Deterministic and Probabilistic Evaluation of Liquefaction Potential: A Case Study from 2015 Gorkha (Nepal) Earthquake

During April 25, 2015 Gorkha (Nepal) earthquake (Mw 7.8), soil liquefaction was observed at several locations in Kathmandu valley. In this study, deterministic and probabilistic evaluation of liquefaction potential was performed for a liquefied site in Bungamati, Lalitpur, Nepal. Two boreholes of depth 20 m each were drilled and standard penetration test was conducted in both boreholes. The factor of safety against liquefaction was calculated using deterministic methods. In the probabilistic study, the probability of liquefaction was calculated using first order second moment (FOSM) method. The FOSM method considers uncertainty in input parameters of the model and output is represented in terms of mean value and standard deviation of the safety factor. Reliability index and the probability of failure were calculated and correlation between factor of safety and probability of failure was obtained. Based on anticipated variability in soil and seismic parameters, factor of safety required for specified risk level is presented.