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Application of Shansep and Hvorslev's Theories to Evaluate the Shear Strength of Over-Consolidated Clays in Mineralogical Fram

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Application of Shansep and Hvorslev's Theories to Evaluate the Shear Strength of Over-Consolidated Clays in Mineralogical Fram APPLICATION OF SHANSEP AND HVORSLEV’S THEORIES TO EVALUATE THE SHEAR STRENGTH OF OVER-CONSOLIDATED CLAYS IN MINERALOGICAL FRAMEWORK _____________________________________ A Thesis Presented to the Faculty of California State University, Fullerton _____________________________________ In Partially Fulfillment of the Requirements for the Degree Master of Science in Civil Engineering _____________________________________ By Krishna Hari Pantha Thesis Committee Approval: Chair: Binod Tiwari, PhD. PE, Dept. of Civil and Environmental Engineering Co-Chair: Beena Ajmera, PhD, Dept. of Civil and Environmental Engineering Phoolendra Kumar Mishra, PhD, Dept. of Civil and Environmental Engineering Fall, 2015 ABSTRACT This paper presents the results of a study, whose aim was to determine the undrained shear strength at different over-consolidation ratios, which is a very important parameter to evaluate the stability of natural and man-made slopes in soft clay. The undrained shear strength of clays was determined using a laboratory test method utilizing the Direct Simple Shear (DSS) apparatus in the geotechnical engineering laboratory at California State University, Fullerton. In this study, the change in undrained shear strength of soil with over-consolidation ratio in a mineralogical framework was studied. Four different soil samples were prepared by mixing commercially available clay minerals such as kaolinite and montmorillonite with quartz at different proportions by their dry weight. These samples included 100% kaolinite, a mixture of 70% kaolinite with 30% quartz, a mixture of 50% kaolinite with 50% quartz and a mixture of 50% montmorillonite with 50% quartz. The plasticity characteristics of these samples were evaluated. Each of the first three samples had five different specimens representing five different over-consolidation ratios (2, 4, 8, 16 and 32). The fourth sample had only two specimens for two different over-consolidation ratios, i.e. 2 and 4. The applied consolidation stresses were 600 kPa, 300 kPa, 150 kPa, 75 kPa and 37.5 kPa for five different over-consolidation ratios of 2, 4, 8, 16 and 32, respectively. Using the direct simple shear device, the undrained shear strength of these samples were measured using a strain rate of 5%/hour. ii The pore pressures generated at different applied stresses was also back calculated from the change in total stresses. The pore water pressure continuously increased up to certain displacement and then after tended to remain constant. The results showed that it was inversely proportional to the over-consolidation ratio. Using the results, the SHANSEP model and Hvorslev’s theory were utilized to check normalized shear strength, and true friction angle and true cohesion of each soil sample, respectively. The result showed that the shear strength depends up on the composition of clay minerals and stress history of the soil. The relationship of the normalized undrained shear strength ratio was directly proportional to the over- consolidation ratio of the soil. Similarly, the true friction angle of the soil depended up on the composition of the clay minerals, but not on the stress history. True friction angles of 19.28°, 20.63°, 21.06° and 35.24° were obtained for Sample Nos.1, 2, 3 and 4, respectively; whereas, the true cohesion of these sample were measured as 8.46°, 7.21°, 4.55° and 0.39° respectively. iii TABLE OF CONTENTS ABSTRACT………………………………………………………………………......... ii LIST OF TABLES……………………………………………………………………... vi LIST OF FIGURES…………………………………………………………………..... viii ACKNOWLEDGEMENTS………………………………………………………….... xiv Chapter 1. INTRODUCTION……………………………………………………………... 1 2. LITERATURE REWIEW…………………………………………………….... 4 Background of Laboratory Shear Strength Testing Device……………………. 4 Shear Strength from DSS Test…………………………………………………. 8 Pore Water Pressure from DSS Test………………………………………….... 9 Effect of the Shearing Rate on the Undrained Shear Strength Properties of the Soft Saturated Clay……………………………………………………... 11 Effect of Moisture Content on Undrained Shear Strength…………………….. 12 Stress History and Normalized Soil Engineering Properties (SHANSEP)…..... 13 The Undrained Shear Strength of Over-consolidated clays…………………… 17 Hvorslev’s Theorem…………………………………………………………… 19 3. MATERIAL AND METHODOLOGY………………………………………... 22 Soils Used……………………………………………………………………… 22 Sample Preparation……………………………………………………………. 23 Preparation of Over-consolidated Samples……………………………………. 23 Direct Simple Shear Test Procedure…………………………………………... 27 4. TEST RESULTS AND DISCUSSION………………………………………... 34 Stress-Deformation Characteristics……………………………………………. 