Abstract
Tunnel construction in complex geological environments such as fault zones and discontinuities are some problems in tunnel stability. This research focused on rock mass characterization and 3D numerical modelling of the finite element method to evaluate the diversion tunnel stability at the Bener Dam in Purworejo Regency. Rock deformation and stress distribution around the tunnel was the main discussions in this study to comprehend the design of a support system that could overcome these geological conditions. The diversion tunnel was located on the right side of the dam, where the fault was found and extended in the area around the intake, passing through the tunnel path. Geological surveys, point load tests, and rock engineering properties tests were then carried out, showing the rock in the location was dominated by andesite breccias with GSI values 30-68 and moderate to high weathering levels. The fault plane obtained in the study area had an N305°E/87° orientation. The simulation result showed a redistribution of displacement within the fault zone. Displacement and maximum stress occurred in the tunnel that intersected the fault zone, resulting in a decrease in the stability of rock around the fault. Therefore, an adjustment of the support system is required.
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