Analysis of engineering geology conditions based on the quality of rock mass in the Tiga Dihaji Dam’s diversion tunnel, South Sumatera, Indonesia

This research has examined the rock mass quality case study in Tiga Dihaji Dam’s diversion tunnel. Observations of geological conditions were carried out on surface and subsurface site show that area consists tuffaceous sandstone carbonate interbeds. The method this is based classification Geological Strength Index (GSI), Rock Mass Rating (RMR), Q-system. results indicate a GSI value 15 - 87.5 (very poor very good), RMR 48 82 (fair Q-system 0.01 – 60.0 (exceptionally good). Meanwhile, interbeds have low value, with 10.5 77.5 to 17.0 56.0 fair), 0 35.2 Moreover, correlation was made between for area. obtained by equation = 2.2885RMR 82.567 (R 2 0.6653), 2.0175ln(Q) + 63.061 0.4987), 7.2119ln(Q) 54.578 0.8095).