car­

bonate and subsequently decreased with Type A soil having 30% calcium carbonate content.

5.5.3 Compaction Moisture Content

Stress-strain curves are shown in Figures 5.11 through 5.13 for uncemented, 15%

and 30% artificially cemented Type A soil (Points I and 4; 2 and 5; and 3 and 6 of Figure

4.3 respectively). The results shown in each figure are for specimens prepared at the same

4000 r-----~----~----~----~~--~

3200

-~ .:.::: -2400 (/) (/) Q) ~ -en 1600 c .-x <I

800

2

--- Without Leaching _.-.- With Leaching

4 6 8 0/0 Axial Stra in

10

J45

Figure S.J 0 Typical stress-strain curves for reconstituted Sierrita soil under 100 kPa confining pressure.

4000r.-----r----,-----~----~--~

3200

i ~2400 .. ! en 1600 "0 °iC cs:

800

- Dr,O'oplimurn

---- We' 0' Oil"""'"'

468 -t_ Axial Strain

a. (73 I: 0 kPa

Figure S.l1

'0

4000 ir__-~--"--"""---r----.

3200

i ~2400 lit lit .. ~

in ,&00 "0 °iC cs:

800

- Dryo'ophmum ---- We'o'opiimum

0' , , , I I o 2 4 6 8 ~

-,_ Allial Strain

b. (73 = 150 kPa

4000r.--..--....,.----~--r__-_,

3200

i ~2400 .. lit

~

en '&00 "0 oM cs:

800

- Dryofoofimum

--- We'ofOll'iITIum

o· . , , , , o 2 4 6 8 ~

-I. Axial Strain

c. (73'" 300 kPa

Typical triaxial stress-strain curves for Type A uncemented soil (Points and 4).

-~ 0\

4000 1'"'. --r--...,.---r----,r---...,

3200

i ~2400 .. I! iii 1500 a 0. ~

- OryOI OptImum

---- Wflo'Op.,,,,_

2 4 6 8 iO

% Axial Strain

ao (73 - 0 kPa

Figure 5.12

4000 1'"'. --..--...,.---r----,r---...,

3200

i ~2400 .. .. !! in 1500 a oK ~

-- Dr,ofoPlimu", --- Wt'o'op"",um

0' , , e , ,

o 246 8 iO

-,. Alial Strain

b. (73:: ISO kPa

4oooir--~--~----~--~r__--_,

3200

'0 a.. ~2400 .. .. !! iii .600 "0 0. ~

-- Or, olop'tmum --- WfI of oP'""u",

0& ~ l ~ ~ ~ -/0 Axial Strain

c. (7,:: 300 kPa

Typical triaxial stress-strain curves for artificially cemented Type A soil with 15% calcium carbonate (Points 2 and 5).

-.z::. -...J

~OOOi~----r-----~----r-----r-----'

- Dryoloplimum 3Z00 ---- Wfioioplimum

i ~ 2"00 I-M tit

! en ISOO g oj(

~ 100

~---------------------, 00 2 ~ 6 II 10

% Alial Strain

a. (73 = 0 kPa

4000~I--~----r---~---r---,

- Dry 01 optimum 3Z00 ---- Wela'oPlimum

i ~ 2400 tit

'" ! en IISOO

:2

: ~,~ .... < .. <-~-~--~-0' , , , , ,

o 2 4 6 II m 0/0 Alial Sirain

b. (73 = 150 kPa

~OOO~I--~~--'---~----~--1

3200

i ~ 2400 tit

~ ;;;1600 -0 oj(

~ 1100

- Orya'aplimum

---- .Iolophmum

0' , , , , , o 2 ~ 6 II m

0/. Axial Strain

c. (73 = 300 kPa

Figure 5.13 Typical triaxial stress-strain curves for artificially. cemented Type A soil with 30% calcium carbonate (Points 3 and 6).

-~ 00

149

compactive effort, and the same compacted density, but at different moisture contents dry

and wet of OMC. The wet-side compaction gives slightly higher strength than does the

dry-side compaction for uncemented specimens. This conflicts with the typical compaction

characteristics in soils. However, the strengths exhibited by artificially cemented specimens

compacted dry of OMC are slightly higher than those compacted wet of OMC. . This is

consistent with the work of Lambe reported in Chapter 4 of Leonards (1962). More

discussion of the effect of compaction on the macro-strength characteristics of soil is

presented in the following chapter.

5.5.4 Curing Period

Four series of tests were carried out on Type A soil artificially cemented with 15%

calcium carbonate and compacted dry of OMC. These series correspond to curing times of

0, 7, 14 and 28 days under the controlled temperature and humidity conditions described

in Section 4.4.2. The dry density and moisture contents were 1.75 gm/cm3 and 11%

respectively. The stress-deformation characteristics of the specimens cured for 0, 7, 14

and 28 days are shown in Figure 5.14. Average values for the peak and residual strength

parameters are given in Table 5.8. Unlike soils treated with Portland cement, it appears

that the curing period has no effect on the strength of soil cemented with calcium

carbonate.

~Or"----~---r----r---~--~

S200

i ~2eoo .. .. .. ~

iii ~OO '0 ';0 <l

-O-CIOyS .......•... 7-do,S

----- 14·dorl .-.-.-. 28-dors

2 4 6 8 % Allial Sirain

a. (1,::: 0 kPa

Figure 5.14

10

COOOrl----~----~~----~----,_----_.

3200

;; Il. ~ 2eoo .. .. ~ en 1600 a •• ct

1100

I l\ ...

----O·dO'. .......... 7-dop

----- IC-dors .-.-.-. 28-dors

-

0' • , I I I

024 6 8 m % Axial Strain

b. (13::: 150 kPa

eooorl-----~-----r---_,----_r------~

3200

i ~2eoo .. .. ~ iii 1600 a •• ct

1100

-O-doyS . .......••• 7-tSoyI

----- "'-dors .-.-.-. 28-dors

0' , , , , , 024 6 8 m

-'0 Allial Strain

C. (13::: 300 kPa

Typical triaxial stress-strain curves for artificially-cemented Type A soil with 15% calcium carbonate.

-VI o

151

Table 5.8 Influence of Curing Period on the Strength Parameters, C and ¢

A verage Peak A verage Residual Strength Parameters Strength Parameters

Curing Period Cohesion ¢ Cohesion ¢ kPa kPa Degrees kPa Degrees

0 275.0 43.50 50.0 39.5

7 275.0 45.50 40.0 41.0

14 262.5 46.75 40.0 43.0

28 287.5 44.50 37.5 42.5

CHAPTER 6

SOIL MICROSTRUCTURE AND COMPACTION CHARACTERISTICS OBSERVED BY THE SCANNING ELECTRON MICROSCOPE

152

Comprehensive electron microscopic studies were conducted on naturally cemented

Sierrita soil and uncemented and artificially cemented Type A soil in order to gain

additional insight into the cementation phenomenon. The use of microscopic analysis of

the soil matrix is believed to be one of the most important means of studying fabric

features to understand the macro-strength properties of cemented soil.

The results of the physical tests suggested that the strength. of cemented soils did

not necessarily increase with increasing calcium carbonate concentration. The hypothesis

was then formed that the distribution of the cementing agent within the soil specimens is

the major factor that affects the strength properties of the cemented soil.

In order to test this hypothesis, the scanning electron microscopic study was

conducted on various samples retrieved from the triaxial test specimens. The

photomicrographs presented in this chapter illustrate the microstructure of cemented soil.

The general discussions of the structural features of these specimens are based on visual

observation of a much larger cross section of samples than is represented by the

photomicrographs presented here. The electron microscope study includes an investigation

of the nature of the interparticle contacts or bonds, the combined effect of water and

cement content, and the general cementation mechanism.

6.1 Introduction

The influence of microstructure on the strength parameters of soils was first

recognized by Terzaghi (1925) and Casagrande (1932). Since then, considerable studies of

153

soil microstructure were carried out by many investigators (for example, Rowe, 1959, 1968;

Bishop and Bjerrum, 1960; Skempton 1964; Nowatzki, 1966; Sloane and Nowatzki, 1967).

To a large extent, the understanding of the importance of microstructure on macro

behavior has been advanced by the development of the scanning electron microscope

(SEM).

