Constitutive behaviour of cement treated marine clay

... properties of cementtreated clay at 7-day post-treatment (% error) 42 Table 4.1 Effect of cement treatment on basic properties of cement- clay mixtures 43 Table 4.2 Percentage of changes of void... microstructure of the cement treated clay is often significantly different from that of the untreated clay Kezdi (1979) suggested that a soil -cement skeleton matrix may be formed due to the inclusion of cement. .. complete framework of behaviour for cement treated clay The second part of this study is focused on the microstructural changes as well as constitutive behaviour of cement- treated soil specimens

CONSTITUTIVE BEHAVIOUR OF CEMENT TREATED MARINE CLAY CHIN KHENG GHEE NATIONAL UNIVERSITY OF SINGAPORE 2006 CONSTITUTIVE BEHAVIOUR OF CEMENT TREATED MARINE CLAY CHIN KHENG GHEE (B.Eng. (Hons.), UTM) A THESIS SUBMITTED FOR THE DEGREE OF DOCTOR OF PHILOSOPHY DEPARTMENT OF CIVIL ENGINEERING NATIONAL UNIVERSITY OF SINGAPORE 2006 Dedicated to my family members for their support and understanding… ACKNOWLEDGEMENTS The author would like to express his profound gratitude and sincere appreciation to his supervisor, Associate Professor Lee Fook Hou for the valued advice, constructive criticisms and endless guidance throughout the research study. Much of the idea in the thesis was imparted during the discussions. Without his help, this research work may not have been materialized. Special thanks also directed to Dr. Ganeswara Rao Dasari, who also guided the author before he left NUS. Grateful acknowledgement is expressed to the technical staff who assisted the author in the experimental soil testing. They are Mr. John Choy Moon Nien, Mdm. Jamilah Bte Mohd and Mr. Foo Hee Ann. Special thanks also to Mr. Ang Beng Oon and Mdm. Ho Chiow Mooi for providing necessary facilities and help during the time when author conducted some of the experimental works in their laboratories. The author also deeply appreciates the financial assistance in the form of research scholarship as well as facilities provided by the National University of Singapore to perform his research study. Acknowledgements are also due to: (a) Dr. Kamruzzaman who guided and assisted the author at the beginning of laboratory soil testing. (b) Assoc. Prof. Tam Chat Tim who provided information and advice on the properties of cement paste. (c) Fellow colleagues of NUS geotechnical division, in particular Pang, Kar Lu, Elly, Dominic, Yen, Ma Rui, Xi Ying, Han Eng, Poh Hai, Hui Kiat, Chen Hui, Heng Thong, Phoon, William, Jonathan, Cheng Yih and others. (d) Fellow housemates: Johnny, Chin Leng, Hock Siang, Ching Beng and Jamie. (e) Author’s girl friend. i CONTENTS ACKNOWLEDGEMENTS i TABLE OF CONTENTS ii SUMMARY vi LIST OF TABLES viii LIST OF FIGURES ix LIST OF SYMBOLS xvi LIST OF DEFINITIONS xxii Chapter 1 1 INTRODUCTION 1.1 Cement-Soil Stabilisation 1 1.2 Some Issues in Cement-Soil Stabilisation 2 1.3 Objectives of Current Research 3 Chapter 2 5 LITERATURE REVIEW 2.1 2.2 2.3 Mechanisms of Cement-Soil Stabilization 5 2.1.1 Properties of Cement 5 2.1.2 Cement-Soil Reactions 5 2.1.3 Structure and Microstructure of Treated Clay 7 Influence of Various Factors on the Strength Index 8 2.2.1 Characteristics of Stabilizing Agents 10 2.2.2 Characteristics and Conditions of Soil 11 2.2.3 Mixing Conditions 13 2.2.4 Curing Conditions 14 Geomaterial Design of Improved Ground by Deep Mixing Method 15 (DMM) 2.4 Behaviour of Cement Treated Soil 18 ii 2.5 Outstanding Issues 20 2.5.1 Ambient Effective Confining Pressure 21 2.5.2 Triaxial Behavioural Framework 24 Chapter 3 27 EXPERIMENTAL METHODOLOGY AND SETUP 3.1 Properties of Base Materials 27 3.1.1 Untreated Marine Clay 27 3.1.2 Ordinary Portland Cement 27 3.2 Variables Investigated 28 3.3 Sampling Procedures 29 3.4 Testing Procedures and Apparatuses 31 3.4.1 Basic Properties 31 3.4.2 Compressibility and Strength Properties 32 3.4.3 Microstructural Properties 33 Summary of Timings and Laboratory Activities on Cement-treated 34 3.5 clay Chapter 4 36 STATES AND MICRROSTRUCTURES OF CEMENT-CLAY STABILISATION 4.1 Formulations of Volume-Mass Model for Cement Stabilised Clay with 36 Curing-Consolidation and Hydration Effects 4.2 Predicted and Measured Volume-Mass Properties of Cement 41 Stabilised Clay 4.3 States of Cement Stabilised Clay under Various Curing Conditions 45 4.4 Microstructure 45 4.5 Pores Structure 46 4.5.1 Pore Size Distribution 46 4.5.2 Permeability – Void Ratio Relationship 48 4.6 Particle Size Distribution 50 4.7 Atterberg’s Limits 54 4.8 Compressive and Strength Behaviour 57 iii 4.8.1 Unconfined Compressive Strength 57 4.8.2 Isotropically Compressive Stress 60 4.8.3 Isotropically Consolidated Undrained (CIU) Compressive 63 Strength 4.8.4 Isotropically Consolidated Drained (CID) Compressive 65 Strength 4.9 Concluding Remarks Chapter 5 66 69 CONSTITUTIVE BEHAVIOUR AND MICROSTRUCTURAL CHANGES UNDER TRIAXIAL LOADINGS 5.1 Defination of Soil Structure 69 5.2 Artificial Soil Structure and Its Characteristics 70 5.3 Effects of Artificial Soil Structure on Compressibility 72 5.3.1 Stress Sensitivity 73 5.3.2 Microstructural Changes under Isotropic Compression 74 Effects of Artificial Soil Structure on Strength 80 5.4.1 Gross Yield Locus and State Boundary Surface (SBS) 81 5.4.2 Shearing Behaviour for Specimen Consolidated at Pre-Gross 83 5.4 Yield 5.4.3 Shearing Behaviour for Specimen Consolidated at Post-Gross 84 Yield 5.5 5.6 5.4.4 p’- q Stress plane and v-lnp’ Compression Plane 89 5.4.5 Microstructural Changes under Triaxial Shearing 90 Strain Softening Behaviour 92 5.5.1 Rupturing and Post-Ruptured State 92 5.5.2 Changes of Microstructures 95 Discussions 98 Chapter 6 100 A FRAMEWORK OF BEHAVIOUR FOR CEMENT TREATED CLAY 6.1 Summary of Cement Treated Clay Behaviour 100 6.1.1 Isotropic Compression 100 iv 6.1.2 Post-Yield Shearing Behaviour 103 6.2 A Behavioural Framework for Cement Treated Clay 106 6.3 Effect of α- and α1-Normalization 109 6.3.1 Triaxial Test Data of Current Study 109 6.3.2 Triaxial Test Data of Kamruzzaman (2002) 110 Chapter 7 113 CONCLUSIONS AND RECOMMENDATIONS 7.1 Conclusions 113 7.2 Recommendations for Future Study 117 FIGURES 119 REFERENCES 190 v SUMMARY Cement-soil stabilisation has been widely used to improve engineering performance of clayey soils in various applications. This thesis investigates the presence of different curing conditions such as atmospheric pressure, isotropically loaded-drained and –undrained curing stress on the microstructure as well as engineering performance of cement treated marine clay. Furthermore, the constitutive behaviour of the treated specimens under triaxial loadings were also examined and related to the microstructural changes. The engineering properties measured include the basic volume-mass properties (moisture content, void ratio, bulk density, specific gravity), Atterberg limits, as well as strength and compressibility properties; while the microstructure was investigated through scanning electron microscopy, mercury intrusion porosimetry and laser diffractometric measurement of particle size distribution. The results show that the level of effective stress which the soil experiences during curing has a significant effect on its post-curing microstructure and is manifested in the macroscopic behaviour. The basic volume-mass properties, strength and compressibility properties were dependant on the end states of the treated specimen, being plotted as specific volume against effective confining stress in linearlog compression plane. Furthermore, the measured volume-mass properties were reasonably in good agreement with those predicted from the proposed model, which accounts for both initial consolidation and hydration effects. The microstructural observation reveals that the cement treated clay adopts a structure which could be described as flocculated with significant intra-aggregate pore volume; this being consistent with the increase in liquid limit for the treated clay. The vi particle size distributions obtained from different effort of remoulded specimens show that the aggregation effect which results from the cement treatment makes it difficult to clearly define a grading curve. The greater the remoulding effort and duration, the greater is the amount of aggregation destroyed, resulting in smaller and smaller particle sizes. The isotropic compression behaviour for cement treated clay is similar to that obtained for natural and artificially cemented soils, which shows sensitivity behaviour. Beyond gross yield, the sensitivity decreases and a post-yield compression line was obtained for cement treated clay originated from different states at posttreatment. The shearing behaviour of the treated clay when normalized for both volume and stress sensitivity shows that the behavioral framework for natural soils by Cotecchia and Chandler (2000) could not be applied in the current study, in particular the stress path under triaxial drained condition. It was found that the current stress sensitivity (sensitivity varies with specific volume during shearing), rather than the initial sensitivity is a more appropriate in the normalization procedures. This is to include for the continuous change in soil structure arises from shearing. Post-peak strain softening behaviour of cement treated clay is associated with rupturing. A progressive decrease in the post-peak friction coefficient with further rupturing was obtained. The SEM observations indicate that break-up of aggregates into smaller aggregates and particles, thus a finer particulate texture on the rupture surface was seen as rupturing is progressed. The post-ruptured envelope was found to be near to or above the critical stress ratio of untreated marine clay. vii LIST OF TABLES Table 2.1 Factors affecting the strength increase (after Terashi, 1997) 10 Table 2.2 E − qu relationships for cement treated soil 17 Table 2.3 Empirical reduction coefficients currently used in Japan (after CDM, 1994) 18 Table 3.1 Basic properties of Singapore upper marine clay 27 Table 3.2 Chemical compositions and physical properties of Ordinary Portland Cement 28 Table 3.2A Summary of timings and activities on cement-treated soil 35 Table 4.1A Measured and calculated volume-mass properties of cementtreated clay at 7-day post-treatment (% error) 42 Table 4.1 Effect of cement treatment on basic properties of cement-clay mixtures 43 Table 4.2 Percentage of changes of void ratio attributed to trapped water 56 Table 4.3 UCT peak strengths for specimens cured under loaded-undrained condition 57 Table 4.4 Determination of gross-yield point through: (a) Standard Casagrande method, (b) Cotecchia and Chandler’s (2000) method and (c) Rotta et al.’s (2003) method 61 Table 5.1 Compressibility indices for untreated clay, treated specimens with various curing stresses, CCL and PYCL 74 Table 5.2 Calculated changes of trapped water in percentage 79 Table 6.1 Estimated specific volume corresponds to gross yield point for various soils 102 Table 6.2 Percentage of grain size distribution of untreated clays used 112 viii LIST OF FIGURES Fig. 2.1 Schematic illustrations of improved soil (after Saitoh et al., 1985) 119 Fig. 2.2 SEM micrographs of lime improved soil (after Locat et al., 1990) 119 Fig. 2.3 Factors control the properties of cement treated soil (after Kezdi, 1979) 120 Fig. 2.4 In-situ mixing tools for soil cement mixtures (after Porbaha et al., 2001) 120 Fig. 2.5 Effect of cement type on compressive strength of soil-cement for: (a) Kanagawa; and (b) Saga soils (after Kawasaki et al., 1981) 121 Fig. 2.6 Effect of different stabilizers on compressive strength of different soils in Sweden (after Ahnberg et al., 1995) 121 Fig. 2.7 Effect of grain size distribution on cement stabilization (after Niina et al., 1977) 122 Fig. 2.8 Effect of soil types on cement stabilization (after Taki and Yang, 1991) 122 Fig. 2.9 Effect of initial water content on cement stabilization (after Endo, 1976) 123 Fig. 2.10 Effect of initial water content on cement stabilization (after Terashi et al., 1980) 123 Fig. 2.11 Effect of mixing time on lime stabilization (after Terashi et al., 1977) 124 Fig. 2.12 Effect of mixing time on cement stabilization (after Nakamura et al., 1982) 124 Fig. 2.13 Effect of blade rotations on in-situ strength (after Mizuno et al., 1988) 125 Fig. 2.14 Effect of curing time on strength (after Kawasaki et al., 1981) 125 Fig. 2.15 Effect of curing temperature on strength (after Saitoh et al., 1980) 126 Fig. 2.16 Effect of curing temperature on compressive strength of silt (after Enami et al., 1985) 126 ix Fig. 2.17 Correlation of unconfined compressive strength between in-situ and laboratory treated soil (after CDM, 1994) 127 Fig. 2.18 Effect of cement content on 1-D eodometer compression curve (after Uddin et al., 1997) 127 Fig. 2.19 Triaxial behaviour of treated clay under (a) drained; and (b) undrained conditions (after Endo, 1976) 128 Fig. 2.20 Effect of strain measurements on modulus of cement treated soil (after Tatsuoka et al., 1997) 128 Fig. 2.21 Comparisons of stress condition between in-situ and laboratory (after Tatsuoka and Kobayashi, 1983) 129 Fig. 2.22 Peak strength envelopes for specimens cured under or without stress (after Consoli et al., 2000) 129 Fig. 2.23 Effect of undrained curing condition (after Tan et al., 2002) 130 Fig. 2.24 Peak strength envelope on effective stress plane (after Tatsuoka and Kobayashi, 1983) 130 Fig. 2.25 Consolidated drained triaxial behaviour with different confining pressures (after Tatsuoka and Kobayashi, 1983) 131 Fig. 2.26 Pore pressure responses with different confining pressures (after Uddin et al., 1997) 132 Fig. 2.27 Pore pressure responses with different cement contents (after Uddin et al., 1997) 132 Fig. 2.28 Undrained stress path behaviour of cement treated clay for (a) 10%; (b) 30%; and (c) 50% of cement contents (after Kamruzzman, 2002) 133 Fig. 3.1 Demoulding the soil-cement sample for isotropic load-curing 134 Fig. 3.1A Distribution curve of air content (in percentage) within cement-clay mixtures just after mixing 134 Fig. 3.1B Liquid and bleeding limits of fresh cement-slurry clay mixes (reproduced from Chew et al., 1997) 135 Fig. 3.2 Laser diffraction Malvern Mastersizer for grain size analysis 135 Fig. 3.3 A fully computer controlled triaxial stress path apparatus 136 x Fig. 3.4 Hitachi 4100 Field Emission Scanning Electron Microscope (FESEM) 136 Fig. 3.5 Mercury Intrusion Porosimeter (Micromeritics Autopore III 9420) for pore size analysis 137 Fig. 3.5A Degree of hydration with time (Sun et al., 2004) 137 Fig. 4.1 Basic volume-mass model for cement treated clay (drained condition) 138 Fig. 4.2 Basic volume-mass model for cement treated clay (undrained condition) 139 Fig. 4.3 Predicted and measured volume-mass properties of cement treated clay under loaded-drained and loaded undrained curing conditions 140 Fig. 4.4 Comparisons between predicted and measured volume-mass properties of cement treated clay 141 Fig. 4.5 Measured specific gravity using (a) both wet and dry methods with loaded-drained curing stresses; and (b) dry method with different episodes of vacuum suction 141 Fig. 4.6 Measured specific gravity using both wet and dry methods together with predicted values for different cement contents 142 Fig. 4.7 End states of treated specimens cured under various curing conditions 142 Fig. 4.8 Microsturcture of specimens after various loaded-drained