Numerical Modeling on Localized Ground Subsidence Induced by the Tunneling in Sand

Abstract

Ground subsidence caused by tunneling is becoming a common problem in China due to rapid developing of underground space. Superstructures may crack and/or incline subjected to localized ground subsidence caused by tunneling. Ground subsidence would also induce breakage of buried pipelines which may even cause ground collapse due to pipe leakage. Mechanism of ground subsidence caused by tunneling in clay has been well understood. Volume of settlement troughs in clay are widely accepted as a constant along the depth, which is equal to ground volume loss in the ground. However, ground subsidence caused by tunneling in sand is still not clear considering the change of volume of settlement trough with depth, which has been observed in practice. Therefore, mechanism of ground subsidence caused tunneling in sand deserves in-depth investigation. In this study, ground subsidence caused by tunneling in three different types of sand with relative densities of 30% (i.e., loose sand), 50% (i.e., medium-dense sand), and 70% (i.e., dense sand), were adopted in finite element (FE) modeling. All soils were modeled using Mohr-Coulomb model. Gaussian-shape displacements were applied at bottom of FE models to simulate the tunneling effect. FE modeling results demonstrate that Gaussian functions can provide a good estimation of soil settlement trough at different depth. Trough width parameter decreased with the depth, while volume of soil settlement increased with the depth. It was also found that volume of settlement trough in the loose sand was greater than those in the medium-dense sand and dense sand, which may be attributed to contraction of the medium-dense and dense sand during the settlement propagating towards the ground surface. A modified empirical equation was proposed to calculate the settlement caused by tunneling in the sand at any depth with consideration of the effect of relative density of the sand. In the proposed method, the volume change of the settlement through was also incorporated.