Evaluation of Slope Stability Due to Earthquake and Rainfall Occurrences

Malaysia is a tropical country with high humidity, heavy rainfall, and unfrequent earthquake, while tremors can exist due to neighbouring regions earthquakes such as Sumatra. The 2004 Sumatera earthquake caused 68 death in Penang, Langkawi, and Kedah. The combined effect of rainfall and earthquake is unknown for the existing slope structures in Penang Island. The research presents the results on slope stability after the impact of rainfall and earthquake using the GeoStudio software. In the first step, the single effect of rainfall shows that longer duration and higher intensity adversely affect slope stability. However, the safety factor was lower when both effects of rainfall and earthquake were considered in the analysis. The combined effect was assessed through two factors of FOS and deformation since the seismic waves imposed as secondary damage to the hill. The results show that higher deformation is recorded for slope geometry with a bigger angle and higher height. The slope is classified as a failed candidate when the factor of safety is less than 1.0. The slope geometry in Sungai Ara was relatively unstable, and the factor of safety (FOS) has not complied with Penang safety guidelines for hill site development 2020. Various slope reinforcement procedures are mainly discussed in relation to Sungai Ara’s slope to improve the slope stability and lead to a higher factor of safety. The research proposes several reinforcement approaches, including retaining walls, soil nailing, and a drainage system. The results demonstrated that the factor of safety improved, and seismic waves deformation reduced, which proved the capability of reinforcement approaches in reducing the effect of rainfall and earthquake.