DISCUSSIONS ON VALUE OF MESO PARAMETERS IN PARTICLE FLOW SIMULATION OF EXCAVATED GRAVEL STRATUM

When the gravel layer is excavated,the main failure mode is not the general macro overall shear failure. Instead,it is a process that a cutting tool cuts into the gap between pebbles and gravels to peel the pebbles and gravels out of the original stratum. This process is more in line with the physical and mechanical hypothesis of particle discrete element. In order to determine the optimal meso parameters of granular materials under excavation conditions,the three-dimensional cutting simulation is carried out for granular materials with different combination of meso parameters. The parameters include particle contact normal stiffness,contact stiffness ratio,inter particle friction coefficient,particle shape,and particle size. The effects of different meso parameters on excavation are analyzed and studied. The calculation results show that a variety of combinations of meso parameters,such as the normal stiffness of particle contact and the contact stiffness ratio can correspond to the same macro elastic modulus value. The combination of meso parameters with large contact stiffness ratio has greater capability for resisting excavation. The combination of multiple meso parameters of particle shape and inter particle friction coefficient can correspond to the same internal friction angle value. The particle material with complex shape has greater capability for resisting digging. Under the same macro parameters,the larger the average particle size,the greater the resisting digging capability. Therefore,when using the particle discrete element to simulate the excavation of gravel stratum,it is also necessary to further calibrate the meso parameters according to the excavation resistance ability of the material and to obtain a simulation effect closer to the actual situation in addition to ensuring that the macroscopic overall shear failure response of the virtual particle material is basically consistent with the real material. The method proposed in this paper can provide a reference for the parameter calibration of other particle discrete element numerical simulation of excavation conditions.