liquefaction mitigation of silty soils using dynamic compaction

129 Figure 8-2 Pre and post-compaction relative density and penetration resistance for silty sand deposit with 40 % initial density …..……… 132 Figure 8-3 Pre and post-compaction relati

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LIQUEFACTION MITIGATION OF SILTY SOILS

USING DYNAMIC COMPACTION

in partial fulfillment of the requirements for the

degree of

Doctor of Philosophy

Department of Civil, Structural & Environmental Engineering

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3203924 2006

UMI Microform Copyright

ProQuest Information and Learning Company

by ProQuest Information and Learning Company

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Copyright by

Rafeek G Nashed

2005

(ii)

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DEDICATION

To

My Wife, My Children and My Mother

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ACKNOWLEDGEMENTS

You, LORD, have done it.” (Psalms 109:26, 27)

First, I would like to forward my great thanks and praises to God

I offer my advisor Professor S Thevanayagam, my most sincere gratitude for his continued support and advice throughout my studies and research efforts His patience, encouragement and generosity are all greatly appreciated; working with him on this research has been an enlightening experience

I would like to thank my committee members, Professor P K Banerjee and

Professor Shahid Ahmad for their patience, wisdom, and leadership I also would like to express my deepest thanks and appreciation to Professor G R Martin for his contribution

as my outside reviewer

I am especially thankful to my wife, who has been through it all with me Thank you for all of your support, encouragement and love Also thanks for my kids who have given my life a new purpose

Finally, financial support from my advisor through a grant from The Federal Highway Administration FHWA through The Multidisciplinary Center for Earthquake Engineering Research MCEER is gratefully acknowledged

iv

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TABLE OF CONTENTS

Dedication……… iii

Acknowledgements ……… ……… iv

Table of contents ……… …….… v

List of Figures ……… ……… …… …… xi

List of Tables ……… …….…… xxiv

Notations ……….……….……… …… xxvi

Abstract ……… xxxvi

1 Introduction ……… ……….… … 1

1.1 Statement of the problem ……… 5

1.2 Research scope and objectives……… 9

1.3 Outline of dissertation ……… … 10

2 Current Practice of Dynamic Compaction Technique ……… … 12

2.1 Historical background……….… 12

2.2 Dynamic compaction applications ………… ……….… 13

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2.2.1 Types of soil improved ……….… 13

2.2.1.1 Granular and cohesive soils … ……….…… 15

2.2.1.2 Collapsible soils ……….…… 16

2.2.1.3 Other deposits ……….….………….……… 17

2.2.2 Field observations ……… … 19

2.2.2.1 Depth of improvement ……….……… 19

2.2.2.2 Degree of improvement ……… 20

2.2.2.3 Limits of improvement ……… ……… 23

2.2.3 Post-improvement assessment techniques ……… … 24

2.2.4 Induced Ground Subsidence ……….……… 28

2.2.5 Ground vibration ……… ……… ……… 30

2.3 Recent field advances ……… ……… 35

3 Current Practice Guidelines ……… 39

3.1 Introduction ……… 39

3.2 Available design guidelines ……… ……… 39

3.3 Summary and conclusion ……… 46

4 Energy Dissipation mechanisms and Densification modeling …… ………… 48

4.1 Introduction ……… 48

4.2 Energy dissipation mechanisms in granular media ……….……… 48

4.2.1 Frictional dissipation mechanism ……… 49

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4.2.2 Viscous dissipation mechanism ……… ……… 52

4.2.3 Particle breakage dissipation mechanism ……… ……… 53

4.3 Densification due to DC ……… ……… 53

4.3.1 Densification modeling in dry deposits ……… ………… 53

4.3.2 Densification modeling in saturated deposits ……… … 56

4.4 Past research on densification modeling due to DC …… ………… … 57

4.5 Summary ……….……… 63

5 Energy Attenuation Due to Surface Impact ……… 65

5.1.Introduction ……….………… … 65

5.2 Energy radiation due to surface impact……… ……… … 66

5.2.1 Energy partitioning from surface impact in elastic half-space … 71 5.3 Attenuation relationships ……… ……… ……… 74

5.4 Energy dissipation due to DC processes ……… ……… 80

5.5 Summary and conclusions ……….………85

6 Proposed Densification Simulation Model ……….……… … 87

6.1 Introduction ……… … ……… ……… 87

6.2 Overview of the simulation model ……… ……… ……… 87

6.3 Governing equations ……… 92

6.4 Induced pore pressure due to energy dissipation …… …… ……… 93

6.5 Pore pressure dissipation ……… ……… 98

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6.5.1 Boundary conditions ……….……… 100

