Abstract
This research has examined the rock mass quality case study in the Tiga Dihaji Dam’s diversion tunnel. Observations of geological conditions were carried out on the surface and subsurface of the study site and show that the study area consists of tuffaceous sandstone and carbonate interbeds. The method of this study is based on the classification of the Geological Strength Index (GSI), Rock Mass Rating (RMR), and the Q-system. The results indicate that tuffaceous sandstone has a GSI value of 15 - 87.5 (very poor - very good), RMR 48 - 82 (fair - very good), and Q-system 0.01 – 60.0 (exceptionally poor - very good). Meanwhile, carbonate interbeds have a low value, with a GSI value of 10.5 - 77.5 (very poor to very good), RMR 17.0 – 56.0 (very - poor fair), and Q-system 0 - 35.2 (exceptionally poor - good). Moreover, a correlation was made between rock mass quality for conditions in the study area. The correlation between GSI and RMR was obtained by the equation GSI = 2.2885RMR 82.567 (R2 = 0.6653), RMR and Q-system RMR = 2.0175ln(Q) + 63.061 (R2 = 0.4987), and GSI and Q-system GSI = 7.2119ln(Q) 54.578 (R2 = 0.8095).
Highlights
The condition of the Selabung river during the rainy season has a large discharge
The geological investigations show the tunnel is in the tuffaceous sandstone and carbonate interbeds, as shown in Figure 3 and Figure 4
The core data analysis results show that the tunnel is between tuffaceous sandstone and carbonate interbeds (Figure 5)
Summary
The condition of the Selabung river during the rainy season has a large discharge. It even often becomes a problem both along the river channel and the surrounding areas. The surrounding area becomes dry and causes water shortages in the agricultural area. For this reason, efforts were made to overcome this condition by constructing the Tiga Dihaji dam, which can be used as a reservoir for water during the rainy season. The Tiga Dihaji Dam is located in the Selabung River, South Ogan Komering Ulu, South Sumatera, Indonesia (Figure 1). In constructing the Tiga Dihaji Dam, a diversion tunnel is needed to divert the flow of river water during the construction process. The elevation of the inlet tunnel is at +221.0 m above sea level, while the outlet tunnel is located at +218.41 m above sea level
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