A Study on the Damage Degree of Shield Tunnels Submerged in Overburden Soil During the Thrust Fault Offset

Abstract

When an under-lain thrust fault slips, especially triggered by earthquakes, the overburden soil may deform and fail so that a fault zone also develops inwardly. The research about the deformation and the failure of the overburden soil is an essential issue to evaluating the safety of ground or underground structures near the potential faulted zone. In this study, a MRT tunnel, closed to a thrust fault and fault dip 60 degree, is considered, both of the sandbox experiment and the numerical analyses are adopted to discuss the damage degree of a tunnel submerged in an overburden soil under the thrust faulting. In the numerical analyses, a small-scale model, simulation of the sandbox, is justified according to the experimental results and used to discuss the base behavior of the overburden soil. In addition, a full-scale model is used to evaluate the damage degree of tunnel segments by defining a dangerous factor. Moreover, considering the real behaviors of sand particles, the distinct element method is adopted as well. In the sandbox experiment, the results indicate that the development of the shear zone was apparently hindered by the existence of a model tunnel near the fault tip, and induced significant deformation of the tunnel. In addition, the results from numerical analyses, the finite element method and the distinct element method, are similar to the experimental results. The numerical analysis results of the full-scale model indicate that the damage degree is increased while the tunnel is close to the fault tip, and the footing wall is more dangerous than the hanging wall. The defined dangerous factor is able to reflect the damage degree of the tunnel. In the distinct element analysis, the full-scale model, it can be observed that a fault zone extends from the fault tip to the ground surface, but discussions on the distribution of stress and moment in the tunnel are not included and will be considered in the future study.