curing stresses (a) 0CON0; (b) 50CON0; (c) 250CON0; and (d) 500CON0 143 Fig. 4.9 Pore size distribution for specimens cured under various stress states 144 Fig. 4.10 Relationship of void ratio and pore radii 144 Fig. 4.11 Permeability - void ratio relationship under various stress states 145 Fig. 4.12 Grading curves for untreated marine clay, cement particles, cementclay mixtures and cement-clay particles in ethanol 145 Fig. 4.13 Grading curves for cement treated clay with different remoulding periods 146 Fig. 4.14 Grading curves for cement treated clay with ultrasonic dispersion 146 Fig. 4.15 Changes of liquid limit at different remoulding periods 147 xi Fig. 4.16 Grading curves for the treated specimens with various loadeddrained curing stresses, after approximately 1-hour remoulding period 147 Fig. 4.17 Plasticity chart for cement treated clay under various stress states during curing period 148 Fig. 4.18 UCT results for specimens treated under drained isotropic curing stress 148 Fig. 4.19 Generalisation of UCT peak strength with post-cured moisture content 149 Fig. 4.20 Generalisation of UCT strength into Lee et al.’s (2005) framework 149 Fig. 4.21 Variation of undrained shear strength for remoulded soils and cement treated clay with liquidity index; remoulded soils data obtained from Skempton and Northey (1953) 150 Fig. 4.22 Isotropic compressive behaviour of cement-treated specimens cured under various curing conditions 150 Fig. 4.23 Determination of gross-yield point through (a) Standard Casagrande method; (b) Cotechia and Chandler’s (2000) method; and (c) Rotta et al.’s (2003) method 151 Fig. 4.24 Consolidated undrained triaxial behaviour for specimens cured with and without load; (a) stress-strain; (b) stress path; and (c) pore pressure - strain 152 Fig. 4.25 Comparisons of stress – strain behaviour from both CIU and UCT tests (specimens cured under loaded-drained condition) 153 Fig. 4.26 Consolidated drained triaxial behaviour for specimens cured with and without load; (a) stress-strain; (b) compression path; and (c) volumetric-deviatoric strains 154 Fig. 5.1 Artificial flocculated treated soil structure with trapped intraaggregate pore 155 Fig. 5.2 Isotropic compression curves for untreated specimen, 0CON0 treated specimen and remoulded 0CON0 specimen 155 Fig. 5.3 Cluster of aggregates seen in remoulded 0CON0 specimen 156 Fig. 5.4 Decrease of stress sensitivity after isotropic gross yield 156 Fig. 5.5 SEM micrographs at different isotropic compression pressures: (a) 0CON0; (b) 0CON50; (c) 0CON500; and (d) 0CON1500 157 xii Fig. 5.6 Changes of microstructures with isotropic compression pressures 158 Fig. 5.7 Changes of pore size distributions with isotropic compression pressures 158 Fig. 5.8 Permeability – void ratio behaviour under isotropic compression pressures 159 Fig. 5.9 Grading curves for 0CONY specimens, after remoulding for about 45 minutes to 1 hour 159 Fig. 5.10 Atterberg’s limits for treated specimens subjected to isotropic compression pressures 160 Fig. 5.11 Undrained triaxial behaviour for pre-cured soil-cement mixtures: (a) stress-strain; (b) pore pressure - strain 160 Fig. 5.12 Undrained stress paths, peak strength envelope and critical state line for pre-cured soil-cement mixtures 161 Fig. 5.13 Normalised stress paths and state boundary surface for pre-cured specimens 161 Fig. 5.14 Stress path under Ko consolidation test with unloading 162 Fig. 5.15 Compression paths for the treated specimens undergo different constant η test, together with their gross yield points 162 Fig. 5.16 Gross yield locus for cement treated clay 163 Fig. 5.17 Undrained and drained stress paths behaviour consolidated at pregross yield (specimens cured under atmospheric pressure) 163 Fig. 5.18 Normalised stress paths behaviour consolidated at pre-gross yield (specimens cured under atmospheric pressure) 164 Fig. 5.19 Normalised stress paths behaviour consolidated at pre-gross yield (specimens cured under 250kPa confining pressure) 164 Fig. 5.20 Triaxial behaviour for treated specimens consolidated at post-gross yield, with maximum 500kPa consolidation pressure 165 Fig. 5.21 Triaxial behaviour for treated specimens consolidated at post-gross yield, with maximum 1000kPa consolidation pressure 166 Fig. 5.22 Triaxial behaviour for treated specimens consolidated at post-gross yield, with maximum 1500kPa consolidation pressure 167 xiii Fig. 5.23 Normalized stress paths behaviour consolidated at post-gross yield, with maximum consolidation pressure: (a) 500kPa; (b) 1000kPa; and (c)1500kPa 168 Fig. 5.24 Peak strengths of the treated specimens consoidated at both pre- and post-gross yield, after normalized for volume and initial stress sensitivity 169 Fig. 5.25 Peak strength envelope for treated specimens with OCR=1 in (a) p’q stress plane; and (b) v-lnp’ compression plane 170 Fig. 5.26 Peak strengths for the treated specimen with OCRs and YSRs in (a) p’-q stress plane; and (b) v-lnp’ compression plane 171 Fig. 5.27 Changes of microstructures of the treated specimens after isotropic consolidation, undrained and drained triaxial shearing 172 Fig. 5.28 Changes of microstructure corresponding to stress states and compression states seen in the triaxial behaviour of cement treated clay 173 Fig. 5.29 Changes of pore size distributions after drained and undrained triaxial shearing with consolidation pressures: (a) 50kPa; (b)500kPa; and (c)1500kPa 174 Fig. 5.30 Stress- strain behaviour of cement treated clay in (a) drained triaxial; and (b) undrained triaxial; strain softening was observed for all specimens 175 Fig. 5.31 Behaviour of unloading-reloading stress paths: (a) during peak, preand-post peak; (b) re-consolidated after rupturing; (c) after rupturing under isotropic re-consolidation pressure of 390kPa and (d) 490kPa 176177 Fig. 5.32 Effects of re-consolidation pressure within SBS on the behaviour of stress path: (a) before rupturing; and (b) after rupturing with swelling or compression consolidation pressure 178 Fig. 5.33 Post-rupture states in (a) p’-q stress plane; and (b) v-lnp’ compression plane; numbers next to the points indicate OCR or YSR values. 179 Fig. 5.34 Changes of microstructure with Mr, as shown in the mechanical behaviour 180 Fig. 5.35 Microstructure at post-rupture states, as shown in the mechanical behaviour 181 Fig. 5.36 Changes of pore structure with Mr, as shown in the mechanical behaviour (refer Figure 5.34 for numbering of states) 182 xiv Fig. 5.37 Entrance pore structure at post-rupture states, as shown in the mechanical behaviour (refer Figure 5.35 for numbering of states) 182 Fig. 6.1 Influence of b parameter on compression after gross yield 183 Fig. 6.2 Idealisation of isotropic compression behaviour for cement treated clay in v-lnp’ plane 183 Fig. 6.3 Normalizing factor for current stress sensitivity 184 Fig. 6.4 Normalizing factor for current stress sensitivity by equating κ=0 184 Fig. 6.5 Stress paths behaviour after normalized by volume and current stress sensitivity for cement treated specimens consolidated at: (a-c) pregross yield; and (d-f) post-gross yield 185 Fig. 6.6 Peak strengths after normalized by volume and current stress sensitivity for cement treated specimen 186 Fig. 6.7 Comparison between α- and αs-normalisations 186 Fig. 6.8 Isotropic compression behaviour of the treated specimens with different cement contents, together with their post-yield compression lines 187 Fig. 6.9 Undrained stress path behaviour at 10% cement content based on αsnormalisation 187 Fig. 6.10 Undrained stress path behaviour at 30% cement content based on αsnormalisation 188 Fig. 6.11 Peak strengths and gross yield loci at different cement contents after normalized for volume and current stress sensitivity 188 Fig. 6.12 Peak strengths and gross yield loci at different cement contents after normalized for volume, current stress sensitivity and composition 189 xv LIST OF SYMBOLS Ac , Aw Cement content Al2O3 Aluminium oxide b Compression destructuring index, Liu and Carter’s (2000) framework C2S Di-calcium silicate C3A Tri-calcium aluminate C3S Tri-calcium silicate C4AF Tetra-calcium alumino-ferrite Ca(OH)2 Calcium hydroxide, or lime CAH Calcium aluminate hydrates CaO Calcium Oxide CASH Calcium Aluminate Silicate Hydrate CCL Curing-Consolidation Line CCS Curing-Consolidation strength for pre-cured specimens CDM Cement Deep Mixing CID Isotropically consolidated drained triaxial test CIU Isotropically consolidated undrained triaxial test CSH Calcium Silicate Hydrate CSL Critical State Line cu Undrained shear strength DMM Deep Mixing Method e Void ratio ec , eot Post-curing void ratio e0 Initial void ratio E0 Initial elastic Young’s modulus E50 Elastic Young’s modulus at 50% of q u Fe2O3 Iron oxide Fs Factor of safety Gs Specific gravity Gsc Specific gravity for soil-cement mixtures after treatment xvi H2O Water ht Hydration at time t ICL Intrinsic compression line, Burland (1990) IL Liquidity index k Coefficient of permeability K0 Coefficient of earth pressure at rest KOH Potassium hydroxide LL Liquid limit m Moisture content m Experimentally fitted value, Lee et al. (2005)’s framework mc Post-cured moisture content MIP Mercury Intrusion Porosimetry Mc Mass of cement solid Ms Mass of soil solid M sc Mass of soil-cement mixtures (solid) after treatment M s+c Mass of soil and cement solids M w,a + g Mass of available water and gel water in the soil-cement mixtures after hydration M w,c Mass of water from cement slurry M w,cc Mass of water after curing-consolidation M w,h Mass of water used for hydration M w, s Mass of water from soil M w, sc Mass of water in soil-cement mixtures after treatment M w, s + c Mass of water from both cement slurry and soil ( M w, sc ) U Mass of water in soil-cement mixtures after treatment in an undrained condition M Stress ratio, q/p’ at critical state Mpeak Stress ratio q/p’ at peak state Mpr Stress ratio q/p’ at post-ruptured state Mr Stress ratio q/p’ during rupturing xvii n Experimentally fitted value, Lee et al. (2005)’s framework NaOH Sodium hydroxide NCL Normally Consolidation Line Nr Intercept of CCL in v-lnp’ plane at p’=1kPa Ns Intercept of PYCL in v-lnp’ plane at p’=1kPa OCR Over-Consolidation Ratio OPC Ordinary Portland Cement PI Plasticity index PL Plastic limit PYCL Post-Yield Compression Line p' Mean normal effective stress, ( σ 1' +2 σ 3' )/3 ' p cure Effective isotropic curing stress p cure Total isotropic curing stress p e*' Equivalent pressure on CCL p e*',s Equivalent pressure on the CCL at the same void ratio as po' ,s ' p gy Mean normal effective stress at gross-yield p i' Pre-shear effective confining pressure p o' Effective isotropic compression stress po' ,s Compression stress at PYCL corresponds to a current p’ state during shear, with both po' ,s and p’ are linked through a κ line (see Figure 6.3) p 'p Mean normal effective stress corresponds to peak state q p p 'y Maximum effective consolidation pressure for unloading-reloading cycle after gross-yield q Deviator stress, σ 1' - σ 3' q0 Experimentally fitted value, Lee et al. (2005)’s framework qp Deviator stress at peak state qu Unconfined compressive strength q uf Unconfined compressive strength for field specimen qul Unconfined compressive strength for laboratory prepared specimen xviii s/c Soil-cement ratio S:C:W Soil-cement-water ratio SBS State Boundary Surface SEM Scanning Electron Microscopy SiO2 Silica Sσ Stress sensitivity u Excess pore water pressure UCT Unconfined compressive test Vep Volume of empty capillary pores created during hydration of cement Vc Volume of cement solid particles Vs Volume of soil solid particles Vsc Volume of soil-cement mixtures (solid) after treatment Vs + c Volume of soil and cement solids V w,c Volume of water from cement slurry V w,cc Volume of water in soil-cement mixtures after curing-consolidation V w, a + g Volume of available water and gel water in the soil-cement mixtures after hydration V w, s Volume of water from soil V w, sc Volume of water in soil-cement mixtures after treatment V w, s + c Volume of water from both cement slurry and soil (Vw, sc ) U Volume of water in soil-cement mixtures after treatment in an undrained condition ν Specific volume, 1+e νκ Intercept of unloading-reloading line in v-lnp’ plane at p’=1kPa w/c Water-cement ratio W L ,ic Liquid limit after specimen subjected to post-curing consolidation pressure W L ,lc Liquid limit for specimen subjected to loaded-drained curing consolidation pressure W L , nc Liquid limit before specimen subjected to post-curing consolidation pressure xix W L ,nlc Liquid limit for specimen cured under atmospheric pressure W L ,tw Amount of water trapped inside the intra-aggregate pore in % XCIDY-Z X refers to effective stress during curing; Y refers to maximum effective consolidation stress at post-treatment; Z refers to effective consolidation stress after unloading for CID test XCIUY-Z X refers to effective stress during curing; Y refers to maximum effective consolidation stress at post-treatment; Z refers to effective consolidation stress after unloading for CIU test XCONY X refers to effective stress during curing; Y refers to effective consolidation stress at post-treatment YSR Yield Stress Ratio α Current stress sensitivity during shearing, see Figure 6.3 αs Simplified current stress sensitivity during shearing, see Figure 6.4 γb Bulk density γd Dry density ∆ei ' Additional voids ratio at p’= p gy , Liu and Carter’s (2000) framework ∆etw Changes of void ratio due to trapped water inside the intra-aggregate pore ∆Vcc Volume of water expelled out during curing-consolidation εa Axial strain εq , ε s Deviatoric strain εv Volumetric strain ε v,cc Volumetric strain during initial curing consolidation of pre-cured specimen ξ Uncertainty factor η Stress ratio, q/p’ κ Slope of unloading-reloading line in v-lnp’ plane after gross-yield κ* Slope of unloading-reloading line in v-lnp’ plane for pre-cured specimen κ gy Slope of compression line in v-lnp’ plane before gross-yield xx λ Slope of normal compression line in v-lnp’ plane after gross-yield for post-cured specimen λ* Slope of normal compression line in v-lnp’ plane for pre-cured specimen ρw Water density σ 1' , σ 3' Principle effective stresses σa Axial stress σ ca Allowable compressive strength σt Tensile strength σ ta Allowable tensile strength σ v' Vertical effective stress σ ve*' Intrinsic equivalent pressure σ v' ,gy Vertical effective stress at gross-yield τa Allowable shear strength xxi LIST OF DEFINITIONS Artificial Soil Structure Soil structure arise from chemical soil improvement processes Curing-Consolidation Line (CCL) Compression line for soil-cement mixtures at pre-cured state (before significant structure has formed) Destructuration Breaking down of bonds between particles or aggregates and the meta-stable particle arrangement Gross Yield Locus Expansion of yield locus due to soil structure Gross Yield Stress Expansion of yield stress due to soil structure Intrinsic Compression Line (ICL) Compression line for soil at reconstituted state Overconsolidation Ratio (OCR) Ratio between yield stress and pre-shear effective confining pressure for specimen consolidated at postgross yield and unloading Post-Yield Compression Line (PYCL) Compression line for treated soil consolidated after gross yield Post-Yield Shearing Behaviour Behaviour of soil after reaching state boundary surface Soil Structure Factors influencing soil behaviour that can not be accounted by void ratio and stress history alone (Leroueil & Vaughan, 1990) Stress Sensitivity Ratio between PYCL and CCL at the same void ratio (for current study). For general case, refer to Cotecchia and Chandler (2000). Yield Loci Collection of yield locus for specimen consolidated after gross yield Yield stress Maximum effective consolidation pressure after grossyield for unloading-reloading cycle Yield Stress Ratio (YSR) Ratio between gross yield stress and pre-shear effective confining pressure for specimen consolidated before gross yield xxii CHAPTER 1 INTRODUCTION 1.1 Cement-Soil Stabilization Introduction of cement into soft ground, or cement-soil stabilization, either in the form of dry cement powder or slurry cement, is a popular method of ground improvement technique. The inclusion of cement into soil-water systems causes physico-chemical changes at a microstructural level and therefore mechanical behaviour of the treated soil at a macroscopic level. The short-term gain in strength is the result of primary hydration reaction, which also leads to a reduction in moisture content during the chemical reaction. This process forms two cementing minerals, namely Calcium Silicate Hydrates (CSH) and Calcium Aluminate Silicate Hydrates (CASH). At the same time, the release of lime into the inter-particle voids leads to the formation of a flocculated structure. Subsequent long term gain in strength is a result of secondary pozzolanic reaction between the lime and the clay minerals (e.g. Kezdi, 1979; Bergado et al., 1996). Over the years, cement stabilization has been developed from surface treatment (such as for road pavement) and extended significantly to a greater depth, wherein cement columns are created through deep mixing. In this method, specially designed machines with several shafts equipped with mixing blades and stabilizer injection nozzles are used to construct in-situ treated soil columns in various patterns and configurations. The use of the Deep Mixing Method (DMM) was probably started sometime in the early to mid-1970s. As DMM is implemented using cement slurry, it is often termed Cement Deep Mixing (CDM) (Porbaha, 1998). Since then, the CHAPTER 1 equipment used has improved and the application of deep mixing as a ground improvement method has been extended throughout the world. 