Effect Of Particle Size Difference On Shear Properties Of Sand And Its Mesomechanical Analysis

As a typical discrete particle material,sand exists widely in nature and is applied in engineering construction.For a long time,the research on sand mechanical properties is mostly based on the continuum theory without considering the influence of the characteristics such as discreteness,non-linearity and heterogeneity etc.Therefore,the complex mechanical behaviors of sand cannot be explained accurately and comprehensively.But the birth and development of the discrete element method provide a more reasonable theoretical basis for solving the mechanical properties of discrete materials such as sand.The discrete element method proposed that the essence of the macro-mechanical phenomenon of sand should be explained by mesomechanism,which is key point for in research of various complicated geotechnical problems.The study on the influencing factors and the reaction mechanism of mechanical properties of sand materials has always been an important subject in the field of geotechnical engineering.Based on the discrete element method,combined with the direct shear test and PFC2 D particle flow numerical simulation,this paper analyzes the influence mechanism of particle size difference on the shear mechanical characteristics of sand from the macro and micro perspectives.The main contents and conclusions are as follows:(1)Through direct shear tests in laboratory,the shear tests of sands with three different particle sizes under various normal stresses were carried out,establishing the PFC2 D numerical model that can reflect the the shear mechanical properties of shear mechanical properties of sand samples in each group.And the effect of some main meso-parameters on the stress-strain characteristics of the simulated test was also analyzed.The results show that the effect of particle size difference on the macromechanical shear properties of sand is mainly reflected in its shear strength and dilatancy deformation.The larger the average particle size of sand,the higher the shear strength,and the more obvious the dilatancy effect.(2)Through tracing the particle trajectories in the shear band of the numerical model,three basic forms of relative movement of sand particles in the shear process were summarized from the commonness of a large number of trajectory characteristics: upper-span type,lower-span type and translational type.Among them,the spanning of particles in the shear zone is an important factor to determine the strength of soil sample dilatancy.Through the analysis of the range of particle coordinates,it was found that the larger the average particle size,the higher the proportion of spanning particles on the sand sample,and the larger the average vertical displacement caused by the spanning of particles.The reason for the difference of macro-dilatancy of each group of samples was explained from the point of view of particle movement.(3)The visual advantage of PFC2 D particle flow software was fully utilized,which makes up for the deficiency of laboratory test in the monitoring of micro parameters.At the same time of horizontal comparison.In this paper,the variation characteristics and rules of the force chain network,porosity,coordination number,displacement field,velocity field and other micro structural parameters of the numerical model in the shear process are studied in detail.The mechanism of the effect of particle size difference on the macro-shear properties of sand samples was analyzed from the meso-scale.The results show that there were significant differences in the variation of the meso-parameters of sand samples with different average particle sizes in the shear process,and the differences of the meso-parameters were mainly reflected in the shear band,while the porosity nephogram,displacement field,velocity field and rotation field can reflect the morphological characteristics and deformation mechanism of the shear band from different angles.