Mutual seismic interaction between tunnels and the surrounding granular soil

Abstract

At areas subjected to earthquake activity, strategic and vital underground structures should be designed to withstand both seismic and permanent loadings. This study aims to investigate the seismic interaction between tunnels and the surrounding granular dry soil. An advanced non-linear dynamic finite element model has been used to simulate such sophisticated problem, considering the full seismic interaction between tunnel, surrounding soil and bedrock motion. Extended Masing model is employed to simulate the nonlinearity and hysteresisty of the soil. Dynamic analysis is based on step-by-step integration schemes. Three artificial earthquake time-histories are used as control motions at the bedrock surface.Extensive comprehensive studies are carried out on a circular tunnel having diameters varying between 6 and 10m, surrounded by homogenous sand layer of 30m total thickness. The effect of sand layer relative density is examined using relative density range between 25% and 90%. The effects of lining thickness as well as tunnel embedment depth are also investigated.Study results show that the maximum exerted straining actions in tunnel lining are directly proportional to the relative stiffness between tunnel and surrounding soil (lining thickness and soil shear modulus). Moreover, it is highly affected by the peak ground acceleration and the tunnel location (embedment depth). A comprehensive study is performed to show the effect of tunnel thickness and tunnel diameter on both the induced bending moment and lining deformation. In general, it is concluded that seismic analysis should be considered in regions subjected to peak ground acceleration greater than 0.15g.