1.2 Some Issues in Cement-Soil Stabilization In practice, upon completion of the DMM installation, the improved ground will be left for curing over a specific period of time, before commencement of construction activities. Tatsuoka and Kobayashi (1983) highlighted the curing conditions of improved ground through deep mixing. According to them, the treated ground is cured under ground temperature with geostatic pressure acting on it. The excess pore water that built up during installation is free to move. Such free movement of water causes ground settlement and the horizontal stress of the improved ground in an anisotropic K0 condition. However, in past laboratory works, soil-cement samples prepared in the laboratory were often not cured under loading. This condition is unlikely to be able to accurately reflect the actual ground condition. In fact, how much effective stress will actually build up in the treated soil mass before the treated material sets and cures is still relatively unknown. It is likely to depend on numerous factors such as permeability of the treated and surrounding ground, speed of setting and proximity to drainage boundaries. The other accompanying issue is how much difference the curing under different effective stress conditions contribute to the properties of the treated ground. This issue therefore forms the first part of the current research. Terashi (2001) noted that the current design method of the improved ground, which utilizes unconfined compression strength, is rather conservative. This is partially attributable to the large difference often observed between data obtained 2 CHAPTER 1 from laboratory-prepared cement-treated soil specimens and field specimens (Sakai et al., 1996). According to the Cement Deep Mixing Association of Japan CDM (1994), the unconfined compressive strength of cement-treated soil collected from the field is usually only half to one-fifth of the strength of laboratory-prepared specimens. Several reasons may possibly account for such discrepancies, such as the mixing conditions in laboratory are properly controled and well defined as compared to field mixing. The other reason might due to the limitations of unconfined compression test, which cannot accurately simulate geostatic and drainage conditions (Tsuchida and Tanaka, 1995; Yu et al., 1997). To improve cost efficiency in design and construction, Porbaha et al. (2000) and Terashi (2001) highlighted a few issues or tasks that should be tackled in the coming decade. One of these is to develop an appropriate failure criterion such as peak and residual strengths that covers a wide range of confining pressure. This indicates a proper behavioural framework for cement-treated clay under triaxial compression test is essential for research. This is the area which is addressed in the second part of the present research. 1.3 Objectives of Current Research Based on both the outstanding issues discussed above, the current research was conducted to achieve the following objectives: i) To study behaviour and performance of cement treated marine clay in the presence of atmospheric, drained and undrained ambient effective load-curing conditions. ii) To study stress-strain behaviour of cement treated marine clay at a macroscopic level, and consequently relates this behaviour to the microstructural changes during both isotropic compression and shearing. 3 CHAPTER 1 iii) To provide a behavioural framework for cement treated marine clay cured under various conditions, in the presence of confining pressure and drainage conditions. The key assumptions and limitations of which the research has been carried out are as follows: (a) The specimen of cement-clay mixtures are prepared in laboratory with a 20% cement content and cured for 7 days. In such a condition, the results are likely to be applicable to such limited configurations. (b) The elementary assumptions are applied to the cement-clay specimen such that the boundaries of the element are properly controlled and the mixture within the element is assumed to be isotropic homogeneous. (c) The specimen has insignificant air content. (d) The phase relationships for cement-clay model derived in this study only account for both hydration and curing-consolidation effects. The pozzolanic reaction is not considered in the phase relationship. (e) The hydration model from cement-water paste (Neville, 1995) is directly applied to the clay-cement-water mixtures, assuming hydration is independent of clay particles. In addition, the rate of hydration derived from cement-water paste is reasonably assumed to be unaffected by the microscopic arrangement between cement-clay particles that are in contact. 4 CHAPTER 2 LITERATURE REVIEW 2.1 Mechanisms of Cement-soil Stabilization 2.1.1 Properties of Cement Ordinary Portland Cement (OPC) is the most commonly used cement in cement-soil stabilization. Its main components are tricalcium and dicalcium silicates (C3S and C2S), tricalcium aluminate (C3A) and tetracalcium alumino-ferrite (C4AF). In accordance with the notation commonly used in cement chemistry, C represents CaO, S represents SiO2, A represents Al2O3 and F represents Fe2O3. In the presence of water, these compounds form colloidal hydrated products of very low solubility. Aluminates react first, and are mainly responsible for setting, i.e. solidification of the cement paste. The later hydration of silicates leads to hardening of cement paste. The hydration reaction forms a rigid gel consisting of hydrated cementitious products, which are calcium silicate hydrates [CSH]; calcium aluminate hydrates [CAH]; and calcium aluminate silicate hydrates [CASH]. Also, the hydration of calcium silicates produces calcium hydroxide [Ca(OH)2], or lime. The Ca(OH)2 together with NaOH and KOH that are present in small amounts, cause a rise in pH of up to about 13.5 in the pore liquid. In cement-soil stabilization, the pH is usually slightly lower, ~12, because of the lower proportion of cement, and possibly pre-existing acidity in the soil. 2.1.2 Cement-Soil Reactions Cement-soil reactions, which involve both hydration and pozzolanic reactions, may be represented by Eqs. (2.1) – (2.4) below: CHAPTER 2 C3S + H2O C3S2HX (hydrated gel) + Ca(OH)2 (primary cementitious products) (2.1) Ca(OH)2 Ca2+ + 2(OH)(hydrolysis of lime) (2.2) Ca2+ + 2(OH)+ SiO2 (soil silica) C-S-H (secondary cementitious product) (2.3) Ca2+ + 2(OH)+ Al2O3 (soil alumina) C-A-H (secondary cementitious product) (2.4) The mechanism of soil cement stabilization involves a series of chemical reactions between clay, cement and water. There are two major chemical reactions which govern the mechanism: the primary hydration and the secondary pozzolanic reactions. The former is represented by Equation (2.1) and occurs between cement and water (from soil or cement slurry), resulting in rapid strength gain due to the formation of primary cementitious products. This is also the reaction which leads to the short-term hardening of cement-treated soil. In addition, lime is produced and the concentrations of Ca2+ and OH- ions in the pore water increases [Equation (2.2)] through the hydrolysis of the lime. The secondary pozzolanic reaction, also termed as solidification, occurs once the pore chemistry in the soil system achieves an alkaline condition when a sufficient concentration of OH- ions is present in the pore water. The resulting alkalinity of the pore water promotes dissolution of silica and alumina from the clays, which then react with the Ca2+ ions, forming calcium silicate hydrate (CSH) and calcium aluminate hydrate (CAH), which are the secondary cementitious products [Equations (2.3) and (2.4)]. These compounds crystallize and harden with time, thereby enhancing the strength of the soil cement mixes. 6 CHAPTER 2 It should be noted that the Eqs. (2.1) – (2.4) only apply to tricalcium silicate (C3S) only, which is the main constituent of OPC. The others main constituents of cement such as dicalcium silicates (C2S), tricalcium aluminate (C3A) and tetracalcium alumino-ferrite (C4AF) are also involved in both the hydration and pozollanic reactions to produce calcium silicate hydrate (CSH), calcium aluminate hydrate (CAH) and calcium aluminate silicate hydrates (CASH). A complete set of chemical equations involving these reactions as well as lime treated clay have been presented by Kezdi (1979) and Bergado et al. (1996). 2.1.3 Structure and Microstructure of Treated Clay The microstructure of the cement treated clay is often significantly different from that of the untreated clay. Kezdi (1979) suggested that a soil-cement skeleton matrix may be formed due to the inclusion of cement with each skeletal unit consisting of a core of hydrated cement gel (tobermorite gel) and secondary cementitious product (CSH and CAH) connecting the adjacent clay particles. In addition, the inter-particle bond strength also increases due to reduction of diffused double (absorbed) layer and flocculation of the secondary cementitious materials. Saitoh et al. (1985) proposed schematic diagrams to illustrate the change in structure of soil-cement mixtures during hardening, as shown in Fig 2.1. They postulated that the initial condition immediately after mixing consists of clusters of clay particles, surrounded by cement slurry. The primary hydration reaction involves only the shell of cement slurry, which forms hardened cement bodies. The secondary pozzolanic reaction involves the inner clay particles, leading to the formation of 7 CHAPTER 2 hardened soil bodies. As they speculated, the strength of the improved soil will depend upon the strength characteristics of both types of hardened bodies. Locat et al. (1990) presented micrographs on the microstructure of limetreated sensitive clay (see Fig 2.2). As Fig 2.2(A) shows, before addition of lime, the clay has an open microfabric, and individual particles and aggregates could be seen. As Fig 2.2(B) shows, after 10 days of curing with quicklime, the soil has been flocculated into larger lumps; Fig 2.2(C-F) show the lumps cemented together by the subsequent pozzolanic reaction products. For cement-treated soil, Chew et al. (2004) noted that, as the cement content increases from 10% to 50%, the flocculated nature of the fabric becomes more evident, with soil particle clusters interspersed by large opening. They attributed this to the dissolution of silica and alumina from the clay minerals and their subsequent reaction with the Ca2+ ions to form CSH and CASH, which are then deposited onto the particle surface. They also highlighted a significant amount of entrapped water within the flocculated particle clusters, similar to the case for lime stabilized clay (Locat el al., 1996). 2.2 Influence of Various Factors on the Strength Index The strength of the lime or cement treated soil can be affected by a number of factors. This is because the basic strength increment is closely related to the chemical reactions which take place between the soil and the stabilizing agent. The early research works carried out to understand the effects of the various factors on the strength of cement-treated soil were based on unconfined compressive strength, qu, 8 CHAPTER 2 which is widely used as an index to represent the effectiveness of the stabilization method. Kezdi (1979) noted that factors affecting the strength of cement-treated soil include the characteristics and conditions of cement (chemistry composition and type), soil (grain-size distribution, chemistry components, plasticity and types) and water (sulphate, pH value and hardness). The secondary factors which also affect the strength of the improved soil include the installation processes (e.g. compaction, mixing, post-treatment) as well as temperature under which the work is carried out. Kezdi’s (1979) model is as illustrated in Figure 2.3. Terashi (1997) summarised the factors that influence the strength of the improved soil into four categories: characteristics of stabilizing agent; characteristics and condition of soils; mixing conditions; and curing conditions (see Table 2.1). He noted that not every factor listed in Table 2.1 could be accurately simulated in the laboratory. This is because in the laboratory testing, mixing and curing conditions are normally altered by adjusting the amount of binder and the curing time; while other site operating parameters are often not that easy to be simulated. For example, the mixing of soil and cement at the construction site used specially designed machine with single or multiple shafts and blades such as that shown in Figure 2.4. However, in laboratory, the standard Hobart mixer is often used. Therefore, the strength data obtained from laboratory tests is not a precise prediction, but only an ‘index’ to the actual strength. The strength parameters obtained from the field testing is therefore essential for design. 9 CHAPTER 2 Table 2.1: Factors affecting the strength increase (after Terashi, 1997) 1. 2. 3. II. Characteristics and conditions of 1. soil (especially important for clays) 2. 3. 4. III. Mixing conditions 1. 2. 3. IV. Curing conditions 1. 2. 3. 