Multiscenario Slope Stability Back-Analysis in Open-Pit Mining: A Case Study from Tanjung Enim, South Sumatra Goestyananda Pratama (a), Imam Achmad Sadisun (a*) Indra Andra Dinata (a) Muhamad Raihan (a,b)
a) Geological Engineering Program, Bandung Institute of Technology
Jalan Ganesha 10, Bandung 40132, Indonesia
b) Natural Science Foundation Program, Ehime University, Ehime, Japan
*iasadisun[at]itb.ac.id
Abstract
The landslide event on March 5, 2025, at 09:15 WIB was triggered by high-intensity rainfall lasting 5.95 hours, with a daily accumulation of 95.16 mm/day. The initial slope analysis showed a stable Factor of Safety (FoS) of 1.46 using the Morgenstern-Price method. However, since a landslide occurred in reality, a back analysis of slope stability was conducted to evaluate the failure mechanisms and contributing geotechnical parameters through engineering geological assessment, slope geometry modeling, and numerical simulations using Slide2 software. The Morgenstern-Price method was applied under various hydrological and dynamic loading scenarios to obtain the critical FoS value of the slope close to the actual landslide event. The 30-day cumulative rainfall infiltration scenario significantly reduced the FoS to 1.01 due to increased saturation in the middle and lower slope zones. The most critical condition occurred under the combined influence of haul load, seismic load, and rainfall infiltration, resulting in the lowest FoS of 0.99. These results indicate that the landslide was primarily triggered by extreme rainfall, which reduced the FoS below the slope stability threshold (FoS > 1.0) and did not meet the standards of SNI 8460:2017 and the Decree of the Minister of Energy and Mineral Resources of the Republic of Indonesia No. 1827K/30/MEM/2018, which require FoS < 1.1 for overall slope stability.
