Gyanu Ratna Tuladhar

Potential Risk of Landslide Damming During Earthquakes

The Mid-Niigata earthquake occurred in 2004 and taught us a lesson about the possibility of landslide damming when the earthquake occurs after the softening of the ground by rainfall. Terano Landslide was considered stable before the earthquake. However, due to the earthquake, the landslide moved extensively and dammed the Imokawa River. A main landslide block was analyzed for a seismic loading condition using the observed peak ground acceleration. Soil samples were collected from numerous sliding surfaces, and fully softened and residual shear strengths were measured. Factor of safeties were calculated for the mobilization of fully softened and residual shear strengths during different peak ground accelerations (PGA) and different pore water pressure ratios. Quantitative risk to landslide damming was evaluated for different PGA and ground water level scenarios, using the Bishops Simplified Stability Analysis Method modified for the dynamic loading. The study results showed that the landslide mass would fail even if the earthquake of PGA more than 0.4g occurred in a dry season.