Combination of lining strengthening and buffer layers for soft and hard rock tunnels junction subjected to seismic waves

Tunnels in the junction of the soft and hard rock always suffer severe damages during the strong earthquakes. This article aims to investigate the seismic effect of the combination of the buffer layer and the steel fibre reinforced concrete (SFRC) linings in tunnel seismic design. Firstly, taking the soft and hard rock junction of Fanjiazhai Tunnel as the research background, the finite difference calculation models considering the modified seismic motion, the mechanical damping, the safety factor and the seismic materials are established to study the seismic response of the tunnel crossing the soft and hard rock junction. Then, the buffer layer and the SFRC lining are applied into the soft-hard rock junction tunnel respectively, the isolation performance of the buffer layer and the strengthening effect of the SFRC lining are analyzed by using the seismic displacement, seismic acceleration and the safety factor. Finally, the combination of the buffer layer and the SFRC lining is employed in the tunnel located in soft-hard rock junction, the effectiveness and the synergistic effect of combination method are proved by numerical analysis. The research results can provide references for seismic fortification of the tunnel crossing soft and hard surrounding rock junction in meizoseismal area.