Wave Numerical Method Of Saturated Site Soil And Its Engineering Application

Liquefiable soil is generally idealized as fluid-saturated porous media(saturated soils)with deformable porous solid skeleton and fluid saturated in the solid pore structure.Research works referring to wave propagation and numerical methods for seismic responses of the saturated soil-pile-superstructure system are carried out.The main research works are summarized as follows:1.The propagation characteristic of the P1,P2 and S waves in fluid-saturated porous medium is studied.Based on the u-w-p formulation of the fluid-saturated porous media proposed by Zienkiewicz,the wave equations and corresponding theory velocities of P1,P2 and S waves in saturated soils are given for the situations of finite,zero and infinite permeability coefficients,respectively.The relations between the permeability,loading frequency and the propagation characteristics of P1,P2 and S waves are analyzed.2.Decoupling in space and time domain,double-explicit finite element methods are constructed based on the u-p formulation of fluid-saturated porous medium.(1)A diagonalization method is applied to both the mass and the fluid compressibility matrices,which decouples the inertia force and compressive deformation of adjacent nodes in the space domain.(2)Based on the diagonal mass and fluid compressive matrices,three doubleexplicit temporal integration methods for the u-p formulation of the fluid-saturated porous media are constructed.It decouples the interaction of nodes in time domain.The stabilization and accuracy of the proposed completed explicit methods are analyzed both in theory and numerical simulation works.The low efficiency of the dynamic problems of large scale and strong-nonlinearity is avoided effectively.3.Without zero permeability assumption of the boundaries,a viscous-spring artificial-boundary condition is proposed based on the u-p formulation of the fluid-saturated porous media.For the energy radiation effect of the truncated infinite media,based on the u-p formulation of the fluid-saturated porous media,an artificial-boundary condition(ABC)is proposed by reasonable assumptions of outgoing waves.The ABC has definite physical meaning and easily implement.It only changes the values on the diagonal of the coefficient matrices and do not affects the stabilization of the time integral method.Without the zero permeability assumption,the ABC avoids the disadvantages of low accuracy and ignoring the second compression waves that are widely used in the existing methods.4.Implements of the double-explicit finite element methods on seismic responses of saturated site soil-pile foundation-superstructure system are conducted.Based on the double-explicit finite element methods,a computing program to analyze the seismic responses of the saturated site soil-pile foundation-superstructure system is developed on the OpenSees platform.The computing program is verified by the simulation of the shaking table test of the saturated site soil-structure system carried out by our research group,and implemented in the dynamic problems of the saturated site soil-pile-superstructure system.