Seismic behavior of circular tunnels: Influence of the initial stress state

Tunnel construction leads to significant perturbations of the initial stress state in the surrounding soils. This implies that during a given earthquake, the seismic behavior of tunnels is probably modified. The aim of this study is to provide an estimation of the influence of the initial stress state caused by construction on the tunnel seismic response, based on the dynamic nonlinear time-history numerical analysis. The tunnel construction is simulated using the convergence-confinement method with various stress release coefficients (lambda). The numerical models consider the soil-tunnel interface conditions, as well as the uncertainties in modulus degradation curves and damping ratios of soil. The frequency characteristics and intensities of input ground motions are involved as well. The results highlight that the stress release process has a more pronounced effect on the seismic axial force increments rather than the seismic bending moment increments with the effect becomes progressively larger as the input motion intensities and the stress release coefficients increase.