Dynamic response mechanism of shallow parallel tunnels in saturated strata under incident of SV waves

At present, a large number of overlapping and adjacent tunnel groups have emerged in the core urban area, and the seismic safety problem of these tunnels has become increasingly prominent. However, the dynamic interaction mechanism between adjacent tunnels and the stratum remains unclear. This paper focuses on shallow parallel tunnels in saturated strata. Based on the Biot poroelasticity theory, the boundary integral equation method is used to establish the dynamic analysis models of horizontal and vertical double-line tunnels in saturated strata, and the proposed model is verified by providing comparisons with the known solutions of typical examples. Furthermore, the response mechanism of the tunnel structure and surrounding pore water pressure under the change of tunnel spacing and SV wave incidence frequency is studied, and the results of a single tunnel were compared and analyzed. The results show that the existence of adjacent tunnels changes the dynamic response characteristics of the existing tunnel compared with a single tunnel, and the tunnel response changes more obviously with the decrease of tunnel spacing. In the meantime, the peak stress of lining increased significantly. The distribution of formation pore water pressure around the double-track tunnel is mainly concentrated in the area between the tunnels, and it increases with the decrease of spacing under the low frequency incidence of SV wave. The dynamic response characteristics of the horizontal double-track tunnel are different from those of the vertical double-track tunnel. As the distance between adjacent tunnels decreases, the existence of horizontal double-track tunnels will significantly amplify the dynamic response of the tunnel structure and surrounding strata, while the vertical double-line tunnel will block the propagation of the vertical incident SV wave, which leads to the decrease of dynamic response of the tunnel and the upper surface. The research can provide a scientific basis for the seismic design of shallow parallel tunnels in saturated strata.