The Elasto-Plastic Damage Constitutive Model Of Loess And Its Engineering Application

In this paper, by means of conventional tri-axial test, high-pressure consolidation test, collapse and moistening test of intact loess Q4 sample with different initial water content and remolded loess sample with different initial water content and different initial dry unit weight, the deformation and strength characteristics, soil structure characteristics, collapse deformation and moistening deformation characteristics of both loess were analyzed. On this basis the elasto-plastic damage constitutive model of loess which can materialize soil structure characteristics were established. The infiltration and elasto-plastic damage 2D FE programs of loess were coded and taken into numerical analysis of a soaking test pit with self weight collapsible loess. Some useful results were found after those.Firstly, analyzed data of tri-axial test, high-pressure consolidation test, collapsible and moistening test of intact loess Q4 and remolded loess, and on basis of deeply studying the deformation and strength characteristics, collapse and moistening deformation characteristics of loess, a soil structure parameter was put forward with the secant modulus of intact loess and remold saturated loess, which can well reflect the loess structure changing and damaged process under loading and moistening.Secondly, based on the theory of thermodynamics and continuum damage mechanics and the energy conversion of loess in load and moistening, the damage variable, load damage and moistening damage of loess and their relations were put forward. The basic framework of the elasto-plastic damage models of loess which were made up of plastic, load damage and moistening damage were also put forward. For the first time the definition of the loess moistening damage variable was put forward, aswell as the equivalent energy index of loess moistening damage which relates to the water content or the saturation degree to describe the moistening damage evolvement procedure. Based on the concept of Simo's energy index, the energy index of loess load damage was put forward. And analyzed structure breakage and degradation of mechanic and strength index, the evolvement procedure of loess load damage was put forward. To join ellipse yield function, hardening parameter with plastic work, associated flow law and damage theory, the elasto-plastic damage constitutive model of loess were derived. Compared the calculation results of model to tests data, it shows that they were close basically, only a few difference in low water content, that means the model can simulate different stress-strain curve types of loess, can control the transition of the stress-strain curve through damage variable, and also can simulate the moistening deformation and collapse deformation.Finally, according to the infiltration characteristics of loess and the permeation theory of unsaturated soils, a 2D FE program of loess infiltration was coded by Matlab finite element toolbox, and its numeration results were fit to practice. Another 2D FE program of elasto-plastic damage models of loess was also coded by Matlab finite element toolbox, based on the elasto-plastic damage models and the theory of nonlinear finite element. These two programs were used to the calculation of a soaking test pit with self weight collapsible loess, and the numerical results were fit to the practical development procedure of the loess collapse and moistening deformation. Also, the loess collapse deformation area could be predicted according to the distribution law of damage variable. Furthermore, the programs can be applied to calculate the deformation and stability of loess projects, and to provide a new way and method to verify the researches of the load deformation characteristics, collapse and moistening characteristics.