Discrete Element Analysis Of Dilatancy In Particle Materials

In recent years, with the rapid development of foundation engineering, earthquake engineering, offshore construction and bridge engineering, soil as a special engineering material has been widely used. Also, soil mechanical properties have been paid wide attention. There were three intrinsic properties of soil-natural, three-phase and broken, which conflicted with the traditional continuum mechanics’assumption of uniform and continuous. Based on the Newton’s second law and the force-displacement law, discrete element method could build a more objective and reasonable model from microscopic point of view.The triaxial test was a complete laboratory test determining soil strength and deformation. Based on the discrete element method, a method of simulating the triaxial test was created. Through the analysis of the relationship between micro and macro parameters, we found it wasn’t a one-to-one correspondence, but cross-influence.Soil dilatancy, as the microscopic mechanism was described, was emphatically analysed. Based on dilatancy angle and micro-mechanical parameters relationship, dilatancy angle decreased with the particle normal stiffness increase was proved, while independent of the ratio of normal and shear stiffness. Dilatancy was related to the material stiffness of the particle itself to a certain extent. Dilatancy angle first increased and then decreased with the the porosity decreased. When the sand was attained to superdense state, due to the porosity decreased, the particles in the shear band were blocked to be uplifted or roll, that caused the dilatancy angle smaller. Dilatancy angle increased with the increase of the particle friction coefficient. Dilatancy angle with confining pressure changed was affected by the number of particles, particle friction angle and confining pressure, the reason needed further validation.According to triaxial tests of iron ore pellets, geometric data and characteristic parameters of the model were confirmed. On the microscopic view, force chains were observed collapsed and re-formed, meanwhile, the force chains also showed obvious anisotropy in the anisotropic stress state. Apparent shear band can be seen from the particle displacement vector. Particles in the band mainly migrated in the way of rotation, while the particles out the band in the way of translation. Comparisons were made between model parameters and test results. The particle friction coefficient was the combined effect of rolling friction, sliding friction and particle fragmentation, the influence of particles breakage on the strength increased with the confining pressure increased. Peak strength was consistent, characteristic strength in the model was lower than the test, which was caused by the elastic modulus. Dilatancy angle in the model was lower than the test, which was caused due to the particle surface roughness, particle breakage, as well as some objective factors in the test. While that still be able to reflect the development trend of shear dilation angle, therefore, we believe the model was reasonable.