electro-osmotic grouting technique for liquefaction-mitigation of low permeability silty soils

Experiments were conducted to prove the feasibility of electro-osmotic injection under 1- D and 3-D conditions, to quantify the increase of liquefaction resistance in silty soils due to

ELECTRO-OSMOTIC GROUTING TECHNIQUE

FOR LIQUEFACTION-MITIGATION OF LOW

PERMEABILITY SILTY SOILS

by

WEIWEI JIA

September 2006

A dissertation submitted to the Faculty of the Graduate School of

the State University of New York at Buffalo

in partial fulfillment of the requirements for the degree of

Doctor of Philosophy

Department of Civil, Structural and Environmental Engineering

UMI Number: 3226603

3226603 2006

UMI Microform Copyright

All rights reserved This microform edition is protected against unauthorized copying under Title 17, United States Code.

ProQuest Information and Learning Company

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by ProQuest Information and Learning Company

ABSTRACT

Electro-osmotic grouting is a new foundation improvement technique proposed to treat low permeability, liquefiable silty soils underneath existing structures for the purpose of liquefaction-mitigation This technique uses a d.c current to introduce water soluble grout materials and reactants into the silty soils Setting time of injected grouts can be controlled by adjusting the concentration and sequence of introduction of various components

Both experimental and numerical studies were performed in this research Experiments were conducted to prove the feasibility of electro-osmotic injection under 1-

D and 3-D conditions, to quantify the increase of liquefaction resistance in silty soils due

to electro-osmotic grouting, and to design grout mixes feasible for electro-osmotic grouting Numerical analyses were performed to simulate grout flows under a 3-D condition, to determine the rate and extent of grout penetration, and to estimate power consumption in electro-osmotic grouting

Study shows that electro-osmotic grouting is a promising technique Colloidal silica and sodium silicate grouts can be injected into low permeability sility soils at the

rate of about cm/s per v/cm, and liquefaction resistance of the silty soils increased signicantly after injection

5

10−

Thesis Advisor: Professor Sabanayagam Thevanayagam

ACKNOWLEDGEMENTS

I wish to express my deepest appreciation to my academic advisor – Dr Sabanayagam Thevanayagam, for his invaluable guidance, suggestions, as well as support and continuous encouragement, without which this work would not be possible Conducting this research work under his guidance was a rewarding experience I believe I will always benefit from it in my future work and study

My sincerely appreciation also goes to Professor Shahid Ahmad and Professor Amjad Aref for their encouragement and support throughout the study

I would like to say thanks to graduate students T Shenthan and T Kanagalingam, who helped a lot in carrying out cyclic and monotonic triaxial tests, and provided valuable suggestions and recommendations in the completion of the dissertation Shenthan also reviewed the whole dissertation and provided valuable comments

My deepest gratitude also goes to my parents and my aunt, for their assistance and encouragement for the successful completion of this study

Funding for this research work is provided by MCEER Hospital Project The financial support is greatly appreciated

Finally, I dedicate this work to my wife, Huifen Zhu

2.2 Current Soil Improvement Techniques For Liquefaction Remediation 15

2.3.2.1.2 Chemical Grouting and Chemical Grouts 24

2.3.2.5 Case Histories of Liquefaction-mitigation with

2.4.1.4 Electro-Migration 34

2.4.3.1 Electro-Kinetic Remediation of Fine-Grained

2.4.3.4 Stabilization of Excavations or Fine-Grained Soils 40

2.4.3.5 Dewater and Consolidation of Fine Grained

3.3.5 Species Conduction Under One- Dimensional Coupled Field 50

3.5.1 Change of Soil Properties During Electro-Osmotic Injection 56

3.5.2 Factors Affecting Power Consumption in Electro-Osmotic Grouting 57

3.6.1 Vertical Layout and its Application – Single-Borehole Layout 59

3.6.2 Vertical Layout and its Application – Multiple-Borehole Layout 60

V 1-D FEASIBILITY STUDY ON ELECTRO-OSMOTIC INJECTION 79

VI UNDRAINED BEHAVIOR AND LIQUEFACTION

6.6.2.2 Results 115 6.7 Application of Lab Test Result in Practical Design 116

6.7.2 Proposed Relationship for (N1)60CSversus E L - Ungrouted Soils 117 6.7.3 Proposed Relationship for (N1)60CS versus E L - Grouted Soils 121 6.7.4 Practical Application of Correlation Chart 124

