Research On 3D Discrete Element Simulation Of Loess Based On Real Particle Shape

Numerical simulation technology based on discrete element method plays an important role in the study of the macro-and mesoscopic characteristics of loess.Compared with physical experiments,the particle flow numerical simulation based on the discrete element method is not only more cheap and has very good repeatability,but also has great advantages in the meso-level research of loess particle size and gradation.At present,most simulations are carried out on round or spherical particles.There are few studies on the simulation of real loess particles.Because of the large errors in the simulation process of round and spherical particles,the real loess particles are used for simulation and it has greater theoretical and practical significance.Based on this,this paper mainly uses AVIZO reconstruction and PFC3 D numerical simulation to establish a three-dimensional real particle random mesostructure model of loess,and uses the PFC5.0 program to carry out three-axis shear test and three-dimensional direct shear test simulation of loess under different confining pressures.The influence of real particles and spherical particles on the deformation and failure of unsaturated loess is analyzed,and the formation and evolution of the shear bands in the loess sample during the deformation and failure process and the displacement and rotation laws of the loess particles are analyzed from the granular meso-scale.The paper got the following conclusions:(1)The shape of the particles has a great influence on the mechanical properties and meso-scale changes of the numerical samples,which is mainly reflected in the dilatancy and shrinkage characteristics,particle coordination number,displacement and rotation characteristics.With the increase of confining pressure,the spherical particle sample undergoes a deformation mode process from shear shrinkage-dilatancy to shear shrinkage,while other simple shape particle samples are always in a state of shear shrinkage with the increase of confining pressure.(2)With the increase of the confining pressure,the sample composed of cylinder,cuboid,and cube particles gradually transitioned from the bulging deformation mode in the middle to the oblique shear deformation mode,and there was no obvious concentration in the parts where the particles rotated greatly;while the spherical shape The particle sample has always been in a lateral bulging deformation mode,and the part where the particles have a large rotation is mainly concentrated at one end of the sample.(3)Comparing the displacement and rotating cloud image of the spherical particle and the real particle model,it is found that the real particle and the spherical particle model are significantly different in simulating triaxial shear and 3D direct shear test.When the confining pressure is low,the spherical particle model undergoes a dilatancy-shrinkage deformation mode.When the confining pressure is high,the spherical particle model is a continuous dilatancy deformation mode,while the real particle model is always the same regardless of high confining pressure or low confining pressure.Deformation mode of shearing.The main reason is that the irregular real particles are not easy to rotate,move and slip during the loading process,so they can only undergo shear shrinkage to adapt to the increasing stress,while the spherical particles are prone to rotation during the loading process.Dislocation and slippage.(4)Whether it is a spherical particle model or a real particle model,the coordination number of particles will increase with the increase of vertical stress,but the coordination number of real particles tends to be stable with the increase of strain,while the coordination number of spherical particles As the strain increases,it will continue to increase,and the coordination number of real particles is always smaller than that of spherical particles.