4. I. Characteristic of stabilizing agent 2.2.1 Type of stabilizing agent Quality Mixing water and additives Physical chemical and mineralogical properties of soil Organic content pH of pore water Water content Degree of mixing Timing of mixing/re-mixing Quantity of stabilizing agent Temperature curing time Humidity Wetting and drying/freezing and thawing, etc. Characteristics of Stabilizing Agents In general, the strength of an improved soil increases with the amount of stabilizing agent. However, the rate of increment is not in proportion to the cement contents (Kawasaki et al. 1981). For Bangkok Clay, Uddin et al. (1997) observed that the greatest increment rate lies in cement contents ranging from 10% to 25%. In this context, the term “cement content” refers to the ratio of solid mass of cement to solid mass of soil. For Singapore marine clay, Kamruzzaman (2002) noted significant increase in the strength of the treated soil within the cement content range of 5-40%. On the other hand, Miura et al. (2001) and Horpibulsuk et al. (2003) noted that the clay-water/cement ratio is a more appropriate parameter for quantifying the strength development of the cement treated soft clays, instead of cement content only. Similarly, Lee et al. (2005) showed that the strength of the improved clay is dependent on both the soil/cement ratio and also the water/cement ratio, or the relative proportion of soil-cement-water ratio. 10 CHAPTER 2 The differences of improvement by using different types of cement have been investigated. Kawasaki et al. (1981) compared the effect of slag cement and ordinary Portland cement for two different types of soils in Japan, Kanagawa and Saga soils. The result in Figure 2.5 shows that the improvement obtained is not only dependent on the types of stabilizing agents, but also the soil types, or more precisely the chemical reactions that are involved between the stabilizing agents and the soils types. Similarly, Ahnberg et al. (1995) compared the effect of cement, lime and mixture of cement and lime mixed with different soils in Sweden, as shown in Figure 2.6. Based on field results from sandy ground with 5% of fines, Saitoh et al. (1990) noted that blast-furnace cement produces higher compressive strength than ordinary Portland cement. Besides cement or lime, a mixture of different stabilizing agents such as fly ash-cement mixture was also attempted (Balasubramaniam et. al, 1998). 2.2.2 Characteristics and Conditions of Soil It is well-recognised that different types of soil (e.g. peat, clay, silt, sand, etc.), which consist of different physical and chemical properties such as grain size distribution, water content, Atterberg limits, type of clay minerals, cation exchange capacity, amount of soluble silica and alumina, pH of pore water and organic matter content, affect the chemical reactions between the soils and stabilizing agents and thus the properties of the treated soil. Niina et al. (1977) highlighted the influence of grain size distribution on the unconfined compressive strength of the cement treated soil. As shown in Figure 2.7, the highest improvement effect was obtained at a sand fraction of about 60%, irrespective of the amount of cement content. Taki and Yang (1991) also revealed that coarse grained soils show a larger strength for a given cement content, compared to fine particle soils such as silt and clay, as shown in Figure 2.8. 11 CHAPTER 2 Among clay types, the effect of different mineralogy was studied by Wissa et al. (1965). Generally, as they highlighted, the soils with higher pozzolanic reactivity will render greater strength. For instance, montmorillonitic and kaolinitic clayey soils were effective pozzolanic agents, compared to clays which contain illite, chlorite or vermiculite. They explained that pozzolanic reaction between clay particles and hydrated lime is dependent on mineral composition, especially the amorphous silica and alumina that are present in the soil. Saitoh et al. (1985) also highlighted the importance of pozzolanic reactivity in the effectiveness of the cement-clay improvement. Apart from the soil types, the increase in water content that is present in the soil has an adverse effect on the strength of the improved soil. Endo (1976) showed the effect of initial water content ranging from 60% to 120% on the strength of laboratory prepared marine clay samples treated with cement. As shown in Figure 2.9, the increase in initial water content significantly reduces the compressive strength of the mixture at any particular cement content. However, as shown by Terashi et al. (1980), at very low moisture content, i.e. near to plastic limit, the degree of improvement is also not significant, as could be readily seen in Figure 2.10. The maximum effects were achieved at around the liquid limit of the original soil. Besides the initial moisture content that is present in the soil, the additional water which arises from cement slurry during mixing also has a significant effect on the strength of the improved soil (Horpibulsuk et al., 2003; and Lee et al., 2005). Therefore, the total amount of water that is present in the mixtures is an important factor that will affect the strength of the treated soils. 12 CHAPTER 2 2.2.3 Mixing Conditions The mixing conditions include factors such as the types of mixer, installation method, timing and degree of mixing. The importance of mixing is to create a treated soil mass with a high degree of uniformity. Such factor is considered as the major sources which caused the huge discrepancies between laboratory and in-situ strengths. Terashi et al. (1977) investigated the influence of mixing time on the unconfined compressive strength with lime stabilization. As Figure 2.11 shows, strength ratio decreases considerably when the mixing time is less than 10 minutes. Beyond 10 minutes, the strength ratio slightly increased. For cement-stabilized clay, Nakamura et al. (1982) also arrived at a similar tendency between the unconfined compressive strength and mixing period for laboratory prepared samples mixed under both cement powder and cement slurry (see Figure 2.12). The figure shows that the decrease in mixing time caused the unconfined compressive strength to decrease, while strength deviation on the other hand increases. In the laboratory, the standardization procedure by the Japanese Geotechnical society (JGS, 2000) arguably suggests a mixing period of 10 minutes as appropriate time to obtain a “sufficient mixing” by using Hobart mixer. For in-situ soil-cement mixing, Mizuno et al. (1988) studied the degree of mixing from the number of rotations of the blades on the quality of the treated soil. Figure 2.13 shows that a smaller coefficient of variation could be obtained for the case when the sum of blade rotations is higher than 360 rpm. Besides, Yoshizawa et al. 13 CHAPTER 2 (1996) also showed that the number of mixing shafts, mixing blades and rotational speed may affect the strength of improved soil. According to them, better improvement could be obtained when using four mixing shafts and higher rotational speed as compared to single shaft with low speed. Apart from these effects, other configurations which may also influence the degree of mixing during installation of soil-cement mixing such as the number of shafts (Nishibayashi et al., 1985), the configuration of mixing blades (Enami et al., 1986), the penetration/withdrawal speed (Enami et al., 1986), the rotational speed of the shafts (Nishibayashi, 1988) and the injection methods (Saitoh et al., 1990) were also studied. 2.2.4 Curing Conditions After the mixing stage, the stabilized mixture will normally be left for treatment before commencement of construction activities. During the treatment period, the curing temperature, stresses, time and humidity are the influencing factors which affect the strength development of the treated soil. In general, the longer the curing period, the better is the strength development, due to the pozzolanic reaction (Kezdi, 1979). Figure 2.14 shows the strength increase of cement treated soil with the curing time (Kawasaki et al., 1981). As can be seen, the strength increases with time irrespective of soil types, and the increment with time is more pronounced for a greater amount of cement content. A similar test results were obtained with Portland cement or fly ash cement (Saitoh, 1988) and these could also be related to the observed decrease in water content during the treatment period (Uddin et al., 1997; Chew et al., 2004; Lorenzo and Bergado, 2004). 14 CHAPTER 2 The influence of curing temperature on the unconfined compressive strength of the laboratory treated soil was studied, as shown in Figure 2.15 (Saitoh et al., 1980). In general, it shows that a higher strength could be obtained under a higher curing temperature. Also, the curing temperature is more dominant for short-term strength but it diminishes as the curing time becomes longer. The curing temperature also has a similar effect on the strength of silty soil treated with cement, as shown in Figure 2.16 (Enami et al., 1985). The increase in unconfined compressive strength is almost linear with curing temperature ranging from 0°C to 30°C, for samples of different ages up to 28 days. For in-situ field condition, the curing temperature does not depend solely on the ground temperature, but also on the heat generated through hydration reaction, the thermal capacities and the dimensions of the improved soil (Babasaki et al., 1996). According to them, the greater bulk of the improved soil, the greater mass of cement been used, and thus the higher the curing temperature will be generated. This, in turn, hastens the chemical reaction and finally gives a higher improved strength within a given curing duration. From the in-situ monitoring, the rate of temperature increment within first ten hours is the greatest, with the maximum recorded being up to 15°C. 2.3 Geomaterial Design of Improved Ground by Deep Mixing Method (DMM) The geomaterial design, which is also called the ‘mix design’ of the improved ground, includes the selection of the appropriate hardening agent, types and amount of hardening agent, water-hardening ratio (for wet method), as well as the working specifications such as the rate of penetration and withdrawal, rotation speed of the mixing tool and etc. This design normally requires information regarding the 15 CHAPTER 2 properties of the untreated soil available at the project site. For initial geomaterial design, the untreated soils at different depths are taken to the laboratory and then mixed with the selected additive(s). For a general case where the prime purpose of the mix design is strength, the relationship between additive content and unconfined compressive strength, qu is determined on the basis of laboratory-prepared samples cured at different ages (usually 3, 7, 14 and 28 days). In the current design practice, the unconfined compressive strength (due to the simplicity and cost-effectiveness of the testing method), is the key parameter for design (Terashi, 2001; CDIT, 2002). This is because the other basic parameters such as tensile strength, Young’s modulus and compression yield stress could be correlated to the qu, as illustrated by Eqs. (2.5)-(2.7). Nonetheless, these empirical correlations should be applied with caution, as they differed significantly from soil to soil. Table 2.2 compiles some of the proposed correlations between Young’s modulus and the unconfined compressive strength, qu for the improved soil with cement. σ t = 0.15qu (2.5) [Terashi et al., 1980] E50 = 350 ~ 1000qu [Saitoh et al., 1980] (2.6) p 'y = 1.3qu [Terashi et al., 1980] (2.7) which σt, E50 and p’y are the tensile strength, elastic Young’s modulus at 50% of qu and consolidation yield pressure, respectively. 16 CHAPTER 2 Table 2.2: E − qu relationships for cement treated soil. References Saitoh et al. (1980) Tatsuoka et al. (1996) Relationship In-situ soil type E50 ~ 350 to 1000 q u Silty Clay ∗ E0 ~ 1000 q u Sand Geotesting Express (1996) E50 ~ 50 to 150 q u Blue Clay Asano et al. (1996) E50 ~ 140 to 500 q u Silty Clay Futaki et al. (1996) E50 ~ 100 to 250 q u Sandy Silt Kamruzzaman (2002) Lee et al. (2005) ∗ E0 ~ 490 q u E0 ~ 80 to 200 q u Marine Clay Marine Clay E0 = Initial elastic Young’s modulus E50 = Elastic Young’s modulus at 50% of ultimate Strength (secant modulus of elasticity) * Base on local strain measurement To incorporate the differences between laboratory and field variability, an empirical relationship between the field strength and laboratory strength is then established. For instance, the CDM Association of Japan (1994) suggested that the unconfined compressive strength of the cement-treated soil in the field, quf, could be estimated as half to one-fifth of laboratory strength, qul, as shown in Figure 2.17. However, the actual ratio is often based on local experience in terms of the improvement effect on the soils found in the region, the properties of the stabilizer, data from preconstruction trial tests, the sensitivity of the project, the experience of the contractor and the expected level of quality control and quality assurance. Based on the design field unconfined compressive strength quf, the treated ground is then checked against internal stability and settlement. The allowable design strengths and partial safety factor outlined by CDIT (2002) are as shown in Eqs. (2.8) to (2.10). σ ca = ξ Fs q uf ξ = ξ1ξ 2ξ 3 (2.8) (2.8b) 17 CHAPTER 2 1 2 = 0.15σ ca τ a = σ ca σ ta (2.9) ≤200kN/m2 (2.10) where σca : allowable compressive strength τa : allowable shear strength σta : allowable tensile strength Fs : factor of safety (usually 2-3) ξ : uncertainty factor due to ξ1, ξ2 and ξ3 (see Table 2.3) ξ1 : correction factor for the effective width of the treated column ξ2 : reliability factor of the overlapping (usually less than unity) ξ3 : correction factor for scattered strength Table2.3: Empirical reduction coefficients currently used in Japan (after CDM, 1994) 2.4 Coefficient ξ1 ξ2 ξ3 Current range of practice 0.7-0.9 0.8-0.9 0.50-0.66 Behaviour of Cement Treated Soil In recent years, the properties and behaviour of cement treated soil has received considerable interests among researchers around the world. The triaxial test is often preferred over the unconfined compression test, as it allows confining pressure and drainage condition to be adjusted to better simulate field conditions (Tsuchida and Tanaka, 1995; Yu et al., 1997). The effect of the induced cementation on the mechanical properties of the treated soil has been widely attributed to soil structure (Leroueil and Vaughan, 1990; Kamruzzman, 2002). The treated soil has a yield locus which is significantly greater than that of the untreated soil, which affects both its compression and shear behaviours. Uddin et al. (1997) highlighted the resistance to compression of the treated clay is markedly enhanced due to cementation effect, and the degree of 18 CHAPTER 2 enhancement increases with cement content as shown in Figure 2.18. Similar results were reported by Kamruzzman (2002). The stress-strain and strength behaviour of the cement stabilized clay under triaxial condition have been extensively investigated (Endo, 1976; Tatsuoka and Kobayashi, 1983; Shibuya et al., 1992; Uddin et al., 1997; Yu et al., 1997; Yin and Lai, 1998; and Kamruzzaman, 2002). Figure 2.19 shows the typical stress-strain behaviour under isotropically consolidated drained (CID) and undrained (CIU) triaxial compression test on laboratory prepared 5% cement treated marine clay (Endo, 1976). The result showed that higher deviator stress could be achieved by increasing the confining pressure, in both drained and undrained conditions. However, in CID, the maximum deviator stress was reached at a relatively high strain level, of about 20% or more. In contrast, the CIU samples reached peak deviator stress at a much lower strain level of about 3%. The CIU samples also failed at stress levels lower than the CID samples, presumably because of the generation of excess positive pore water pressure. The small strain stiffness of cement-treated soil has been measured using local strain transducer (Goto et al., 1991; Shibuya et al., 1992; Tatsuoka et al., 1997). Tatsuoka et al. (1997) reported that the strain measured from local transducer showed much higher stiffness than that of the conventional method (see Figure 2.20). In addition, the stiffness is almost constant and independent of initial loading, unloading and reloading cycle with the elastic range of strain of about 0.01%. Yin and Lai (1998) reported that the secant modulus of elasticity (conventional strain measurement) increased with the increase in cement content and confining pressure, but decreased 19 CHAPTER 2 with the increased of initial water content. They also suggested that at very high confining stresses, the cemented structure may have been partially destroyed, thereby reducing the stiffness. These literatures show that the external strain measurement is unlikely to capture the behaviour of the treated soil at small strain level. The permeability or the hydraulic conductivity of cement treated soil has also been investigated (e.g. Jefferies, 1981; Kilpatrick and Garner, 1992; Deschens et al., 1995; and Kamruzzaman, 2002). This property is important for the design of cut-off walls where seepage needs to be prevented. For certain areas which are subjected to earthquake, the dynamic properties are also important. Several studies have been made to investigate the dynamic properties of cement-treated soil (e.g. Chang and Woods, 1987; Yeoh and Airey, 1994; Baig and Nazarian, 1997). A recent state of the art report for geomaterial characterization in deep mixing technology is presented by Porbaha et al. (2000). 2.5 Outstanding Issues Notwithstanding the extensive amount of research works cited above, some issues relating to cement-treated soils remain unresolved. Firstly, the actual ground condition in which the deep mixing is carried out is yet to be simulated properly in the laboratory, in particular the ambient effective confining pressure with different drainage conditions. Secondly, the behaviour of improved soil has been examined through macro-mechanics or engineering behaviour, but the behavioural framework especially in triaxial testing has yet to be established. In view of these outstanding issues, the sections covered below will discuss some of the literatures that are available, with regard to these issues. 20 CHAPTER 2 2.5.1 Ambient Effective Confining Pressure The deep mixing technology is usually employed to increase strength and reduce compressibility of thick marine clay. In this method, the installation firstly involves penetration of mixing blades into the ground until it reaches a required depth (i.e. up to 40-60m). The slurry admixtures are then transported through the shafts by compressed air and fed into the soft soil while withdrawal of the mixing blades occurs at the same time. The treated soil is later cured under ambient effective stress before execution of construction works. Under this condition, the pore water pressure that is built up during mixing will gradually dissipate with curing proceeding in parallel. However, this situation is not readily simulated in the laboratory. This was highlighted by Tatsuoka and Kobayashi (1983), which the laboratory samples they prepared in their study were different in at least two points from the in-situ conditions, namely: “…….. (i) Although the in-situ stress condition may be anisotropic, triaxial specimens were isotropically consolidated (see Figure 2.21a). (ii) The dissipation of pore pressure and cementation take place simultaneously after mixing for in-situ soil. However, the triaxial specimens were cured under atmospheric pressure and then reconsolidated to effective stress; namely, specimens were re-consolidated after most of cementation took place (see Figure 2.21b). …” Nevertheless, Uddin et al. (1997), Yin and Lai (1998) and Kamruzzaman (2002) etc adopted the same approach as Tatsuoka and Kobayashi (1983). As noted by Bergado et al. (1996), specimens prepared under such condition may undergo post- 21 CHAPTER 2 curing degradation of soil structure under high confining pressure. At present, many researchers (e.g Leroueil and Vaughan 1990; Burland, 1990) have highlighted the important influence the ambient effective stress has on the behaviour of natural structured soils. Given this, it is perhaps not unreasonable to expect that effective stress may also have significant effects on the behaviour of improved soil during curing. Consoli et al. (2000) carried out some tests on cemented sand reproduced from laboratory and highlighted the importance of curing stress (Figure 2.22). They suggested that samples of cemented soils should be taken at different depths, to represent different geostatic stresses, and tested under their respective confining stresses for determination of their real behaviour. According to them, such a procedure is better than the samples taken from a depth and re-consolidated at different confining pressure, as to simulate different depths or geostatic stresses. This is because for sands with high permeability, dissipation of excess pore pressure with loadings could be expected. On the other hand, Tan et al. (2002) concluded that the effect of curing stress is negligible for low permeability clay in unconfined compressive test based on two samples which cured under 0kPa and 50kPa of curing load in an undrained condition (see Figure 2.23). However, because of the undrained conditions used in their study, it is likely that effective stress conditions in the specimens did not change significantly during curing. In contrast, Suzuki et al. (2004) and Chin et al. (2004) reported that the drained curing under confining stress improved both the compressibility and strength behaviour of cement treated clay, due to the densification of the soil skeleton. This 22 CHAPTER 2 again will depend on how much the excess pore water pressure will dissipate before the sample sets. Similarly, Bergado (2004) highlighted that the effect of drained curing stress could be replaced with different moisture content during mixing stage, but the specimens were cured under atmospheric stress condition. He proposed that parameters such as post-curing void ratio (eot) and cement content (Aw) should be used to characterize the strength and compressibility of high water content cementclay mixture in deep mixing. This is because these parameters combined together the influences of clay water content, cement content and curing time as well as curing stress. However, in their study, no theoretical basis was provided to explain the changes of void ratio during treatment period under various curing conditions, although the importance of void ratio on the post-cured mechanical behaviour of cement treated soil has been highlighted. Thus, although the effects of drained and undrained curing stress on mechanically behaviour of cement improved soils have been independently investigated, a framework to relate and generalize these curing conditions has not yet been established. Furthermore, a theoretical basis is needed to explain the mechanisms of cementation coupled with densification during the treatment period. In the field condition, the dissipation of pore water pressure in the treated soil mass before the material sets and cures depend on numerous factors such as permeability of the mixtures and the surrounding ground, speed of setting and proximity to drainage boundaries. Although it is unlikely to simulate exactly the complicated field boundary conditions in a laboratory, element testing however could be made to investigate both consolidation and chemical reactions effects on the properties and behaviour of cement treated soils in a well defined laboratory conditions, viz. drained, undrained 23 CHAPTER 2 and atmospheric curing conditions. In view of this, there is a need to further investigate the effects of different curing conditions, as well as to provide a framework that could be used to generalize the post-treatment mechanical behaviour of cement treated clay, especially under triaxial condition. This forms the theme of the first part of the present study. 2.5.2 Triaxial Behavioural Framework Much research works have been conducted into the constitutive behaviour of natural soils (e.g. Burland, 1990; Leroueil and Vaughan, 1990; Coop and Atkinson, 1993; Cotecchia and Chandler, 1997; Leroueil, 1997; Cuccovillo and Coop, 1999; Liu and Carter, 1999; Cotecchia and Chandler, 2000 etc…). However, much less has been done on cement-treated soft clays. Tatsuoka and Kabayashi (1983) suggested that the effective stress principle can be applied to analyze the behaviours of cement treated clay under drained and undrained conditions (see Figure 2.24). They found that the peak strength of the treated soil in both drained and undrained triaxial conditions increased with the amount of cement content. However, the peak strength envelope was a bilinear line. This is due to the fact that the undrained sample which was consolidated to low confining pressure normally failed near to or on the tension cutoff line. On the other hand, for drained triaxial, as the confining stress increases, the stress-strain relationship change from strain softening to strain hardening, while the volumetric strain changes from dilation to contraction (Figure 2.25). Such behaviour in turn caused the drained samples (with high confining stress) to fail at higher effective stress levels, far away from the tension cut-off line. Similarly, Yu et al. (1997) also observed the effect of confining pressure on the drained triaxial behaviour of cement treated soil. 24 CHAPTER 2 Uddin et al. (1997) investigated the effect of confining pressure on the pore pressure behaviour of cement treated marine clay (Figure 2.26). He noted that, at low confining pressure (about 50-100 kPa), the cement treated soil shows small positive pore pressure and then dropped to negative values after peak strength. On the other hand, at higher confining pressure, substantial excess pore pressure was generated prior to peak which was followed by dilatant behaviour after peak. In addition, for a given confining pressure, the dilation behaviour was found to increase with the amount of cement content, as shown in Figure 2.27. Kamruzzaman (2002) noticed that the undrained stress paths of cement treated soil under different cement contents actually followed a similar pattern of behaviour (Figure 2.28). The increase in the confining stress changes the behaviour of the specimens from an “over-consolidated” type, characterized by dilatant and negative excess pore pressure, to a “normally consolidated”, characterized by compression and positive excess pore pressure. Undrained stress path was often observed to reach a peak stress either near to the tension cut-off line or on the Hvorslev envelope. Beyond peak, strain softening dictated the behaviour. However, in Kamruzzaman’s (2002) study, there was no further test conducted to include for the triaxial drained condition. As such, no framework or explanation was provided to generalize both undrained and drained stress paths under different loading conditions, nor for the specimens cured under different curing stresses. Furthermore, the microstructure of cement or lime treated soils has been investigated by a number of researchers (e.g. Locat et al., 1996; Rajasekaran and 25 CHAPTER 2 Narasimha Rao, 2000; Chew et al., 2004). A flocculated structure is often observed, leading to postulation of significant intra-aggregate pore or water trapped inside the cluster of aggregate. While the increment in strength has frequently been explained through microstructure and cement-soil chemical reactions, the changes to the microstructure during different curing and loading conditions have not been widely researched. As such, the details of the degradation of soil microstructure during different loading conditions remain largely unknown. Presently, there is as yet no complete framework of behaviour for cement treated clay. The second part of this study is focused on the microstructural changes as well as constitutive behaviour of cement-treated soil specimens. This is undertaken with a view to enhancing the current understanding, with an objective that some form of framework for cement treated clay can be established. 26 CHAPTER 3 EXPERIMENTAL METHODOLOGY AND SETUP 3.1 Properties of Base Materials 3.1.1 Untreated Marine Clay The untreated marine clay used in the present study was collected from 4 to 5m depth below seabed, at a dredge site offshore of Pulau Tekong. According to the subsoil condition of Singapore, the sediment is deposited around 10,000 years ago (Pitts, 1992; Tan et al., 2003), which is known as Singapore upper marine clay of Kallang formation. Upon collection, the basic properties were determined. Table 3.1 summarizes the basic properties of the untreated marine clay used in this study. Table 3.1: Basic properties of Singapore upper marine clay Properties Values Properties Values Liquid Limit, LL (%) Plastic Limit, LL (%) Plasticity Index, PI (%) Moisture Content, m (%) Liquidity Index, IL Initial void ratio, eo Specific gravity, Gs 90 40 50 72 0.64 1.93 2.68 Grain Size Distribution: Sand (%) Silt (%) Clay (%) Total Unit weight, γb (kN/m3) Dry Unit weight, γd (kN/m3) K0 7 71 22 15 8.72 0.62 3.1.2 Ordinary Portland Cement The additive used to treat Singapore upper marine clay in this study is Ordinary Portland Cement (OPC). The definition of cement content ( Ac ) used in this study is the ratio of dry weight of cement to the dry weight of clay particles and is expressed in percentage. The chemical compositions and physical properties of OPC obtained from supplier are given in Table 3.2. CHAPTER 3 Table 3.2: Chemical compositions and physical properties of Ordinary Portland Cement Chemical compositions Values Physical Properties Values Lime Saturation Factor (L.S.F) Magnesia, MgO (%, m/m) Sulphuric Anhydride as SO3 (%, m/m) Loss on Ignition (%, m/m) Silica, SiO2 (%, m/m) Calcium Oxide, CaO (%, m/m) Iron Oxide, Fe2O3 (%, m/m) Aluminium Oxide, Al2O3 (%, m/m) 0.95 1.9 2.5 29.0 7 155 1.3 20.7 64.6 2.4 5.8 Sodium Oxide, Na2O (%, m/m) 0.53 Consistency (%) Penetration (mm) Initial Setting Time (min) Final Setting Time (min) Soundness (mm) Fineness (m2/kg) Specific Gravity, Gs 2-days Strength (N/mm2) 28-days Strength (N/mm2) Potassium Oxide, K2O (%, m/m) 0.45 3.2 185 > 2) failed near the tensile failure envelope. The post-peak stress path is quite variable, but many show a slight increase in mean effective stress towards the ultimate failure. This is suggestive of dilatancy near ultimate failure. 