7.3 Guidelines for Simulation of Electro-osmotic Grouting 139

7.4.2 The Electric Field and Electro-osmotic Flow Field 142

7.5.1 Theoretical Analysis On Unit Power Consumption 145

8.4.1 Numerical Model of the Electro-Osmotic and Electric

8.4.3 Numerical Solution to The Hydraulic Flow Problem 161

8.4.4 Analysis 161

IX FEASIBILITY STUDY OF FIELD APPLICATION OF

9.2.2 Rationale for Selection of Electro-Osmotic Grouting for

9.6 Estimate Of Grouting Duration And Grout Penetration 184

APPENDIX A TEST SUMMARY OF THE 1-D ELECTRO-

APPENDIX B: TEST SUMMARY OF THE STUDY ON

UNDRAINED BEHAVIOR AND LIQUEFACTION

APPENDIX C: TEST SUMMARY OF THE 3-D ELECTRO-

LIST OF TABLES Table 1.1 Conventional Liquefaction-mitigation Techniques 2

Table 2.1 Cost Estimates for Current Grouting Techniques 21

Table 2.2 Limits of Penetration of Cement into Granular Soils 29

Table 2.3 Relationships Between the Viscosities of 29

Table 3.2 Advantages and Disadvantages of Proposed Strategies 61

Table 4.5 Specifications of Nyacol® 215 Colloidal Silica 70

Table 4.6 Specifications of LUDOX SM-30 Colloidal Silica 70

Table 4.9 Gel Test on Colloidal Silica – LUDOX SM-30 76

Table 6.1 The Size, Electric Gradients, and Durations of Injection

Table 6.2 Undrained Cyclic Triaxial Tests on N® Sodium Silicate

Table 6.3 Test Parameters for Undrained Cyclic Triaxial Tests on

N® Sodium Silicate Treated Specimens 107 Table 6.4 Undrained Compression Triaxial Tests On N® Sodium

Table 6.5 Test Parameters for Undrained Compression Triaxial

Tests on N® Sodium Silicate Treated Specimens 109 Table 6.6 Undrained Cyclic Triaxial Tests on LUDOX SM-30 Colloidal Silica

Table 6.7 Test Parameters for Undrained Cyclic Triaxial Tests on

LUDOX SM-30 Colloidal Silica Treated Specimens 112 Table 6.8 Undrained Compression Triaxial Tests on LUDOX SM-30

Table 6.9 Test Parameters for Undrained Compression Triaxial

Tests on LUDOX SM-30 Colloidal Silica Treated Specimen 114

Table 9.2 Soil Factor of Safety against Liquefaction and

Required (N1)60CS for Liquefaction-mitigation Purpose 169

LIST OF FIGURES

Figure 2.1 Tilted buildings - Niigata Earthquake, Japan, 1964 8

Figure 2.2 Tilted Buildings - Kocaeli, Turkey, Earthquake of

Figure 2.3 Sheffield Dam Suffered a Flow Failure Triggered by the

Figure 2.4 Tension Cracks on the Banks of the Motagua River

Figure 2.5 Sand Boils in Loma Prieta Earthquake, USA, 1989 11 Figure 2.6 Schematic Diagram of a Lateral Spread (Youd 1992) 12 Figure 2.7 Diagram of a Flow Failure Caused by Liquefaction

and Loss of Strength of Soils Lying on a Steep Slope 13 Figure 2.8 Diagram of Structure Tilted Due to Loss of

Figure 2.9 Diagram of Horizontal Ground Oscillation Caused by

Liquefaction in the Cross-Hatched Zone Decoupling the

Figure 2.10 Applicable Grain Size Ranges for Liquefable Soil

Figure 2.13 Two-Shot and One-Shot Methods of Chemical Grouting 28

Figure 2.15 Schematic Diagram of Electro-Kinetic Remediation 38 Figure 2.16 Schematic Diagram of Flow Barrier for Chemical

