The Study On The Numerical Simulation And Geometric Characteristics Of Shear Band Of Sand

Shear band controls the shearing failure for many earthworks,such as slope,foundation et al.In order to investigate the formation and the characteristics of shear band,numerical simulation methods,included large deformation analysis FEM(AFENA based on RITSS)and DEM(PFC2D),are used to simulate the shearing behavior of sand and study the effects of mesh size,constraints and defects on the shear simulation and shear band characteristics of sandy soil.The numerical simulation results demonstrate that:(1)In the finite element simulation,the shear stress-shear strain of the specimen is basically the same,the influence of the mesh size and the constraint can be neglected.The maximum volumetric strain that can be achieved in the final specimen is related to the geometry of the specimen and the size of the mesh.The density of the mesh will affect the shear band formation of the sample,which has a certain influence on the volume change of the sand compaction process.Under normal circumstances,the larger the mesh,the maximum volume can be reached.In the finite element simulation,there is a certain correlation between the shear band width and the grid size of the biaxial shear,which is about 1.63 times the average size of the global grid.Therefore,the global grid size of the biaxial shear should be chosen according to the average particle size of the soil,and it is recommended to take 5-8 times the average particle size of the soil.(2)The shape of shear bands is related to the constraints,and the formation of shear bands is greatly affected by the defects.The location of the defect has a great influence on the shape,width and dip angle of the shear band,and the size of the defect will have some influence on the formation of shear band.The weakness of the soil outside the compaction zone will control the formation of shear bands.When there is a defect in the sample,the shear band formed in the sample is often at the defect point,but when the defect is located in the compaction zone,the shear may not pass through the defect point.The weakness of the soil outside the compaction zone will control the formation of shear bands.The size of the defect also has some influence on the formation of shear bands.(3)In the biaxial shear simulation of PFC,the friction coefficient between particles is more obvious than that of sand.The greater the friction coefficient between particles is,the higher the shear strength of sand is.PFC was used to simulate the formation of shear bands under different particle sizes,and the shear band width was about 10 times of the particle size.(4)The results of PFC and finite element simulation show that:in the process of biaxial shear of dense sand,the soil in the shear zone reaches the critical state gradually,and the nature of the soil outside the shear band is basically unchanged.The angle of shear band is slightly larger with the increase of shear deformation.There is a great difference between the strain in the shear band and the macro strain.