2. CIU specimens which were sheared at lower OCR of ~2 show stiff response up to a peak strength. Their stress path is roughly vertical, which suggests largely elastic behaviour up to the peak strength. The post-peak stress path shows either almost no change or else a slight decrease in the mean effective stress. 115 CHAPTER 7 3. CIU specimens which were sheared normally consolidated or slightly overconsolidated also show a stiff response up to a peak strength, but their stress paths trace out a curved line which resembles the cap of a yield surface, thereby suggesting plastic behaviour. The post-peak stress path usually shows a slight decrease in the mean effective stress. 4. CID specimens which were sheared at high OCR (say ~10) also show stiff response up to peak strength. The post-peak strain softening region is accompanied by volumetric dilation. 5. CID specimens which were sheared at lower OCR show a peak strength which occurs well after the elastic-plastic transition points. The elasticplastic transition points are marked by large volumetric compression up to the peak stress, followed by a slightly volumetric increase at post-peak, presumably as a result of swelling induced by unloading. 6. A yield locus can be deduced by connecting up the peak stress points of CIU specimens and CID specimens sheared at high OCR, as well as the elasticplastic transition points. (g) The normalized stress paths for volume p*’e and initial stress sensitivity Sσ in the current study show that the behavioural framework for natural soils postulated by Cotecchia and Chandler’s (2000) could not be applied in its entirety, in particular for drained sheared specimens with low OCR. It was found that the constant stress sensitivity Sσ used in Cotecchia and Chandler’s (2000) framework only accounts for the initial soil structure after consolidation, but not the change in soil structure arises from drained shearing. This is supported from both SEM observations and pore structure analysis which indicate significant 116 CHAPTER 7 microstructure changes during shearing were associated with volumetric changes. (h) The proposed behavioral framework for cement treated clay, which uses p*’e and current stress sensitivity α (α varying with specific volume) as normalization parameters, shows that the normalized stress paths for both undrained and drained shearing follow a similar pattern of behaviour. This could adequately be described by a general gross yield locus or yield loci on the State Boundary Surface (SBS). The triaxial data of Kamruzzaman (2002) also agree well with the proposed normalization procedures. (i) Post-peak strain softening behaviour of cement treated clay is associated with rupturing. A progressive decrease in the post-peak friction coefficient (Mr) with rupturing was obtained. The SEM observations indicate that the break-up of aggregates into smaller aggregates and particles, thus a finer particulate texture on the rupture surface was seen as rupturing is progressed. (j) The post-ruptured ultimate strength envelope for cement treated clay was not a straight line. In all cases, the frictional coefficient is near to or above the critical state frictional coefficient of the untreated marine clay. This is also mirrored in the microstructure of specimen sheared at low mean normal effective stress, where a highly aggregated structure still remains, vis a-vis the much finer texture for specimens sheared to failure at high mean normal effective stress. 7.2 (a) Recommendations for Future Study The behavioural framework postulated for cement-treated clay in this study is based on 20% cement content and 7-day curing period. Since the strength property of the treated soil is dependent on both cement content and curing 117 CHAPTER 7 period, it is uncertain whether the framework which uses normalization procedures could also be applied to various configurations of cement-treated soils. This issue is therefore necessary for further research. (b) The cement-treated clay sample prepared in this study is more representative of deep mixing method. A further study could be made to include for high cement content as well as high water/cement ratio to simulate the operations of jet grouting. Furthermore, the triaxial behaviour of in-situ cement-treated specimens is essential for investigation, in a way such that the field samples are also conformed to the proposed behavioural framework. (c) A constitutive model for cement treated clay under triaxial loadings could be formulated based on the constitutive behavior presented in the study. This is necessary such that the improved ground could be reasonably incorporated into finite element analysis. 118 FIGURES Figure 2.1: Schematic illustrations of improved soil (after Saitoh et al., 1985) Figure 2.2: SEM micrographs of lime improved soil (after Locat et al., 1990) 119 FIGURES Figure 2.3: Factors control the properties of cement treated soil (after Kezdi, 1979) Figure 2.4: In-situ mixing tools for soil cement mixtures (after Porbaha et al., 2001) 120 FIGURES Figure 2.5: Effect of cement type on compressive strength of soil-cement for: (a) Kanagawa; and (b) Saga soils (after Kawasaki et al., 1981) Figure 2.6: Effect of different stabilizers on compressive strength of different soils in Sweden (after Ahnberg et al., 1995) 121 FIGURES Figure 2.7: Effect of grain size distribution on cement stabilization (after Niina et al., 1977) Figure 2.8: Effect of soil types on cement stabilization (after Taki and Yang, 1991) 122 FIGURES Figure 2.9: Effect of initial water content on cement stabilization (after Endo, 1976) Figure 2.10: Effect of initial water content on cement stabilization (after Terashi et al., 1980) 123 FIGURES Figure 2.11: Effect of mixing time on lime stabilization (after Terashi et al., 1977) Figure 2.12: Effect of mixing time on cement stabilization (after Nakamura et al., 1982) 124 FIGURES Figure 2.13: Effect of blade rotations on in-situ strength (after Mizuno et al., 1988) Figure 2.14: Effect of curing time on strength (after Kawasaki et al., 1981) 125 FIGURES Figure 2.15: Effect of curing temperature on strength (after Saitoh et al., 1980) Figure 2.16: Effect of curing temperature on compressive strength of silt (after Enami et al., 1985) 126 FIGURES Figure 2.17: Correlation of unconfined compressive strength between in-situ and laboratory treated soil (after CDM, 1994) Figure 2.18: Effect of cement content on 1-D eodometer compression curve (after Uddin et al., 1997) 127 FIGURES Figure 2.19: Triaxial behaviour of treated clay under (a) drained; and (b) undrained conditions (after Endo, 1976) Figure 2.20: Effect of strain measurements on modulus of cement treated soil (after Tatsuoka et al., 1997) 128 FIGURES In-situ σ’v=γ’h h σ’ σ’h=Koσ’v In-situ This investigation This investigation σ'c Mixing σ’c Cured 28 days Time σ’c Figure 2.21: Comparisons of stress condition between in-situ and laboratory (reproduced from Tatsuoka and Kobayashi, 1983) Figure 2.22: Peak strength envelopes for specimens cured under or without stress (after Consoli et al., 2000) 129 FIGURES Figure 2.23: Effect of undrained curing condition (after Tan et al., 2002) Figure 2.24: Peak strength envelope on effective stress plane (after Tatsuoka and Kobayashi, 1983) 130 FIGURES Figure 2.25: Consolidated drained triaxial behaviour with different confining pressures (after Tatsuoka and Kobayashi, 1983) 131 FIGURES Figure 2.26: Pore pressure responses with different confining pressures (after Uddin et al., 1997) Figure 2.27: Pore pressure responses with different cement contents (after Uddin et al., 1997) 132 FIGURES Figure 2.28: Undrained stress path behaviour of cement treated clay for (a) 10%; (b) 30%; and (c) 50% of cement contents (after Kamruzzman, 2002) 133 FIGURES Figure 3.1: Demoulding the soil-cement sample for isotropic load-curing 1 Mean, µ = 1.29% Standard deviation, σ = 0.46% Normal distribution, f(x) 0.8 0.6 0.4 P(X>2%)=0.06 0.2 0 0.4 0.8 1.2 1.6 2 2.4 2.8 Air content (%) Figure 3.1A: Distribution curve of air content (in percentage) within cement-clay mixtures just after mixing 134 FIGURES 10 Volumetric water / Solids ratio 8 bleeding limit 6 workable range 4 current study 2 liquid limit 0 0 0.2 0.4 0.6 0.8 1 Cement Content, C/(S+C) Figure 3.1B: Liquid and bleeding limits of fresh cement-slurry clay mixes (reproduced from Chew et al., 1997) Figure 3.2: Laser diffraction Malvern Mastersizer for grain size analysis 135 FIGURES Figure 3.3: A fully computer controlled triaxial stress path apparatus Figure 3.4: Hitachi 4100 Field Emission Scanning Electron Microscope (FESEM) 136 FIGURES Figure 3.5: Mercury Intrusion Porosimeter (Micromeritics Autopore III 9420) for pore size analysis Figure 3.5A: Degree of hydration with time (Sun et al., 2004) 137 Vs soil (solid) Ms (a) Vw,s water from soil Mw,s Vc Vw,c cement water from cement slurry Mc Mw,c basic components (b) soil (solid) cement Vs Vc Vw,s+c Ms+c Mw,cc (c) soil + cement (solid) remaining water after curingconsolidation water expelled Vs+c Vw,cc ∆Vcc Stage-2 just after mixing and curing-consolidation Msc Mw,a+g soil-cement mixtures (solid) available water and gel water Vsc Vw,a+g empty capillary pores Vep (d) = Msc Mw,sc Stage-3 after certain curing period (drained condition) Figure 4.1: Basic volume-mass model for cement treated clay (drained condition) Ms Mc Mw,s+c water from soil and slurry cement Stage-1 just before mixing soil-cement mixtures (solid) water in soil-cement mixtures Vsc Vw,sc FIGURES 138 Vs soil (solid) Ms (a) Vw,s water from soil Mw,s Vc Vw,c cement water from cement slurry Mc Mw,c basic components (b) soil (solid) cement Vs Vc Vw,s+c Ms+c Mw,s+c (c) soil + cement (solid) Vs+c water from soil V and slurry cement w,s+c Stage-2 just after mixing without curing-consolidation (undrained condition) Msc Mw,a+g soil-cement mixtures (solid) available water and gel water Vsc Vw,a+g empty capillary pores Vep (d) = Msc Mw,sc Stage-3 after certain curing period (undrained condition) Figure 4.2: Basic volume-mass model for cement treated clay (undrained condition) Ms Mc Mw,s+c water from soil and slurry cement Stage-1 just before mixing soil-cement mixtures (solid) water in soil-cement mixtures Vsc Vw,sc FIGURES 139 120 3.2 100 2.8 80 2.4 Void ratio, e Moisture content, m (%) FIGURES 60 2 1.6 40 Measured Measured Predicted 20 Predicted 1.2 loaded-drained loaded-drained loaded-undrained loaded-undrained 0.8 0 0 100 200 (a) 300 400 500 0 600 100 200 (b) Loaded curing stress, pcure (kPa) 16.4 300 400 500 600 500 600 Loaded curing stress, pcure (kPa) 3 Measured Measured Predicted Predicted loaded-drained 16 loaded-drained loaded-undrained 2.8 Specific gravity, Gs Bulk density, γb (kN/m 3) 15.6 15.2 2.6 14.8 2.4 14.4 14 2.2 0 100 200 (c) 300 400 Loaded curing stress, pcure (kPa) 500 600 0 100 200 (d) 300 400 Loaded curing stress, pcure (kPa) Figure 4.3: Predicted and measured volume-mass properties of cement treated clay under loaded-drained and loaded undrained curing conditions 140 FIGURES 3.5 Measured and predicted after 7-day curing estimated hydration = 60% +10% moisture content, m 3 bulk density, γb (g/cm3) void ratio, e specific gravity, Gs 2.5 Test measurement 1:1 dry density, γd (g/cm3) -10% 2 1.5 1 0.5 0 0 0.5 1 1.5 2 2.5 3 3.5 Model prediction Figure 4.4: Comparisons between predicted and measured volume-mass properties of cement treated clay 3 3 specimen cured without stress (atmospheric pressure curing) 2.8 2.8 Specific gravity, Gs Specific gravity, Gs predicted wet method 2.6 dry method 2.6 dry method 2.4 2.4 2.2 2.2 0 100 200 (a) 300 400 Loaded-drained curing stress, p'cure (kPa) 500 600 0 100 200 300 (b) 400 500 600 700 800 Suction, mmHg Figure 4.5: Measured specific gravity using (a) both wet and dry methods with loaded-drained curing stresses; and (b) dry method with different episodes of vacuum suction 141 FIGURES 3 2.8 Specific gravity, Gs predicted wet method 2.6 dry method 2.4 2.2 0 5 10 15 20 25 Cement content, Ac (%) Figure 4.6: Measured specific gravity using both wet and dry methods together with predicted values for different cement contents 4 Zero curing-consolidation strain hydration during curing period Specific volume, ν=1+e 3.6 Curing-Consolidation Line (CCL) 3.2 2.8 initial after mixing 2.4 just after curing-consolidation end of 7-day curing period (loaded-undrained) end of 7-day curing period (loaded-drained) 2 1 10 100 1000 Loaded curing stress, p'cure (kPa) Figure 4.7: End states of treated specimens cured under various curing conditions 142 (a) (b) (c) (d) Figure 4.8: Microsturcture of specimens after various loaded-drained curing stresses (a) 0CON0; (b) 50CON0; (c) 250CON0; and (d) 500CON0 FIGURES 143 FIGURES 1 0CON0 50CON0 100CON0 500CON0 0.8 Finer than 0.6 0.4 medium pore small pore large pore 0.2 0 0.001 0.01 0.1 1 10 100 Pore radii, µm Figure 4.9: Pore size distribution for specimens cured under various stress states 3 0CON0 50CON0 100CON0 500CON0 Void ratio (finer than) 2 1 small pore medium pore large pore 0 0.001 0.01 0.1 1 10 100 Pore radii, µm Figure 4.10: Relationship of void ratio and pore radii 144 FIGURES 2.8 xCONx xCON30 x=30 2.4 Void ratio, e x=50 e=0.227lnk + 1.777 x=100 2 x=250 1.6 x=500 unloading e=0.354lnk + 1.414 1.2 0.1 1 10 Permeability, k (x10 -10 m/s) 100 Figure 4.11: Permeability - void ratio relationship under various stress states 100 Untreated marine clay OPC (cement) cement-clay mixture in ethanol just mixed derived cement-clay mixtures Finer than, % 80 60 40 20 0 0.1 1 10 Particle size, µm 100 1000 Figure 4.12: Grading curves for untreated marine clay, cement particles, cement-clay mixtures and cement-clay particles in ethanol 145 FIGURES 100 cement-clay mixture in ethanol 15 mins 30 mins 45 mins 1 hr 2 hrs 4 hrs Finer than, % 80 60 40 20 0 0.1 1 10 Particle size, µm 100 1000 Figure 4.13: Grading curves for cement treated clay with different remoulding periods 100 cement-clay mixture in ethanol 4 hrs 4 hrs + UD 1min 4 hrs + UD 2mins 4 hrs + UD 5mins 4 hrs + UD 10mins Finer than, % 80 60 40 20 0 0.1 1 10 Particle size, µm 100 1000 Figure 4.14: Grading curves for cement treated clay with ultrasonic dispersion 146 FIGURES 130 Liquid Limit, LL (%) 125 120 115 110 105 0 50 100 150 200 250 300 Remoulding period, mins Figure 4.15: Changes of liquid limit at different remoulding periods 100 cement-clay mixture in ethanol 45 mins 1 hr 0CON0 50CON0 100CON0 250CON0 500CON0 Finer than, % 80 60 40 20 0 0.1 1 10 Particle size, µm 100 1000 Figure 4.16: Grading curves for the treated specimens with various loadeddrained curing stresses, after approximately 1-hour remoulding period 147 FIGURES 70 CE 60 ME freshly mixed untreated clay 50 CV Plasticity index, % 0CON0 40 MV CH 250CON0 50CON0 500CON0 100CON0 30 CI MH 20 10 MI CL ML 0 0 20 40 60 80 Liquid limit, % 100 120 140 Figure 4.17: Plasticity chart for cement treated clay under various stress states during curing period 1100 Drained isotropic curing stress, p'cure without curing stress p'cure=50kPa 1000 p'cure=100kPa 900 p'cure=250kPa p'cure=500kPa 700 600 Unload elastically (sweating disappear) Localisation of strain at rupture plane flaws start to form and propagate 500 Axial stress, σa (kN/m2) Axial stress, σa (kN/m2) 800 400 300 Rupture plane Intact part Specimen breaks apart whole intact specimen been compressed 200 Axial strain, εa (%) 100 0 0 1 2 3 4 5 6 7 8 Axial strain, εa (%) Figure 4.18: UCT results for specimens treated under drained isotropic curing stress 148 FIGURES 1400 Isotropic loaded-drained with S:C:W=5:1:6 Isotropic loaded-undrained with S:C:W=5:1:6 1200 Isotropic loaded-drained