Figure 3.1 Schematic Diagram of Electro-Osmotic Injection 43

Figure 3.2 Electro-Kinetics under Electro-Osmotic Injection 51

Figure3.3 Transport of Silicate in Electro-Osmotic Injection 54

Figure 4.2 Typical Progress of Gelation of the Colloidal Silica

Figure5.3 1-D Electro-Osmotic Injection Feasibility Test

Figure 5.4 1-D Electro-Osmotic Injection Feasibility Test on

Figure 5.5 1-D Electro-Osmotic Injection Feasibility Test on AV-100 92

Figure 6.1 Gradation of #55 Sand, #90 Silt, and the Soil Mix 96

Figure 6.3 Schematic diagram of Electro-Osmotic Cell (a) 98

Figure 6.4 Schematic Diagram of the Experimental Setup

Figure 6.8 Undrained Cyclic Test Result (CSR = 0.2, σv0’ =100 kPa.) 108 Figure 6.9 Undrained Triaxial Compression Strength of

Figure 6.10 Undrained Cyclic Test Result (CSR = 0.2, σv0’ =100 kPa.) 113 Figure 6.11 Undrained Triaxial Compression Strength

of Colloidal Silica Treated Specimens 115 Figure 6.12 Relationship Between Relative Density and (N1)60

Figure 6.13 Relationship Between D r and E L for Clean Sand 118 Figure 6.14 Relationship Between (N1)60 and E L for Clean Sand 118 Figure 6.15 Assumed Relationship Between Relative Density and

60

1)

(N For Silty Sand With Fines Content Lower Than FC th 120

Figure 6.17 Relationship Between (N1)60CS and E L 121 Figure 6.18 E L versus e Relationship for Silty Soils 122 Figure 6.19 Relationships Between (N1)60 and E Lfor

Figure 6.20 (N1)60CS Values for Pre- and Post-Grouted Soil 124

Figure 7.1 Field Application Strategy 1- Vertical Grouting 128

Figure 7.3 Example Configuration of Electro-osmotic Grouting 140 Figure 7.4 Hydraulic Model for Simulation of Electric Field in Figure 7.3 140 Figure 7.5 Numerical Simulation of an Electro-Osmotic Injection Problem 141

Figure 7.8 Unit power consumption versus Soil Electric Conductivity 148 Figure 7.9 Unit power consumption versus Soil Electro-Osmotic Permeability 149 Figure 7.10 Unit power consumption versus Soil Porosity 149

Figure 7.12 Unit Cost versus Soil Electric Conductivity 150 Figure 7.13 Unit Cost versus Soil Electro-Osmotic Permeability 151

Figure 8.3 Schematic Diagram of the Experimental Setup of

Figure 8.4 Current versus Time – Bench Scale Test 156 Figure 8.5 Cumulative Grout Flow versus Time – Bench Scale Test 157 Figure 8.6 Unit Power Consumption versus Time – Bench Scale Test 157 Figure 8.7 Cumulative Grout Flow versus Time - Control Test 157

Figure 8.11 Test and Theoretical Results of the Bench Scale Test 163 Figure 8.12 Grout Flow Lines and Penetration at 1 Day 163

Figure 9.1 Plan and Elev of a Hospital Office Building 167 Figure 9.2 (N1)60CS of Sandy Silt – Pre-treatment Value and

Figure 9.4 (N1)60CS of Sandy Silt – Pre-treatment Value, Post-Treatment

Value, and Value Required for Liquefaction-mitigation 172

NOTATIONS

e

i = Electrical potential gradient

c = Concentration of species

CSR = Cyclic stress ratio

D = Dielectric constant of the fluid

D = Diffusion coefficient of species in free solution at infinite dilution

i = Electrical potential gradient

i = Electrical potential gradient

I = Electrical current

i

J = The mass flux of the ith chemical species in soil pore fluid

k, k h = Soil hydraulic permeability

e

k = Soil electro-osmotic permeability

p = Mean effective confining pressure

R = Universal gas constant

SPT = Standard penetration test

or implementing liquefaction remediation measures to minimize the risk There are many existing structures built on soils of high liquefaction and deformation potential For critical structures built on liquefiable soils, such as hospitals and lifelines, the only option available is to improve the soil to mitigate its liquefaction potential, and the demand for such improvements is very urgent, since it is necessary that these critical buildings function well during earthquakes The reason is apparent: hospitals are necessary to take care the injured people during earthquakes, and water supply systems are necessary for domestic use and to put out fires caused by the earthquake, etc

