A FE-IBE method for linearized nonlinear soil-tunnel interaction in water-saturated, poroelastic half-space: I. Methodology and numerical examples

Abstract

Currently, finite element method is the most widely used method for seismic analysis of underground tunnels. However, the finite element method has an apparent difficulty in modelling unbounded soils, therefore, artificial boundaries are often used to solve this problem, but it becomes much more complicated when the unbounded soils are water-saturated, poroelastic media. This paper provides an alternative technique for seismic analysis of tunnels in unbounded water-saturated, poroelastic soils, with excellent accuracy and efficiency. Based on the Biot's theory of wave propagation in a poroelastic medium, this paper proposes a 2-D finite element-indirect boundary element (FE-IBE) coupling method for seismic analysis of tunnels in water-saturated, poroelastic half-space. The soil nonlinearity is dealt with equivalently linear approach, while the tunnel lining remains linear. One particular advantage of the proposed coupling method is that it allows separate computation for the FE subdomain and the IBE subdomain while avoids iterative process, which is well suitable for parallel computation. Another desirable feature of the proposed coupling method is that it can account for nonlinear soil effect for both the FE subdomain (near field) and the IBE subdomain (far field). In the first part of this paper, the FE-IBE coupling method is presented in detail and the accuracy of this coupling method is verified extensively through comparisons with published results. Besides, the capability of the proposed coupling method is further demonstrated by applying it to analyze seismic responses of tunnels in water-saturated, poroelastic half-space, with emphasis on the effects of soil nonlinearity and interaction between twin tunnels. In the second part of this paper, using results obtained by the FE-IBE coupling method as benchmark, the applicability of two widely used analytical solutions to seismic design of tunnels with soil nonlinearity is investigated. Of particular interest is the influence of dynamic soil-tunnel interaction and interaction between solid frame and pore water.