Slope stability analysis of inlet tunnel portal slope at Bintang Bano irrigation area, west Nusa Tenggara, using limit equilibrium method

Bintang Bano Irrigation Area aims to optimize water consumption downstream of Bintang Bano Dam and distribute it to irrigate agricultural land in Rempe, Seteluk, Seloto, and Senayan villages. Engineering geology investigations have been conducted, but slope stability has yet to be analyzed. The objective of this research is to assess the stability of slope at the inlet portal of Bintang Bano irrigation tunnel using The Bishop Simplified and Morgenstern-Price limit equilibrium methods, which analyze the slope stability under static and earthquake load and use the result to determine the appropriate inlet tunnel portal slope. The primary data collection consisted of soil and rock assessments obtained from the surface of inlet tunnel portal. Determination of rock mass quality based on the Geological Strength Index (GSI) and laboratory tests. The inlet portal slope comprises poor-quality andesite and residual soil, according to the surface rock's determination of the rock mass quality. The horizontal earthquake load coefficient (kh) in this location is 0.139. Slope failures will likely occur because the relatively low SF values do not meet the standards specified in SNI 8460:2017. Based on these results, the inlet tunnel portal slope can be moved backward to get a better quality of rock masses. © 2024 Author(s).