Stability Analysis of Evasion Tunnels Using the Rock Tunneling Quality Index (Q-System) Method On the Construction of the Bagong Dam Trenggalek, East Java

The Bagong Dam evasion tunnel is part of the dam construction which functions to drain water flow so that work can be done. In planning evasive tunnels, it necessary study geological, geotechnical and structural conditions tunnel. This intended provide an overview subsurface engineering geological research area, as determine stability then recommendations for support used. method used Rock Tunneling Quality Index (Q-System) buffer in process. Based on analysis there are three rock layers, namely: sandstone, breccia limestone. Q-System analysis, mass class value ranges from 0.451 0.651 with Very Poor quality 1.162 quality. At four drill points BH-09, BH-03, BH-10 BH-11, recommendation obtained type (B+5) SRF+B