Empirical Approach For Preliminary Support and Excavation Method Design Based On Engineering Geological Study Of Mbay Dam Diversion Tunnel

This paper presents excavation methods and support systems in the diversion tunnel of the Mbay Dam, East Nusa Tenggara, Indonesia, based on rock mass quality ratings. The rock mass quality was classified through geological surveys, core drilling evaluations, and laboratory tests. The results showed that the lithology along the tunnel alignment was pyroclastic breccia. Using the Rock Mass Rating (RMR) classification system, which was the single classification at the time of designing the Mbay Dam Diversion Tunnel, the pyroclastic breccia rock mass was classified III and IV (fair and poor). Meanwhile, according to the Q-System classification, the second classification used, pyroclastic breccias were also classified as fair and poor. Therefore, according to the RMR classification, the recommended excavation methods were top heading and bench. Support systems suitable for rock mass quality in the Mbay Dam diversion tunnel were rock bolt, wire mesh, shotcrete, and steel sets, with different variations and types depending on the rock mass class and classification used.