Traditional foundation improvement methods are usually not feasible for treating soil underneath existing structures due to poor site accessibility and the undesirable level

of noise and vibration caused by the working machine to occupants and equipment inside the structures (Table 1.1) (Thevanayagam et al 2002)

Among current ground improvement techniques for liquefaction remediation, permeation grouting may be the most effective one when accessibility to the soil is highly limited, such as soils under existing structures Permeation grouting may also be the only

option available when less complicated densification methods are not applicable due to the objectionable level of noise and vibration these methods may produce But when silt content of soil is higher than 10 to 15%, even permeation grouting is ineffective The low permeability of silty soils makes it impractical, if not impossible, to effectively inject the grouts by permeation New technology needs to be developed to treat the liquefiable low permeability silty soils underneath existing structures

Table 1.1 Conventional Liquefaction-mitigation Techniques

(From Thevanayagam et al 2002)

Densification/

Drainage/

Reinforcement

Permeation Grouting Yes (Fines

Solidification

Electro- Osmotic Grouting

(This study)

* = feasible with supplementary wick drains; ** = uncertain

To meet such a demand, a new permeation grouting technique based on osmotic injection of binding agents and additives into silty soils is presented in this dissertation

electro-When a d.c (direct current) voltage is applied across a saturated soil, the following phenomena occur (Mitchell 1993): (i) pore fluid flows from anode to cathode

(called electro-osmosis), (ii) positively charged dissolved ions flow from anode to cathode, and negatively charged dissolved ions flow from cathode to anode (called electro-migration) Electrolysis Reactions at the electrodes may also induce changes in the pH and ion concentrations, and hence affect the soil properties and flow of ions and pore fluid Past experience with clayey soils indicate that the electro-osmotic fluid flow

velocity is in the order of cm/s/V/cm or larger (Mitchell 1993) Experience in electro-kinetic treatment of contaminated soils (Acar et al 1992, Acar et al 1994, Acar et

al 1996, Chen et al 1999) indicates that pore fluid and electrode chemistry significantly affect the pore fluid chemistry and flow behavior With due consideration of these factors, it may be possible to use d.c current to introduce water-soluble grouts and hardening agents into low permeable silty soils by judiciously introducing various grout components near the electrodes By controlling the concentrations and sequence of introduction of various components, and by careful selection of grouting material and reactants, the hardening time of the introduced grout mix can be controlled

liquefaction resistance in silty soils due to electric-osmotic grouting Laboratory study also involved selection of grout materials and reactants, and design of the appropriate grout mix feasible for electro-osmotic injection Numerical analyses were performed to simulate grout flows under a 3-D condition, to determine the rate and extent of grout penetration, and to estimate power consumption in electro-osmotic grouting

The results indicated that selected grouts can be injected into low permeability sility soils at a reasonable rate, and liquefaction resistance of the silty soils increased signicantly after injection

1.3 ORGANIZATION

Chapter 2 of this dissertation presents a brief historical review of liquefaction phenomena and traditional ground improvement techniques for liquefaction-mitigation A brief introduction of electro-kinetic phenomena is also included in this chapter Chapter 3 focuses on the new electro-osmotic grouting technique Electrolysis reactions and species conduction during electro-kinetic processing of soils, species conduction during electro-osmotic injection, and factors affecting the implementation of the electro-osmotic injection are discussed in this chapter Proposed strategies for field implementation of the technique are also provided in this chapter Chapter 4 introduces the grout materials and reactants investigated in the study Grout mix specifically designed for electro-osmotic grouting is also discussed in this chapter Chapter 5 describes the experimental program

to study the feasibility of 1-D electro-osmotic injection, including the electro-osmotic injection device, test procedure, and measurements and observations performed in the study A group of 1-D electro-osmotic injection tests were conducted and presented in

this chapter A total of three types of grout materials were investigated Chapter 6 presents the results of undrained triaxial tests on pre- and post-electro-osmotic treated specimens Both monotonic tests and cyclic tests were conducted to evaluate the increase

in soil resistance to flow liquefaction and cyclic mobility due to electro-osmotic grouting Chapter 7 presents the theoretical study of grout movement under a 3-D electric field Numerical methods were proposed to simulate grout movement in electro-osmotic grouting Factors affecting the implementation electro-osmotic injection and construction cost are further discussed in this chapter Chapter 8 presents the results of a 3-D bench scale electro-osmotic injection test, which was used to evaluate the feasibility of implementation of the new technique in the field Numerical analysis is conducted to simulate the bench scale test and to analyze the test results To demonstrate the applicaton of this new technique, a sample design of electro-osmotic grouting for liquefaction-mitigation of silty soils underneath a hypothetical two-story hospital building is presented in Chapter 9 Conclusions based on the current study and recommendations for future study are presented in Chapters 10 and 11, respectively

