INTEGRATED GEOTECHNICAL AND HYDROLOGICAL ASSESSMENT OF RAINFALL-INDUCED SLOPE FAILURE AT MOUNT TUNAK

Abstract

Slope stability is a critical concern in geotechnical engineering, particularly in regions with high rainfall where infiltration can reduce soil shear strength. This study assesses the effects of rainfall infiltration combined with external loading on slope stability at Mount Tunak, Lombok, Indonesia. Rainfall intensities for multiple return periods were derived from Rembitan Station records (2014–2023), and soil properties were characterized through laboratory and in-situ investigations. Numerical analyses were conducted using PLAXIS 2D V.24 with sensitivity evaluations on cohesion, internal friction angle, and permeability. The initial Factor of Safety (SF) ranged from 1.263 to 1.074, indicating marginal stability, and validation using the Limit Equilibrium Method (LEM) in Rock Science yielded similar values (1.201–1.197). Under rainfall infiltration associated with a 10-year return period, the SF decreased to 1.044–0.895, representing a critical condition. Reinforcement using soldier piles with lengths of 5 m, 8 m, and 12 m increased the SF by 2.20%–84.58%. The results demonstrate that rainfall-induced pore pressure significantly governs slope instability and confirm that soldier piles are an effective mitigation strategy for safeguarding infrastructure in tourism-oriented hilly terrains.