By using the SEM, spatial relationships between adjacent particles and small groups

of particles are observed. The instrument can also be used to observe the different faces

of a soil sample at a complete range of magnification from lOX to 300,OOOX, allowing

particular areas to be observed at gradually increasing magnification. Instruments having a

high depth of focus can provide three-dimensional images, which enable surfaces

containing coarse and fine particles to be observed without loss of resolution. Further­

more, some instruments allow three-dimensional pictures to be taken by tilting the soil

sample between observations.

Since the SEM can be used to investigate a wide range of features including

weathering, surface texture, sand grains, mineral particles, and the interparticle action of

soils, it is ideally suited for studying the structure of the calcium carbonate cemented soils

investigated in this research. As indicated previously, in Section 4.5, SEM was used in this

research. Magnifications ranged from 400X to 5000X. The working voltage,

magnification, scale line and value, and photograph number are shown on each of the

photomicrographs presented in the subsequent sections.

6.2 Scanning Electron Microscope Study on Uncemented Type A Soil

Electron photomicrographs of the fabric of uncemented Type A soil compacted dry

of optimum are presented in Figure 6.1. At a magnification of 499X (Figure 6.Ia), the

soil matrix is considered to be flocculated and to consist of sand, silt, and some clay-sized

154

a.

Figure 6.1 Electron photomicrograph of Type A soil compacted dry of OMC. (a) Magnification 499X, (b) Boxed area in (a) magnified 4990X.

ISS

particles. It is also observed to be dense with interlocking particle arrangements due to

their angularity and high sphericity. The microstructure contains numerous small cavities.

These cavities are shown at higher magnification (4990X) in Figure 6.lb.

The microstructure of the same soil compacted at the same compactive effort and to

the same compacted density, but wet of OMC, is shown in Figure 6.2. The fabric is

clearly more dispersed with the cavities between the coarser particles filled by the finer­

size particles. Figure 6.2b shows a larger number of fine-size particles on the coarser-size

particles' surfaces than was evident for the dry of optimum condition. This indicates that

the compaction moisture content affects the distribution of particle sizes within the soil

mass, i.e., it affects the fabric of the soil and, in turn, its strength characteristics.

These photomicrographs clearly showed the effect of compaction moisture content

on the microstructure of soils. The strength characteristics of the soil, shown in Figure

5.11, in tum, are in agreement with their fabric arrangement.

6.3 Scanning Electron Microscope Study on Artificially Cemented Type A Soil

In this section, photomicrographs showing the effects of both calcium carbonate

content and water content on fabric and its ultimate influence on the stress-strain

characteristics of artificially cemented Type A soil are presented. These photomicrographs

are of artificially cemented Type A soil with 15% and 30% calcium carbonate compacted

on both sides of optimum moisture contents (Points 2, 3, 5 and 6 of Figure 4.3).

Photomicrographs of reagent grade calcium carbonate powder and naturally cemented

Sierrita soil are also presented for reference.

Figure 6.3 shows the typical arrangement of the particles of reagent grade calcium

carbonate powder. The appearance of the microstructure at a low magnification (488X) is

156

a.

b.

Figure 6.2 Electron photomicrograph of Type A soil compacted wet of OMC. (a) Magnification 425X, (b) Boxed area in (a) magnified 4240X.

157

a.

Figure 6.3 Electron photomicrograph of calcium carbonate. (a) Magnification 488X, (b) Boxed area in (a) magnified 4890X.

158

shown in Figure 6.3a. The detailed particle shapes as well as clear interparticle contacts are

shown at high magnification (4890X) in Figure 6.3b. The photomicrographs shown in

Figure 6.3 provide a guide for the comparison of the distribution of the calcium carbonate

within the soil in the following sections.

6.3.1 Type A Soil Artificially Cemented with 15% Calcium Carbonate

The electron microscope investigation was conducted on specimens of Type A soil

artificially cemented with ] 5% calcium carbonate and compacted to the same dry density

but at both sides of optimum moisture content. The specimen preparation was described

in Section 4.4.2.

The microscopic observations of specimens compacted dry of optimum moisture

content are shown in Figure 6.4. The microstructure at a magnification of 424X is

presented in Figure 6.4a. The photomicrograph shows a concentration of calcium

carbonate between the points of contact of the soil grains. In this structure, the binder

holding the soil grains apart is similar to stone sets in mortar. Under the higher

magnification (4250X), in Figure 6.4b, details of the binder microstructure (calcium

carbonate) at the point of contact between two grains may be seen.

The microscopic observations of specimens compacted wet of optimum moisture

content are shown in Figure 6.5. The low magnification (42SX) photomicrograph in

Figure 6.5a shows the overall distribution of calcium carbonate within the composite soil

structure. Increasing the magnification to 4260X shows the calcium carbonate particles

attached to the surface of a larger soil grain. In comparison to the previous structures

shown in Figures 6.23 and 6.4a, the calcium carbonate, in Figure 6.5a, is more uniformly

distributed around the larger soil grains. However, neither a flocculated nor a dispersed

structure is evident in any of the photomicrographs.

159

a.

b.

Figure 6.4 Electron photomicrograph of Type A soil artificially cemented with 15% calcium carbonate and compacted dry of OMC. (a) Magnification 424X, (b) Boxed area in (a) magnified 4250X.

160

a.

b.

Figure 6.5. Electron photomicrograph of Type A soil artificially cemented with 15% calcium carbonate and compacted wet of OMC. (a) Magnification 425X, (b) Boxed area in (a) magnified 4260X.

161

From'these photomicrogrciphs, it appears that increased compaction moisture content

has a dispersive effect on the distribution of calcium carbonate within the composite soil

structure. The artificially cemented (lS% calcium carbonate) soil compacted dry of

optimum moisture content exhibited a concentration of the calcium carbonate between -the

points of contact of the bulky grains.

It also appears that the concepts of flocculation and dispersion apply to the overall

fabric of the binder only. The calcium carbonate in the same soil compacted wet of

optimum was more uniformly distributed and did not tend to be concentrated at contact

points between larger grains. For this reason, the cementation effect could be expected to

be less.

6.3.2 Type A Soil Artificially Cemented with 30% Calcium Carbonate

The photomicrographs shown in Figure 6.6 are typical of the fabric of Type A soil

artificially cemented with 30% calcium carbonate and compacted dry of optimum moisture

content. The microstructure at a magnification of 490X is shown in Figure 6.6a. The

photomicrograph illustrates the relation between the cementing agent and grain particles

within the soil structure. The calcium carbonate particles are concentrated between the

larger particles. However, unlike the soil with I S% calcium carbonate, there is little grain­

to-grain contact among the coarser particles. The concentration and distribution of the

calcium carbonate particles located between the soil grains is evident under the increased

magnification of 4910X, shown in Figure 6.6b.

When the soil mixture is compacted wet of optimum moisture content, another type

of structure results. Figure 6.7a shows the coarser grains located in the calcium carbonate

matrix. It is clear that the coarser grains are completely coated by the calcium carbonate

and grain-to-grain contacts do not exist. Figure 6.7b shows the structure at a higher

162

a.

b.

Figure 6.6 Electron photomicrograph of Type A soil artificially cemented with 30% calcium carbonate and compacted dry of OMC. (a) Magnification 490X. (b) Boxed area in (a) magnified 4910X.

163

a.

b.

Figure 6.7 Electron photomicrograph of Type A soil artificially cemented with 30% calcium carbonate and compacted wet of OMC. (a) Magnification 426X, (b) Boxed area in (a) magnified 4260X.

164

magnification of 4260X. A comparison of this photomicrograph with that shown in Figure

6.3b clearly demonstrates that only the calcium carbonate structure is shown in Figure 6.7b,

i.e., no coarser soil grains are present.

A comparison of Figures 6.7a and 6.6a suggests that the macro structure is greatly

influenced by the compaction moisture content. At higher water contents, there is better

distribution of calcium carbonate throughout the soil mixture because the water acts as a

transporting medium for the calcium carbonate powder.

6.4 Scanning Electron Microscopic Study on Naturally Cemented Sierrita Soil

The electron microscope study of naturally cemented Sierrita soil was made in a

manner similar to that for the artificially cemented Type A soil. Representative

photomicrographs of the Sierrita soil are shown in Figure 6.8. The specimen for this study

was prepared by trimming a block of naturally cemented soil by hand. The calcium

carbonate content was found to be approximately 21%. Figure 6.8a shows the

microstructure at a magnification of 488X. It shows what appears to be a consolidated

mass with small voids. In this structure, both materials, cementing agent and soil grains

are combined in one structure. However, increasing the magnification to 4890X (Figure

6.8b) presents a detailed structural arrangement of the soil. Highly compressed and

weathered calcium carbonate particles are shown in Figure 6.8b.

