Empirical Designs of Excavation Method and Support System of the Intake Tunnel of Meninting Dam, West Nusa Tenggara, Indonesia

The intake tunnel of Meninting Dam has been designed based on RMR but with less detailed drill core evaluation in the tunnel area, which will lead to less accuracy in the design. The objective of this study was to evaluate the tunnel’s excavation method and support system using the latest data based on rock mass classification of RMR, GSI, and Q–system. The investigation was conducted by surface geological mapping and core drilling evaluation. The results showed that the tunnel area consists of pyroclastic breccia intercalated with lapilli stone. Based on the rock mass quality, the tunnel can be divided into two sections: Section A has fair quality rock, and Section B has poor quality rock. Based on the empirical designs, the recommended rock and tunnel excavation in Section A by hammer and top heading bench, and Section B by ripping and top heading bench. The recommended supports in all sections were using a combination of rockbolts, shotcrete, and wire-mesh. Even though the empirical approach is helpful in the preliminary design, a numerical study is needed to verify the empirical design so the recommended excavation and support system can be safely applied.