Chapter 2

LITERATURE REVIEW

2.1 LIQUEFACTION RELATED PHENOMENA

2.1.1 Introduction

Since the Good Friday earthquake in Alaska and the Niigata earthquake in Japan

in 1964 (Eckel 1970, Bartlett et al 1992, Harmada et al 1992, National Research Council 1968), liquefaction has attracted the attention of researchers and engineers all over the world Spectacular examples of liquefaction damage, including slope failures, bridge and building foundation failures, and flotation of buried structures were observed in both earthquakes (Eckel 1970, Bartlett et al 1992, Harmada et al 1992, National Research Council 1968) Thereafter, liquefaction phenomena have been studied extensively by many researchers and engineers (Finn et al 1995) In the same time, ground improvement techniques have been developed for liquefaction-mitigation and many of these techniques have been applied successfully (Welsh 1987, Kramer et al 1991, Port and Harbor Research Institute 1997, Cooke et al 1999)

2.1.2 Liquefaction

Liquefaction is a phenomenon wherein shear resistance of sediments below the water table decreases and the sediments behave as a viscous liquid rather than a solid when subjected to monotonic, cyclic, or dynamic loading at constant volume (Eckel

1970, Bartlett et al 1992, Harmada et al 1992, National Research Council 1968) The

types of sediments most susceptible are clay-free deposits of sand and silts; occasionally, gravel liquefies Liquefaction phenomena that result from this process can be divided into two main groups: flow liquefaction and cyclic mobility

Flow liquefaction can occur when the shear stress required for static equilibrium

of a soil mass (the static shear stress) is greater than the shear strength of the soil in its liquefied state The static or dynamic loads may simply bring the soil to a state at which its strength drops sufficiently to allow the static stress to produce the flow failure Once triggered, the strength of the soil is no longer sufficient to withstand the static stresses The large deformations produced by flow liquefaction are actually driven by static shear stresses Flow liquefaction is often characterized by large and rapid movements, which can produce disastrous effects The bearing capacity failures of Kawagishi-cho apartment buildings during the Niigata Earthquake 1964 in Japan (Figure 2.1), the bearing capacity failure of buildings in Kocaeli earthquake 1999 in Turkey (Figure 2.2), and the flow slides failures of Sheffield Dam (Figure 2.3), are examples of flow liquefaction

As these case histories illustrate, flow failures can involve the flow of considerable volumes of material which undergoes very large movements that are actually driven by static stresses The disturbance needed to trigger flow liquefaction can

be very small in some instances

Cyclic mobility is another liquefaction phenomena, which occurs when the static

shear stress is less than the shear strength of the liquefied soil Deformations due to cyclic mobility develop incrementally because of the static and dynamic stresses that exist

during an earthquake Lateral spreading, a common result of cyclic mobility, can occur

on gently sloping and on virtually flat ground close to rivers and lakes The 1976 Guatemala earthquake caused lateral spreading along the Motagua River (Figure 2.4) It can be observed that the cracks parallel to the river in the picture to the right

On level ground, because static horizontal shear stress that could drive lateral deformation do not exist, level-ground liquefaction can produce large, chaotic movement known as ground oscillation during earthquake shaking But it produces little permanent lateral soil movement The high pore water pressure induced by liquefaction can cause pore water to flow rapidly to the ground surface This flow can occur both during and after an earthquake If the flowing pore water rises quickly enough, it can carry sand particles through cracks up to the surface, where they are deposited in the form of sand volcanoes or sand boils (Figure 2.5, Loma Prieta, USA, 1989)