6.5.2 Convergence and stability ……….……… 103

6.6 Soil Densification ……….…… ……… 105

6.7.Modeling DC processes at a site ……….……… 108

6.8 Summary ……… ……… 112

7 Verification of the Proposed Model ……….……… 114

7.1 Introduction ……… ……… 114

7.2 Kampung Paker site, Malaysia ……….……… 115

7.3 Newport News, Virginia ……… ……… ……… 117

7.4 Steinaker dam modification project, Utah ……….….……… 122

7.5 Conclusions ……… …… ……… ………… 125

8 Effects of Site Conditions and Construction Procedure - Parametric study 127

8.1 Introduction ……… ………….……… 127

8.2 Effect of initial density of deposit (pre-(D r ) eq)……….… … 132

8.3 Effect of deposit’s hydraulic conductivity (k) and fines content (FC) … 134

8.4 Effect of level of energy delivery WH ………… ……… … 137

8.5 Effect of impact grid pattern ……… ……… 139

8.6 Effect of impact print spacing S ……… ……… 143

8.7 Effect of number of impacts N I ……… ……… 144

8.8 Effect of time cycle between impacts T ……… ……… 146

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8.9 Effect of wick drains spacing S w ……… ……… ……… 148

8.10 Summery and conclusions ……… ……… 151

9 Design Guidelines for Dynamic Compaction of Silty Soils ……… 153

9.1 Introduction ……… … …… 153

9.2 Design procedure ……… …… ……… 154

9.3 Design charts ……… ……… 157

9.4 Regression analyses ……… ……… 168

9.4.1 Building and testing a model ……… 169

9.4.2 Regression model ……… ……… 171

9.5 Design examples ……… 173

9.5.1 Design example 1 ……… ………… 174

9.5.2 Design example 2 ……… … 177

9.6 Summary and conclusions ……… 184

10 Summary and Conclusions ……… ……… 186

10.1 Summary and major findings ……… ……… …… 186

10.2 Suggestions for future research ……… 190

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Appendix A Penetration Resistance in Sands and Silty Sands ….…… …… … 192 Appendix B Energy Required to Cause Liquefaction … ……… … 211 Appendix C Dynamic Compaction Simulation Software …….……… … 220 Appendix D Software User Manual ……… … 227 Appendix E Simulation Results for A Dynamic Compaction Project ……… … 231 References ……… 263

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LIST OF FIGURES

Figure 1-1 Examples of liquefaction damage ……… 3 Figure 1-2 Dynamic compaction process ……… 6 Figure 1-3 Dynamic compaction ……… … …….… 8 Figure 2-1 Range of soil gradation of deposits suitable for DC ….… ………… 16 Figure 2-2 Maximum depth of influence versus drop energy …… …….…….… 21 Figure 2-3 Maximum depth of influence versus drop energy …… …….…….… 21 Figure 2-4 Variations of degree of improvement with depth …… ……… ….… 22 Figure 2-5 Pre and post-improvement evaluation, Newport News, Virginia … 26 Figure 2-6 DC induced ground subsidence………… … ……… … … 29 Figure 2-7 Normalized crater depths for collapsible soils ……….……… …… 30 Figure 2-8 Attenuation of ground vibration ……… 31 Figure 2-9 Attenuation of normalized PPV versus normalized distance … …… 33 Figure 2-10 Attenuation of ground vibration for collapsible soils ….….….……… 34 Figure 2-11 PPV for different soil deposits …… ……….…….……….… 34 Figure 2-12 Installation patterns for prefabricated vertical drains … … ……… 36 Figure 3-1 Pounder mass and drop height for various DC equipment ……… … 42 Figure 4-1 Simplified cubic model of equal spheres …….……… 49 Figure 4-2 Elastic spheres under normal and shear loads ……… … 50

