Research On Dynamic Triaxial Numerical Simulation Of Graded Broken Stones Based On Three-dimensional Discrete Element Method

Graded broken stone was typical granular material which had obvious granular structural features,nonlinear mechanical properties and large variability.Its physical and mechanical properties were complicated.However,it was difficult to reflect the mechanical properties,deformation and failure mechanism of granular materials essentially by taking continuum mechanics theory and general laboratory test methods.Therefore,this paper has the important practical significance to carry out three-dimensional dynamic numerical triaxial test through PFC5.0-3D and application of graded broken stones.New “generate” logic was applied to create specimen.Balls and parallel bond model were utilized to simulate the boundary conditions.Granules were compacted by three walls to simulate pressure shaping.After that,the method of three-dimensional dynamic triaxial simulation test of graded broken stones was constructed.The reliability of software modeling was verified by comparing experimental data in the literature with this paper.The reliability verification of dynamic triaxial numerical test method was constructed with PUMA laboratory test data.The numerical simulation of long-term loading and unloading cycle was carried out to determine 200 cycles in numerical test.Real particle shape and sphere were applied into the dynamic triaxial numerical test respectively.The results show that spherical structure can not be used to analyze the structure-force characteristics of material,and simulation result is quite large and the real particle shape is recommended.According to these model parameters and test conditions,the test results are listed.(1)Rubber ball layer thickness are chosen and maximum movement rate of top wall are 1e1 m / s based on the size of single granual test.The affect of micro-mechanical parameters to dynamic triaxial numerical text was analyzed.The results show that the aggregate modulus is suggested 30 GPa ~ 40 GPa and friction coefficient is 0.4 to 0.6 range.(2)The effect of grain composition on permanent deformation of graded gravel was studied.The results show that the volume fraction of 19 ~ 26.5mm and 16 ~ 19 mm particle size should be control between 55%~65% to help forming the skeleton structure.The volume fraction of 4.75 mm particle size which is used as padding particle should be control 20%~25%.Moreover,the maximum dosage of 9.5mm and 13.2mm particle size which are used as transition particle should be control under 20%.(3)The permanent deformation mesoscopic characteristics of graded stones are summarized and analyzed to reveal permanent deformation mechanism of graded stones.These features is sorted according to the degree of permanent deformation analysis.The result is that porosity and micro stress and strain > particle contact > particle motion>particle structure> energy response.