In comparing Figure 6.8b with Figures 6.3b, 6.6b and 6.7b, the calcium carbonate

particles are clearly shown. However, the particles are indurated due to the combined

effects of weather and overburden pressure.

165

a.

Figure 6.8 Electron photomicrograph of naturally cemented Sierrita soil. (a) Magnification 488X, (b) Boxed area in (a) magnified 4890X.

6.5 Scanning. Electron Microscopic Study of the Calcium Carbonate Distribution Within Artificially Cemented Type A Soil

166

In order to obtain a larger scale view of the fabric of two artificially cemented

specimens to determine the distribution of the calcium carbonate within the soil grains, a

mosaic was constructed of pictures taken at SOOX magnification scale. Sixteen

photomicrographs were constructed into a mosaic for artificially cemented Type A soil

with 15% CaC03 and 30% CaC03 • The mosaics are shown in Figure 6.9. Each mosaic

was constructed from a series of photos obtained by using X- and Y-axis controls to

determine an overall continuous picture of the investigated area. The X- and Y-axis

readings were determined by back calculation from the magnification scale and the actual

dimensions of the photomicrographs. Some overlaps between these photos occurred due to

the image enhancement process.

The mosaic in Figure 6.9a shows the distribution of the calcium carbonate in

specimens of Type A soil artificially cemented with 15% calcium carbonate and compacted

dry of optimum moisture content. Hence, each photomicrograph of this mosaic represents

similar conditions given in Section 6.3.1 and shown in Figure 6.4a. The figure clearly

shows that calcium carbonate exists at the points of contact between the coarser silt and

sand particles. Cavities are evident throughout the structure. From observation of these

photomicrographs, it can be inferred that the distribution of the fine calcium carbonate

particles is limited to the edges of the coarser soil particles. This observation is in

agreement with that from Figure 6.4a.

The mosaic of photomicrographs of artificially cemented Type A soil with 30%

calcium and compacted dry of optimum moisture content is presented in Figure 6.9b. The

calcium carbonate particles are more recognizable when Figure 6.9b is compared with

Figure 6.9a. It may also be observed in Figure 6.9b that the fine calcium carbonate

167

a. Artificially cemented with 15% CaC03

•

b. Artificially cemented with 30% CaC03

•

Figure 6.9 Mosaic of photomicrographs of artificially cemented Type A soil compacted dry of OMC.

168

particles are located on and between the soil particles. Similar observation can be seen by

comparing Figure 6.9b with Figures 6.6a and 6.3a.

These observations are in agreement with the strength characteristics measured

during triaxial strength testing (Figure 5.9).

CHAPTER 7

STABILITY ANALYSIS OF CUT SLOPES IN CALCIUM CARBONATE CEMENTED SOILS

7.1 Introduction

169

The results of slope stability analyses are largely dependent upon the geometry of

the slope, the unit weight of the soil, 'Y, and the values of the soil's shear strength

parameters, c and ifJ, for the conditions of loading and drainage being analyzed. In

naturally cemented soils, all these factors except for the in situ cohesion can be readily

determined. Since the in situ cohesion of naturally cemented soils is easily destroyed

during sampling or specimen preparation procedures, its value is difficult, if not

impossible, to determine by using standard geotechnical laboratory strength testing

techniques. Reliable estimates of the in situ cohesion of naturally cemented soils can be

obtained from back analysis of the stability of the slope. The friction angle of cemented

soils, on the other hand, is independent of the degree of cementation. It is, however,

strongly dependent on the nature of the surface in contact, the type of material, the

condition of the surface, etc. Therefore, the in situ friction angle of cemented soils can

generally be determined by conventional laboratory strength testing of deaggregated

specimens.

In this chapter, a method of estimating a value for the in situ cohesion of naturally

cemented Sierrita soil (alluvial fanglomerate) at the Twin Buttes Open Pit Mine is

presented. An evaluation of the effect of calcium carbonate content and compaction

moisture content of artificially cemented Type A soil on the stability of a 150-foot high

vertical slope of this material is also presented.

7.2 Field Observations of Slope Failures in Soil Slopes in the Twin Buttes Open Pit Mine

170

The common type of slope failure in the fanglomerate materials of the Twin Buttes

Open Pit Mine is shallow sliding. The sliding usually occurs along planes approximately

parallel to the slope's face and involved the upper 20 to 30 feet of soil. Four typical

failure surfaces are shown in Figure 7.1. The failed mass consists of a number of

approximately 5-foot thick blocks of soil. The failure is localized and associated with

faults running through the strata and dividing the land slide from the rest of the slope.

7.3 Choice of Slope Stability Analysis

Bishop's Simplified Method (1955) was used in this study. In the method, a

potential failure mass is broken down into a number of discrete vertical slices. The

method satisfies vertical equilibrium for each slice, and moment equilibrium for the entire

mass. However, the method does not satisfy horizontal equilibrium or moment equilibrium

for each slice.

According to Wright et al. (1973), the average values of factor of safety determined

by Bishop's Simplified Method are close to those determined by using the internal stress

distributions calculated by linear and nonlinear finite element analyses. Furthermore, the

average values of factor of safety calculated by Bishop's Simplified Method are in

agreement with those calculated by other methods such as Janbu's Generalized Procedure

of Slices (1957) and Morgenstern and Price's Method (1965). Therefore, Bishop's Simplified

Method provides an accurate, "conservative" factor of safety in homogeneous deposits

where sliding block surfaces are expected.

The computer program CSLIPI (DeNatale, 1986) was used to calculate the stability

of the vertical slopes at the Twin Buttes Mine. The program calculates the factor of safety

171

a. c.

b. d.

Figure 7.1 Typical slope failures in cemented soil slopes in Twin Buttes Open Pit Mine.

172

determined by the stability analysis of Bishop's Modified Method, with a search routine

based on the Simplex Method of NeIder and Mead (1965). The advantage of this program

is its ability to search for the most likely failure surface associated with the minimum

factor of safety in a very time-efficient manner (DeNatale, 1988).

7.4 The Shear Strength Parameters in Naturally Cemented Sierrita Soil

In order to determine the in situ cohesion of naturally cemented Sierrita soil by

back computation from slope stability analyses, other data such as in situ friction angle and

unit weight are required. The friction angle in this study was determined to be 43.50 , as

indicated in Section 5.4. This value is consistent with the values reported in previous

studies of this material (Golder Associates, 1975; DeNatale et al., 1987). The in situ

density was found to be 130 pcf (2.08 gm/cm3). With these values of tP and " a cohesion

of 2330 psf (111.6 kPa) was obtained for failure of a vertical slope of 150 ft. (45.72

meters) height. This value is in agreement with the values obtained by back analysis of

the stability of existing slopes at Twin Buttes Mine by others (see Table 7.1). The actual

cohesion is expected to be much higher than that obtained by this method as evidenced by

two observations that suggest that the strength exhibited by this material is similar to that

exhibited by good quality rocks. This is concluded by the experimental tunnel behavior of

these materials. The Arizona SSC Project excavated two horizontal tunnels three years ago.

The tunnels were excavated in the face of the slopes at approximate depths of 120 and 240

feet. The tunnels were about 8 feet wide, 12 feet high and 15 to 20 feet in depth. The

tunnels were horseshoe shaped and were unsupported (as shown in Figure 7.2). The roof

and walls of the iLmnels were stable and no noticable movement was observed. According

to the Geomechanics Classification proposed by Bieniawski (1976) of the South African

Council for Scientific and Industrial Research (CSJR), the tunnel material may be classified

as fair-to-good rock.

173

Table 7.1 The Summary of the Previous Back Analysis Determination of the Cohesion in the Vicinity of the Sierrita Site

Assumed Slope Friction Safety Minimum Angle Height Angle Factor Cohesion Reference p(deg) H(ft) (deg) F (psf)

85 50 40 1.00 1390 Golder Associates (1974) " .

