Modelling of ground vibration from tunnels in a poroelastic half-space using a 2.5-D FE-BE formulation

This paper presents an improved two-and-a-half-dimensional (2.5-D) finite element-boundary element (FE-BE) model to predict train-induced vibrations from a tunnel with an arbitrarily shaped cross-section embedded in a poroelastic half-space. The proposed model considers both the saturated porous characteristic of the soil and the free surface effect. A 2.5-D BE model based on the Green’s function for a poroelastic half-space is developed to simulate the soil surrounding the tunnel. The discretization of the infinite ground surface is not required, which avoids spurious reflections induced by mesh truncations and significantly reduces the mesh size of boundary elements. The 2.5-D BE model for saturated soils and the 2.5-D FE model for tunnels are coupled via the boundary conditions on the soil–tunnel interface. The track components are coupled with the tunnel-soil model to more accurately predict vibrations induced by underground railways. After being verified via comparison with an existing model, the proposed model is used to assess train-induced vibrations from a quasi-rectangular tunnel in a poroelastic half-space. Analysis of vibrations induced by the single-line load and double-line load on rails is conducted, respectively. The results show that the insertion gain, which is greater than 30 dB, is highly dependent on the frequency and observation position. When the saturated soil is simplified as the equivalent single-phase elastic soil, the soil displacement tends to be overestimated while the soil stress is underestimated. A saturated soil model may more accurately describe train-induced vibrations from a tunnel in the water-rich region.