Discrete Element Method Simulation Analysis Of Pressure Variation Characteristics In Sand Piles And Silos

Sand is a widely used engineering material,and it is also a kind of material composed of particles.The contact force is transferred through the force chain between particles.Due to the arrangement,friction and rotation of sand particles,the force distribution on the force chain is uneven,which makes the main part of the force chain undertake most of the force,resulting in arch effect.The central stress depression at the bottom of sand piles and the"granary effect"of stress saturation at the bottom of silo are all caused by the arching effect in granular materials.In this paper,based on PFC simulation software,the discrete element method is used to simulate the cone stacking and silo stacking.By comparing the simulation results with the experimental results,the more accurate calculation parameters can be obtained and further used in the subsequent simulation.By changing the friction coefficient,stacking height,particle size distribution,particle shape and so on,the influence law of internal stress is studied,and based on the arch effect of force chain transmission,its mechanism is analyzed.⑴According to the method of layered stacking,the simulated stacking can show the stress deep at the bottom of the stacking and the"granary effect"in the silo stacking.The results show that the friction coefficient has a great influence on the stacking angle and the stress depression at the bottom of the cone-shaped pile.With the increase of the friction coefficient?_b between particles,the stacking angle increases obviously,while the friction coefficient?_f between particles and the bottom has an obvious influence on the stacking angle when?_b is less than 0.6.The degree of stress depression at the bottom increases with the increase of friction coefficient?_f and?_b.similarly,the effect of friction coefficient?_bbetween particles is more significant;⑵When round particles are selected,the grain size distribution is consistent with that of sand.When the friction coefficient?_b between particles is 0.8 and the friction coefficient?_f between particles and bottom is 0.6,the stacking angle,bottom stress level and stress depression degree of the model are closest to the data measured in the sand stacking test,and the results calculated by this parameter can reflect the stress changes in the actual sand pile more truly;⑶The particle size distribution and shape have great influence on the stress distribution.According to fuller grading curve,the bottom stress depression degree of dense accumulation body is the largest,while the bottom stress depression degree of accumulation body with single particle size is the smallest.The stress depression at the bottom of the cone-shaped accumulation formed by non-circular particles is smaller than that of the circular particles,but the accumulation angle is larger.Because the non-circular particles occlude each other,the force chain is more stable,but the continuity of the force chain is lower and the dispersion is larger;⑷The stress at the bottom of the silo will appear local minimum at the stacking center and the side wall,which is called stress depression.With the increase of stacking height,the bottom stress gradually becomes saturated,and finally reaches the state of constant bottom stress.The normal stress on the side wall of the silo changes linearly in the upper part of the pile,which is similar to the Coulomb earth pressure theory;⑸The friction coefficient?_c between the side wall and the particles has a significant effect on the stress distribution in the silo.When?_c increases,the height at which the bottom stress reaches saturation decreases.When?_c is 0,the bottom stress will increase with the increase of height,and there will be no"granary effect".The bottom stress level is much higher than that of other control groups,and the normal stress of side wall changes linearly with the height.