Figure 2.1 Tilted buildings - Niigata Earthquake, Japan, 1964

(http://www.ce.washington.edu/~liquefaction/html/what/what2.html) M=7.5, 310 of the 1500 reinforced concrete buildings in Niigata City were damaged; 200

buildings on shallow Foundations or Friction Piles in loose sand/silty sand settled without

significant structural damage due to liquefaction Same type of buildings built on firm

strata at 20 m deep did not suffer damage

(a) Adapazari Area

(b) Liquefied soils Figure 2.2 Tilted Buildings - Kocaeli, Turkey, Earthquake of August 17, 1999

Figure 2.3 Sheffield Dam Suffered a Flow Failure Triggered by

the Santa Barbara Earthquake in 1925 (EERC)

Figure 2.4 Tension Cracks on the Banks of the Motagua River Following the 1976 Guatemala Earthquake (USGS)

Figure 2.5 Sand Boils in Loma Prieta Earthquake,

USA, 1989 (USGS)

2.1.3 Ground Failure Associated with Liquefaction

Ground failure associated with liquefaction can be manifested in several forms These include sand boils, lateral spreads, flow failures, ground oscillation, bearing capacity failures, and post-liquefaction settlement

Sand boils: Although not strictly a form of ground failure because alone they do

not cause ground deformation, sand boils are diagnostic evidence of elevated pore water pressure at depth and an indication that liquefaction has occurred (NRC 1985) On level ground, high pore water pressure caused by liquefaction may cause water venting to the ground surface If the flowing pore water rises quickly enough, it can carry sand particles through cracks up to the ground surface, where they will settle and form conically shaped sand deposit

Lateral spreads involve lateral displacement of large superficial blocks of soil

driven by gravitational and inertial force as a result of liquefaction in subsurface layers (NRC 1985) (Figure 2.6) Movement occurs in response to the combined gravitational and inertial forces generated by earthquakes Lateral spreads develop normally on very gentle slopes (between 0.3 and 3 degrees) (Youd et al 1978) Youd (1978) has reported displacements associated with lateral spreads ranging from one meter to tens of meters Such lateral displacement can pull buildings apart and destroy buried pipelines During many earthquakes, lateral spreads may produce more damage than any other form of liquefaction (NRC 1985)

Figure 2.6 Schematic Diagram of a Lateral Spread (Youd 1992)

Flow failures are perhaps the most catastrophic ground failures caused by

liquefaction (NRC 1985) (Figure 2.7) They generally occur in saturated loose sands with slopes ranging between 10 and 20 degrees (Youd et al 1978) If flow failure happens, large amounts of material may flow many tens of meters at relatively high speeds of tens

of km/h The movement will not stop until the driving forces are reduced to values less than the viscous shear resistance of the flowing material The moving soil may be composed of completed liquefied mass, or of intact material block floating in liquefied material

Figure 2.7 Diagram of a Flow Failure Caused by Liquefaction and

Loss of Strength of Soils Lying on a Steep Slope (Youd 1992)

Bearing capacity failures: When the soil supporting a building or other

structures liquefies and loses its strength, the ability of soil to support foundations is reduced Buildings will tilt and settle down (Figure 2.8) During 1964 Niigate earthquake

in Japan (Figure 2.1) and 1999 Kocaeli earthquake in Turkey (Figure 2.2), there were buildings suffered bearing capacity failures and tilted severely This kind of failures generally occurs in deposits of saturated cohesionless soil that extend from near the ground surface to a depth of at least half of the building width If the deposit where liquefies is shallower, then differential settlement, but not overturning of the structure, can be resulted (Youd et al 1978)

Ground Oscillation: When the ground is flat or the slope is too gentle to allow

lateral displacement, liquefaction at depth may decouple overlying soil layers from the underlying ground, allowing the upper soil to oscillate back and forth and up and down in the form of ground waves (NCR 1985) These oscillations are usually accompanied by opening and closing of fissures and fracture of rigid structures such as pavements and pipelines (Figure 2.9)

Figure 2.8 Diagram of Structure Tilted Due to Loss of Bearing Strength (Youd 1992)

Figure 2.9 Diagram of Horizontal Ground Oscillation Caused

by Liquefaction in the Cross-Hatched Zone Decoupling the Surface Layers From the Underlying Ground (Youd 1992)

Settlement: In many cases, the weight of a structure will not be great enough to

cause the large settlements associated with soil bearing capacity failures described above However, smaller settlements may occur as soil pore-water pressure dissipate and the soil consolidates after the earthquake (EERI 1994) These settlements are ordinarily small, but they also may cause considerable damage Densification and ground settlement is commonly associated with and enhanced by liquefaction