80 100 40 1.00 ]670 Golder Associates (1974)

8] 132 40 1.00 2150 Golder Associates (1917)

74 176 48 1.00 ]620 Golder Associates (1917)

60 100 37 2.31 3200 DeNatale et aI. (1987)

45 100 37 2.88 3200 DeNatale et aI. (1987)

, "" " ,'';''''' •. , :,>

'. -. - .... . . ......... .- ... ,.

,':',. , .

Figure 7.2 The excavated tunnel at the slope side, 120 feet below the ground surface.

174

175

Further evidence of the rock-like quality of the naturally cemented soil at the Twin

Buttes Pit is found in Figure 7.2. It can be seen from the sunlight reflecting on the

sidewalls that the slope angle of this wall is exceeds 9()0, i.e., portions of the slope are

overhanging. Such slopes are not characteristically found in most soils.

7.s Slope Stability Analysis in Reconstituted and Artificially Calcium Carbonate Cemented Soils

The results of the slope stability analyses presented in this section are intended to

demonstrate the effect of calcium carbonate content on the overall safety factor of slopes

cut in cemented soils. The various slope stability analyses are presented in Table 7.2. The

data for this table are plotted in Figure 7.3. As demonstrated in this figure, three lines

were established for 0%, 15%, and 30% calcium carbonate content. Each line represents

the friction and cohesion components. The location of points I through 6 in the figure

represent the c, ,p, and F values for those points as presented in Table 7.2. A group of

safety factor contours can be established from the data that correlate these three variables

with calcium carbonate content. Hence, this figure can be classified as a slope stability

chart for artificially cemented soil. However, thls chart represents only the condition for

vertical slope heights of 150 feet. Other charts can be developed in a similar manner for

other heights and other slopes. The chart indicates that the cementation has little or no

effect on the safety factor when the soil's friction angle is equal to 26.5°, Point 6.

In order to demonstrate the validity of this chart, the c, ,p, F and calcium carbonate

percentage values of the reconstituted Sierrita soil were plotted. As indicated in Table 7.2,

the cohesion and friction angle for the Sierrita soil are 3655 psf and 43.5°, respectively.

These values plot as Point R in Figure 7.3. Connecting Point R with Point 6, and using

Table 7.2 Summary of Slope Stability Analyses

Calcium Carbonate Content Density

Points % pef

I 0 105.5

2 15 109.0

3 30 109.0

4 0 105.5

5 15 109.0

6 30 109.0

Rb 14-23 110.0

a Research point shown in Figure 4.3 b Reconstituted Sierrita Soil

Friction Angle Cohesion (deg) (psf)

41.5 4699

43.5 5744

39.0 26JJ

43.5 4955

41.75 5483

26.5 2872

43.5 3655

176

Safety Factor

(F)

i.535

1.756

1.072

1.643

1.663

0.895

1.373

6000~----~----~----~----~

Safety Factor

- 5000 .... '" Q. -g 4000

'" Q) .s:::. o U 3000 I

~'6-----~3~0~~~o~C-O-CO-3-~------~

2000~----~----~----~----~ 25 30 35 40 45

Friction Angle (degrees)

Figure 7.3 Slope stabiJity chart for calcium carbonate cemented soil.

177

178

linear interpolation between 15% and 30% on the cementation content lines, the

cementation content for this sample was found to be about 23%. This value agrees with

the range given in Section 5.3.3 and reported in Table 7.2. By linear interpolation of the

safety factor, a value of 1.37 was obtained. This also agrees with the value of 1.373 shown

in Table 7.2.

CHAPTER 8

SUMMARY AND CONCLUSIONS

8.1 Summary

179

This study was initiated with the object of investigating the strength characteristics

of the naturally cemented Sierrita soils. However, all efforts to obtain undisturbed samples

failed for the following reasons:

1. The cementation in the naturally cemented soils was highly susceptible to

disturbance and was destroyed during the sampling process.

2. The degree of cementation and strength within the soil deposits were highly

variable.

3. The presence of larger particles (boulder size) within the soil mass made

sculpturing of specimens for strength testing virtually impossible.

Therefore, two types of soils were used in this research, Type A soil obtained from

the University of Arizona Campbell Avenue Farm, and Sierrita soil obtained from the

Twin Buttes Open Pit Mine south of Tucson. The study was intended to investigate the

different factors affecting the strength behavior of cemented soils, specifically the

influence of the amount and the distribution of the cementing agent within the soil

composite structure. Only Type A soil was used in the comprehensive investigation of the

artificially cemented phase because it contained little or no calcium carbonate, as

determined by laboratory tests. The Type A soil was composed of sand and silt-size

particles with some clay. The Sierrita soil was used in the reconstituted sample phase. The

Sierrita soil was composed mainly of sand, gravel, a small amount of silt, and occasional

180

large sized boulder and cobble particles. The calcium carbonate content was found to

range from 14 to 23%.

The pronounced objectives of this research were:

I. To develop a testing program that would provide consistent results,

2. To investigate the engineering characteristics of cemented soils,

3. To define the macro strength properties of cemented soil, and

4. To evaluate the behavior of slopes in natural and artificially cemented soils.

8.2 Conclusions

The following conclusions were reached either from the analyses of data collected

throughout this study or from comparison of these data with those obtained from other

investigations:

1. The distribution of calcium carbonate within the artificially cemented soil

specimens is a significant factor influencing their strength characteristics.

Visual examination of the various microstructures of the artificially cemented

soil under the scanning electron microscope showed that a variety of such soil

structures and calcium carbonate distribution can be developed depending upon

the calcium carbonate content and the compaction moisture content. The

microstrength properties of cemented soil depend, to a large extent, on the

position of the calcium carbonate between the soil grains. Strength gain occurs

when the calcium carbonate is concentrated at the points of contact of the soil

grains.

181

2. The previous findings of other investigators that the compressive strength of

cemented soils increases as the cementation content increases was found not to

be generally true for calcium carbonate cementation. For example, the strength

obtained from soil artificially cemented with 30% calcium carbonate was found

to be much lower than that obtained from soil artificially cemented with 15%

calcium carbonate. This suggests that there is some threshold calcium carbonate

content up to which strength increases because of cementation effects, but

beyond which the soil mass begins to take on the strength properties of the

calcium carbonate.

3. Compressive strength gain occured in Type A soil specimens that were

artificially cemented with 15% calcium carbonate. The strength gain was about

16% the strength of uncemented Type A soil specimens.

4. The calcium carbonate cemented soils are visibly brittle and fail under small

strain «1%) during triaxial compression tests at low confining pressure. As the

confining pressure increases, the peaks of the stress-strain relationships gradually

broaden, a characteristic of work-softening materials. The confining pressure

also clearly influences the initial tangent modulus, Ei which increases as the

confining pressure increases.

5. Molding moisture content of the compacted specimens controls the

microstructure of the composite soil structure. However, flocculation and

dispersion as a function of moisture content were clearly observed only in the

fine grained, pure calcium carbonate specimens. The calcium carbonate in the

Type A soil compacted wet of optimum moisture content was more uniformly

182

distributed and did not tend to concentrate at contact points between soil grains.

For this reason, the cementation effect was less than that for Type A soil

compacted dry of optimum moisture content where such concentration did

occur. Consequently, it appears that for artificially cemented soil prepared at

wet of optimum compaction moisture contents, cementation and molding water

content, eliminate each other's effects.

6. The compressive strength exhibited by uncemented Type A soil specimens com­

pacted wet of optimum moisture content exceeded that exhibited by the same

specimens compacted dry of OMC. This is in apparent contradiction with the

typical behavior of compacted soils. A possible explanation is the presence of a

larger number of fine-size particles existing on the coarser-size particles'

surfaces than was evident for the dry of optimum condition. The presence of

these fine-size particles increases the surface friction of the soil grains, in tum

increasing the strength of the soil mass.

7. The friction angle, 1$, is affected by particle shape and surface texture. It is not

affected by the cementation action. This is evident by comparing the peak and

residual friction angles of the reconstituted Sierrita soil. The friction angle was

found to be equal in both cases.

8. The tests carried out on the reconstituted specimens of Sierrita soil indicate that

different peak strengths occur for the same confining pressure. This suggests

the existence of different amounts of cementing agent within the natural soil

sample. The magnitude of the peak strength increased or decreased depending

upon the amount and distribution of the cementing agent which varied within

each specimen. This is expected to be true for the in situ soil as well.

