Loading...

Effects of Static Shear Stress on Liquefaction Strength of Babolsar Sand Investigated under Cyclic Simple Shear and Static Triaxial Tests

Mohammadi, Morteza | 2010

1127 Viewed
  1. Type of Document: M.Sc. Thesis
  2. Language: Farsi
  3. Document No: 40411 (09)
  4. University: Sharif University of Technology
  5. Department: Civil Engineering
  6. Advisor(s): Haeri, Mohsen
  7. Abstract:
  8. Soil liquefaction is a phenomenon in which soil loses much of its strength or stiffness for a generally short time but nevertheless long enough for liquefaction to be the cause of many losses. Thus, many researchers have worked on the factors which affect this phenomenon. Effects of initial static shear stress on liquefaction strength of loose and medium dense Babolsar sand specimens were investigated in this study. Babolsar sand is fine to medium uniform sand classified as SP in USCS. Tests were performed with cyclic simple shear and static triaxial devices. All tests were performed under consolidated undrained conditions. Cyclic simple shear tests were performed under constant vertical load and controlled cyclic shear stress conditions on specimens 70 mm in diameter and 22 mm in highet; compresional triaxial tests were performed under strain controlled condition, on specimens 100 mm in diameter and 200 mm in highet. All samples were prepared using wet tamping method. Cyclic simple shear test specimens were prepared in one layer while those of triaxial compression test were prepared in four layers with effects of undercompaction taken into consideration. All specimens were saturated following the standard back pressure method until the Skempton B-value was at least 0.96. Consolidation pressure and initial static shear stress were exerted under drained conditions and were followed by undrained shearing in cyclic simple shear tests. Cyclic simple shear test specimens were prepared with relative densities (Dr) of 30% and 60% under Initial effective consolidation pressures (〖σ'〗_v0) of 100 kPa and 200 kPa and initial static shear stress factors of 0.05, 0.1, and 0.2. Triaxial compression tests were performed under mean effective consolidation pressures of 100, 200, 300, 400 kPa and relative densities of 20%, 40%, 60%. In order to analyze the data, three different failure criteria were taken into consideration; namely, excess pore pressure ratio equal to unity, 5% double amplitude shear strain, and 5% cumulative shear strain. Cyclic strength curves were plotted according to which variation of Correction Factor for Initial Shear Stress (k_α) with static shear stress ratio (α) were obtained. The results show that at a given relative density values of k_α for higher effective vertical stresses are greater than those of lower effective vertical stresses. Furthermore, values of k_α are greater for specimens with lower relative densities. Initial state of specimens taken into consideration in stress space of triaxial tests reveals that the increase of initial static shear stress decreases the possibility of stress reversal and increases the liquefaction strength of specimens when static shear stress is high enough. Two new parameters - potential of cyclic shear strain development (Pc) and potential of monotonic shear strain development (Pm) - were introduced in order to formulate mechanisms of strain development which showed to be dependent on both initial state and cyclic loading conditions; the parameters which were rendered independent The first parameter -potential of cyclic shear strain development – showed a general increasing trend with an increase in values of static shear stress ratio
  9. Keywords:
  10. Liquefaction ; Babolsar Sand ; Initial Static Shear Stress ; Steady State ; Static Triaxial Test ; Cyclic Simple Shear

 Digital Object List

 Bookmark