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Figure 4-3 Theoretical hysteresis loop due to oscillating tangential force for

two spheres in contact …… ……… ……… 51

Figure 4-4 Loose granular soil behavior under surface impact ……… 54

Figure 4-5 Dry soil deformation due to surface impact …….……… 55

Figure 4-6 Densification mechanism of saturated deposits ……… 57

Figure 4-7 Wave equation model ………….……… ……… 63

Figure 5-1 Stresses in x-direction on a small element of an infinite elastic medium ……… …….……… ……… 67

Figure 5-2 Waves induced from surface impact on the surface of half-space … 68

Figure 5-3 Characteristic motions of seismic waves ………… …….… … … 70

Figure 5-4 Amplitude ratio versus dimensionless depth of Rayleigh wave ……… 71

Figure 5-5 Effect of different percentage of energy portioning among generated waves……… …… ……… … 73

Figure 5-6 Typical impact grid pattern for silty deposits ………….……… 81

Figure 5-7 Energy Partitioning and Attenuation estimation a) Rayleigh-wave b) Body-wave ………….… ……….……… 82

Figure 6-1 Energy-based liquefaction mitigation using DC ……… … 88

Figure 6-2 Illustrations of DC densification process ……….…… 90

Figure 6-3 DC impact grid pattern and Axisymmetric flow through wick drain … 91 Figure 6-4 Normalized excess pore pressure versus normalized dissipated energy ……….… ……… 96

Figure 6-5 Model versus experimental results ……… ….…….……… 98

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Figure 6-6 Two-dimensional nodal system representing influence

zone of a wick drain ……….……… ……… 100 Figure 6-7 Dissipation model boundaries (no wick drains) ……….…… 102 Figure 6-8 Dissipation model boundaries (wick drains) ……….….……… 102 Figure 6-9 Effect of keeping track of soil status for the finite difference

nodal system only …… ……… 105 Figure 6-10 Pre and post-liquefaction volume compressibility …….……… 106 Figure 6-11 Effect of relative density on volumetric strain …… ………… … 107 Figure 6-12 Effect of confining stress on volumetric strain ……… 107 Figure 6-13 Compressibility of sand verses pore pressure build-up ……… …… 108 Figure 6-14 Typical impact grid pattern for sandy deposits ……….……… 109 Figure 6-15 Simulated pore pressures across drains’ circle of influence ……… 111 Figure 6-16 Flow chart showing steps of modeling DC processes ……… 112 Figure 7-1 Soil profile ……….……… 115 Figure 7-2 Pre and post-compaction measured and simulated relative density 115

Figure 7-3 Impact grid pattern ……….……… 116

Figure 7-4 a) Pre-compaction soil density profile, b) Impact grid pattern ……… 118 Figure 7-5 a) Soil density profile after impacts on location 1, 1st pass,

b) Impact location ……… ……… 118 Figure 7-6 a) Soil density profile after impacts on location 2, 1st pass,

b) Impact location ……… 119 Figure 7-7 a) Soil density profile after impacts on location 3, 1st pass,

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b) Impact location ……….……… … 119 Figure 7-8 a) Soil density profile after impacts on location 4, 1st pass,

b) Impact location ……… ……….… 120 Figure 7-9 a) Soil density profile after impacts on location 1, 2nd pass,

b) Impact location ……… 120 Figure 7-10 a) Soil density profile after impacts on location 2, 2nd pass,

b) Impact location ……… 121 Figure 7-11 a) Soil density profile after impacts on location 3, 2nd pass,

b) Impact location ……… ……… 121 Figure 7-12 Pre and post-compaction measured and simulated SPT blow count 122 Figure 7-13 Soil profile ……… ……… … 123

