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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