183

9. Visual examination of the fabric of naturally cemented Sierrita soil showed the

microstructure to be consolidated. Highly compressed and weathered calcium

carbonate particles dominated the soil structure. The calcium carbonate content

was found to range from 14 to 23%. The combined effects of weathering and

overburden pressure appear to have indurated the calcium carbonate particles.

The general appearance of the microstructure resembles that of a consolidated

mass with small irregular-shaped voids.

10. Conventional curing periods used for portland cement stabilized soils have no

effect on the strength characteristics of soil cemented with calcium carbonate.

Unlike portland cement, calcium carbonate does not react chemically with water

to produce new agents that cement the soil grains together.

11. Values for in situ cohesion obtained from back analysis of the stability of

existing slopes at Twin Buttes Mine were found by others. These values for

cohesion are conservative because a factor of safety equal to 1 was assumed in

their analysis. When cohesion values defined from laboratory tests performed in

this study are used in slope stability analyses of the same slopes, factors of

safety greater than unity are observed. These results are validated by the fact

that the existing slopes in the cemented alluvium at Twin Buttes have never

shown evidence of instability, in themselves, although some local failures have

occurred. In other words, the slopes considered here were clearly at a factor of

safety greater than unity and hence conservative cohesion values were obtained

be previous researchers.

184

12. A slope stability chart was established for Type A soil artificially cemented with

calcium carbonate. The chart applies only to the very specific geometric

conditions of the slope analyzed. The application of this chart to other calcium

carbonate cemented soil is justified provided all other conditions (e.g., the

percent calcium carbonate, unit weight, etc.) are the same. The chart

demonstrates clearly a previous conclusion of the research, i.e., that calcium

carbonate content alone does not determine the strength characters of cemented

soils.

8.3 Recommendations

The following recommendations are made for extending the results of this

in vestigation.

1. It would be extremely valuable to conduct a series of tests on specimens

artificially cemented with percentages of calcium carbonate content other than

those used in this study so that the "threshold" calcium carbonate content could

be determined and the slope stability charts enhanced.

2. The engineering properties of cemented soils with larger (boulder and cobble­

size) particles should be investigated.

3. An expanded program to examine the microstructure of naturally cemented soil

and define its general structureal appearance with emphasis on the nature of the

grain-to-grain contact should be conducted using scanning electron microscopy.

4. Similar investigations of the artificially cemented Type A soil should be

performed with different soil types.

185

s. Effect of leaching conditions on the engineering behaviors of cemented soils

should be investigated.

6. The dynamic behavior of calcium carbonate cemented soils should be

investigated.

APPENDIX A

PHASE RELATION IN SOILS WHOSE PORE WATER CONTAINS A IDGH PERCENTAGE OF DISSOLVED SALTS

186

This appendix is a presentation of the equations derived by Noorany (1984) for

determining the accurate expression for phase relation in soils whose pore water contains a

"high" percentage of dissolved salts.

The following terms are used extensively throughout the derivation process:

"Is c unit weight of soil solid (excluding the salt)

"10 c unit weight of distilled water at 40C (I gm/cm3, 62.4 Ib/ft3)

"Isw c unit weight of salt water

Gs = specific gravity of the solids (excluding the salt)

r c salinity:: W sa /W sw

or

Wsa = r Wsw

By using the terms described above and referring to Figure 2.7b, the following

equations can be derived:

Ww = Wsw - Wsa = Wsw - r Wsw = (I-r) Wsw

Ww :: W - Wd :: Wsw (I-r)

where

W = wet weight

W d = oven-dried weight (10SOC)

which yields

Wsw = W- Wd (1 - r)

= W - Wsw = W- { w - Wd} 1 - r

W(I-r) - W + Wd Wd - r W = ..

(I - r) (1 - r)

Wsw [W-Wd] 1 Vsw = 'Ysw = (I - r) 'Ysw

Ws Ws [Wd - r w] 1 Vs = 1; = Gs 'Yo = (1 - r) as 'Yo

Total unit weight, 'Yt

W 'Yt = V

Buoyant unit weight, 'Yb

'Yb = 'Yt - 'Ysw

Dry unit weight, 'Yd

- Ws [Wd - r w] 1 'Yd = V = (I - r) V

"Water" content (moisture content on a "dry" solid weight basis)

Ww W - Wd W = - = ---:":~=-

Wd Wd

"Fluid" content (moisture content on a "net" solid weight basis)

- Wsw W=--Ws

Substitution from Eqs. (I) and (2) yields

187

(I)

(2)

(3)

(4)

(5)

(6)

(7)

(8)

(9a)

or

Void ratio, e

or

Porosity, ii

_ [W - Wd] [ 1 ] W = (1 _ r) Wd - r W

(1 - r)

- =W~-_W....::d;,..,. W= Wd - r W

- Vv V - Vs V V e = - = = - - 1 = -:-----'-::---- - 1 V s V s V s [w d - r w]

(1 - r)

- V(1 - r) Gs 10 e = - 1

Wd - r W

- e n==--1 + e

Percentage degree of saturation, S

[w - Wd] 1 S == Vsw x 100 == (1 - r) 1;;

Vv [Wd - r w] 1 V- --(1 - r) Gs 10

.. S = -x 100 • - [ Gs (W - W d) ] 10 V(1 - r) Gs 10 - Wd + r W 1sw

188

(9b)

(10)

(11 )

(12)

Consequently, the following are the correct relationships which can be derived for

soils in "salt" water

W W d = (1 + w)

(13)

By combining Eqs. (8), (9) and (13),

Ws= _..:.w~_ (1 + w)

1d -= --''--­(1 + w)

- w w = ~---"---I-r-rw

- V Gs 'Yo (1 + w) _ 1 e= W

By combining Eqs. (10), (12), (13) and (16),

- W Gs ['Yo) e=-- -S 'Ysw

189

(14)

(15)

(16)

(17)

(18)

The justification of the importance of these terms is demonstrated in the following

example.

A sample of saturated pelagic clay was taken from the floor of the ocean. The wet

weight (W) VIas 103.70 gm, the volume (V) was 77.97 cm3 and the oven-dried weight (Wd)

was 33.50 gm. The specific gravity of the solid (excluding the salt), Gs ' was 2.76, while

the specific gravity of oven-dried soils (including the salt), q, was 2.70.

A typical value of the salinity of (r) is 0.035 (35 ppt) for the seawater was used for

computing the correct values of the phase relation properties, and is shown in Table A.I.

The values of the phase relation, computed by the conventionill equation given by Holtz

and Kovacks (1981) is also shown in Table A.1.

Table A.I

190

Comparison Between the Values Representing Pelagic Clays Phase Diagram Computed from Equation Derived by Noorany (1984) and Those Computed from the Conventional Equations

Equation Equation Percent Correct Value No. Incorrect Value No. Error

W = 235 96 w .. 210 8 10.64

e = 5.801 10 e = 5.424 4 6.50

ii = 0.853 11 n = 0.844 11 1.02

id = 0.397 7 'Yd = 0.429 15 8.07

S = 101.63a 12 S = 102.86a 12 1.21

aThe correct value of the degrees of saturation should be 100%, however, these values reflect the error in weight and volume measurements.

191

APPENDIX B

DETAILED EXPERIMENTAL PROCEDURE

B.I Introduction

This section provides an outline description of each of the components comprising

the system. A more detailed description of the GDS Digital Pressure Controller and the

Bishop-Wesley Triaxial Cell can be found in the manufacturer's brochure.

B.l.l The Controlling Computer

The controlling computer provides the means by which the' operator initiates and

controls test execution.

- To support an interface of each of the three GDS Digital Pressure

Controllers confonning to the IEEE-488 communications standard.

- Sufficient speed to control the range of tests at the testing rates required.

- Operator interface to control test execution.

- A method of archiving test results for later analysis.

- A means of providing hard copy of test results.

B.1.2 The GDS Digital Pressure Controller

The GDS Digital Pressure Controller is the means by which the required pressures

and volume changes are generated for the Triaxial Cell. The controller is capable of

setting a required pressure and of making a required volume change; in addition it can

provide reading for the current status of pressure and volume change.

192

The Triaxial Cell needs to have three pressures independently variable, and hence

three controllers are required.

The GDS Digital Pressure Controller can perform the following actions:

- Achieve and maintain a required pressure.

- Achieve a required volume change.

- Make a single step volume change of ±O.S mm3•

- Reset volume reading to zero.

