Three-dimensional Scattering Of Oblique Incident Seismic Waves By Intermountain Basin And Underground Lined Tunnel

In reality,there have been many topographies or structures,the size of which along axis is much larger than cross-setion.Then two and a half-dimensional(2.5-D)simulation can be used to solve the seismic response of these structures or topographies.In addition to reflecting three-dimensional(3-D)sesismic responses,this method also has the advantage of low computational cost and smaller storage occupation than truly 3-D analysis.In this paper,2.5-D multi-domain indirect boundary element method(IBEM)is developed and applied to study 3-D scattering of seismic waves by intermountain basin topography and infinitely long lined tunnel buried in a layered transversely isotropic(TI)half-space.And the main contents are displayed as follows.1.3-D scattering of elastic waves by intermountain basin topography.Firstly,the model of intermountain basin in layered elastic half-space was decomposed into independent closed mountain domains,closed basin area and open layered half-space.The scattered fields of closed regions were simulated by the full space Green's functions of moving distributed loads along axis.And the scattered fields in opening region were simulated by multi-layerd half-space Green's functions of moving distributed loads along axis.Later,boundry conditions were established to solve the vitual uniform load to obtain the total wavefield responses.The accuracy was verfied by comparing with the results of single semi-circular ridge and valley reported by other authors.Numerical analysis was carried out for the case of a intermountain basin topography in homogeneous elastic half-space and in single layer over bedrock respectively in frequency and time domain.The results show that there is significant dynamic interaction between the sedimentary basin and adjacent mountains.And mountain heights have significant effects on the scattering of waves.2.3-D responses of long lined tunnel in layered transversely isotropic half space.The model of lined tunnel in multi-layered TI half-space was decomposed into independent closed lining domain and open multi-layered TI half-space.The full-space Green's functions of moving distributed loads along axis were used to simulate the scattering fields in closed domain,and the multi-layered TI half-space Green's functions of moving distributed loads along axis acting on an inclined line were used to simulate the scattering fields in the opening domain.Next,the virtual distributed loads were solved by boundary conditions,and the total dynamic responses can be obtained.The accuracy of this method was verified by comparing with the results of isotropic half-space.And then,numerical calculations were executed in a homogeneous TI half-space and a single layered TI half-space,including the amplitude of ground surface displacement near the tunnel,the displacement and dynamic stress concentration factor of the lining wall.The results show that,dynamic characteristics of lined tunnel and layered half-space are influenced by the modular ratio of TI media,the frequency and angle of incident waves,which furthermore changes the dynamic interaction between layered TI soil and the lined tunnel.