Scattering Of Elastic Waves And The Problem Of Internal Source By A Tunnel Embedded In Saturated Poroelastic Half-space

With the rapid economic development in China today, the urban transportation network get great improved continuously so that many of people travel out depend on the metro. Therefore, the study of scattering of plane P and SV waves and the transient response of internal source by a tunnel embedded in saturated poroelastic half-space has a very important theoretical and practical significance about the engineering of earthquake and antiknock as well as disaster prevention and mitigation engineering.Based on Biot’s theory of two-phase medium, a high-precision indirect boundary integral equation method is proposed to solve the scattering of P and SV waves by a two-dimensional tunnel in saturated poroelastic half-space. The ground displacement amplitudes, dynamic stress concentration of the tunnel, the pore pressure on the outer surface of the tunnel are investigated under different circumstances, and the frequency spectrum analysis is also addressed. Numerical analysis shows that the characteristics of seismic waves propagation and scattering depend on the porosity of the surrounding medium, frequency and angle of the incident wave, 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 ground displacement amplitude amplification degree decreases with increasing porosity. With the increase of the incident frequency the dynamic stress distribution becoming more and more complex while multiple peak areas appear, and the stress concentration seems more obvious in the case of oblique incidence. With the increase of embedded depth, the spectrum 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 seismic wave incidence.This paper study on the transient dynamic response of elastic tunnel embedded in saturated poroelastic half space under internal blast loading. Response time history about the ground displacement, tunnel dynamic stress, radial displacement and pore pressure of surrounding rock under blast load are given by calculating, and analyzed the difference response time history between the saturated half space and the whole space. Research shows that permeable and impermeable conditions has little impact on response time history under blast load. With the increase of porosity, the influence of saturated poroelastic half space under blast load is reduced while effects of tunnel is increased; The ground displacement amplitudes is decreased with the depth increasing, namely the thicker overlying soil the affected by blast load is smaller. Response time history of the saturated half space and the whole space are the same as soon as when the blast load is applied, then the upper of tunnel is obviously affected by the surface reflection wave so that the amplitude of dynamic stress and radial displacement of surrounding rock in case of smaller embedded depth are bigger than the whole space.