Landslide Potential Analysis on Hilly Terrain Based on the CPT Data along the Malang-Kediri Road, Indonesia

Landslides are known to cause significant infrastructure damage and subsequently generate substantial economic losses. One area that is particularly susceptible to such events is the roadway connecting Malang-Kediri and Batu City, Indonesia. This corridor carries a high volume of traffic; therefore, any landslide occurrence has severe implications, including the complete disruption of transportation access. This study investigates the slope factor of safety (FS) to evaluate landslide potential along the Malang-Kediri connecting road using Cone Penetration Test (CPT) data. The FS of the existing slopes was assessed using CPT results as the primary field data to estimate soil physical and mechanical properties. Numerical simulations were conducted using GeoStudio (GeoSlope) Version 8.0 to compute FS values for natural, dry, and saturated (rainy-season) conditions. All analyses were performed under at-rest conditions, without including ground improvement measures. The results indicate that 4 out of 9 modeled scenarios exhibit instability: Slope S-1 under scenarios 2 and 3, and Slopes S-2 and S-3 under scenario 3. In general, slopes became unstable in scenario 3, where the combined effects of traffic loading and elevated pore water pressures substantially reduced shear resistance. Under these conditions, slopes demonstrated failure potential when FS < 1.07. The calculated FS values at points S-1, S-2, and S-3 were 0.55, 0.59, and 0.74, respectively, indicating critical instability. Field observations reveal that soft, organic, clay-rich soils in the upper layers dominate the unstable slope sections. These materials possess low shear strength and are highly susceptible to deformation under excessive loads. Consequently, under scenario 3 loading conditions, the inherent weakness of these soil layers contributes significantly to slope failure. Further investigations are necessary to design appropriate soil improvement strategies and slope reinforcement measures to mitigate future landslide risks along this critical transportation corridor.