Recommendation of excavation method and support system based on engineering geology at Riam Kiwa Dam diversion tunnel, South Kalimantan, Indonesia

Abstract

River flow diversion is one of the most critical factors that must be considered for the success of dam construction. Soil and rock can support and load; therefore, understanding their strength and properties before tunnel construction is essential. Tunnel excavation and support depend totally on rock mass quality. Surface geological mapping, drill core analysis, and laboratory testing characterized the engineering geology conditions. Rock Mass Rating (RMR) and Japan Society of Civil Engineers (JSCE) methods were compared to determine rock mass quality and recommend excavation and support systems. Results showed that slightly weathered andesite lava and tuff lapilli lithologies dominate the tunnel alignment. Based on RMR, the rock masses quality along the tunnel alignment consists of poor and fair, and based on JSCE, the tunnel alignment consists of D I and C II rock categories with L and M massive rock types. Top heading and bench are recommended for tunnel excavation based on RMR, and the double bench and full-face method with an auxiliary bench cut are recommended for tunnel excavation based on JSCE. Although the characteristics of other support systems vary marginally, support systems based on RMR and JSCE recommend rock bolts and shotcrete as the primary tunnel support systems.