Numerical Simulation on Structural Safety of Deep-Buried Tunnel Crossing Hard and Soft Rock in Strong Earthquake Areas

Deep-buried tunnels in mountainous areas often lack seismic protection except when crossing faults. However, tunnels crossing abrupt transitions of soft and hard rock strata can suffer significant seismic damage during strong earthquakes. Hence, it is crucial to study the seismic safety of such tunnels. This study compares the structural forces of the tunnel crossing soft and hard rock strata, homogeneous hard rock, and homogeneous soft rock during strong earthquakes. It analyzes and evaluates the dynamic response characteristics and seismic safety of the tunnel under these conditions. The results indicate that the tunnel’s lateral safety is highest when crossing homogeneous hard rock, followed by soft hard rock and homogeneous soft rock. As the distance from the soft and hard rock interface increases, the tunnel's transverse and longitudinal stress safety becomes more like that of the corresponding homogeneous rock. Seismic damage can occur near the soft-hard interfaces due to longitudinal internal forces, with some contribution from transverse internal forces.