ONE-DIMENSIONAL TIME-DOMAIN METHOD FOR FREE FIELD IN LAYERED SATURATED POROELASTIC MEDIA BY PLANE WAVE OBLIQUE INCIDENCE

The input of free field under oblique incidence of seismic waves is one of the urgent problems to be solved in the seismic analysis of large structures. Because of the complexity of the problem, there are few studies on the free field of layered saturated poroelastic media at present. In this paper, a 1-D time-domain finite element method is proposed to simulate the plane wave motion in layered saturated poroelastic media overlaid on bedrock subjected to the oblique incidence plane wave. The method is on the basis of Biot dynamic theory for saturated poroelastic media. Firstly, the spatially 2-D problem is transformed into a 1-D time-domain problem along the vertical direction according to Snell’s law. 1-D finite element equations for poroelastic media are established by discretization principle and finite element. Then an exact artificial boundary condition for elastic media is used to model the wave absorption and input effects of the truncated bedrock half space. The global finite element equations for the system of layered saturated poroelastic media overlaid on bedrock are developed according to the drained or undrained boundary conditions between the poroelastic medium and the bedrock. By solving the 1D equations, the displacements of nodes in any vertical line can be obtained combining the method of central differences and Average acceleration of Newmark, and the wave motions in layered poroelastic medium system are finally determined based on the characteristic of traveling wave. The method is verified and by comparing with the frequency-domain transfer matrix method with fast Fourier transform in analyzing two engineering site.