Numerical Analysis of Inlet Slope Diversion Tunnel at Cijurey Dam, Bogor Regency, West Java, Indonesia

Abstract Diversion tunnel is an important supporting structure in dam construction. During construction phase, diversion tunnel is essential to divert river flow from the upstream to the downstream sides. Therefore, this study aimed to analyze stability of inlet slope diversion tunnel against slope failure using numerical analysis with the software Rockscience (RS2). The data required were engineering geological mapping and core analysis, including determining the lithology type and rock mass quality based on Rock Mass Rating (RMR), Geological Strength Index (GSI), laboratory testing, and earthquake coefficient, which were used as input parameters in the rock science software. The result showed that slope condition during post-construction, as well as the normal, flood, and minimum water levels, reached unstable conditions with static and dynamic load. Consequently, reinforcement for slope was found to be essential in strengthening stability. This could be achieved using soil nailing/tie back with a diameter of 48 mm, a length of 18 m at a spacing of 1 m, and shortcrete with a thickness of 10 cm to increase Strength Reduction Factor (SRF).