Evaluation method on ground movement using continuum ground model

Abstract

To analyze the ground movement and the influence of shield tunneling above tunnel structures, the continuum ground model with segmental lining is in use. The analysis region in the transverse section should confirm that the side boundaries do not give significant effects on the analysis results. On the other hand, the lower analysis region is selected based on the empirical value to fit the analysis result for the measured data in practice. The effects of tunnel excavation in the numerical analysis are classified into two parts: one is the unloading effect because of the removal of the soil weight at the tunnel section, and the other is the effect of stiffness reduction inside the tunnel. The former heaves the ground around the tunnel, of which the magnitude increases as the distance from the tunnel invert to the bottom of the analysis region increases. This influence increases as the ground stiffness decreases. This is because the numerical analysis is based on the stress–strain relationship and the displacement comes from the distance multiplying with strain in the case of the elastic model. The latter one causes the upper part of the ground around the tunnel to move toward the tunnel, which decreases the ground reaction. The analysis results include both effects. This study shows both effects on ground displacements separately, taking the lateral region size W and the lower region size d as parameters, and discusses the method to evaluate the analysis results.