Investigation of tandikat landslide, west Sumatra, Indonesia

Abstract

A disastrous earthquake struck Padang, West Sumatra Province on September 30, 2009, at 5:16 p.m. with magnitude of 7.6, triggered landslides in Tandikat, Padang Pariaman Regency which took hundreds of lives. These landslides occurred on loose pumice layered mountain during rainfall. The combination of intensive rainfall and strong earthquake probably decreased the slope stability. This study proposes to learn more about initial failure mechanism of earthquake-induced landslide of Tandikat area using strain energy approach. Integrated study through field investigation, laboratory work and numerical modeling were conducted. Strain energy concept was used to assess pore water pressure increase during cyclic loading. In order to attain dynamic properties required, stress-controlled cyclic triaxial (CTX) test were used. Model of pore water pressure ratio related to cumulative dissipated strain energy (E) was developed. The estimation of E during the actual earthquake motion was performed by finite element code ABAQUS. The predicted excess pore water pressure was used to assess slope stability during earthquake motion using infinite slope assumption. In terms of initial effective confining pressure, lower effective confining pressure of pumice sand need small E to reach the value of 0.8 of pore pressure ratio than that of higher effective confining stress. The result shows that shallow landslide due to earthquake more likely to occur than deep seated type landslide in the area. From slope stability analysis result, slope failure occurred prematurely prior to maximum peak of earthquake acceleration implying great influence of pore water pressure generation to slope failure.