A Hydro-mechanical Coupled Constitutive Model For Unsaturated Soils And Its Numerical Analysis

Most soils in the nature are in the unsaturated state. Geotechnical engineers face a lot of unsaturated soil engineering problems and it is consensus that using the theory of saturated soil mechanics analysis for dealing with the issue of unsaturated soil is to be safe. But these methods to deal with problems, is still at the stage of semi-empirical theory.How to adopt a more objective and scientific methods for the study of the characteristics of unsaturated soil and the application in the engineering problem, is one of the most important direction for the development of unsaturated soil mechanics at present. On the basis of a three phase coupled constitutive unsaturated soil constitutive model, the hydro-mechanical coupled constitutive model for unsaturated soils and its numerical method are studied, the possibility of the model for being applied to the actual is explored. The paper mainly contains the following parts:(1) Combined with the actual situation, the influence parameters of liquid phase for solid phase and the update parameter for liquid phase of the three phase coupled constitutive unsaturated soil constitutive model are simplified, and the hydraulic and mechanical coupling constitutive model which is suitable for numerical calculation of unsaturated soil is derived.(2) The semi-implicit constitutive integration algorithm is used for the analysis. The calculation subroutine which can output the tangent stiffness matrix of the model is developed with the fortran language. The constitutive subroutine is used for the simulation calculation to analyse the existing test results. The model calculation results is compared with the existing experimental results, including the characteristics of the soil behavior under different path in the isotropic consolidation, dry-wet circulation and triaxial shear test.(3)Based on the thesis of solid-liquid coupling, the nonlinear experience SWCC model is introduced, which hypothesizes the relations between entry value and volume changes. The model is updated in the numerical calculation and the results of the calculation is compared with the dry-wet circulation test data, which can give a evaluation for the new SWCC model.(4)Using the UMAT subroutine function of secondary development, expands the constitutive model to the large-scale finite element analysis software, ABAQUS. The single and multiple elements of elastoplastic problems are analyzed. The extension effect of constitutive model from stress-strain relationship for one point to multiple cell entity response was verified.