Backanalysis of rainfall induced landslide in Sabah by Perisi Model

Rainfall has been recognized as the main landslide triggering agent particularly in Malaysia. Therefore, this project focuses on the significance of extreme rainfalls on suction variations and slope stability using PERISI (Preliminary Evaluation of Rainfall-Induced Slope Instability) program. Previous study showed that the extreme rainfall is characterized by geographical location. Hence, Intensity Duration Frequency (IDF) curve for Kota Kinabalu was developed in this study for 10 year return period based on 30 year data. PERISI was used to study the effect of rainfall infiltration on the stability of the two cases of slope failure in Kota Kinabalu Sabah. The study show that the critical rainfall duration depends on the soil’s moisture retention ability and permeability. The soils at Site 1 and 2 are classified as sandy SILT and Highly Plastic CLAY respectively. Analysis showed that combination of 1 day major rainfall and 14 days antecedent was found to cause slope failure in Site 1 while 30 days cumulative rainfall has caused slope instability in Site 2. The comparison between dry and extreme condition in the factor of safety analysis also indicate that rainfall has a great effect on the slope stability