Discrete Element Method Analysisof Rotational Impedance Effecton Mechanical Propertiesof Sand

Based on the discrete element method,this paper uses the particle flow software PFC5.0 to conduct a series of true triaxial simulation tests and direct shear simulation tests,discussing the influence of rotational impedance on the mechanical properties of sand from both macroscopic and microscopic perspectives.It has certain guiding significance to improve the understanding of the work behavior of sand and other granular materials.The main research contents are as follows:(1)Determine the constitutive model by studying the properties of sand particles,refer to the micro-parameters of previous numerical experiments and combine with the macroscopic results of indoor experiments for parameter calibration,and determine the micro-parameters of the true triaxial numerical model and the direct shear numerical model;adjust the rolling resistance coefficient,and use different confining pressures and different normal stresses to carry out numerical simulation experiments.(2)The results of the true triaxial numerical simulation of sand show that at the macro level,as the rolling resistance coefficient increases,the peak deviatoric stress and its corresponding peak internal friction angle increase correspondingly,and the strain-softening phenomenon gradually intensifies.At the microscopic level,the rotational resistance inhibits the relative rotation between sand particles,resulting in a decrease in the average coordination number between sand particles;in the peak state,the rotational resistance mainly increases the probability density of the normal strong contact force and the size of the contact force;The three-dimensional histogram visually qualitatively analyzes the influence of different rotational impedances on the normal contact force and stress-induced anisotropy and combines the second invariant to characterize the fabric tensor,normal contact force tensor,tangential contact force tensor,and branch The anisotropy of the vector tensor is found to increase with the increase of the rolling resistance coefficient.(3)The direct shear numerical simulation test results show that the macroscopic stress-strain characteristics and the change of the strength index with the anti-rotation coefficient are similar to the true triaxial numerical test;the formation and evolution process of the shear zone was explored by marking the samples in blocks.At the micro-level,the strong contact force chains in the specimen gradually converge toward the shear band as the shear progresses,and are distributed diagonally along with the shear box.The strong contact ratio decreases with the increase of the anti-rotation coefficient;analyzing the evolution law of the force chain rose diagram,it is found that the anisotropy of the normal contact force and the tangential contact force and the corresponding principal direction angle all increase with the increase of the rolling resistance coefficient.(4)Based on the true triaxial numerical test and direct shear numerical test,the influence of rotational impedance on particle contact anisotropy is analyzed by comparing the changes of fabric component and partial fabric with strain under different rolling resistance coefficient conditions.Rotational resistance at different shear stages has different influences on the contact anisotropy of particles in various directions;combined with fabric-stress-strain evolution,the influence of rotational impedance on the contact anisotropy of sand particles is further explored,and it is found that rotational impedance has a significant effect on the evolution of strong contact anisotropy between particles,but it has a significant effect on the stress-fabric The influence of non-coaxial angle is not obvious.