Figure 7-14 Pre and post-compaction measured and simulated N1 ………… … 123

Figure 7-15 Impact grid pattern for Steinaker dam modification project, Utah 125

Figure 8-1 Impact grid pattern A ……….……… 129

Figure 8-2 Pre and post-compaction relative density and penetration

resistance for silty sand deposit with 40 % initial density … ……… 132 Figure 8-3 Pre and post-compaction relative density and penetration

resistance for silty sand deposit with 60 % initial density …… …… 133

Figure 8-4 Maximum achievable depth of improvement d max

for different pre-(Dr ) eq ……… …….……… 134 Figure 8-5 Degree of improvement for different pre-(D r ) eq ……… 134 Figure 8-6 Pre and post-compaction relative density and penetration

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resistance for silty sand deposit with k=10-7 m/s, FC=25% …….… 135

resistance for sandy silt deposit with k=10-8 m/s, FC=40% …………136 Figure 8-8 Maximum achievable depth of improvement d max for

different hydraulic conductivities ……… ……… 137 Figure 8-9 Degree of improvement for different hydraulic

conductivities ……… ……….……… 137 Figure 8-10 Pre and post-compaction relative density and penetration

resistance for three different levels of energy per impact WH …….… 138 Figure 8-11 Maximum achievable depth of improvement dmax

for different levels of energy per impact WH ………….……… 138

Figure 8-12 Degree of improvement for different levels of energy

per impact WH ……… 138 Figure 8-13 Impact grid pattern B ……… …… ……… 139

resistance for pattern A ……… ……… … 141

resistance for pattern B ……… … …… 141

Figure 8-16 The maximum achieved depth of improvement dmax

for different impact grid patterns ……… 142 Figure 8-17 Degree of improvement for different impact grid patterns ………… 142 Figure 8-18 Pre and post-compaction relative density and penetration

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resistance for different impact print spacings S ……… 143

Figure 8-19 The maximum achievable depth of improvement dmax

for different impact print spacings S ……… 144

Figure 8-20 Degree of improvement for different impact print spacings S ……… 144

resistance for different number of impacts per location N I ………… 145

Figure 8-22 Degree of improvement for different number of impacts

per location NI ……….……… 146

resistance for impact time cycle of 2 min……… 147 Figure 8-24 Pre and post-compaction relative density and penetration

resistance for impact time cycle of 4 min……… ……… 147

Figure 8-25 Maximum achievable depth of improvement dmax for

different impact time cycle T ……… 148

resistance for a wick spacing of 1.0 m ……… 149

resistance for a wick spacing of 2.0 m ……… … 150

Figure 8-28 The maximum achieved depth of improvement d max

for different wick drain spacing Sw ……… … 150

Figure 9-1 Design procedure ………….………… ….……… …… 156

Figure 9-2 Impact grid pattern adopted for design guidelines ……… 159

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Figure 9-3 DC design charts for k=10-7 m/s, FC=25 %, pre_(D r ) eq= 40 %

(pre-(N1 ) 60cs=7.5), S=15.0 m (a) NI = 12, Sw = 1.5 m, T = 2 min

(b) NI = 12, Sw = 1.5 m, T = 4 min (c) NI = 12, Sw = 1.0m,

T = 4min (d) N I = 8, S w = 1.5 m, T = 2 min (e) N I = 8,

Sw = 1.5 m, T = 4 min (f) NI = 8, Sw = 1.0 m, T = 4 min ……… … 160 Figure 9-4 DC design charts for k=10-7 m/s, FC=25 %, pre_(D r ) eq= 60 %

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(b) N I = 12, S w = 1.5 m, T = 4 min (c) N I = 12, S w = 1.0m,

T = 4min (d) NI = 8, Sw = 1.5 m, T = 2 min (e) NI = 8,

Sw = 1.5 m, T = 4 min (f) NI = 8, Sw = 1.0 m, T = 4 min ……… … 165

(pre-(N1 ) 60cs=7.5) , S=12.0 m (a) NI = 12, Sw = 1.5 m, T = 2 min

Figure 9-11 Pre_, and req (N 1 ) 60cs profile ……… …… 174

Figure 9-12 Design chart (k=10-7m/s, Pre-(N1 ) 60cs=7.5) … ……… 174

Figure 9-13 Pre_, and Post_(N 1 ) 60cs profile for Example 1 ……… 176

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Figure 9-14 Design example 2 ……….…… ……… 177

