Relationship Between Rock Mass Rating (RMR), Q-System, and Geological Strength Index (GSI) of Rock Masses at the Dolok Dam’s Diversion Tunnel, Central Java

Relationships between the Rock Mass Rating (RMR), Tunneling Quality Index (Q), and Geological Strength Index (GSI) have been proposed by several researchers. Being empirically developed, however, the proposed relationships are not always applicable for all geological conditions. This research aims to develop the relationship between RMR, Q, and GSI values of interbedded limestone and marl rock masses based on the results of surface engineering geological mapping and drill core evaluation along construction site of the Dolok Dam diversion tunnel. The results indicate that the rock masses at the tunnel inlet have RMR, Q, and GSI values ranging from 26 to 43, 0 to 3.47, and 24 to 54.5, respectively. On the other hand, the rock masses at tunnel outlet have lower RMR, Q, and GSI values ranging from 19 to 36, 0 to 2.27, and 21 to 53.12, respectively. The proposed statistical relations are in reasonable agreement with those of the previous studies. The results of this research are expected to allow quick assessment of rock mass classifications, particularly for initial design of tunnels in sedimentary rock masses.