IBIEM solution to scattering of plane SV waves by tunnel lining in saturated poroelastic half-space

Based on the Biot's theory of two-phase medium, a high-precision indirect boundary integral equation method (IBIEM) is proposed to solve the scattering of SV waves by a two-dimensional tunnel lining in saturated poroelastic half-space. The ground displacement amplitudes, dynamic stress concentration of the tunnel and pore pressure on the outer surface of the tunnel are investigated under different circumstances, and the frequency spectrum analysis is also made. Numerical analysis shows that the propagation and scattering characteristics of seismic waves depend on the porosity of the surrounding medium, frequency and angle of the incident waves, tunnel depth, etc. The drainage state of tunnel outer surface has little impact on the ground displacement amplitudes and dynamic stress concentration of the tunnel. The features of the dynamic stress concentration in the tunnel strongly depend on the incident angle and medium porosity; as the porosity increases, the dynamic stress concentration becomes more significant. The pore pressure on the outer surface of the tunnel can reach four times the peak stress amplitude of the incident waves, and that for incidence waves of 30° is significantly greater than that of the vertically incident case. The spectral characteristics at displacement of different points on ground surface may change within a small distance, and the amplification effect seems more obvious in the case of oblique incidence. With the increase of embedded depth, the spectral curves of ground displacement and dynamic stress concentration of the tunnel oscillate more rapidly, but the amplitude will decrease. In addition, according to equivalence of velocity ratio, the single-phase medium model can approximately simulate the displacement and stress fields of tunnel - saturated medium system for SV wave incidence.