Analytical solution for evaluating deformation response of existing metro tunnel due to excavation of adjacent foundation pit

Abstract

The excavation of foundation pit generates soil deformation around existing metro tunnel with shield driving method, which may lead to the deformation of tunnel lining. It is a challenge to evaluate the deformation of shield tunnel accurately and take measures to reduce the tunnel upward displacement as much as possible for geotechnical engineers. A new simplified analytical method is proposed to predict the longitudinal deformation of existing metro tunnel due to excavation unloading of adjacent foundation pit in this paper. Firstly, the additional stress of soils under vertical axisymmetric load in layered soil is obtained by using elastic multi-layer theory. Secondly, the metro tunnel is regarded as a Timoshenko beam supported by Winkler foundation so that the shear effect of tunnels can be taken into account. The additional stress acting on the tunnel due to excavation unloading in layered soil are compared with that in homogeneous soil. Additionally, the effectiveness of the analytical solution is verified via two actual cases. Moreover, parametric analysis is conducted to investigate the responses of the metro tunnel by considering such factors as the variation of subgrade coefficient, offset distance from the excavation center to tunnel longitudinal axis as well as equivalent shear stiffness. The proposed method can be used to provide theoretical basis for similar engineering project.

Keywords

metro tunnel / simplified analytical method / additional stress / Timoshenko beam / Winkler foundation

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