with S:C:W=5:1:5.8 UCT peak strength, kN/m2 1000 800 fitted qu,peak=12560/1.046mc for Aw=20% and T=7 days 600 400 200 0 50 60 70 80 90 100 Post-cured moisture content, m c (%) Figure 4.19: Generalisation of UCT peak strength with post-cured moisture content 5000 Parameters Unconfined Compressive Strength, kN/m2 s/c=1 4000 Lee et al.'s Current study (2005) study q0 4,000 kPa m 0.62 0.6 n 3.0 3.2 4,000 kPa s/c=2 s/c=4 3000 current study s/c=5 (fitted) s/c=5 2000 1000 0 1 2 3 4 5 6 7 8 9 Water / Cement Ratio Figure 4.20: Generalisation of UCT strength into Lee et al.’s (2005) framework 149 FIGURES 2 Horten clay (LL=30%, PL=16%) 1.8 London clay (LL=73%, PL=25%) Shellhaven clay (LL=97%, PL=32%) 1.6 Gosport clay (LL=80%, PL=30%) Liquidity index, IL 1.4 Wood (1990) cu=2x100(1-IL) kPa 1.2 Liquid limit 1 Cement treated clay (current study) 0.8 0.6 0.4 0.2 Plastic limit 0 -0.2 0.1 1 10 100 1000 Undrained shear strength, cu (kN/m2) Figure 4.21: Variation of undrained shear strength for remoulded soils and cement treated clay with liquidity index; remoulded soils data obtained from Skempton and Northey (1953) 3.8 PYCL CCL 3.6 Specific volume, ν 3.4 3.2 3 hydration effect during treatement period 2.8 0CON0 50CON0 100CON0 250CON0 500CON0 U100CON0 U500CON0 end states after 7-D treament Curing-consolidation points Gross-yield points (Average value) 2.6 2.4 2.2 1 2 5 10 20 50 100 200 500 1000 2000 5000 Consolidation pressure, p' (kN/m2) Figure 4.22: Isotropic compressive behaviour of cement-treated specimens cured under various curing conditions 150 FIGURES 4 3.6 Specific volume p'gy 3.2 2.8 2.4 2 1 10 100 1000 10000 Consolidation pressure, p' (log scale) (a) 4 parallel to ICL ICL 3.6 Specific volume p'gy 3.2 2.8 2.4 2 1 10 100 1000 10000 Consolidation pressure, p' (log scale) (b) 3.4 p'gy Specific volume 3.2 3 2.8 2.6 2.4 0 400 800 1200 1600 2000 Consolidation pressure, p' (linear scale) (c) Figure 4.23: Determination of gross-yield point through (a) Standard Casagrande method; (b) Cotechia and Chandler’s (2000) method; and (c) Rotta et al.’s (2003) method 151 FIGURES 1200 Solid line: with curing stress, pcure'= 50, 100, 250, 500kPa and consolidated at p0'= 50, 100, 250, 500kPa respectively 1100 Dashed line: without curing stress consolidated at p0'= 50, 100, 250, 500kPa 1000 Deviatoric stress, q (kN/m2) 900 800 700 600 500 400 300 200 100 0 0 0.02 0.04 0.06 0.08 0.1 0.12 0.14 0.16 0.18 0.2 Deviatoric strain, εq (a) 1400 500 Solid line: with curing stress, pcure'= 50, 100, 250, 500kPa and consolidated at p0'= 50, 100, 250, 500kPa respectively 1300 Solid line: with curing stress 1200 Dashed line: without curing stress consolidated at p0'= 50, 100, 250, 500kPa 400 1000 Consolidated at p o' po'=50kPa p'cure & p'o=100kPa po'=100kPa p'cure & p'o=250kPa po'=250kPa p'cure & p'o=500kPa po'=500kPa 350 pore pressure, u (kPa) Deviatoric stress, q (kN/m2) 1100 Dashed line: without curing stress Cured and consolidated at p'cure & p'o=50kPa 450 900 800 700 600 tension cut off line 500 300 250 200 150 400 300 100 200 50 100 0 0 0 100 200 300 400 Mean normal effective stress, p' (kN/m2) (b) 500 600 0 0.02 0.04 0.06 0.08 0.1 0.12 0.14 0.16 0.18 Deviatoric strain, εq (c) Figure 4.24: Consolidated undrained triaxial behaviour for specimens cured with and without load; (a) stress-strain; (b) stress path; and (c) pore pressure - strain 152 0.2 FIGURES 1200 Solid line: CIU test Dashed line: UCT test 1100 De vi atoric stre ss, q (kN /m 2) p'cure=50 kPa 1000 p'cure=100 kPa 900 p'cure=250 kPa p'cure=500 kPa 800 700 600 500 400 300 200 100 0 0 0.02 0.04 0.06 0.08 0.1 0.12 0.14 0.16 0.18 0.2 Deviatoric strain, εq Figure 4.25: Comparisons of stress – strain behaviour from both CIU and UCT tests (specimens cured under loaded-drained condition) 153 FIGURES 1800 solid line with curing stress, pcure' = p0' dashed line without curing stress, p0' 1600 50kPa 100kPa 250kPa 500kPa 50kPa 100kPa 250kPa 500kPa Deviatoric stress, q (kN/m2) 1400 1200 1000 800 600 400 200 0 0 0.02 0.04 0.06 0.08 0.1 0.12 0.14 0.16 0.18 0.2 0.22 0.24 0.26 0.28 0.3 Deviatoric strain, εq (a) Mean normal effective stress, p' (kPa) 0 200 400 600 800 1000 1200 0.2 0.2 0.16 Volumetric strain, εv 0.14 0.12 0.1 0.18 0.16 50kPa 100kPa 250kPa 500kPa 50kPa 100kPa 250kPa 500kPa 0.14 Volumetric strain, εv 0.18 solid line with curing stress, pcure' = p0' dashed line without curing stress, p0' 0.08 0.12 solid line with curing stress, pcure' = p0' dash line without curing stress, p0' 0.1 0.08 50kPa 100kPa 250kPa 500kPa 50kPa 100kPa 250kPa 500kPa 0.06 0.06 0.04 0.04 0.02 0.02 0 0 0 0.02 0.04 0.06 0.08 0.1 0.12 0.14 0.16 0.18 0.2 0.22 0.24 0.26 Deviatoric strain, εq (b) (c) Figure 4.26: Consolidated drained triaxial behaviour for specimens cured with and without load; (a) stress-strain; (b) compression path; and (c) volumetric-deviatoric strains 154 FIGURES (a) (b) (d) (c) Figure 5.1: Artificial flocculated treated soil structure with trapped intra-aggregate pore 4.4 4.2 Curve-C 4 PYCL 3.8 CCL isotropic gross yield (430 kPa) Curve-B 3.6 Specific volume, ν 3.4 3.2 3 2.8 2.6 Curve-A 2.4 2.2 untreated marine clay ν at LL~3.25 2 1.8 0CON0 Untreated marine clay curing-consolidation points 0CON0 remoulded 1.6 1.4 1 2 5 10 20 50 100 200 500 1000 2000 5000 Consolidation pressure, p' (kN/m2) Figure 5.2: Isotropic compression curves for untreated specimen, 0CON0 treated specimen and remoulded 0CON0 specimen 155 FIGURES Figure 5.3: Cluster of aggregates seen in remoulded 0CON0 specimen 6 p'gy = 430 kPa 5 Stress sensitivity, Sσ 4 3 2 1 0 0 500 1000 1500 2000 Isotropic compression stress, p'o (kPa) Figure 5.4: Decrease of stress sensitivity after isotropic gross yield 156 (b) (c) (d) Figure 5.5: SEM micrographs at different isotropic compression pressures: (a) 0CON0; (b) 0CON50; (c) 0CON500; and (d) 0CON1500 (a) FIGURES 157 FIGURES 4.4 4.2 4 PYCL 3.8 CCL isotropic gross yield (430 kPa) 3.6 Specific volume, ν 3.4 3.2 3 2.8 2.6 2.4 2.2 2 0CON0 specimen 1.8 Curing-consolidation points 1.6 SEM points 1.4 1 2 5 10 20 50 200 100 500 1000 2000 5000 Consolidation pressure, p' (kN/m2) Figure 5.6: Changes of microstructures with isotropic compression pressures 1 0.8 Finer than 0.6 small size pore medium size pore large size pore 0.4 0CON0 0CON50 0CON500 0CON1500 50CON0 500CON0 0.2 0 0.001 0.01 0.1 1 10 100 Pore radii, µm Figure 5.7: Changes of pore size distributions with isotropic compression pressures 158 FIGURES 2.8 p'gy = 340 kPa (average) 2.4 Void ratio, e p'gy = 800 kPa (average) 2 Line-A e=0.227lnk + 1.777 1.6 Loaded-drained curing 0CONY 100CONY 1.2 0.1 1 10 100 Permeability, k (x10-10 m/s) Figure 5.8: Permeability – void ratio behaviour under isotropic compression pressures 100 cement-clay mixutre in ethanol 45 mins remoulding 1 hour remoulding 0CON0 0CON50 0CON500 0CON1500 Finer than, % 80 60 40 20 0 0.1 1 10 100 1000 Particle size, µm Figure 5.9: Grading curves for 0CONY specimens, after remoulding for about 45 minutes to 1 hour 159 FIGURES 70 CE 60 ME untreated clay 50 freshly mixed CV Plasticity index, % 0CON0 0CON50 40 MV CH 0CON1500 (4) 30 (3) 0CON500 (1) (2) MH CI 20 load-cured specimens (1) 50CON0 10 (2) 100CON0 MI CL (3) 250CON0 (4) 500CON0 ML 0 0 20 40 60 80 Liquid limit, % 100 120 140 Figure 5.10: Atterberg’s limits for treated specimens subjected to isotropic compression pressures 400 300 CCL-CIU50 CCL-CIU100 CCL-CIU250 CCL-CIU400-300 CCL-CIU50 CCL-CIU100 CCL-CIU250 CCL-CIU400-300 250 Pore pressure, u (kN/m 2) Deviator stress, q (kN/m 2) 300 200 200 150 100 100 50 0 0 0 0.05 0.1 0.15 Deviatoric strain, εs 0.2 0.25 0 0.05 0.1 0.15 0.2 0.25 Deviatoric strain, εs Figure 5.11: Undrained triaxial behaviour for pre-cured soil-cement mixtures: (a) stress-strain; (b) pore pressure - strain 160 FIGURES 500 CCL-CIU50 CCL-CIU100 CCL-CIU250 CCL-CIU400-300 peak points Critical state points Deviator stress, q (kN/m2) 400 300 Curing-consolidation strength (CCS) 200 Critical State Line (CSL) 100 0 0 100 200 300 400 Mean normal effective stress, p' (kN/m2) Figure 5.12: Undrained stress paths, peak strength envelope and critical state line for pre-cured soil-cement mixtures 2 1.6 tension cut-off line 1.2 q/pe'* pre-cured SBS 0.8 0.4 0 0 0.4 0.8 1.2 p'/pe'* Figure 5.13: Normalised stress paths and state boundary surface for precured specimens 161 FIGURES 1200 Ko consolidation Ko gross yield point 1000 ηΚ =1.24 ο Ko=0.31 tension cut-off line η=3 and Ko=0 Deviator stress, q (kN/m2) 800 ηΚ =1.5 ο Ko=0.25 600 unloading 400 200 isotropic compression line η=0 and Ko=1 0 0 200 400 600 800 1000 Mean normal effective stress, p' (kN/m2) Figure 5.14: Stress path under Ko consolidation test with unloading 3.8 parallel to CCL 3.6 3.4 Specific volume, ν CCL 3.2 3 2.8 gross yield points 2.6 isotropic compression Ko compression 2.4 η=1.75 η=1.5 2.2 1 2 5 10 20 50 100 200 500 1000 2000 5000 Consolidation pressure, p' (kN/m2) Figure 5.15: Compression paths for the treated specimens undergo different constant η test, together with their gross yield points 162 FIGURES 800 gross yield points 700 gross yield locus 600 gross yield locus Deviator stress, q (kN/m2) tension cut-off line 500 400 300 200 100 0 0 100 200 300 400 500 Mean normal effective stress, p' (kN/m2) Figure 5.16: Gross yield locus for cement treated clay 1000 0CID50 0CID100 0CID250 0CIU50 0CIU100 0CIU250 800 Deviator stress, q (kN/m2) gross yield points gross yield locus 600 tension cut-off line 400 200 p'gy=430kPa 0 0 100 200 300 400 500 600 Mean normal effective stress, p' (kN/m2) Figure 5.17: Undrained and drained stress paths behaviour consolidated at pregross yield (specimens cured under atmospheric pressure) 163 FIGURES 7 0CID50 0CID100 0CID250 0CIU50 0CIU100 0CIU250 6 gross yield points gross yield locus pre-cured specimens tension cut-off line 5 q/p'*e 4 3 2 1 p'gy=430kPa 0 0 1 2 3 4 5 p'/p '*e Figure 5.18: Normalised stress paths behaviour consolidated at pre-gross yield (specimens cured under atmospheric pressure) 3 gross yield points gross yield locus 250CID50 250CID500 250CID1000 250CIU50 250CIU500 250CIU1000 2 q/p'*e tension cut-off line 1 p'gy=1309kPa 0 0 0.4 0.8 1.2 1.6 2 p'/p'*e Figure 5.19: Normalised stress paths behaviour consolidated at pre-gross yield (specimens cured under 250kPa confining pressure) 164 0 200 600 800 (c) (a) Mean normal effective stress, p' (kN/m2) 400 SBS tension cut-off line 1000 1200 0 0.1 0.2 0.3 post- gross yield (loaded 500kN/m2) 0cid500 0cid500-250 0cid500-50 0ciu500 0ciu500-250 0ciu500-100 0iso-com (b) Deviatoric strain, εs Figure 5.20: Triaxial behaviour for treated specimens consolidated at post-gross yield, with maximum 500kPa consolidation pressure 2.6 2.8 3 3.2 3.4 3.6 0 400 800 1200 1600 Specific volume, ν Deviator stress, q (kN/m2) 2000 FIGURES 165 0 200 400 800 1000 1200 1400 1600 (c) (a) Mean normal effective stress, p' (kN/m2) 600 SBS tension cut-off line 1800 2000 2200 0 0.05 0.15 0.2 (b) Deviatoric strain, εs 0.25 post- gross yield (loaded 1000kN/m2) 0cid1000 0cid1000-500 0cid1000-50 0ciu1000 0ciu1000-500 0ciu1000-50 0iso-com 0.1 0.3 Figure 5.21: Triaxial behaviour for treated specimens consolidated at post-gross yield, with maximum 1000kPa consolidation pressure i 2 2.4 2.8 3.2 3.6 0 1000 2000 3000 Specific volume, ν Deviator stress, q (kN/m2) 4000 0.35 FIGURES 166 1.6 2 2.4 2.8 3.2 3.6 0 1000 2000 3000 4000 Specific volume, ν Deviator stress, q (kN/m2) 5000 200 400 600 (c) (a) Mean normal effective stress, p' (kN/m2) 800 1000 1200 1400 1600 1800 2000 2200 2400 2600 2800 3000 0 0.05 0.15 0.2 (b) Deviatoric strain, εs 0.25 post- gross yield (loaded 500kN/m2) 0cid1500 0cid1500-500 0cid1500-50 0ciu1500 0ciu1500-500 0ciu1500-50 0iso-com 0.1 0.3 Figure 5.22: Triaxial behaviour for treated specimens consolidated at post-gross yield, with maximum 1500kPa consolidation pressure 0 SBS tension cut-off line 0.35 FIGURES 167 FIGURES 8 0cid500 0cid500-250 0cid500-50 0ciu500 0ciu500-250 0ciu500-50 7 6 tension cut-off line Idealized SBS q/pe*' 5 4 3 2 1 0 0 1 2 3 4 5 p'/pe*' (a) 8 0cid1000 0cid1000-500 0cid1000-50 0ciu1000 0ciu1000-500 0ciu1000-50 7 6 tension cut-off line q/pe*' 5 Idealized SBS 4 3 2 1 0 0 1 2 3 4 5 p'/pe*' (b) 8 0cid1500 0cid1500-500 0cid1500-50 0ciu1500 0ciu1500-500 0ciu1500-50 7 6 tension cut-off line q/pe*' 5 4 Idealized SBS 3 2 1 0 0 1 2 3 4 5 p'/pe*' (c) Figure 5.23: Normalized stress paths behaviour consolidated at post-gross yield, with maximum consolidation pressure: (a) 500kPa; (b) 1000kPa; and (c)1500kPa 168 FIGURES 1.6 consolidated at pre-gross yield consolidated at post-gross yield p'gy=430kPa p'o=500kPa p'gy=732kPa p'o=1000kPa p'gy=1309kPa p'o=1500kPa tension cut-off line 1.2 gross yield locus q/p*'e/Sσ 0CID250 0CID1500-500 0CID500-250 0.8 250CID1000 0CID1000-500 0CID500 0CID1000 0CID1500 0.4 0 0 0.2 0.4 0.6 0.8 1 p'/p*'e/Sσ Figure 5.24: Peak strengths of the treated specimens consoidated at both pre- and post-gross yield, after normalized for volume and initial stress sensitivity 169 FIGURES 5000 OCR=1 A 0CID1500 Mpeak=1.47 Deviatoric stress, q (kN/m2) 4000 tension cut-off line 0CID1000 Mpeak=1.62 3000 peak strength envelope (OCR=1) 2000 0CID500 Mpeak=1.61 0CIU1500 Mpeak=1.91 1000 0CIU1000 Mpeak=2.02 B 0CIU500 Mpeak=2.43 C 0 O 0 1000 (a) 2000 3000 Mean normal effective stress, p' (kN/m2) 4 peak strength (OCR=1) p'≅po'/2 3.6 0CIU500 Specific volume, ν 3.2 0CIU1000 0CIU1500 2.8 0CID500 2.4 0CID1000 isotropic compression of 0CON0 specimen PYCL CCL OCR=1 2 0CID1500 1.6 20 10 (b) 30 50 100 200 300 500 1000 2000 3000 5000 Mean normal effective stress, p' (kN/m2) Figure 5.25: Peak strength envelope for treated specimens with OCR=1 in (a) p’-q stress plane; and (b) v-lnp’ compression plane 170 FIGURES 5000 OCR=1 varies YSR varies OCR Deviatoric stress, q (kN/m2) 4000 tension cut-off line 3000 peak strength envelope (OCR=1) 2000 3 2 30 30 3 2 1000 20 20 5 8.2 1.6 4.1 8.2 2 1.6 2 10 4.1 0 0 1000 2000 3000 Mean normal effective stress, p' (kN/m2) (a) 4 peak strength (OCR=1) p'≅po'/2 3.6 8.2 4.1 1.6 8.2 5 4.1 2 10 Specific volume, ν 3.2 1.6 OCRs or YSRs 20 2 2 20 30 2.8 30 3 3 2 2.4 isotropic compression of 0CON0 specimen PYCL CCL OCR=1 various YSR various OCR 2 1.6 10 20 30 50 100 200 300 500 1000 2000 3000 5000 Mean normal effective stress, p' (kN/m ) (b) Figure 5.26: Peak strengths for the treated specimen with OCRs and YSRs in (a) p’-q stress plane; and (b) v-lnp’ compression plane 2 171 0CIU50 0CIU500 0CIU1500 0CON 50 0CON 500 0CON 1500 After undrained shearing After drained shearing 0CID1500 0CID500 0CID50 Figure 5.27: Changes of microstructures of the treated specimens after isotropic consolidation, undrained and drained triaxial shearing After isotropic consolidation FIGURES 172 FIGURES 5000 4 peak strength at PYCL (OCR=1) p'≅po'/2 OCR=1 varies YSR varies OCR 4000 6 3.6 8.2 1 tension cut-off line 4.1 5 4.1 2 10 3 3.2 Specific volume, ν Deviatoric stress, q (kN/m2) 2 1.6 8.2 3000 peak strength envelope (OCR=1) 2000 SEM points 3 2 30 1 0CIU50 5 4 30 2 0CID50 3 0CIU500 4 0CIU1500 5 0CID500 6 0CID1500 3 2 1000 20 20 5 8.2 1.6 4.1 8.2 2 1.6 3 2 1 0 20 2 2 20 30 2.8 30 3 4 3 2 5 SEM points 2.4 OCR=1 1 0CIU50 2 2 10 4.1 1.6 OCRs or YSRs 2 0CID50 varies YSR 3 0CIU500 varies OCR 4 0CIU1500 5 0CID500 6 0CID1500 isotropic compression of 0CON0 specimen PYCL CCL 6 1.6 0 1000 2000 Mean normal effective stress, p' (kN/m2) 3000 10 20 30 50 100 200 300 500 1000 2000 3000 Mean normal effective stress, p' (kN/m2) 1 4 2 5 3 6 Figure 5.28: Changes of microstructure corresponding to stress states and compression states seen in the