Figure 9-15 Pre_, and req (N1 ) 60cs profile ……….……… 178

Figure 9-16 Design chart (k=10-7m/s, Pre-(N1 ) 60cs=16.0, S = 15.0 m) ……… … 178

Figure 9-18 Pre_, and req (N1 ) 60cs profile ……… ……… 181

Figure 9-20 Pre_, and req (N1 ) 60cs profile for deposit in example 4 ………… … 183

Figure A-1 Correlations of SPT blow count with relative density for sand ……… … 194

Figure A-2 Relationship between relative density and (N1)60 for clean sands ……… ……… ……… 195

Figure A-3 N1 / Dr2 = a + b plotted against the mean grain size ………… … 196

Figure A-4 N1 / Dr2 = a + b plotted against the mean grain size (in-situ ground freezing sampling) ……… …… 197

Figure A-5 Relation between N1 / D r 2 ratio and void ratio range ……… … … 199

Figure A-6 CPT resistance, relative density correlation ……….… ……… … 201

Figure A-7 SPT – CPT relation ……….……… ……… …… … 202

Figure A-8 Data from liquefaction case histories ……….…… ……… 205

Figure A-9 Different fines content correction ……….……… …… …… 206

Figure A-10 CPT correction ……… ………….… ……… 208

Figure A-11 Flowchart illustrating the CPT fines content correction …… …… 209

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Figure B-1 Stress-strain hysteresis loop ……… ……… 212

Figure B-2 Energy to liquefaction versus void ratio for different fine Contents ……… 214

Figure B-3 Energy to liquefaction versus (e c ) eq ……… ……… 215

Figure B-4 Energy to liquefaction versus (Drc ) eq ……… … 215

Figure B-5 Energy to liquefaction versus (e f ) eq ………….……….…… ……… 216

Figure B-6 Energy to liquefaction versus (Drf ) eq ……… ………….………… 216

Figure B-7 Energy to liquefaction in clean sand and silt ….……… ……… 217

Figure B-8 Relative density versus (N1)60 for clean sand ……….……… 218

Figure B-9 Relationship between energy to liquefaction and (N1)60 ……… … 218

Figure D-1 Input file example ……… ……… 230

Figure E-1 a) Pore pressure profile after impact No 1 b) Pore pressure profile just before next impact c) Soil density profile d) Impact location … 232

Figure E-5 a) Pore pressure profile after impact No 8 b) Pore pressure profile

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just before next impact c) Soil density profile d) Impact location … 236

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LIST OF TABLES

Table 1-1 Recent major ground liquefaction ……… ……… ……… 2

Table 1-2 Liquefaction mitigation techniques ……… ……… … 5 Table 2-1 DC terminology ……… ……… 14

Table 2-2 Soil deposit suitability for DC ……… ………… 16

Table 2-3 n values for different DC projects ……… …….…… 20

Table 2-4 Range of the anticipated improvements for different deposits … …… 23 Table 2-5 Post-improvement soil properties - Upper limits ……… 24 Table 2-6 Surface subsidence for different deposits ……… 28

Table 3-1 Recommended n values for different soil types ……… 41

Table 3-2 Equipment requirements for different pounder weights ……… 43 Table 3-3 Applied energy guidelines ……… 43 Table 3-4 Anticipated depth of improvement for different soil deposits …… … 46

Table 5-1 Spreading attenuation coefficient n s for various sources ….… … … 76 Table 5-2 Attenuation coefficient α for different classes of soil

materials and two different frequencies ……… ……… 78

Table 8-1 DC operational parameters for impact pattern A ……….……… 130

Table 8-2 DC operational parameters for impact pattern B ………….………… 140

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Table 9-1 Regression coefficients ……… 172 Table 9-2 Limits of independent variables ………….……….… ……… 172 Table 9-3 Example 1 design parameters ……… ……… 175 Table 9-4 Example 2 design parameters ……… 179 Table 9-5 Example 3 design parameters ……… 181