34 Pore Pressure-deformation Characteristics……………………………………. 34 Stress Path……………………………………………………………………... 36 Stress Ratio…………………………………………………………………….. 36 Shear Envelopes……………………………………………………………….. 39 Normalized Shear Strength…………………………………………………….. 41 iv Equivalent Consolidation Pressure…………………………………………….. 42 True Cohesion and True Friction Angle……………………………………….. 46 Relationship between True Friction Angle, True Cohesion with Liquid Limit and Plasticity Index……………………………………………………… 50 5. CONCLUSION………………………………………………………………… 53 REFERENCES…………………………………………………………………………. 55 APPENDICES…………………………………………………………………………. 57 A. SAMPLE NO.1 (100% KAOLINITE) CURVES)…………………………….. 57 B. SAMPLE NO.2 (70% KAOLINITE WITH 30% QUARTZ) CURVES………. 68 C. SAMPLE NO.3 (50% KAOLINITE WITH 50% QUARTZ) CURVES……..... 78 D. SAMPLE NO.4 (50% MONTMORILONITE 50% QUARTZ) CURVES……. 87 E. RELATIONSHIP OF L.L., P.I. WITH TRUE FRICTION ANGLE AND TRUE COHESION…………………………………………………………….. 96 v LIST OF TABLES Table Page 2-1 Undrained shear strength ratio ( Cu / 'vc ) and OCR relationship …………….. 18 3-1 Proportions of soil by their dry weight (%) and physical properties of the tested samples…………………………………………………………… 22 3-2 Sample details…………………………………………………………………... 24 3-3 Loading steps relative to OCR………………………………………………….. 27 4-1 Total and Effective Cohesion and Friction Angle of There Samples…………... 39 4-2 Normalized Shear Strength and OCR (Sample No.1)………………………….. 41 4-3 Effective normal stress and void ratio (Sample No.1)………………………….. 42 4-4 Effective Stress and Equivalent Consolidation Pressure……………………….. 43 4-5 Calculation of σ'3, q and σ'e (Sample No.1)…………………………………….. 45 4-6 True Cohesion and Friction Angle for Sample Nos. 1, 2, 3 and 4 ……………... 49 A-1 Relation between Effective Stress and Void Ratio……………………………... 65 A-2 Relation between q/σ'e and σ'3/σ'e………………………………………………. 66 A-3 Relation between Normalized Shear Strength and OCR……………………….. 66 A-4 L. L., P. I. and Normalized Shear Strength……………………………………... 67 B-1 Relation between Effective Stress and Void Ratio……………………………... 76 B-2 Relation between q/σ'e and σ'3/σ'e………………………………………………. 76 B-3 Relation between Normalized Shear Strength and OCR……………………….. 77 vi B-4 L. L., P. I. and Normalized Shear Strength…………………………………...... 77 C-1 Relation between Effective Stress and Void Ratio…………………………….. 85 C-2 Relation between q/σ'e and σ'3/σ'e……………………………………………… 86 C-3 Relation between Normalized Shear Strength and OCR………………………. 86 C-4 L. L., P. I. and Normalized Shear Strength…………………………………….. 86 D-1 Relation between Normalized Shear Strength and OCR………………………. 91 D-2: Relation between Effective Stress and Void Ratio (Source: Tiwari and Ajmera, 2011) ………………………………………….... 92 D-3: Relation between q/σ'e and σ'3/σ'e ……………………………………………… 95 E-1: Relation between LL and PI with ɸe and ɸc ……………………………………. 98 vii LIST OF FIGURES Figure Page 2-1 Double Direct Shear as Performed by Alexander Collin in 1846 (Sower, 1963).. 4 2-2 SGI Simple Shear Device 1936 (Kjellam, 1951)……………………………….... 5 2-3 NGI DSS device (DeGroot et al, 1992)………………………………………….. 6 2-4 GeoComp Universal Shear Device (Marr, 2003)……………………………….... 7 2-5 DSS Device Set-up in Geotechnical Engineering Lab at CSUF………………… 7 2-6 Standard DSS Test Component (ASTM 2000)………………………………….. 8 2-7 Normalized undrained shear strengths for TC, DSS, and TE test results as a function of Plasticity Index (Ladd and DeGroot, 2003)………………………….. 9 2-8 Comparison of pore pressure from constant volume and undrained DSS test results (Dyvik et al. 1988)……………………………………………………….. 10 2-9 Variation of Normalized Undrained Shear strength with Axial Strain Rate and Over-consolidation Ratio (Source: Sheahan et al. (1996)……………………….. 11 2-10 Variation of Undrained Shear Strength with Moisture Content (Source: Hong et al. (2006)…………………………………………………….. 12 2-11 Variation of Normalized CKoUDSS Strength Parameters with OCRs for 5 Clays (Ladd & Foott 1974)……………………………………………………... 14 2-12 Example of Normalized Behavior Using Idealizes Triaxial Compression Test (After Ladd and Foote, 1974)…………………………………………………… 15 2-13 Normalized CKoU Direct-Simple Shear Test Data for Overconsolidated Boston Clay (After Ladd and Foote, 1974)……………………………………... 16 viii 2-14 Undrained shear strength ratio Cu/σ'vc versus OCR ( Strozyk and Tankiewicz {2014})................................................................................................................. 18 2-15 Effective Stress versus Void Ratio (Hvorslev, 1937) ………………………… 20 2-16 Effective Stress versus Shear Stress (Hvorslev, 1937) ……………………….. 21 3-1 Placement of the Batch mixture Soil into the Oedometer Ring………………... 24 3-2 Sample Set-up for Consolidation Test………………………………………….. 25 3-3 Consolidometer apparatus used in this study…………………………………… 25 3-4 Displacement versus Time Curves……………………………………………... 26 3-5 Apparatus Required to Assemble the Sample into the Shear Box……………… 28 3-6 Simple Shear Apparatus Used in This Study…………………………………… 28 3-7 Placement
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