- Provide readings on the current pressure, volume change, and status of

the device.

B.1.3 The Bishop-Wesley Triaxial Cell

The Triaxial Cell is the means of applying the generated test conditions to a test

specimen. Reference to Bishop and Wesley (I975) shows that the ceU has the following

capabilities

- A method of applying all-round pressure to the test specimen--this is

called the cell pressure or radial stress.

- A method of controlling the pore water pressure within the test specimen.

By not allowing any volume change by the pore water pressure controller,

undrained conditions can be simulated.

- Drained conditions can be simulated by setting a constant pore water

pressure or back-pressure.

- A method of applying axial stress to the test specimen by controlling the

pressure in the lower chamber and hence compressing or extending the

specimen. For triaxial extension, a special top cap connector is available.

193

B.2 Test Initiation

B.2.l Setting Up

On setting up a test, the following procedure should be observed.

B.2.l.l Triaxial Cell. Prepare the triaxial cell with de-aired water in the lower

chamber, the pore water ducts, and in the cell. Position the test specimen with the top cap

ball seating 2 mm from the conical regjsterfixed to the load cell.

B.2.I.2 Pressure Datum. For each pressure controller, set the pressure by adjusting

the zero offset with the open end of the pressure outlet tube held at the mid-height of the

test specimen. The hold volume control wjIJ be engaged at this time. Then connect the

tube to the triaxial cell.

B.2.I.3 Set Pressure. Engage "HOLD VOLUME" on the lower chamber pressure

controller and dial in the required cell pressure and back pressure on the appropriate

controllers.

B.2.l.4 Controller Connections. Link the controllers together in a "daisy chain"

configuration using the two HP-I B cables.

B.2.l.S Computer Connections. Insert the HP-IB interface module into the HP-8S

and connect the attached HP-JB cable into the nearest controller.

B.3 Calculation of Friction

B.3.1 Method

This frictional pressure is calculated by measuring the lower chamber pressure after

having moved the ram up and after having moved the ram down. The frictional pressure

is then half the difference between the two readings.

194

The first stage is to set the test initial conditions by setting

Pc .. Uru

and

Ppr = Uo

The initial setup involved placing the test specimen 2 mm from the loading ram and

so the test specimen has no axial loading from the lower pressure controller at this time.

The next stage is step tJ. vL + 500 mm3 and measure Pmax, then step tJ. ,,__ by

-500 mm3 and measure Pmin'

The friction correction f can then be calculated as:

f = (PLmax - PLmin )/2

B.3.2 Effect of Friction on Calculation

The value of pressure in the lower chamber corrected for friction is calculated as

follows:

where

B.3.3 Docking

PLc = PL + f c(n)

c(n) = -I if tJ.vL(n) > tJ.vL(n-I)

c(n) = +1 if tJ.vL(n) < tJ.vL<n-I)

c(n) = c(n-I) if tJ.vL(n) = tJ.vL(n-l)

Prior to axial loading, the operator should bring the loading ram into contact with

the top cap. This is done by slowly screwing the loading ram down until the pressure in

the lower chamber is observed to increase.

195

The ball seating between the specimen top cap and the loading ram can exhibit

slip/stick. It is, therefore, recommended practice to apply a thin layer of silicone grease to

the loading ram cup prior to setting up the test specimen.

Sensitive docking may be achieved by slowly operating the loading ram, adjusting

the screw and observing the lower chamber pressure. When this increases above the

undocked pressure by, say I kPa, docking is cOmpleted.

At this time, the volume change in the display of the lower chamber controller is

set to zero as the basis for displacement measure in the test specimen.

B.4 Unconsolidated-Undrained Triaxial Test.

In this test, the consolidation phase is excluded. The specimen is subjected to axial

loading with a constant radial stress and with the pore water controller locked.

B.4.1 Initial Conditions

Pc = value entered at program start (confining pressure)

PL = Pc + £.P (as a result of docking procedure).

B.4.2 Test Execution

a. To start the test, the timer is started.

b. A set of readings is taken from the controllers.

c. The rate of displacement, £. VL, is calculated according to the following:

Axial Deformation Control

Axial deformation is computed from the volume change measured by the lower

chamber pressure controller. This volume change measurement will include expansion

in the coiled metal tube connection between the controller and the cell, and expansion

196

caused by stretching of the Bellofram rolling diaphragm. In common with

conventional dial gauge measurement, this method of assessing axial deformation

makes no allowance for compression of the internal load cell if present. By inserting

a solid brass "test specimen", the axial deformation (displacement of the base pedestal)

based on volume change into the lower chamber was compared with the displacement

indicated by a sensitive dial gauge mounted in the usual way. For a pressure variation

of 2000 kPa in the lower chamber, the volume change owing to expansion of the

metal tubing (in this case, copper) and stretching of the Bellofram seal amounted to

approximately 0.5% of apparent axial strain.

where

The required value of axial deformation (~L) at any time can be calculated as:

~L = R(t - to)

to = time of test initiation

t = current time

R = required rate at which test is to proceed

~Vl=a~L

therefore the volume change in the lower chamber required to cause an axial

deformation of AL is:

~ V l = a R(t - to>

The rate is described in Chapter 4, Section 4.4.1.5.

d. Continue at (b) above.

197

APPENDIX C

SUMMARY OF TEST DATA

198

Table C-l. Summary of Triaxial Compression Test Results for Type A Soil Without CaC03 and Dry Side of Optimum Moisture Content.

Effective Effective Peak Confining Stress Axial Stress

Dry Density 0'3 0'1 Test No. gm/cm3 (kPa) (kPa)

AB-OO-Ol 1.6914 0 958.7628

AB-OO-Ol 1.6879 0 808.0824

AB-OO-Ol 1.6907 0 896.3044

AB-00-l1 1.6896 150 1821.8518

AB-OO-12 1.6949 ISO 1846.9174

AB-OO-13 1.6890 150 1795.4427

AB-00-21 1.6872 300 2441.2617

AB-OO-22 1.6897 300 2493.0623

AB-OO-23 1.6868 300 2405.0568

199

Table C-2. Summary of Triaxial Compression Test Results for Type A Soil Without CaC03 and Wet Side of Optimum Moisture Content.

Effective Effective Peak Confining Stress Axial Stress

Dry Density °3 °1 Test No. gm/cm3 (kPa) (kPa)

BA-OO-Ol 1.6948 0 957.8631

BA-OO-Ol 1.6893 0 769.5692

BA-OO-Ol 1.6916 0 950.7905

BA-OO-ll 1.6863 150 1729.1566

BA-00-12 1.6913 150 1969.7644

BA-00-13 1.6886 150 1869.2188

BA-00-21 1.6871 300 2480.2984

BA-00-22 1.6947 300 2672.1952

BA-00-23 1.6928 300 2568.6655

200

Table C-3. Summary of Triaxial Compression Test Results for Type A Soil With 15% CaC03 and Dry Side of Optimum Moisture Content.

Effective Effective Peak Confining Stress Axial Stress

Dry Density (73 (71

Test No. gm/cm3 (kPa) (kPa)

AB-15-01 1.7471 0 885.4739

AB-15-01 1.7506 0 1153.8594

AB-15-01 1.7498 0 1155.4705

AB-15-11 1.7490 150 2098.7132

AB-15-12 1.7500 ISO 2062.1947

AB-15-13 1.7549 ISO 2183.7812

AB-15-21 1.7562 300 2915.7334

AB-15-22 1.7465 300 2770.0993

AB-lS-23 1.7491 300 2861.3182

201

Table C-4. Summary of Triaxial Compression Test Results for Type A Soil With 15% CaC03 and Wet Side of Optimum Moisture Content.

Effective Effective Peak Confining Stress Axial Stress

Dry Density °3 °1 Test No. gm/cm3 (kPa) (kPa)

BA-15-01 1.7472 0 885.4696

BA-15-01 1.7477 0 917.1209

BA-15-01 1.7546 0 990.4538

BA-15-II 1.7490 ISO 1814.5471

BA-15-12 1.7504 ISO 1951.2502

BA-15-13 1.7499 ISO 1916.1760

BA-15-21 1.7524 300 2586.1212

BA-15-22 1.7529 300 2586.0756

BA-15-23 1.7517 300 2476.1159

202

Table C-5. Summary of Triaxial Compression Test Results for Type A Soil With 30% CaC03 and Dry Side of Optimum Moisture Content.

