Study On Numerical Simulation Of Particle Flow For Direct Shear Test In Sand And Clay And Wet Particle Suction

It has become a hot topic in soil mechanics to study soil from the mesoscopic view and establish macro-meso mechanical behavior relationship.The macroscopic soil mechanics test,the discrete element particle flow(Particle Flow Code,PFC)simulation and the mesoscopic theory were synthesized to study the mechanical behavior and evolution law of sand and clay from the macroscopic and mesoscopic perspectives in this paper.The main contents and conclusions are as follows:(1)The direct shear test of sand was simulated based on the PFC2D software.Spherical particle and the linear constitutive model were adopted.Three mesoscopic parameters in the simulation were calibrated by sensitivity analysis on its mesoscopic parameters and comparison with the macroscopic test data in reference.The shear strength curve of simulation are in good agreement with the macroscopic test,which veri:fies the reasonability and validity of PFC in simulating the macroscopic mechanical properties of sand;(2)The cohesion,internal friction angle and shear strength curve of silty clay in Nanning were obtained by fast shear test.The direct shear analysis model was established by PFC2D software.The shear test process of silty clay was simulated by the linear bond contact constitutive model,as well as the sensitivity analysis of five mesoscopic parameters.The curve which coincided with the macroscopic mechanical parameters of silty clay were obtained by calibrating the mesoscopic parameters,which verified the feasibility of particle flow method in simulating the macroscopic mechanical properties of non-circular granular silty clay and provided a new idea for the mesoscopic simulation and macro-meso analysis method in clay;(3)The motion state and distribution of particle in shear process were analyzed by PFC2D software with respect to the calibration results of the linear bond constitutive model of silty clay.The results show that the force chain network play a decisive role in external load of the whole shearing process.The coordination number and porosity are corresponding to contact and force chain network.The porosity decreases first during the loading process,then it increases at lower left and lower right as the direction of shearing concentrates in the region from the lower left to the upper right with the weak force chain.The anisotropy is obvious during the shear process and the mechanical properties are mainly affected by the normal contact force.The particles are constantly rolled,dislocated and rearranged in shear process,and the anisotropic direction is always in the direction of strong resultant force;(4)Two corresponding matric suction geometric solutions were derived from the geometric form of liquid bridge between equal and unequal diameter particles and the formula for calculating matric suction was given.The results show that the solution is more accurate than the classical Young-Laplace approximation solution in large particle spacing;(5)A cell analysis model of circular platform with unequal diameter particle was established based on the theoretical analysis of wet particle liquid bridge suction,and the variation of matric suction,capillaryforce and tangential force under different tangential displacements were studied.The relationship between cell shear stress and shear displacement of equal and unequal particles under different mesoscopic parameters was systematically studied.The results indicate that the shear stress of liquid bridge increases first and then decreases with the increase of tangential displacement.The peak shear stress of liquid bridge increases with the decrease of particle radius ratio,and it increases with the increase of saturation at lower saturation.The research on the suction between wet particles has an important influence on the macroscopic properties of soil,and the study of the peak shear stress between wet particles is of great significance to the cohesion of soil.