Simulation Of Soil Mechanical Behaviors Using Discrete Element Method Based On Particle Flow Code And It Application

Soil is not same general material, which has much complicated properties and highly nonlinear. It is neither perfect elastic material nor perfect plastic material. In geotechnical engineering field the material of modeling is geotechnical material, which has the typical properties of fragmentation, dispersing and flowage. In soil mechanics theory, the soils are regarded as continua as a rule after the substance morphology is fallen into gaseity, liquid and solid. Now the continuum theory is used in most of numerical methods. All soil is discontinuous to some extent. So it has been acquainted early to study the stress and distortion properties of soil form the point of microcosmic view, but such study is too complicated to build quantitative relations between microcosmic and macrocosmic and depend on the power of computer and particle model.Within PFC2D (Particle flow code in two dimensions) and PFC3D (Particle flow code in three dimensions) discrete materials such soils were simulated by disks or by spheres and overcame the defect of the continuum theory to establish the relationships of microcosmic parameters and macroscopical parameters; The excavation process was simulated by using PFC firstly in the paper; PFC simulated a series of triaxial tests on steel spheres with pyramid and rhombic packings and the stress-strain curve of sand. And It can be started with micromechanics to study structured properly of soil, and should be noted to disclose the geometry character of soil particle arranging and the mechanic characters of soil particle to study not only the generation of the shear band but also the stress-stain curve in a quite similar manner to those observed in natural granular soils.From the simulations with different physical tests, establishing the functions between microcosmic parameters and macroscopical parameters including of soil angle of internal friction, modulus of deformation, peak strength of soil reinforced and unconfined compression strength of clay. Based on these functions, the paper simulate the process of excavation, and the sheet pile wall and the strut are simulated by joining together a row of disks of equal radius with parallel bonds, and soil is simulated by particles. The resulting displacements, bending moments and shearing forces within the wall, axial forces of struts and earth pressures acting on the wall are studied as well as the behavior within the soils for subsequent excavation steps. The soil microcosmic spatial structure results in its more complexity. It can be started with micromechanics to study spatial structure properties of soil, and should be noted to disclose the geometry character of particle spatial arranging. At the same time, discuss the heterogeneity and anisotropy of different spatial structures. Numerical simulation of three-dimensional assembly of spheres was carried out based on discrete element method and the theory of particle flow where the slip model was used to constituted PFC mode of packing configurations. This paper simulated a series of triaxial tests on steel spheres with pyramid and rhombic packings corresponding with real laboratory compression test. Numerical simulations captured the observed laboratory response well and the relative difference between numerical and theoretical angle of mobilized does not exceed 2.5%. The microscopic fabric (the coordination number, the porosity and the slip fraction) evolve with the development of axial strain is studiedThe PFC3D model of the sand that is consistent with the lab results of Chengde middle close-grained sand have been formed via vast parameters trial-and-error process. Numerical simulation tests were carried out using the distinct element method (DEM) by paying much attention to the micro-deformation mechanism leading to the development of shear bands and the microscopic fabric (coordination number, porosity and slip fraction) evolved regularly with the development of axial strain. Contrasting the stress-strain curves of the PFC3D sand model with Chengde middle close-grained sand under various confining is done in this paper. Analyzing the influencing rules of the stress-strain curves as the microcosmic parameters, such as particle normal stiffness, ratio of normal stiffness to tangent stiffness, friction coefficient, and initial porosity of the PFC model is done in this paper. And the properties of the shear band are studying.