Time-dependent longitudinal responses of a shield tunnel induced by surcharge load: Theoretical prediction and analysis

Abstract

The surcharge load at the ground surface inevitably breaks the original equilibrium state between the underneath tunnel and the surrounding soil, which will impact the service performance of a subway tunnel. This paper presents a novel semi-analytical approach for assessing the time-dependent, longitudinal responses of a subway tunnel in soft soil strata induced by the surcharge load. The solution is developed based on the framework of the classical ‘‘two-stage method” but innovatively incorporates the effects of ground stratification, the consolidation process, and the longitudinal stiffness reduction of the lining. Biot’s poroelastic theory in conjunction with the Laplace- Fourier transform technique is selected to model the deformation of the stratified ground, while the Timoshenko beam on a Pasternak foundation is employed to model the mechanical responses of the tunnel. The proposed semi-analytical solution is validated not only by comparison with benchmark solutions and a finite element model, but also by predicting a well-documented field measurement. Parametric analyses are conducted to investigate the effects of the elastic modulus and the permeability coefficient of the stratified ground on the longitudinal responses of the tunnel. It is expected that the proposed solution can serve as a useful tool for evaluating the effects of the surcharge load on the longitudinal responses of a subway tunnel.

Keywords

Time-dependent / Longitudinal responses / Stratified ground / Subway tunnels / Ground surface surcharge / Consolidation