Distinct Element Research On The Mechanism Of Silo Unloading Considering The Dilatancy Of Storage Materials

Silo is a kind of structure used to store granular materials, which is often used in the storage of grain, cement, coal, etc.. For the designers of the silo, there are special difficulties in the structural design of the silo. Grain occurs shear dilatancy during discharging and the dynamic lateral pressure of grain on the silo wall is much bigger than the static lateral pressure. But there is no unified theory of dynamic lateral pressure to explain the mechanism of dynamic lateral pressure increase during discharging. In this paper, we will study the lateral pressure of the silo with PFC3 D, which is a discrete element software, and analyze the shear dilation of the silo during unloading. The main research contents are as follows:(1) Bulding the discrete element numerical model of Triaxial testing of wheat, and get the stress-strain curves of wheat, then compare with the results of laboratory Triaxial testing of wheat. Calibrationing the microscopic parameters, such as normal stiffness, tangential stiffness and friction coefficient, of wheat in PFC3 D, and study the influence of various micro parameters on macro parameters. And we analysis of the shear expansion of wheat in the Triaxial testing.(2) Using wheat’s micro parameters in PFC3 D to establish wheat silo model, and use stratified charging way to simulate the real loading process. We get the static lateral pressure of silo in full material state changing with the depth, and compare the PFC3D’s results with Janssen formula’s calculation results, test results and PFC2D’s results. And analysis of storage porosity changing with depth.(3) Making the silo unload, we get the dynamic lateral pressure of silo changing with the depth, and compare the PFC3D’s results with normative theory results, test results and PFC2D’s results, finally we get the the following conclusions: with the increase of the depth of the silo,the dynamic lateral pressure of the silo increased gradually, and it is much bigger than the static lateral pressure. Then based on this PFC3 D numerical model, study the effects of inclination of the funnel, the size of the discharge opening, the internal and external friction coefficient of particles and filling method on dynamic lateral pressure.(4) The porosity description is introduced to describe the characteristics of the material expansion, so the relationship between the shear expansion of the material and the increasing mechanism of the dynamic lateral pressure of the silo is studied. When discharge begins, all the particles complete the transition from the static state to the state in a relatively short period of time. In this process, particles collide with each other and mutual extrusion, resulting in a material storage density, porosity decreases, the collision and extrusion is more pronounced in the hopper and a straight cylinder junction. When porosity decreases to a certain value,granular material will transverse expansion. And the porosity increases, particle expansion on both sides, but silo wall hinders this expansion, which leads the dynamic lateral pressure grows, and the overpressure phenomenon will be generated.