Theory And Finite Element Analysis Of Finite Non-linear Consolidation Of Soft Clay Ground

There is lots of deep soft clay layer distributing along sea shores and river banks, foundation treatment must be done when highway, railway, airport, etc. are constructed in soft clay areas. As soft soil foundations treated by preloading method, vacuum preloading method and the method of combining these two, their settlements are large and reach several meters at some cases. When volume deformation of soil mass in consolidation process is large, considerable errors will be brought out as the consolidation process is analyzed by the small strain consolidation theory of Terzaghi or Biot. As the strain of soil mass in consolidation process is large, properties of soil mass change obviously, the stress-strain relation is nonlinear and the permeability of the soil mass changes a lot, the nonlinearity of geometry, the nonlinearity of material and the nonlinearity of permeability must be considered together in large-strain(that is finite strain) soil mass consolidation analysis. These three nonlinearities in the process of large-strain soil mass consolidation produce more complexity and difficulty in the study of large-strain consolidation of soil. Up to now, few research results, which three nonlinearities are considered together in large-strain soil mass consolidation, are presented. In this dissertation, theory and analytical solution and finite element solution of finite non-linear consolidation of soil are studied, effects of the nonlinearity of geometry, the nonlinearity of material and the nonlinearity of permeability on consolidation of soil are analyzed.By studying the Gibson's one-dimensional finite non-linear consolidation(1DFNLC) theory, the analytical solutions of the simplified governing equation of the Gibson's 1DFNLC are presented with separation of variables method of solution of the diffusion equation. Using the analytical solutions, differences between the solutions of the 1DFNLC theory and the solutions of the Terzaghi's 1D small strain consolidation theory are studied. Assumptions, which are used by different researchers to simplify governing equations of the 1DFNLC, and differences of conclusions of 1DFNLC obtained from the assumptions are analyzed.According to finite deformation theory of the continuum mechanics, by Lagrangian Formulation, the equation of equilibrium, the equation of geometry, the equation of constitutive relation and the equation of continuity of three-dimension finite non-linear consolidation of soil mass are established. These four equations constitute general governing differential equations of finite non-linear consolidation of soil mass.The Updated Lagrangian Formulation of the governing differential equations of finite non-linear consolidation of soil mass are set up, and finite element analysis method for finite non-linear consolidation of soil are presented considering the nonlinearity of geometry, the nonlinearity of material and the nonlinearity of permeability together.The effects of large strain, decreasing compressibility and decreasing permeability during process of the 1D finite strain consolidation of soft soil foundation are studied by the finite element analysis method for finite non-linear consolidation of soil. The research results of this paper shows that the compression index c_c and the permeability change index c_k are two important soil parameters which influence 1D large strain consolidation process of soft soil foundation. Some important conclusions of the 1D finite non-linear consolidation of soft soil foundation are obtained by comparing solutions of the finite element method with solutions of the Terzaghi's 1D small strain consolidation theory, and with solutions of the analytical method.The effects of geometry nonlinearity, material nonlinearity and permeability nonlinearity on two-dimension finite non-linear consolidation of soft clay ground are investigated, based on comparing solutions of the finite non-linear consolidation theory with solutions of the small strain consolidation theory of a soft clay foundation, some important conclusions of two-dimension finite non-linear consolidation of soft clay ground are obtained.As an engineering example of two-dimension finite non-linear consolidation of soft clay ground, consolidation behaviors of a soft clay road bed under filled load are analyzed by the finite element method of finite non-linear consolidation of soil, the differences between solutions of finite non-linear consolidation theory and solutions of the small strain consolidation theory of a soft clay ground are further studied by comparing the consolidation behaviors a soft clay road bed with those obtained from the small strain consolidation theory.