Numerical Simulations of Centrifugal Experiments on Seismic Behavior of Shallow Overburden Tunnels with Pre-ground Improvement

Pre-ground improvement is an auxiliary method for mountain tunnels with shallow overburdens in loose sandy grounds. Although pre-ground improvement provides stabilization to the tunnel face and suppresses the settlement of the ground surface, the seismic behavior of the tunnels is not well understood. Previously, the authors performed dynamic centrifugal model experiments and confirmed the basic seismic behavior of shallow overburden tunnels with pre-ground improvement. However, the experiments did not reproduce the tunnel construction process; in other words, the stress release from the ground due to the tunnel excavation was not considered. In this study, therefore, reproduction analyses of the centrifugal model experiments were performed using a two-dimensional elasto-plastic finite element method, and the applicability of the numerical method was examined. Furthermore, analyses reproducing the stress release from the ground were also conducted using the same numerical method. From the results, it was confirmed that the experiments were simulated accordingly by using the proposed numerical method. Moreover, it was found that, in terms of the seismic behavior of shallow overburden tunnels with pre-ground improvement, the numerical results and the experimental results showed the same tendencies whether or not the stress release from the ground due to the tunnel excavation was considered.