The Direct Shear Test On Clay Materials Based On Particle Flow Code

It is an economical approach to determine the shear strength of soil by direct shear test,However,it is not quite easy to observe the micro-failure mechanism of the material in the shear box.Compared with the granular material,more parameters in the microscopic level need to be considered for the clay particles due to the existence of physical-chemical interaction,and thus its macroscopic performance is different from that of sand.In this paper,the clay particles are taken as an example to study the shear failure mechanism of the bonded granular material in the process of direct shear test from the macroscopic and microscopic level.In this paper,the basic physical properties of the tested soil samples are measured,and the shear strength index of soil samples is determined by laboratory direct shear test.Then,the PFC model of direct shear test is established based on particle flow theory.The nonlinear inversion system of macroscopic and microscopic parameters based on BP neural network is established according to PFC contact constitutive relation.By comparing the macroscopic mechanical parameters of the soil,the micro-mechanics parameters corresponding to the samples were determined,and then the results were compared with the laboratory test results.The results of numerical model are considered to be consistent with that of the laboratory experiment.The results of the simulation can be obtained as follows: 1)From the point of view of particle motion(translation and rotation)and particle distribution(porosity),the number of particles in the sample is analyzed by the amount of translational and rotation of the particles and the change of local porosity.The change of motion characteristics and local porosity is an important microscopic expression in the process of shear band formation and development.2)According to the evolution curve of anisotropic parameters,the contribution of the mesostructure parameters to the macroscopic shear strength is quantified.The normal contact force is the main carrier of the load in the specimen,and the contribution to the shear strength is the largest.The proportion of normal contact force,tangential contact force and contact law are about 60%,30% and 10% respectively,and the three laws have the same evolution rule.3)From the point of view of comprehensive anisotropy and shear stress ratio,the macroscopic mechanical behavior of the specimen is consistent with the development of the microstructure,so it can be regarded as the result of its microstructure coupling.4)The thickness of the measuring circle in the shear box can be obtained by the principal stress deflection of the different measuring points.The direction of the principal stress on the shear zone is about 90 ° from the initial 90 ° along the horizontal direction and stabilized about 50 ° The change of the main direction of the anisotropy is the embodiment of the micro-level of the principal stress plane rotation.5)The statistical analysis of the number and spatial position of the crack at different times shows that the fracture of the bond is mostly distributed in the shear zone and the number of tensile cracks is larger than that of the total number of shear cracks The number of cracks in the same mass,and the total number of the difference is not the same,indicating that there is no essential difference in the failure mode,but the development of different cracks.At the micro level,the size of the confining pressure has no significant effect on the number of bond breaks.