Refinement and application of variable particle-size methods in 3D discrete element modelling for large-scale problems

A refinement method is proposed to solve the difference in the macroscopic elasticity and the interpenetration in interface area between different particle-size areas in the DEM. In simulations of 3D DEM large-scale problems, small balls are used in the near field core area to simulate the real soil, while the far field boundary regions are filled with larger balls. In addition, a mixed area is set between different particle-size areas with the same relative density. The number of particles in the model can be reduced enormously, which improves largely the calculation efficiency. For scaling particle systems, the scale relationship is established on the static condition by the identical macro elasticity of uniform granules. The relationship satisfies the consistency of stress, strain and strain energy. The results of a series of triaxial test simulations verify the uniformity of macro elasticity. A method to generate a certain density mixture with two different particle sizes is proposed. The results of DEM simulations illustrate that the deformation property of mixed area is consistent with that of the uniform particles. Finally, the results of cone penetration test simulations show that the proposed method is effective. This study may provide a new approach to the application of 3D discrete element modelling in the large-scale geotechnical engineering.