Seismic Performance of Anchor Rod and Isolation Layer Combination System: A Case Study of Mountain Tunnel

The portal section of mountain tunnels usually suffers severe damage during earthquakes. The purpose of this paper is to investigate the seismic performance of the combined system of anchor rod and isolation layer in the portal section of the mountain tunnel. The numerical model was established based on the actual terrain of the engineering site and included the tunnel pillar portal structure, horizontal seismic wave input, and absorbing boundary conditions. Four cases were considered: without measures, anchor rod, isolation layer, and combination of anchor rod and isolation layer. Comparative analysis of the dynamic response and seismic performance of the structure under seismic action for each case. The results show that: (1) The combination measures reducing the maximum peak acceleration of the tunnel pillar portal and lining to 0.33[Formula: see text]g and 0.36[Formula: see text]g, respectively, achieving acceleration reduction rates of 30% and 36.8%; (2) The combination measures increases frictional resistance through anchor rod, providing restraint and support to the surrounding rock, and the isolation layer further mitigates the interaction between the surrounding rock and the lining, reducing the stress on the lining. This synergy reduces the maximum relative displacement of the tunnel portal pillar by 43.7% to 9.4[Formula: see text]mm, and the lining by 58% to 7.8[Formula: see text]mm; (3) The combination measures reduce the maximum peak principal stress of the lining to 1.48[Formula: see text]MPa, achieving a stress reduction rate of 68.23%. Effectively enhancing the seismic performance of the tunnel and reducing damage and failure.