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NOTATIONS

A s cross sectional area of the soil column

AE required applied energy

a 0 dimensionless frequency parameter

a max peak horizontal acceleration

C 0 , C 1 , C 2 coefficients

C D parameter relating normalized penetration resistance to square of

relative density

C f coefficient of friction of the contact surfaces

C r coefficient of consolidation for radial flow

C u coefficient of uniformity

C v coefficient of consolidation for vertical flow

Cα attenuation constant

c radius of annulus of slippage

c s dashpot damping coefficient

CPT cone Penetration Test

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CRR cyclic resistance ratio

CSR cyclic stress ratio

D e diameter of drain influence cylinder

D p coarse grain particle size

(D r ) eq equivalent relative density

(D rc ) eq equivalent intergranular relative density

(D rf ) eq equivalent intergranular relative density

Δ(D r ) eq improvement inequivalent relative density

d distance

d max maximum depth of improvement

(d max ) req revised required depth of improvement

d p fine grain particle size

d w equivalent diameter of the drain

E energy delivered to ground due to impact

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E cB (R) total energy content of body wave along a hemispherical surface at

radius R

at radius r

E L energy spent to cause liquefaction

(E L ) pre-DC energy per unit volume of soil required to cause liquefaction

pre-densification using DC technique

(E L ) post-DC energy per unit volume of soil required to cause liquefaction

post-densification using DC technique

E EQ dissipated energy per unit volume due to the design earthquake

ΣE DC cumulative dissipated energy per unit volume due to DC processes

E R(r, zi) Rayleigh wave energy per unit depth along the cylindrical surface

at radius r

e void ratio

e c intergranular void ratio

(e c ) eq equivalent intergranular void ratio

e f interfine contact void ratio

(e f ) eq equivalent interfine void ratio

e max.HC maximum void ratio of the host coarse- grained soil

e max,HF maximum void ratio of the host fine- grained soil

e min.HC minimum void ratio of the host coarse- grained soil

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e min.HF minimum void ratio of the host fine-grained soil

