Excavation method and support system in the diversion tunnel of Tiga Dihaji Dam, South Sumatera, Indonesia based on the rock mass quality

Abstract

This study determined the excavation method and the support system in the diversion tunnel of Tiga Dihaji Dam, South Sumatera of Indonesia. Investigation performed in this study included surface geological mapping and evaluation of core drilling that are useful for determining rock mass quality. Geological conditions in the tunnel consist of tuffaceous sandstone lying unconformity over interbedded calcareous sandstone and calcareous siltstone. Based on the Geological Strength Index analysis, the excavation method for tuffaceous sandstone by hammer and blasting, and digging and ripping for the interbedded calcareous sandstone and calcareous siltstone. The support system is the installation of rock bolts of 3 m long with spaced 2.5 m on tuffaceous sandstone, 4 - 6 m long with spaced 1 - 1.5 m on interbedded calcareous sandstone and calcareous siltstone, and with shotcrete thickness of 50 -200 mm (Rock Mass Rating). While in the Q-system classification were 2.7 m long rock bolts with spaced 2.7 m on tuffaceous sandstone, 2.7 m long rock bolts with spaced 1 - 2.4 m, and a shotcrete thickness of 25 cm on interbedded calcareous sandstone and calcareous siltstone.