The Western Ghats of India are facing frequent disruptions due to rainfall-induced landslides and slope failures. In recent years, the Western Ghats have experienced devastating landslides, resulting in prolonged traffic blockages lasting for days or even weeks, wreaking havoc on lives and infrastructure. Kerala state has experienced exceptionally heavy rainfall in 2018 since 1918. This study focuses on analyzing a rainfall-induced landslide (Latitude 10.0490841 N, Longitude 76.8382505 E) that occurred near Adimali town in the Idukki district of Kerala state, India on 16th August 2018. The consequences of the landslide were severe traffic disruptions on Adimali to Munnar roads. The objective of this study is to identify the failure mechanism of the landslide through extensive geotechnical investigations. Dew point potentiometer test was used to obtain the Soil Water Characteristic Curve and suction of the soil. Weathering characterization of soil was conducted by using FE-SEM and EDAX analysis. Additionally, slope stability analysis was carried out using limit equilibrium analysis to evaluate and understand the failure mechanism of the landslide. The factor of safety during failure at the critical depth is 0.934, and the factor of safety increases with the depth. Simultaneously, the pore water pressures rose to 20 kPa, thereby indicating the slope failure mechanism. Rainfall infiltrates into the soil and reduces its shear strength due to the rise of pore water pressure, thereby causing the landslide. As rainfall infiltration is the primary triggering factor, proper mitigation measures need to be implemented on the landslide’s susceptible transportation corridors.