Effective Effective Peak Confining Stress Axial Stress

Dry Density 113 111

Test No. gm/cm3 (kPa) (kPa)

AB-30-01 1.7498 0 386.9108

AB-30-01 1.7443 0 303.5445

AB-30-01 1.7542 0 417.2251

AB-30-11 1.7495 150 1216.2168

AB-30-12 1.7551 150 1338.8939

AB-30-13 1.7484 150 1193.3069

AB-30-21 1.7474 300 1784.4073

AB-30-22 1.7466 300 1707.5112

AB-30-23 1.7527 300 1831.8920

203

Table C-6. Summary of Triaxial Compression Test Results for Type A Soil With 30% CaC03 and Wet Side of Optimum Moisture Content.

Effective Effective Peak Confining Stress Axial Stress

Dry Density °3 0'1 Test No. gm/cm3 (kPa) (kPa)

BA-30-01 1.7460 0 292.4303

BA-30-01 1.7504 0 343.9084

BA-30-OI 1.7451 0 271.8005

BA-30-11 1.7474 150 852.8594

BA-30-12 1.7565 150 917.6052

BA-30-13 1.7427 150 805.9632

BA-30-21 1.7454 300 1227.5797

BA-30-22 1.7477 300 1221.2840

BA-30-23 1.7569 300 1301.3426

204

Table C-7. Summary of Triaxial Compression Test Results for Type A Soil With 15% CaC03 • Dry Side of Optimum Moisture Content and 7 Days Curing.

Effective Effective Peak Confining Stress Axial Stress

Dry Density u3 u1 Test No. gm/em3 (kPa) (kPa)

07-15-01 1.7559 0 1238.6990

07-15-01 1.7498 0 1156.5786

07-15-01 1.7520 0 1206.3630

07-15-11 1.7532 150 2235.6716

07-15-12 1.7500 ISO 2165.2927

07-15-13 1.7518 ISO 2144.6329

07-15-21 1.7525 300 3027.9483

07-15-22 1.7520 300 2885.6930

07-15-23 1.7454 300 2778.9366

205

Table C-8. Summary of Triaxial Compression Test Results for Type A Soil With 15% CaC03 • Dry Side of Optimum Moisture Content and 14 Days Curing.

Effective Effective Peak Confining Stress Axial Stress

Dry Density CT3 0'1 Test No. gm/cm3 (kPa) (kPa)

14-15-01 1.7423 0 907.9865

14-15-01 1.7476 0 1021.6997

14-15-01 1.7471 0 1021.7047

14-15-11 1.7488 150 2135.6253

14-15-12 1.7591 150 2390.5871

14-15-13 1.7480 150 2206.2165

14-15-21 1.7502 300 3030.4681

14-15-22 1.7481 300 2855.9258

14-15-23 1.7499 300 2920.7724

206

Table C-9. Summary of Triaxial Compression Test Results for Type A Soil With 15% CaCO,. Dry Side of Optimum Moisture Content and 28 Days Curing.

Effective Effective Peak Confining Stress Axial Stress

Dry Density u, u1 Test No. gm/cm' (kPa) (kPa)

28-15-01 1.7532 0 1198.7716

28-15-01 1.7535 0 1115.4374

28-15-01 1.7478 0 1018.3806

28-15-11 1.7493 ISO 2176.5659

28-15-12 1.7540 ISO 2259.8127

28-15-13 1.7474 ISO 2039.8553

28-15-21 1.7531 300 2900.6991

28-15-22 1.7519 300 2895.9601

28-15-23 1.7498 300 2832.1083

207

Table C-IO. Summary of Triaxial Compression Test Results for Fanglomerate Assemblage Soils (Sierrita Site).

Effective Effective Peak Confining Stress Axial Stress

Dry Density 0'3 0'1

Test No. gm/cm3 (kPa) (kPa)

ABO 000 1.7800 0 397

ABO 011 1.7698 0 188

ABO 001 1.7571 0 147

GHAN 01 1.7428 50 2169

ABDU 01 1.7739 50 548

SERT 02 1.7092 50 1037

GHAN II 1.7280 100 1849

SERT 12 1.7235 100 1352

SERT 11 1.7280 100 1221

GHAN 21 1.7591 200 3653

ABDU 31 1.7881 300 2129

ABDU 32 1.8110 300 2451

LAB ooOa 1.7851 100 800

APPENDIX D

STRESS-DEFORMA nON CHARACfERISrICS FOR TRIAXIAL COMPRESSION TESTS ON UNCEMENTED,

ARTIFICIALL Y CEMENTED, AND RECONSTITUTED SOILS

208

4000~----~----~----~----~----~

3200 -~ ~

- 2400 en en G,) ~ .... en 1600 -c .-)(

<[

800

.,'E':~, I ." .. \\

Confining Pressure, era

--- OkPa ----- 150 kPa 0_._.- 300 kPa

l '''--'''' 0\., r. '\'-" /1 \ \\ • .:...~~ •• ~===._._o_

~'I, \\ _o_._"_~ ..... _ /', \ ~-. ...

\ -- . -----..---~ \ ..... -----------------~=--------~---

2 4 6 8 10 0/0 Axial Strain

209

Figure D.l Stress-deformation characteristics for uncemented Type A soil compacted at dry side of OMC.

4000~----~-----r----~~----'-----~

3200 -~ .x - 2400 en en e .... en

.- ....... ~-." IV·-'-". .. '\ II .,.

f. ~-:.' ,\

Confining Pressure,cr!

---OkPa

----- 150 kPa ._.-.- 300 kPa

1600 '\~ '-)\\' .. ,..... '. "I \ ,._ ............. ,...,,..,,,,..,,, .......... . . 2 1/ 1\ \ .-._._._._._._._.

~ _I' 1\ \ 800 .11 \~a..:~~~ ________ _

2 4 6 8 10 0/0 Axial Strain

210

Figure D.2 Stress-deformation character.istics of uncemented Type A soil compacted at wet side of OMC.

4000~----~----~----~----~------

3200 -o ,:s-,. CL ' • .:J&. /1' - 2400 .' U \ o ~" ,

I;,. 1\

Confining Pressure, (7'3

---OkPa

----- 150 kPa ._._.- 300 kPa

e ilJr-~ .. \ - ,ill ,1, n ., CJ) 1600 l·., ,I, ,\ '-'-.-.. =:=:="=',:. .. ~ h~ 1\ .-:::,_._ .... -._._._._. <t 800 I \~.s--.... _________ _

2 4 6 8 % Axial Strain

10

211

Figure D.3 Stress-deformation characteristics of Type A soil artificially cemented with IS% Caco, and compacted at dry side of OMC.

4000~----~--~~--~~--~~--~

!200 -~ .:;e. ....... 2400

rJ) rJ)

f -en 1600 o .-)(

<[

SOO

Ii· -:':"~' . ~ . , i •.

t . \' ~b~ ,l

Confining Pressure, era

---OkPo ----- '150 kPo ._._.- !OO kPo

~r 1/ \\' .:\.,. ~

" ,,' ..... ~-.-.-.-.-.-.-. \' -----_._._ .. _._._._. i \~\ I. ,_~ ___________ _

2 4 6 8 10 0/0 Axial Strain

212

Figure 0.4 Stress-deformation characteristics of Type A soil artificially cemented with lS% Caco3 and compacted at wet side of OMC.

4000~----r-----r-----~----~----~

3200 -~ .:til! - 2400

C/) C/)

~ -(f) 1600 o

800

~~,

Confining Pressure, eTa

---OkPa ----- 150kPa ._._.- 300 kPa

I: '1·, II \... -_.-._._._._._._.-._.-.. .'----.. -. _.- ' ......... _-----.... II ._._. -. ,.,~~ .// ~~----------­~, ~~---~---l -------

,'1 'I

2 4 6 8 % Axial Strain

10

213

Figure D.S Stress-deformation characteristics of Type A soil artificially cemented with 30% Caco3 and compacted at dry side of OMC.

214

4000~-----~,-----r-.-----r-.-----r-.-----'

Confining Pressure, eTa

3200 t- --- OkPa • -~ ----- 150 kPa ._._.- 300 kPa

.:tI! -2400 ~ -f/) f/) GJ ... .. en 1600 t- . o .-)( <[

Figure D.6

.- ._._._.-.-.-_ ...... --$ :0--..., ...... ':: : .... "....~ __ nol"l!llloo_ ........ .."

