Limit Equilibrium Method of Slope Stability Analysis: A Case Study Outlet Tunnel Portal of Bagong Dam, East Java, Indonesia
S. K. Digdoyo1,2,a), I G. B. Indrawan3, and R. Hidayat3

1Master^s Student, Department of Geological Engineering, Universitas Gadjah Mada, Indonesia
2PT Hutama Karya (Persero), Indonesia
3Lecturer, Department of Geological Engineering, Universitas Gadjah Mada, Indonesia

Abstract

Bagong Dam, located in Trenggalek Regency, is a dam with tunnel as a diversion channel. The tunnel was designed as a horseshoe type with a diameter of 4.00 m and a length of 416 m. The previous research for tunnel stability analysis has been done empirically, therefore research for determining geological and engineering geological condition and its effect to tunnel stability, numerically are needed. The purpose of this study is to present the rock mass classification using Rock Mass Rating (RMR) and to analyze the slope stability at the tunnel outlet using The Bishop Simplified and Morgenstern-Price Limit Equilibrium Method (LEM), which analyzes slope stability with or without earthquake loads. The results will be used to determine the appropriate slope for the tunnel outlet portal. Data for the LEM analysis were obtained from surface geological mapping, subsurface core samples, and laboratory tests of rock samples. The geological engineering at the outlet tunnel of Bagong Dam consists of andesite breccia interlayered with clay from poor to fair quality, and then fair-quality limestone. The horizontal earthquake load coefficient (kh) at this location is 0.175. Slope failure is unlikely because safety factor values can be achieved using the original slope design.

Keywords: Bagong Dam, Rock Mass Rating, slope stability, Limit Equilibrium Method

Topic: Hydrology, hydrogeology, and geology engineering