Identification of Rainfall Scenario Triggering Slope Failures in Pagar Alam and its Surrounding Area

Pagar Alam and its surrounding area are located in the Bukit Barisan Mountain Rang, thus, the topography is hilly and mountainous. National Road segments passing the area often experience slope failure, which causes distraction to the transportation of people and goods. Past observations showed that slope failures are related to frequent and prolonged rainfall. This paper presents the results of a numerical study on the mechanism of rainfall-induced slope failures in Pagar Alam. The study aimed to identify the critical rainfall scenario triggering slope failures. Data observation indicates that even though wet season started in October, most slope failures occurred between January and April. Thus, initial moisture is required to start the mechanism of failure. The transient pore-water pressure was assessed using SEEP/W while the slope stability was evaluated using Slope/W. The analysis showed that the critical rainfall scenario is a combination of antecedent and major rainfall. The duration of the antecedent rainfall is influenced by the slope angle.