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

800 I- .~::;==---e==----------c= ~ -~~-~-~-~~~-t ~

2 4 6 8 10 0/0 Axial Strain

Stress-deformation characteristics of Type A soil artificially cemented with 30% Caco~ and compacted at wet side of OMC.

-~ .:liI:

4000~----~----r---~~--~~--~

3200 .-. I.... \

,. ..... " o. of !\

Confining Pressure, cr 3

---OkPa

----- 150 kPa 0_0_'- 300 kPa

-2400 /. i· i ,,"1 _ 01. en en E - . -, "1 il '1\ ·1,

en 1600 .~ \!ll \L._._._._._._o_._._._. ~ ~.--.-.-.-.-.-.-.-.-.-. 'I '0-'_'_0_0_'_'_'-'-' c .-

)(

<[

aoo ~~--------------, ~-------------­,---------------

°O~~~2~~e4~~~6~~~e~EB~IO % Axial Strain

215

Figure D.7 Stress-deformation characteristics of Type A soil artificially cemented with J S% CaCO~. compacted at dry side of OMC. and 7 days curing.

-~ ~

4000~----~,~----~,------~,------~,----~

3200 ~ . -.

Confining Pressure, C7'!

---OkPo ----- 150 kPo 0-'_'- 300 kPo

.

...... 2400 en

~ tWit [,: .. ,0' ~:r,,~\ i \

. en Q) ~ .. en -o )(

<[

I 'l.l \._._._._.- ._._._._._ .. 1600 I- I \ ...... _.-.-._._._._._._._.-..

~ I~ .-._._._._._._._._._._.-

~ ~~~~~NM~~~~ 800 ,1 -~.

2 4 6 8 10 % Axial Strain

216

Figure D.S Stress-deformation characteristics of Type A soil artificially cemented with IS% CaCO,. compacted at dry side of OMC. and 14 days curing.

4000~----~'~----~'------~'------~1----~

3200 ~ -o ... ,::.~ Q. I "r :: 2400 "" i ",\\ en t', .,' ~ l~,~ '" .,

Confining Pressure, era

---OkPa ----- 150 kPa ._._.- 300 kPa

.

.

.:: t, I~\\· en 1600 _ ~ 'I \ .~,}..-.-.-.-.-.-.-.-.-~ o I I, \

.;C fla.' \ ~ sao ~ ll~'-__ .-.w~ ................... ~~'IIf!I_

\ 2 4 6 e 10

0/0 Axial Strain

217

Figure D.9 Stress-deformation characteristics of Type A soil artificially cemented with IS% Caco~, compacted at dry side of OMC, and 28 days curing.

APPENDIX E

MOHR CIRCLE DIAGRAMS FOR TRIAXIAL COMPRESSION TESTS ON UNCEMENTED, ARTIFICIALLY CEMENTED, AND RECONSTITUTED SOILS

218

_2000 o a.. ~ -... (/) U) Cl) '--(/) 1000 t..­O cu .c. en

Figure E.l

/ / "

~ " , '. / ".~r /.,.' ,

1000

Confining Pressure, 003 A,D OkPa B, E 150kPa C, F 300kPa

A, B, C Peak Strength

0, E, F Residual Strength

2000 3000 4000 Normal Stress & (kPa)

Mohr diagrams for triaxial compression tests on un cemented Type A soil compacted at dry side of OMC.

N -\0

_2000 o a.. .::tt; -... U) en e -en 1000 ~

C Q)

.s:::. en

Figure E.2

// /

// ,,' // ",'

/ ,,' ~ . --'

Confining Pressure,D"3 A,D OkPa B. E 150kPa C, F 300kPa

A, B, C Peak Strength

0, E. F Residual Strength

1000 2000 3000 4000 Normal Stress u·(kPa)

Mohr diagrams for triaxial compression tests on uncemented Type A soil compacted at wet side of OMC.

~ o

_2000 o a.

.:::.! -... en en Q) ~ .....

(J) 1000 ~

o Q)

.r::. (J)

" /

/

/ .'-/

.-' " , /,,' , /. ,,' " .~

Confining Pressure.u3 A.D OkPo B. E 150kPa C, F 300kPa

A, B, C Peak Strength 0, E, F Residual Strength

0'" I; •• I .; I " II

1000 2000 3000 4000 o

Figure E.3

Normal Stress' CT (kPa)

Mohr diagrams for triaxial compression tests on Type A soil artificially cemented with 15% CaC03 and compacted at dry side of OMC.

~

-o a. .:Jt!. -... en en Q) '--

2000

(f) 1000 '-o Q) .c: en

Figure E.4

1000

, -,.

Confining Pressure, 0"3 A,O OkPo B, E 150kPo C, F 300kPa

A, S, C Peak Strength

0, E, F Residual Strength

2000 3000 4000 Normal Stress .0" (kPa)

Mohr diagrams for triaxial compression tests on Type A soil artificially cemented with IS% CaC03 and compacted at wet side of OMC.

~ N

_2000 o

Q. ~ -... f/) f/) Q) ~ +-U) 1000 ~

o Q)

.s:::.. U)

Figure E.S

1000

Confining Pressure, 0"3 A,D OkPa B, E 150kPa C, F 300kPa

A, B, C Peak Sfrength

0, E, F Residual Strength

2000 3000 4000 Normal Stress 0- (kPa)

Mohr diagrams for triaxial compression tests on Type A soil artificially cemented with 30% .CaC03 and compacted at dry side of OMC.

~ w

_2000

~ .:w:: -.. U) U) Q) L--en 1000 L­a Q)

.t.:= en

00

Figure E.6

, ,,;,

J' "

1000

"

, .'

"

Confining Pressure'0"3 A,D OkPa B, E 150kPa C, F 300kPa

A. B. C Peak Strength

D. E. F Residual Strength

2000 3000 4000 Normal Stress rr (kPa)

Mohr diagrams for triaxial compression tests on Type A soil artificially cemented with 30% CaC03 and compacted at wet side of OMC.

~ J>.

-o a. ~ -.. en en Q) ... -

2000

(f) 1000 ... c Q) .t: (f)

Figure E.7

1000

, , , , ,

, , , ,

Confining Pressure'0"3 A.O OkPa B. E 150kPa C. F 300kPa

A, B. C Peak Strength 0, E, F Residual Strength

2000 3000 4000 Normal Stress a- (kPa)

Mohr diagrams for triaxial compression tests on Type A soil artificially cemented with 15% CaC03t compacted at dry side of OMC. and 7 days curing.

~ v.

_2000

~ ~ -.. en en ~ -(f) 1000 ... c cu

.c:: en

1000

, , ,

Confining Pressure'0"3 A,O OkPa B, E 150kPa C, F 300kPo

A, B, C Peak Strength

0, E, F Residual Strength

2000 3000 4000 Normal Stress'U (kPa)

Figure E.S. Mohr diagrams for triaxial compression tests on Type A soil artificially cemented with 15% CaC03• compacted at dry side of OMC, and 14 days curing.

~ 0\

_2000

~ .:II! -... en en C1) .... -en 1000 .... o C1) .c (J)

Figure E.9

/

1000

Confining Pressure,CT3 A,D OkPa B, E 150kPa C, F 300kPa

A. B. C Peak Strength

0, E, F Residual Strength

2000 3000 4000 Normal Stress u (kPa)

Mohr diagrams for triaxial compression tests on Type A soil artificially cemented with IS% CaCO:s. compacted at dry side of OMC, and 28 days curing.

Jj "

_2000 CJ (L .::II! -... en en Cl) '--en 1000 ... o Cl) .c en

00

p

1000 2000 3000 4000 Normal Stress (T (kPa)

Figure E.JO Mohr diagrams for peak strength of triaxial compression tests on fanglomerate assemblage soils (Sierrita site).

~ 00

_2000 c a.

.)t! -.. en en ~ -en 1000 ... c Q)

.c en

R

1000 2000 3000 4000 Normal Stress rr (kPa)

Figure E.II Mohr diagrams for residual strength of triaxial compression tests on fanglomerate assemblage soils (Sierrita site).

~ \0

230

REFERENCES

Alfi, A.A., "Experimental Study of a Strongly Cemented Sand," unpublished Thesis, Department of Civil Engineering, Stanford University, 1978.

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