PLASTIC ZONE PREDICTION USING FINITE ELEMENT METHOD ON CIKONENG DECLINE TUNNEL AT PT. CIBALIUNG SUMBERDAYA.

• Main Author: Pangacella Putra, Bayurohman
• Format: Theses
• Language: Indonesia
• Online Access: https://digilib.itb.ac.id/gdl/view/83372
• Institution: Institut Teknologi Bandung

Underground Mining activity will always face deformation and instability of the rock mass around the underground openings. A large deformation was reported to occur on decline tunnel of PT. Cibaliung Sumberdaya (PT. CSD). Prior to this event, the same problem occured at the same tunnel, which the tunnel wall had been refurbished into the the proposed original shape. This implies that the plastic zone had developed around the tunnel and the same support system couldn’t resist the increasing load. Therefore, an analysis of plastic zone around the excavation should be carried out. Conducted analysis started by modelling the excavation the tunnel to get the prediction of the first plastic zone thickness. Then, back analysis was carried out to estimate the decreasing strength of the rock mass inside the plastic zone. After that, using the same model as the the back analysis, the increasing thickness of plastic zone can be determined.With the increasing plastic zone in size, there is more load to be supported by support system. Therefore, analysis of recommended support system in needed to suggest the effective support system that can prevent the increasing plastic zone and causing the same problem. The strain from back analysis result shows the similarity compared to the monitoring result when the modulus deformation E and strength parameter mb and s of Hoek Brown failure criteria of the materials inside the plastic zone is 50% of its peak strength. The analysis of recommended support system shows that decline tunnel need a combination of supports of 200 mm thick shotcrete, 1 m spacing of rock bolt in the direction of tunnel advance, and 1 m in section spacing of reinforcement beam. Although, floor of the tunnel should be given extra consideration because it is predicted to experience high load that could excess its strength. In that case, installing rock bolt which length greater than the plastic zone thickness can help stabilizing the tunnel floor.