F 1 (k c ) normalizing function to account for kc

F 2 (D r ) normalizing function to account for Dr

FC L limiting fines content

FC th threshold fines content

amplitude at the surface

i portion of the fine grains that contributes to the active intergrain

contacts

j radius of contact area between grains

K parameter relating Rayleigh wave velocity to shear wave velocity

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K 2 energy constant

K c fines correction factor for CPT resistance

K s fines correction factor for SPT resistance

k r hydraulic conductivity of soil for radial flow

k s soil spring stiffness coefficient

k v hydraulic conductivity of soil for vertical flow

M s constraint modulus of the soil column

m coefficient depends on grain characteristics and fine grain packing

m s mass per unit area of weight

m v soil volume compressibility

N 1 normalized penetration resistance for overburden pressure

(N 1 ) 60 normalized penetration resistance for overburden pressure and rod

energy

(N 1 ) cs equivalent clean sand SPT resistance

N I number of drops at each drop location

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N w wave number

ΔN f fines content correction for SPT resistance

n constant; number of independent variables

n s spreading attenuation coefficient

P a reference pressure in the units as σ’ v0

P a2 reference pressure in the units as qc, and σv0

Q normalized CPT penetration resistance

q c1 cone penetration resistance corrected for overburden pressure

q c1N normalized (i.e dimensionless) cone penetration resistance

corrected for overburden pressure

(q c1N ) cs equivalent clean sand normalized CPT resistance

Δ(q c1 ) fines content correction for CPT resistance

R radius of the hemispherical wave front of body waves

R 2 coefficient of multiple determination

R d size disparity ratio = Dp / d p

R g radius of spherical grain

r radial distance from the energy source

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r 0 pounder radius

S w wick drains spacing

s width of a band-shaped drain cross section

SPT standard Penetration Test

SS E residual sum of squares

SS T total corrected sum of squares

SS R regression sum of squares

T time cycle between passes / impacts

T’ * maximumtangential force

t thickness of a band-shaped drain cross section

u I instantaneous excess pore pressure due to surface impact

u * , v * , and w * displacements in x-, y-, and z- directions

v particle velocity in radiated stress wave

v i appropriate wave velocity

v p compression wave velocity

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v R Rayleigh wave velocity

W N normalized dimensionless energy

w cumulative dissipated energy per unit volume of soil

Σw energy loss per unit volume of soil

wB energy loss per unit volume due to body wave

w R energy loss per unit volume of soil due to Rayleigh waves

X independent variables matrix

Z dependent variable vector

ˆ

Z fitted values vector

z instantaneous position of wave front

z c depth beneath the center of impact

Δz vertical distance between nodes

α material damping attenuation coefficient

αsp parameter relating shear wave velocity to compression wave

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γ shear strain

γw unit weight of water

2

εe soil vertical strain

ει axial strain in i direction

η dimensionless constant relating the dynamic excess pore pressure

to the dissipated energy density

θ parameter depends on soil type and test condition

σc normal stress on the contact

σc ’ effective confining stress

σ’ h0 horizontal effective overburden pressure

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σι total normal stress in i direction

σv0 total overburden pressure

σ’ v0 effective overburden pressure

τc tangential traction on the contact

Δφ increase in friction angle at various distances

Δφb increase in friction angle beneath the pounder

χ parameter depends on soil type and test condition

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The current practice for evaluating feasibility and choosing the operational parameters of the DC technique at a site depends mainly on field trials, past experience at similar sites, and empirical equations based on reported records Rational analytical methods are needed to improve the state of practice

This dissertation presents an analytical simulation model for the densification process of saturated sand deposits without wick drains, and silty deposits supplemented with wick drains during DC Pore pressure generated during DC processes is simulated based on an energy based liquefaction model The densification during dissipation is modeled using consolidation theory

Based on the model effects of silt content, hydraulic conductivity, initial soil density and techniques’ operational parameters such as energy per impact, number of impacts per location, impact grid pattern, impact grid spacing, wick drains spacing, and

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time cycle between impacts on the densification of soils improved by DC have been studied The model performance has also been verified through documented case histories and found to compare reasonably well A rational design procedure has been developed for liquefaction mitigation of loose sand and non-plastic silty soils The design model has been used to determine the densification achievable using DC in silty deposits supplemented with wick drains A design procedure and design examples are presented

The computational methodology presented herein is a powerful tool for design analyses of DC taking into account the site conditions for different deposits and operational parameters The model is expected to advance the use of DC in sands and silty soils, and reduce the reliance on expensive field trials as a design tool

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CHAPTER I

INTRODUCTION

Liquefaction of loose saturated granular soils represents a continuing threat to the performance of buildings, highways, bridges, lifelines and other facilities and often causes major economic loss, loss of life and injury in almost every earthquake (Table 1-1) The first widespread observations of damage attributed to liquefaction were made in the 1964 Niigata, Japan, and 1964 Alaska earthquakes The high incidence of

liquefaction during earthquakes, together with its potential for damage, has made the phenomenon a prime subject of concern in earthquake engineering Fig 1-1 shows major examples of the severe damage resulted from liquefaction In Niigata 1946, apartment buildings suffered bearing capacity failures and simply supported spans bridge collapsed due to lateral spreading In Alaska 1946, liquefaction of sands and silts caused many destructive landslides and embankments failures In Loma Prieta earthquake 1989 and Kobe 1995, liquefaction caused major damage to waterfront facilities, structures, and buried pipelines where loose saturated, sandy soils were susceptible to liquefaction Numerous sand boils that were observed provided indisputable evidence of the

occurrence of liquefaction

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Table 1-1 Recent major ground liquefaction (modified from Japanese Geotechnical Society,

1998)

Nihonkai-chubu 1983 7.7

Flat ground and foot of sand dune slope were

liquefied

Loose sandy soils in the marine district, San

Francisco, was liquefied

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