DEM SIMULATION ON EFFECT OF COARSE GRAVEL CONTENT TO DIRECT SHEAR STRENGTH AND DEFORMATION CHARACTERISTICS OF COARSE-GRAINED SOIL

Mechanical behaves of coarse grained soil is greatly influenced by the content of coarse gravels. The shear characteristics of four groups of strong weathered basalt coarse grained soils are investigated under different coarse gravel contents on large-scale direct shear apparatus to obtain the strength and deformation parameters in this paper. Based on the theory of discrete element method(DEM),four direct shear samples under vertical pressure of 100kPa are carried out using the parallel bond model(PBM)with multiplicity coarse gravel content. The parameters are calibrated. Then we simulate the relationship among shear stress, shear deformation and vertical deformation. The simulation also simultaneously analyzes the particle movement and force in order to settle the mechanism for the fact that coarse content affects shearing properties. Results show that the inherence for shear strength increasing with the increase of coarse gravel content at the same vertical stress is due to the increase of particle stiffness and the increase of friction coefficient. The peak of stress-strain curve can be well simulated by the PBM.But the soften segment cannot be well fitted. Simulation of shear-vertical displacement curve does not fit perfectly to the testing value. The effects of coarse particles on the peak force chains were significantly evident than those of fine particles during the shearing process. It is considered that the vortex area is the thickness of shear band, approximately 1/3-1/5 of the height of shear box.