triaxial behaviour of cement treated clay 173 5000 FIGURES 1 0.8 Finer than 0.6 medium size pore small size pore 0.4 large size pore 0.2 0CON0 0CON50 0CIU50 0CID50 0 0.001 0.01 0.1 1 10 100 Pore radii, µm (a) 1 0.8 Finer than 0.6 medium size pore small size pore 0.4 large size pore 0.2 0CON0 0CON500 0CIU500 0CID500 0 0.001 0.01 0.1 1 10 100 Pore radii, µm (b) 1 0.8 Finer than 0.6 medium size pore small size pore 0.4 large size pore 0.2 0CON0 0CON1500 0CIU1500 0CID1500 0 0.001 0.01 0.1 1 10 100 Pore radii, µm (c) Figure 5.29: Changes of pore size distributions after drained and undrained triaxial shearing with consolidation pressures: (a) 50kPa; (b)500kPa; and (c)1500kPa 174 FIGURES 5000 0cid50 0cid100 0cid250 0cid500 0cid500-250 0cid500-50 0cid1000 0cid1000-500 0cid1000-50 0cid1500 0cid1500-500 0cid1500-50 Deviatoric stress, q (kN/m2) 4000 3000 2000 1000 0 0 0.05 0.1 0.15 0.2 0.25 0.3 0.35 0.4 Deviatoric strain, εs (a) 2000 0ciu50 0ciu100 0ciu250 0ciu500 0ciu500-250 0ciu500-100 0ciu1000 0ciu1000-500 0ciu1000-50 0ciu1500 0ciu1500-500 0ciu1500-50 Deviatoric stress, q (kN/m2) 1600 1200 test stopped prematurely 800 400 0 0 0.05 0.1 0.15 0.2 0.25 Deviatoric strain, εs (b) Figure 5.30: Stress- strain behaviour of cement treated clay in (a) drained triaxial; and (b) undrained triaxial; strain softening was observed for all specimens 175 FIGURES 800 700 tension cut-off line D Deviator stress, q (kN/m2) 600 500 B 400 H SBS F I 300 RL3 UL3 RL1 RL2 200 UL1 UL2 100 UL4 G 0 0 E J 100 A C 200 300 400 500 Mean normal effective stress, p' (kN/m2) (a) 800 700 tension cut-off line M0 D Deviator stress, q (kN/m2) 600 M1 M2 M3 500 L B O M 400 H F I 300 RL3 SBS P RL5 UL3 RL1 RL2 200 RL4 UL2 UL6 100 UL1 UL5 UL4 G 0 0 100 J E N Q 200 K A C 300 400 500 Mean normal effective stress, p' (kN/m2) (b) Figure 5.31: Behaviour of unloading-reloading stress paths: (a) during peak, pre-and-post peak; (b) re-consolidated after rupturing 176 FIGURES 800 700 tension cut-off line M0 D Deviator stress, q (kN/m2) 600 M1 M2 S M3 500 L 400 300 RL3 O M P F I H B T M4 SBS RL6 RL5 UL3 UL7 RL2 200 RL4 UL1 UL5 UL2 UL6 100 RL1 UL4 G 0 0 U K E N Q J 100 200 A R C 300 400 500 Mean normal effective stress, p' (kN/m2) (c) 800 700 tension cut-off line M0 D Deviator stress, q (kN/m2) 600 M1 M2 W M3 500 L 400 O M P H F I 300 RL3 RL2 200 UL7 RL8 RL4 UL2 UL6 M5 SBS RL6 RL5 UL3 100 S B T Z X M4 RL7 UL8 RL1 UL1 UL5 UL4 G 0 0 100 J E N Q 200 U KY C 300 R 400 VA 500 Mean normal effective stress, p' (kN/m2) (d) Figure 5.31: Behaviour of unloading-reloading stress path after rupturing under isotropic re-consolidation pressure: (c) 390kPa; and (d) 490kPa 177 FIGURES 800 tension cut-off line 700 M0 E 600 Deviator stress, q (kN/m2) B 500 F SBS 400 UL2 300 RL1 UL1 200 100 G 0 100 200 A D C 0 300 400 500 Mean normal effective stress, p' (kN/m2) (a) 800 tension cut-off line 700 M0 E M1 600 Deviator stress, q (kN/m2) B M M2 N 500 F I SBS J 400 RL3 UL4 UL2 300 RL1 UL3 UL1 200 RL2 100 K H 0 0 100 O G 200 C A LD 300 400 500 2 Mean normal effective stress, p' (kN/m ) (b) Figure 5.32: Effects of re-consolidation pressure within SBS on the behaviour of stress path: (a) before rupturing; and (b) after rupturing with swelling or compression consolidation pressure 178 FIGURES 5000 OCR=1 (peak strength) varies YSR (peak strength) varies OCR (peak strength) Deviatoric stress, q (kN/m2) 4000 post-rupture strength tension cut-off line 3000 peak strength envelope (OCR=1) 2000 3 2 30 30 3 2 1000 20 20 5 8.2 1.6 4.1 8.2 post-ruptured strength envelope 2 1.6 2 10 4.1 0 0 1000 2000 3000 Mean normal effective stress, p' (kN/m2) (a) 4 peak strength line (OCR=1) p'≅po'/2 3.6 8.2 4.1 1.6 8.2 4.1 10 5 1 2 3.2 Specific volume, ν 20 1.6 30 20 2 2 30 2.8 3 1 1 2 3 2.4 1 isotropic compression of 0CON0 specimen PYCL CCL post-ruptured strengths 2 1 1.6 10 20 30 50 100 200 300 500 1000 2000 3000 5000 Mean normal effective stress, p' (kN/m2) (b) Figure 5.33: Post-rupture states in (a) p’-q stress plane; and (b) v-lnp’ compression plane; numbers next to the points indicate OCR or YSR values. 179 FIGURES 2000 SEM points Mr=1.53 1800 1600 4 4 Deviator stress, q (kN/m2) 1400 1200 Mr=1.19 1000 5 Mr=2.00 Mr=1.71 Mr=Mpr=1.61 800 600 5 Mr=Mpr=0.97 6 6 1 1 2 400 3 2 3 200 0 0 400 800 Mean normal effective stress, p' (kN/m2) 1200 0 0.05 0.1 0.15 0.2 0.25 Deviatoric strain, εs 1 4 2 5 3 6 Figure 5.34: Changes of microstructure with Mr, as shown in the mechanical behaviour 180 FIGURES 4 5000 peak strength line (OCR=1) p'≅po'/2 OCR=1 (peak strength) varies YSR (peak strength) varies OCR (peak strength) 4000 3.6 1 4.1 8.2 8.2 post-rupture strength 2 tension cut-off line 3000 2000 6 2 1000 20 20 5 8.2 1.6 4.1 8.2 0 1 0 1.6 2 10 2 post-ruptured strength envelope 2 5 4.1 4 3 1000 2000 Mean normal effective stress, p' (kN/m2) 2 2 30 2.8 3 4 1 1 5 2 3 SEM points 2.4 1 0CID50 2 2 0CIU50 3 0CIU500 3 0CIU500 4 0CIU1500 4 0CIU1500 5 0CID500 5 0CID500 6 0CID1500 6 0CID1500 2 1.6 3000 1.6 20 0CIU50 1 0CID50 2 3 1 2 30 SEM points 3 30 3 5 20 peak strength envelope (OCR=1) 30 1.6 4.1 3.2 Specific volume, ν Deviatoric stress, q (kN/m2) 10 10 20 30 1 isotropic compression of 0CON0 specimen PYCL CCL post-ruptured strengths 50 100 200 300 500 1000 6 1 2000 3000 5000 2 Mean normal effective stress, p' (kN/m ) 1 4 2 5 3 6 Figure 5.35: Microstructure at post-rupture states, as shown in the mechanical behaviour 181 FIGURES 1 Mr=2.00 M 2 r=1.71 1 2 3 Mr=Mpr=1.61 4 Mr=1.53 5 Mr=1.19 3 0.8 6 5 1 4 6 Mr=Mpr=0.97 Smaller than 0.6 0.4 0.2 small size pore medium size pore large size pore 0 0.001 0.01 0.1 1 10 100 Pore radii, µm Figure 5.36: Changes of pore structure with Mr, as shown in the mechanical behaviour (refer Figure 5.34 for numbering of states) 1 1 6 2 3 5 0.8 4 Post-rupture states Smaller than 0.6 1 2 0CID50 0CIU50 0CIU500 0CIU1500 4 5 0CID500 3 0.4 0CID1500 6 0.2 small size pore medium size pore large size pore 0 0.001 0.01 0.1 1 10 100 Pore radii, µm Figure 5.37: Entrance pore structure at post-rupture states, as shown in the mechanical behaviour (refer Figure 5.35 for numbering of states) 182 FIGURES 3.8 parallel to CCL 3.6 gross-yield point Specific volume, ν 3.4 CCL 3.2 3 b=0.25 2.8 2.6 0CON0 specimen b=0.05 b=0.25 b=1 b=2 2.4 2.2 10 20 50 200 100 500 1000 2000 5000 Consolidation pressure, p' (kN/m2) Figure 6.1: Influence of b parameter on compression after gross yield CCL λ∗ PYCL λ atmoshperic pressure κgy curing p'o=p'gy URL, κ Specific volume, ν p'o=p'y curing under effective stress κgy p'o=p'gy URL, κ p'o=p'y p'o=p'y Consolidation pressure, p' (kN/m2) Figure 6.2: Idealisation of isotropic compression behaviour for cement treated clay in v-lnp’ plane 183 FIGURES CCL λ∗ PYCL λ Specific volume, ν κgy current p' state during shear URLs, κ current stress sensitivity α= p'o,s/p*'e,s p*'e p*'e,s p' p'o,s Consolidation pressure, p' (kN/m2) Figure 6.3: Normalizing factor for current stress sensitivity CCL λ∗ PYCL λ κgy current p' state during shear Specific volume, ν κ=0 URLs, κ current stress sensitivity αs= p'o,s/p*'e p*'e,s=p*'e p' p'o,s Consolidation pressure, p' (kN/m2) Figure 6.4: Normalizing factor for current stress sensitivity by equating κ=0 184 FIGURES 1.6 1.6 0CID50 0CID100 0CID250 0CIU50 0CIU100 0CIU250 1.2 gross yield points gross yield points 50CID50 50CIU50 gross yield locus gross yield locus tension cut-off line 1.2 q/p'*e/α q/p'*e/α tension cut-off line 0.8 0.4 0.8 0.4 p'gy=732kPa p'gy=430kPa 0 0 0 0.2 0.4 0.6 0.8 0 1 0.2 0.4 0.6 0.8 1 p'/p'*e/α p'/p'*e/α (a) (b) 2 1.6 0CID500 0CID500-250 0CID500-50 0CIU500 0CIU500-250 0CIU500-100 gross yield points 250CID50 250CID500 250CID1000 250CIU50 250CIU500 250CIU1000 gross yield locus 1.6 gross yield points gross yield locus 1.2 tension cut-off line tension cut-off line q/p'*e /α q/p'*e/α 1.2 0.8 0.8 0.4 0.4 p'o=500kPa p'gy=1309kPa 0 0 0.2 0.4 0.6 0.8 0 0 1 0.2 0.4 0.6 0.8 1 p'/p '*e /α p'/p'*e/α (d) (c) 2 2 0CID1000 0CID1000-500 0CID1000-50 0CIU1000 0CIU1000-500 0CIU1000-50 1.6 gross yield points 0CID1500 0CID1500-500 0CID1500-50 0CIU1500 0CIU1500-500 0CIU1500-50 gross yield points gross yield locus 1.6 gross yield locus tension cut-off line tension cut-off line 1.2 q/p'*e /α q/p'*e /α 1.2 0.8 0.8 0.4 0.4 p'o=1000kPa 0 p'o=1500kPa 0 0 0.2 0.4 0.6 p'/p '*e /α (e) 0.8 1 1.2 0 0.2 0.4 0.6 0.8 1 1.2 p'/p '*e /α (f) Figure 6.5: Stress paths behaviour after normalized by volume and current stress sensitivity for cement treated specimens consolidated at: (a-c) pre-gross yield; and (d-f) post-gross yield 185 FIGURES 1.6 consolidated at pre-gross yield consoildated at post-gross yield p'gy=430kPa p'o=500kPa p'gy=732kPa p'o=1000kPa p'gy=1309kPa p'o=1500kPa tension cut-off line 1.2 q/p*'e/α gross yield locus 0.8 0.4 0 0 0.2 0.4 0.6 0.8 1 p'/p*'e/α Figure 6.6: Peak strengths after normalized by volume and current stress sensitivity for cement treated specimen 1.6 α normalisation tension cut-off line αs normalisation 1.2 q/p*'e/α or q/p'o,s gross yield locus 0.8 0.4 0 0 0.2 0.4 0.6 0.8 1 p'/p*'e/α or p'/p'o,s Figure 6.7: Comparison between α- and αs- normalisations 186 FIGURES 4.2 PYCL (10%) 4 PYCL (20%) PYCL (30%) 200 500 3.8 CCL (20%) Specific volume, ν 3.6 3.4 3.2 Kamruzzaman's (2002) data 3 10% cement content 30% cement content 0CON0 50CON0 100CON0 250CON0 500CON0 U100CON0 U500CON0 end states after 7-D treament Curing-consolidation points Gross-yield points (Cotecchia & Chander's (2000) method) 2.8 2.6 2.4 2.2 1 2 5 20 10 50 100 1000 2000 5000 Consolidation pressure, p' (kN/m2) Figure 6.8: Isotropic compression behaviour of the treated specimens with different cement contents, together with their post-yield compression lines 1.2 consolidated at pre-gross yield Kamruzzaman's (2002) data 10% cement content σ'3=50kPa σ'3=100kPa peak strengths 1 fitted gross yield locus consolidated at post-gross yield σ'3=300kPa σ'3=500kPa σ'3=1000kPa tension cut-off line q/p'o,s 0.8 0.6 0.4 0.2 0 0 0.2 0.4 0.6 0.8 1 1.2 p'/p 'o,s Figure 6.9: Undrained stress path behaviour at 10% cement content based on αs-normalisation 187 FIGURES 1.2 consolidated at pre-gross yield σ'3=50kPa Kamruzzaman's (2002) data 30% cement content σ'3=100kPa fitted gross yield locus 1 σ'3=300kPa consolidated at post-gross yield peak strengths σ'3=500kPa σ'3=1000kPa tension cut-off line q/p'o,s 0.8 0.6 0.4 0.2 0 0 0.2 0.4 0.6 0.8 1 1.2 p'/p'o,s Figure 6.10: Undrained stress path behaviour at 30% cement content based on αs-normalisation 1.6 Kamruzzaman's (2002) data (Clay from onshore excavation project) this study (Clay from offshore dredge site) 10% cement 20% cement 30% cement apex of gross yield locus 1.2 M=1.92 M=1.78 tension cut-off line M=1.54 q/αp*'e or q/p'o,s gross yield locus 0.8 0.4 0 0 0.2 0.4 0.6 0.8 1 p'/αp*'e or p'/p'o,s Figure 6.11: Peak strengths and gross yield loci at different cement contents after normalized for volume and current stress sensitivity 188 FIGURES 0.8 Kamruzzaman's (2002) data (Clay from onshore excavation project) this study (Clay from offshore dredge site) 10% cement 20% cement 30% cement tension cut-off line 0.6 q/Mαp*'e or q/Mp'o,s gross yield locus 0.4 0.2 0 0 0.2 0.4 p /αp ' 0.6 *' e ' or p /p 0.8 1 ' o,s Figure 6.12: Peak strengths and gross yield loci at different cement contents after normalized for volume, current stress sensitivity and composition 189 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Soils & Found., Vol. 37(4), 93-103. 197 [...]... set of chemical equations involving these reactions as well as lime treated clay have been presented by Kezdi (1979) and Bergado et al (1996) 2.1.3 Structure and Microstructure of Treated Clay The microstructure of the cement treated clay is often significantly different from that of the untreated clay Kezdi (1979) suggested that a soil -cement skeleton matrix may be formed due to the inclusion of cement. .. ratio of solid mass of cement to solid mass of soil For Singapore marine clay, Kamruzzaman (2002) noted significant increase in the strength of the treated soil within the cement content range of 5-40% On the other hand, Miura et al (2001) and Horpibulsuk et al (2003) noted that the clay- water /cement ratio is a more appropriate parameter for quantifying the strength development of the cement treated soft... Mass of cement solid Ms Mass of soil solid M sc Mass of soil -cement mixtures (solid) after treatment M s+c Mass of soil and cement solids M w,a + g Mass of available water and gel water in the soil -cement mixtures after hydration M w,c Mass of water from cement slurry M w,cc Mass of water after curing-consolidation M w,h Mass of water used for hydration M w, s Mass of water from soil M w, sc Mass of. .. study behaviour and performance of cement treated marine clay in the presence of atmospheric, drained and undrained ambient effective load-curing conditions ii) To study stress-strain behaviour of cement treated marine clay at a macroscopic level, and consequently relates this behaviour to the microstructural changes during both isotropic compression and shearing 3 CHAPTER 1 iii) To provide a behavioural... CHAPTER 1 INTRODUCTION 1.1 Cement- Soil Stabilization Introduction of cement into soft ground, or cement- soil stabilization, either in the form of dry cement powder or slurry cement, is a popular method of ground improvement technique The inclusion of cement into soil-water systems causes physico-chemical changes at a microstructural level and therefore mechanical behaviour of the treated soil at a macroscopic... soft clays, instead of cement content only Similarly, Lee et al (2005) showed that the strength of the improved clay is dependent on both the soil /cement ratio and also the water /cement ratio, or the relative proportion of soil -cement- water ratio 10 CHAPTER 2 The differences of improvement by using different types of cement have been investigated Kawasaki et al (1981) compared the effect of slag cement. .. treatment Vs + c Volume of soil and cement solids V w,c Volume of water from cement slurry V w,cc Volume of water in soil -cement mixtures after curing-consolidation V w, a + g Volume of available water and gel water in the soil -cement mixtures after hydration V w, s Volume of water from soil V w, sc Volume of water in soil -cement mixtures after treatment V w, s + c Volume of water from both cement slurry and... Ordinary Portland Cement 28 Table 3.2A Summary of timings and activities on cement- treated soil 35 Table 4.1A Measured and calculated volume-mass properties of cementtreated clay at 7-day post-treatment (% error) 42 Table 4.1 Effect of cement treatment on basic properties of cement- clay mixtures 43 Table 4.2 Percentage of changes of void ratio attributed to trapped water 56 Table 4.3 UCT peak strengths... untreated marine clay, cement particles, cementclay mixtures and cement- clay particles in ethanol 145 Fig 4.13 Grading curves for cement treated clay with different remoulding periods 146 Fig 4.14 Grading curves for cement treated clay with ultrasonic dispersion 146 Fig 4.15 Changes of liquid limit at different remoulding periods 147 xi Fig 4.16 Grading curves for the treated specimens with various loadeddrained... pressure responses with different cement contents (after Uddin et al., 1997) 132 Fig 2.28 Undrained stress path behaviour of cement treated clay for (a) 10%; (b) 30%; and (c) 50% of cement contents (after Kamruzzman, 2002) 133 Fig 3.1 Demoulding the soil -cement sample for isotropic load-curing 134 Fig 3.1A Distribution curve of air content (in percentage) within cement- clay mixtures just after mixing