Kenetic Analysis For Foundation-Soil Coupled System

The dynamic characteristic of a foundation-saturated soil coupled system is studied in this paper. Three models are considered:1. just vertical loads on the top surface of foundation-saturated soil coupled system;2.not only the vertical loads on top the surface of saturated soil coupled system,but also lateral loads on the left surface of system;3. on the basis of the first case, inhomogeneity of the saturated soil is considered.Based on the porous media theory and elastic mechanics, the governing equations of incompressible fluid-saturated soil and elastic foundation are presented in the case of small deformation respectively, initial conditions as well as the joint conditions are derived. Different boundary conditions and non-uniform functions which represent material inhomogeneity for three different models are proposed.Numerical simulation method is proposed to solve the problem correctly. The differential quadrature element method is used to discretize the governing equations of the coupled system on the spatial domain and a general method is presented to deal with the continuity and discontinuity conditions on the interface between the foundation and the saturated soil. Thus, a set of nonlinear ordinary differential equations is yielded in time domain which is then discretized by using second-order backward difference scheme. Finally, the Newton-Raphson method is adopted to solve the discretization equations, the dynamic characteristics of the coupled system are analyzed, and the effects of number of grid points are considered.The dynamic characteristic of a foundation-saturated soil coupled system is investigated. Through parameter study, the transient dynamic characteristic of saturated soil and foundation has been revealed. Also, the influence of soil inhomogeneity and boundary condition on coupled system is considered which can provide theoretical basis and reference data for foundation engineering design.As can be seen from the results, the differential quadrature element method is a high precision numerical method, which needs less nodes to reach good solution convergence.