One Dimensional Time-domain Algorithm For Seismic Response Analysis Of Deep Sea Foundation Site

At present,the large-scale sea crossing project is developing rapidly in China,but the seismic research is not enough,and the important reason is the lack of understanding of the special site for the ground motion.According to the characteristics of deep sea foundation,based on the wave theory of fluid saturated porous medium and ideal fluid medium,a one-dimensional time-domain finite element method for seismic response analysis of bedrock-layered saturated soil-water foundation system is proposed.Combined with exact artificial boundary conditions,the computer program is worked out to analyze the influence of the change of water depth for ground motions on the deep sea foundation site.The main work of this paper is as follows:1.A one-dimensional time-domain finite element method for seismic response analysis of deep sea foundation site is presented.Based on the wave theory of saturated porous media and ideal fluid media,one-dimensional dynamical finite-element expressions applied to saturated soil layer and fluid layer is decuced by this method according to Snell theorem.Based on the boundary conditions and the exact dynamic artificial boundary conditions,the whole analytical equations of the bedrock-layered saturated soil-water foundation system are established,and the equations are solved by the time-step integral method combining the central difference method and the Newmark method,and the corresponding FORTRAN program is compiled.The algorithm can be used to study the ground motion of deep sea foundation,and can provide the input of earthquake motion for the seismic response analysis of Offshore Engineering2.Combined with the classical wave theory,the frequency domain analytical solution of the seismic response analysis of bedrock-layered saturated soil-water foundation under plane wave incidence is derived,and the time domain solution is obtained by inverse Fourier transform.Comparing the one-dimensional time domain finite element solution with the analytical solution,the validity of the time domain finite element method is proved.3.Using the one-dimensional time-domain finite element method for seismic response analysis of the deep sea foundation site,the influence of a certain deep sea foundation site with the change of water depth on the ground motion of the deep-sea foundation is analyzed under P wave of angle 60° incident.The main conclusions are as follows:a)The peak vertical displacement increases first and then decreases with the increase of water depth,and the peak value of horizontal displacement decreases first and then increases with the increase of water depth.When the water depth reaches a certain value,the water depth no longer affects the peak value of displacement.When the water depth is constant,the peak value of displacement decreases gradually along the depth of the soil.b)The change regulation of vertical acceleration peak with water depth is as follows.With the increase of water depth,the peak value of vertical acceleration increases first,then decreases,and then increases.The peak value of horizontal acceleration of soil surface decreases first and then increases with the increase of water depth.c)The peak value of the horizontal normal stress of the soil skeleton,the vertical normal stress of the soil skeleton and the pore water pressure increase with the depth of water and then decrease gradually.