The ground failures associated with liquefaction can cause great damage to structures sitting on it Building foundation can slide or unevenly settle, cause the tilt and damage of building, or collapse of bridges; the buried pipes would rupture; buried structures with a bulk unit weight lower than that of liquefied soil would be lifted up Liquefied soil also exerts much higher pressure on retaining walls, which can make them

to tilt and slide The movement of retaining wall can cause settlement of retained soils and collapse of structures on the ground surface Increased water pressure can also trigger landslide and cause damage to dam or road

2.2 CURRENT SOIL IMPROVEMENT TECHNIQUES FOR LIQUEFACTION REMEDIATION

In general, current techniques for liquefaction remediation can be classified into two categories: 1) Improve the soil so that liquefaction will not occur; 2) Reinforce the structure to minimize damage when liquefaction occurs Discussions in this chapter will focus on the first category

Soil liquefaction potential can be reduced by the following types of ground improvement: cementation and solidification, densification, drainage, dewatering, and inclusion/reinforcing, or a combination of these methods

Cementation and solidification methods are also called physical and chemical

methods These methods alter the engineering characteristics of the soil and thereby make

it inherently more stable It is considered a highly reliable remedial measure against liquefaction Cementation and solidification involves injecting another material into soil,

or mixing them in place The injected material may take the soil’s pore volume and decrease the potential for densification; or it can increase shear strength and bearing capacity of soil by hardening and bonding the soil particles together Commonly used cementation and solidification methods can be divided into grouting and soil mixing Grouting in general can involve densification Compaction grouting involves densification and it was classified as a densification method Permeation (chemical) grouting and jet grouting are examples of grouting methods that do not involve densification Soil mixing is a technique whereby soil is physically mixed with cementitious materials using a hollow stem auger and paddle arrangement Soil mixing produces an improved volume of soil that is very well defined

Densification: Studies have shown that dense saturated soil has much more

liquefaction resistance than loose soil Soil densification can reduce the void ratio, increase the relative density, thus decreasing the potential for volume change that would lead to liquefaction Densification is generally considered highly reliable, and it has been

the most popular method of reducing earthquake related liquefaction potential Vibro densification, dynamic compaction, compaction grouting, compaction piles are all examples of densification

Drainage methods consisting of installing vertical columns of “free draining”

gravel, coarse sand, or prefabricated wicks in the ground The drains are used to limit the development of excess pore pressure during earthquakes and thus prevent liquefaction Drainage techniques that may be appropriate and practical for the mitigation of liquefaction hazards include: gravel drains, sand drains, and prefabricated drains Gravel drain method can also be considered as densification method as the main function of it is

to densify the surrounding soil rather than providing drainages

Dewatering: Lowering the ground water level by dewatering reduces the degree

of saturation, thereby preventing the development of excess pore pressure during earthquakes Dewatering is a difficult and very expensive task, since both upstream and downstream seepage cutoffs are usually required, and pumps must be maintained constantly

Inclusion/Reinforcing techniques increase the strength and stiffness of

foundation soils by inclusion of some other material with a much higher tensile strength These methods include: soil nailing, metal and geosyntehtic reinforcement, concrete and steel piles, stone columns, and sheet piles Inclusions can introduce a stiff element, or creates a stiff composite soil The reinforced part will take large portion of the applied

load, thus increase liquefaction resistance of the whole soil body The inclusion also can control deforming of liquefiable soil, increase the shear resistance of soil Depending on the installation method, it also may densify the surrounding soil and thusreduce the liquefaction potential

Selection of the most appropriate method for a particular purpose will depend on many factors, including the type of soil to be improved, the level of improvement needed, the magnitude of improvement attainable by a method, and the required depth and areal extent of treatment The applicable grain size ranges for various liquefable soil improvement methods are shown in Figure 2.10

2.3 TRADITIONAL GROUTING TECHNIQUES

2.3.1 Grouting

Grouting is a procedure by means of which grout is injected into voids, fissures, crevices or cavities in soil or rock formation in order to improve their properties, specifically to reduce permeability, to increase strength or to lessen the deformability of the formations (Nonveiller 1989) To achieve this purpose, boreholes need to be drilled into the formation, and then the grout is supplied into the borehole and injected into the voids around the boreholes, usually under pressure Compaction grouting is a recent development relying not on infilling, but on densification of suitable soils by displacement (Figure 2.11)

