Research on the dynamic behavior of transversely isotropic saturated media due to meeting subway loads using an improved 2.5D FE-BE method

Abstract

The focus of this contribution is to develop an improved 2.5-dimensional (2.5D) FE (finite element)-BE (boundary element) method for a tunnel structure-transversely isotropic saturated soil system subject to underground moving train loads. In the proposed model, the rectangular tunnel invert, the lining, and the region of interest within the soil continuum use the 2.5D FE method. The remaining region of half space is replaced with a viscous spring boundary along the lateral sides and boundary element along the bottom. The theory of acoustic propagation in saturated media is extended to include transversely isotropy, viscoelasticity and boundary elements. An existing case is calculated using the enhanced model, and the results are compared with the previous literature to validate the accuracy and reliability of the proposed method. A parametric analysis is further conducted, and the factors considered in the analysis of ground-borne vibrations induced by trains meeting in the rectangular tunnel include the soil permeability, the groundwater level, and the depth of the tunnel. Numerical comparisons show that the saturated soil above the tunnel moderates the displacement undulation caused by quasistatic axle loads of the train, but this is not the case if the load has a non-zero excitation frequency. Moving train loads with excitation produce larger excess pore water pressure amplitude than do the quasi-static loads over a wide range along the travelling direction. The effect of meeting trains depends on the running speeds of both lines in opposite directions to some extent. Other conclusions useful to practical engineers are contained in the parametric study.