Masters Thesis

Evaluation of Cyclic Mobility on Fine Grained Soil Due to Earthquake Induced Ground Motion

Liquefaction and cyclic mobility are two major modes of ground failure that occur due to earthquake loads. Cyclic mobility is initiated due to a reduction in shear strength of the soil. to evaluate the likelihood of occurrence of such failures, it is important to understand the shear strengths of soil before and after earthquake loading. for this study, samples were collected from the Kathmandu Valley in Nepal after the 2015 Mw 7.8 Gorkha earthquake from an area that experienced failure. Three additional soil samples from the Portuguese Bend area, California, a known area for landslides, were also evaluated during this study. Testing included static shear testing and cyclic loading followed by post-cyclic shear testing to determine the strength degradation that occurs post-cyclically and other cyclic properties of the samples. Results from this study show indications of increased cyclic resistance corresponding to increased plasticity index and lower consolidation stresses, power function representation of cyclic strength curves as identified in previous studies, a reduction in post-cyclic shear strength degradation with an increase in plasticity index, and greater retention of relative stiffness in montmorillonite dominated soil compared to kaolinite dominated soil during cyclic loading. Slight deviations from the predicted trends were observed for a few natural samples, which could potentially be due to their marine environment during formation process or the variable clay minerology found in these natural soils.

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