Theory Study And Finite Element Analysis On Particle Scale And Rotation Effects Of Soil Deformation

Soil is a non-continuous granular media, made of mineral particles with multiple scales,water and air gathered together by a certain way. The macro mechanical properties of soil are closely related to particle size and particle movement behavior and have a very significant particle scale and rotation effects. However, classical continuum mechanics is built on a single macro scale and can not characterize particle size and particle rotation, and discrete mechanics usually applies to uniform particle system with a single scale and the amount of calculation is huge, while the strain gradient plasticity theory is mostly applicable to metal materials, whether the theory can be applied to soil is yet to be studied. In this paper, the effect of particle properties and particle size on the macroscopic mechanical properties of soil is summarized through soil properties influence test and using the "matrix-reinforcing particles" cell structure model, the elastic-plastic theory considering soil particle scale and rotation effects is established(hereinafter referred to as "scale theory"). And then, the scale theory finite element program is developed with the aid of ABAQUS user subroutine interface. Numerical simulation and theoretical analysis show that finite element method of scale theory can solve problems of classical elastic-plastic theory and reasonably predict the special mechanical behavior caused by particle scale and rotation effects in the process of soil deformation. Based on the above work, the results achieved are mainly the following aspects:(1) According to soil properties influence test considering the mineral composition and granularity composition, this paper summarizes the influence of particle properties and particle size on macroscopic mechanical properties and the interaction law between particles at different scales. By using the "matrix-reinforcing particles" cell structure model and introducing intrinsic scale factor for characterization of particle size and rotation variable for describing rotational deformation in the constitutive relations as well as redefining the equivalent shear strain and equivalent shear stress with intrinsic scale factor, and then based on the energy principle and the Von Mises yield criterion, this paper establishes the scale theory and its finite element matrix.(2) The finite element program based on the scale theory is developed through the secondary development of user defined element subroutine interface of finite elementsoftware ABAQUS. On this basis, the scale and rotation effects of the hole stress concentration problem is analyzed. The correctness of this program is verified by comparing with the results of finite element calculation of the classical elastic-plastic theory, and the intrinsic relationships among the stress concentration, the particle size and particle rotation are presented. Then, the rationality of scale theory is explained from the deformation mechanism.(3) Using the scale theory finite element program, numerical simulation and theoretical analysis are carried out on the phenomenon of soil softening and deformation localization. In the process of localization of soil deformation, the scale theory can solve the numerical calculation difficulties and the serious grid dependence of the classical elastic-plastic theory,and the further analysis of relationships among the occurrence and development of shear band,particle size and particle rotation, reveals the special deformation behavior and deformation mechanism due to the characteristics of soil particles.(4) Using the scale theory finite element program, the problem of bearing capacity of foundation and the problem of slope sliding are simulated. The whole process of the nonlinear deformation of soil softening is realized. Moreover, the result is different from the classical elastic-plastic theory. Meanwhile, the influence of particle size on the deformation and load characteristics of soil is discussed, and the deformation and failure mechanism of soil considering particle size and rotation effects is proposed, which can provide theory and data reference for future engineering disaster prevention and control.