Effect of a Shock-Absorbing Material on Seismic Responses of the Longitudinal Buried Tunnel Using Theoretical Analysis and Finite Element Modeling

Underground structures such as tunnels are one of the important elements in the transportation network that may show different seismic behavior compared to structures built on the ground due to being buried in the ground and bearing high stresses. Therefore, it is very important to pay attention to the behavior of these structures during seismic loading. In this study, in order to apply the damping approach in the soil-tunnel interaction system, a two-dimensional finite element model is employed with the help of ABAQUS software. For this purpose, the data of four known earthquakes are used to apply seismic load to the soil-tunnel system. Furthermore, depths of 15, 20, 25, 30 and 40 m for the tunnel and thicknesses of 0, 15 and 25 cm for the damper are considered, during which various parameters such as horizontal displacement, stress and tunnel strain response are evaluated. Moreover, to evaluate the effect of the type of damper, the results of the strain and stress applied to the tunnel crown for two types of dampers were compared with each other. It is important to state that the optimum thickness of the damper layer was reported to be 25 cm. The results show that putting a damper layer between the tunnel and the soil can reduce the tunnel’s maximum stress and strain for different seismic waves excitation up to 47% and 37%, respectively. The horizontal displacement of the tunnel in the saturated state is slightly higher than that of the unsaturated state. By and large, the application of shock-absorbing material, especially those with higher elastic modulus, can have an acceptable damping effect on the seismic response of the tunnel-soil interaction system, which is quite helpful for the anti-seismic design of tunnels.