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# Effect of Initial Static Shear Stress on Liquefaction Resistance of Babolsar Sand Using Cyclic Simple Shear Tests

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Pouragha, Mehdi
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2008

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- Type of Document: M.Sc. Thesis
- Language: Farsi
- Document No: 39218 (09)
- University: Sharif University of Technology
- Department: Civil Engineering
- Advisor(s): Haeri, Mohsen
- Abstract:
- Initial static shear stress caused by slopes or nearby structures' foundations can affect the behavior of the soil which is concerned many investigators during previous three decade. In this investigation, the effect of initial static shear stress on the liquefaction resistance of Babolsar sand has been probed using cyclic simple shear tests. Three different initial relative densities (Dr0=20%, 40% and 60%) and three different initial normal stresses (σv0= 50, 150 and 250 kPa) were considered in tests and four various initial static shear ratios (α) ranging between 0.0 and 0.3 were applied which leads to more than 190 distinct experiments. All tests were conducted under constant volume and stress controlled conditions. In order to explain the variation of liquefaction resistance ratio (Kα), variation of cyclic shear modulus (G) and two other new-defined parameters were monitored for different values of initial static shear ratios (α). The first new-defined parameter, Strain Amplitude Expansion Ratio (Rex), represent the expansion of cycles strain amplitude and the second parameter, Strain Accumulation Ratio (Ra), represent the rate of irreversible strain accumulation in cycles. Results show that considerable decrease in Rex for a small driving static shear stress ratio, α, would cause a change in controlling failure criterion and an increase in Kα. For greater values of α, cyclic shear modulus (G) and Strain Accumulation Ratio (Ra) both increase; the increase in cyclic shear modulus would raise Kα and the increase in strain accumulation ratio would lower Kα. Thus the variation of Kα with α is affected by these two contradictive effects which cause an increasing behavior in some intervals of α and decreasing in others.

- Keywords:
- Initial Static Shear Stress ; Cyclic Simple Shear ; Sands ; Liquefaction Resistance ; Constant Volume