Geotechnical investigation of landslide incident in Hulu Kelang, Malaysia

Malaysia has a tropical climate and receives high rainfall intensity, especially during the monsoon season, and is often associated with landslide disasters. This study conducts a geotechnical investigation and numerical simulation to examine the causatives factors and failure mechanism of a landslide incident occurred on 18 September 2021 in a residential area in Hulu Kelang, Selangor, Malaysia. The landslide moved and shifted 2536m² of land. This study conducts a desk study, site visits, field tests, soil sample collection and laboratory tests at the disaster area. The preliminary investigation showed that the bedrock in Kemensah Heights is beteween granite, phyllite and schist rocks. The 23mm/hr, 18mm/hr and 19.2mm/hr rainfall intensity for the three day before the landslide raised the groundwater table to 3 to 4 m below the ground level. The laboratory tests revealed that the soil is silty SAND comprising primarily 42% sand and 28% silt. The cohesion internal friction angle, unit weight, particle density and permeability were 11.3kN/m², 29°, 16.5kN/m³, 2.63Mg/m³ and 5.96 x 10¯³mm/s, respectively. The researchers performed a TLS survey to measure the slope dimension at the Kemensah Heights landslide; the 35m high, 80m wide and 60m long slope forms a 35° slope angle. The JKR probe test revealed two distinct soft and hard layers at a shallow depth which could have influenced the slope stability. The slope stability was evaluated using Plaxis 3D and Slope/W to determine the Factor of Safety (FOS) value. Both simulations showed that the FOS value was ranging between 1 and 1,095, indicating the slope is approaching the critical state. The critical potential failure plane obtained from the simulations showed good agreement with that observed from site. The failure plane was classified as a toe failure. The study concluded that there are four key triggering factors in the Kemensah Heights landslide, 1) antecedent rainfall, 2) excessive surcharge load, 3) soil type, and 4) the existence of two distinct soft and hard soil layers.