The Non-Linear Constitutive Model Of Collapse Loess With Structural Damage Under Loading And Moistening And Its Application

The stress state and water content of the loess is corresponding to special soil structure and the microcosmic structure variation results in the macroscopical mechanics changing. With the couple action of loading and moistening, the natural structure of the loess will be damaged and there will be collapse deformation. It is important to explore the variation principle of structure, the mechanics characteristic of stress-strain and moistening deformation. In this paper the variation law of stress-strain with different water content and consolidation pressure and the law of structural damage due to moistening, consolidation and shearing deformation had been study firstly by considering the structural damage under loading and moistening. An non-linear constitutive model of collapse loess had been established which can reflect the structural damage and moistening deformation (LSM Model), and then the increment iteration method of tangent modulus and the direct iteration method of secant modulus for FEM analysis had been put forward. The numerical analysis with the LSM Model can be carried out by making use of the exploiture function of the general FEM programme-ANSYS. At last, the principle of the deformation, strain–softening characteristic and the deformation process of the loess highroad foundation had been analyzed under moistening and loading. The main results as follows:①The deformation and strength and the evolvement principle of structural damaged of the collapse loess had been revealed under moistening, isotonic compressing and shearing, and then a damage parameter reflecting the process of structural damaged had been set up.②From the view point of structure altering uniformly, it is pointed that the hardening and softening stress-strain curves of structural loess all reflect the damage process of nature structure and the remodeling process of the fresh structure. Hence a unification constitutive model reflecting the soil structure can be established to describe the principle of deformation and strength.③The non-linear constitutive model (LSM Model)of collapse loess having been established can not only describe the structural damage and hardening and softening stress-strain curves, but also reflect characteristicof deformation and strength with water content and stress changing in succession. With the non-linear model the numerical analysis of deformation and strength can be carried out under the couple condition of moistening and stress changing which not only abandons the conservative method of evaluating the collapsing deformation after adequately inundate and saturated, but also combine the research of soil structure theory and constitutive model into a unit.④Based on the User Programmable Features of ANSYS, the general method of introducing user-defined constitutive model into ANSYS FEM software is explored. The method of stress integration of LSM Model at Gauss point for the FEM analysis had been put forward, for there is no fit constitutive model for soil material in ANSYS.⑤Under moistening and roadbed loading, the numerical calculation results of loess foundation of highway, which with special boundary condition, indicates that the LSM Model can reflect the variation principle of the actual deformation and soil structure of the intact loess, can simulate the softening and hardening of the intact loess, and also can gain the magnitude of deformation due to moistening. The relation between the load and settlement of the nature structural soil foundation reflects the gradual damage and softening process of the soil structure.