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Effect of Pore-Water Surface Tension on Tensile Strength of Unsaturated Sands

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Effect of Pore-Water Surface Tension on Tensile Strength of Unsaturated Sands EFFECT OF PORE-WATER SURFACE TENSION ON TENSILE STRENGTH OF UNSATURATED SAND PRATEEK JINDAL A THESIS SUBMITTED TO THE FACULTY OF GRADUATE STUDIES IN PARTIAL FULFILLMENT OF THE REQUIREMENTS FOR THE DEGREE OF MASTER OF SCIENCE GRADUATE PROGRAM IN EARTH AND SPACE SCIENCE YORK UNIVERSITY TORONTO, ONTARIO January 2016 PRATEEK JINDAL, 2016 ABSTRACT Tensile behaviour of unsaturated sand was investigated both experimentally and theoretically. A custom-built direct tension apparatus was employed to perform direct tension tests on unsaturated silica sand specimens at different saturations levels and packing dry densities. Attempt was made to understand the effect of surface tension of pore-liquid and tensile loading rate on the tensile strength. It was found that the tensile strength decreases, as the surface tension of the pore-liquid decreases and rate of loading increases. However, tensile strength does not decrease as a simple multiple of ratio of surface tension of pore-liquid. The experimental results were also compared with the predicted results from two theoretical tensile strength models, namely, micro-mechanical and the macro-mechanical models. Results predicted using the micro-mechanical model agreed well with the experimental results, but only for specimens containing distilled water in the pendular saturation regime. On the other hand, the macro-mechanical model followed the experimental trend across pendular and funicular saturation regimes for specimens containing distilled water reasonably well. However, at reduced surface tension of pore-liquid, both models significantly under-predicted the experimental tensile strength results. ii ACKNOWLEDGEMENTS Foremost, I would like to express the deepest appreciation to my thesis supervisor and mentor, Dr. Jitendrapal Sharma, who has the attitude and the substance of a genius. Without his guidance and relentless encouragement, my thesis would not have been possible. I would also like to thank him for his financial support throughout the course of the researchwork. Thanks for everything, Dr. Sharma. In addition, a big thank you to my co-supervisor Dr. Rashid Bashir, whose expertise in unsaturated soil mechanics helped me to structure my research and thesis. He has shared valuable insights in the relevance of the study and made this research successful. I would also like to thank my thesis committee members, Dr. Dan Palermo and Dr. Ryley Beddoe, for their kindness, encouragement and insightful comments. I would also like to express my appreciation to Dr. Dieter Stolle and Mr. Peter Koudys from McMaster University, for their contribution to the development of the direct tension apparatus. My special thanks to Adam Hammerlindl from University of Saskatchewan for his tremendous assistance in setting up the direct tension apparatus and LabVIEW system. I would also like to thank my friends and colleagues at University of Saskatchewan and York University – Mohit, Azza, Sunil, Zeeshan, Arafat, Ramtin, Jacob and Eros for their endless support and motivation. I would also take this opportunity to thanks Mitacs Globalink Graduate Fellowship program for providing financial assistance, which went a long way in making this research possible. Last, but not least, I would like to thank my mom, dad, and Nikita for their unconditional love and support during the course of my Masters studies and throughout my life. iii This one is for you, Ma. iv TABLE OF CONTENTS ABSTRACT… ......................................................................................................................... ii ACKNOWLEDGEMENTS .................................................................................................. iii TABLE OF CONTENTS ....................................................................................................... v LIST OF TABLES ................................................................................................................ vii LIST OF FIGURES ............................................................................................................. viii LIST OF SYMBOLS ............................................................................................................ xii GREEK SYMBOLS ......................................................................................................................... xii ROMAN SYMBOLS ...................................................................................................................... xiii 1 INTRODUCTION.................................................................................................... 1 1.1 UNSATURATED SOIL MECHANICS IN GEOTECHNICAL ENGINEERING ............... 3 1.2 PROBLEM STATEMENT .................................................................................................... 5 1.3 OBJECTIVES ........................................................................................................................ 6 1.4 THESIS ORGANIZATION ................................................................................................... 6 2 BACKGROUND KNOWLEDGE AND LITERATURE REVIEW ................... 8 2.1 UNSATURATED SOIL MECHANICS ................................................................................ 8 2.1.1 Soil suction ......................................................................................................................... 8 2.1.2 Capillarity and surface tension ............................................................................................ 9 2.1.3 Soil-moisture characteristic curve ..................................................................................... 12 2.2 TENSILE STRENGTH THEORETICAL MODELS .......................................................... 14 2.2.1 Micro-mechanical Model of Tensile Strength .................................................................. 15 2.2.2 Macro-mechanical Model of Tensile Strength.................................................................. 22 2.3 EFFECT OF REDUCED SURFACE TENSION ON MATRIC SUCTION AND TENSILE STRENGTH ......................................................................................................................... 29 2.4 REVIEW OF TENSILE STRENGTH EXPERIMENTS ON UNSATURATED GRANULAR MATERIALS ................................................................................................ 35 2.4.1 Pietsch and Rumpf 1967 & Pietsch 1968 ......................................................................... 35 2.4.2 Schubert 1984 ................................................................................................................... 36 v 2.4.3 Mikulitsch and Gudehus 1995 .......................................................................................... 38 2.4.4 Pierrat and Caram 1997 .................................................................................................... 39 2.4.5 Kim 2001 .......................................................................................................................... 41 2.4.6 Lu et al. 2007 .................................................................................................................... 43 2.4.7 Lu et al. 2009 .................................................................................................................... 45 2.5 REVIEW OF TENSILE STRENGTH MEASUREMENT TECHNIQUES ........................ 49 3 MATERIALS AND METHODOLOGY ............................................................. 59 3.1 MATERIAL CHARACTERIZATION ................................................................................ 59 3.2 EXPERIMENTAL APPARATUS ....................................................................................... 61 3.3 SPECIMEN PREPARATION .............................................................................................. 68 3.4 EXPERIMENTAL PROCEDURE ....................................................................................... 71 3.5 EXPERIMENTAL PROGRAM ........................................................................................... 72 4 OVERVIEW OF THE DIRECT TENSION TESTS .......................................... 75 5 ANALYSES USING THEORETICAL TENSILE STRENGTH MODELS .... 84 5.1 ANALYSIS USING MICRO-MECHANICAL MODEL .................................................... 84 5.2 ANALYSIS USING MACRO-MECHANICAL MODEL .................................................. 91 6 CONCLUSIONS AND RECOMMENDATIONS ............................................... 97 6.1 SUMMARY OF EXPERIMENTAL RESULTS AND THEORETICAL MODELING ..... 97 6.2 FUTURE SCOPE OF WORK .............................................................................................. 99 6.3 FINAL NOTE ..................................................................................................................... 100 REFERENCES .................................................................................................................... 102 Appendix A CALIBRATION OF LOAD CELL and LVDT ...................................... 111 A.1 Load Cell Calibration ......................................................................................................... 111 A.2 LVDT Calibration .............................................................................................................. 113 Appendix B FRICTION CALCULATION IN DIRECT TENSION APPARATUS 116 vi LIST OF TABLES Table 2.1 Ratio of tensile strength and surface tension (Pierrat and Caram 1997) ........... 40 Table 3.1 Experimental program ......................................................................................
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