Stability Evaluation of Bener Dam Diversion Tunnel During Construction

Bener Dam Diversion Tunnel is located in two rock units such as andesite and andesite breccia. Based on the engineering geology investigation, the subsurface tunnel will penetrate andesite breccia with good rock mass quality (fresh-moderately weathered), while surrounding the tunnel consist of andesite breccias with moderate and poor rock mass quality. Geological and engineering geology conditions are used as the basis for stability analysis of excavation methods and determining primary tunnel support systems. Geological Strength Index is used for determining rock mass parameters. The stability analysis of the openings and tunnel supports was carried out using an empirical and numerical method approach. The results of the empirical analysis of support system stability were then evaluated using the finite element method. The most suitable excavation method is applied by blasting. Evaluation of the support system based on rock mass rating with the finite element method modeling shows that the lowest safety score in the tunnel geomechanical zone is in zone 2 with a safety factor value at the final support is 1.786, however in general they are in a good condition which are safe from the initial excavation until the installation of supports stage.