Grouting has a wide application in civil engineering, this includes: to reduce permeability of soil mass to control seepage and loss of water (Persoff et al 1999,

Figure 2.10 Applicable Grain Size Ranges for Liquefable Soil Improvement Method (Green 2001)

Polivka et al 1957); to increase the strength of material below the foundation of heavy structures, or to reduce the deformability of the material in the foundation (Graf et al

1979, Andrus et al 1995, Gallavresi et al 1992, Graf 1992); to stabilize the foundation soil to aid the construction (Gallavresi et al 1992, Polivka et al 1957); to connect distinct structural elements into a homogeneous structure by injecting the seams between them with grout compounds; and to improve cohesionless soils to decrease their liquefaction potentials (Gambin 1991, Graf 1992, Graf et al 1979)

replacing pore water with grout to limit excess pore water pressure during earthquake, and/or by binding the soil particles together with chemicals to increase the soil strength

In jet grouting, the soil is mixed with grout by cutting and fracturing the soil with pressure water or air jets The mixed soil is of high strength and soil columns formed by the improved soil can also act as reinforcing elements in the soil mass

high-Cost for grouting techniques (Andrus et al 1995) includes cost to mobilize and demobilize the equipment; cost to install grout-pipe, start at about $50 per meter of pipe, and double for low headroom (no pipe installment is need in jet grouting, but a hole of 90~150mm in diameter need to be drilled); and the cost of injection labor and grout materials A summary of the cost for current grouting techniques is shown in Table2.1

Table 2.1 Cost Estimates for Current Grouting Techniques

(From Andrus et al 1995)

The cost will double for low headroom work

$20 per m 3 of improved soil

Cost of labor and materials is based

on assumption that volume of grout injected is 10% of total volume of treated soil

Permeation

grouting $15,000~

$25,000

Over $50 per meter

of pipe The cost will double for low headroom work

Start at $130 per m 3 of improved soil for micro- fine cement grout, and about $200 per m 3 for sodium silicate grout

Cost of labor and materials is based

on a 20% grout take, and a total grout volume greater than 200 m 3

Jet grouting Over $35,000 - Start at $320 per m 3 of

improved soil

The cost does not include handling, removal, and disposal of the large quantities of waste slurry produced

2.3.2 Permeation Grouting

Permeation grouting is the injection of low viscosity particulate or chemical fluids into soil pore space without any essential change to the original soil volume and

structure As indicated before, permeation grouting reduce soil liquefaction potential by the next two ways: 1) replacing the water in soil voids with grout, decrease the possibility

of soil compression during earthquakes; 2) binding the soil particles together with chemicals thus increase the soil strength History of permeation grouting can be traced back to the late 1800s (Bowen 1975) This technique has been successfully used to control groundwater flow, stabilize excavation in soft ground, underpin existing foundations, and prevent seismically induced settlement and liquefaction A conceptual diagram of permeation grouting is shown in Figure 2.12

2.3.2.1 Materials for Permeation Grouting

Permeation grouting is feasible for a wide variety of mixtures, which can be classified into two categories: suspensions, and chemical grouts The ingredients for the preparation of grouting suspensions are Cement, Clay, sand, additives for stability, and water The most widely used chemical grouts are aqueous solutions, which can be divided into several chemical families include: sodium silicate formulations, acrylamides, lignosufites, phenoplasts, and aminoplasts

2.3.2.1.1 Materials for Suspensions

The main ingredient for the preparation of grout suspensions is Portland cement, generally available on the market in various types The chemical composition must comply with a standardized range of contents of , MgO, 3 , of added

inters, fly ash and pozzolanic material The most important property for the selection of cement for grouting is its fineness, which should be as high as possible when granular soil with narrow fissures is to be grouted Clay is added as a fine grain filler to reduce the cement consumption, and it also improves the stability and the viscosity of the suspension Mainly used clays for grouting include kaolinite and montmorillonite clays Sand is added to stable grout suspensions when a system of large fissures has to be injected The grain size distribution and the maximum grain size should match the fissure size and suit the available grouting pumps Additives are added to maintain a stable suspension

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