Probability of Liquefaction induced Ground Failure under the Earthquake Scenario in Kathmandu Valley

Abstract

Kathmandu valley is highly susceptible to liquefaction hazard due to the presence of liquefiable soil up to considerable depth, the presence of shallow ground water table and occurrence of earthquakes at regular intervals. Past studies have also shown the occurrence of liquefaction with examples of observed ejection of sand boil and formation of cracks throughout the valley during 1934 Nepal-Bihar earthquake. Events similar to these were also observed during recent 2015 Gorkha Nepal earthquake in twelve different locations within the valley. In this study, standard penetration test (SPT) based probabilistic model has been used taking 113 borehole logs data collected from within the valley to determine liquefaction-induced probability of ground failure under 2015 earthquake scenario with moment magnitude M w of 7.8 and peak ground acceleration of 0.16g.Calculations were done in MS Excel 2013 and results were plotted in ArcGIS 10.2 to produce liquefaction induced potential ground failure map.The result shows that 20.13%, 35.13%, 15.46%, 13.67% and 15.43% of the study area lie in very high, high, medium, low and very low risk of liquefaction hazard, respectively. About 83% of the observed liquefied locations after the earthquake were found in very high and high risk while the rests were found in medium risk of liquefaction hazard.