Research On Crack Propagation Mechanism Of Rock-like Material With Double Flaws Based On Discrete Element Numerical Method

Crack propagation and coalescence in rock mass is always a hot topic in rock mechanics research.Many rock engineering instable failures are caused by the propagation and coalescence of internal cracks.At present,when the rock or rock-like materials are tested for crack propagation,it is difficult to obtain the accurate information of crack development in the rock mass due to the accuracy of observation instruments and equipment.In this paper,the crack propagation law of double-flaw gypsum specimens is taken as the starting point.Considering the advantages of discrete element research for fracture and large deformation,based on the results of laboratory experiments,the improved PBM contact model is used to establish a prefabricated double-flaw rock-like numerical test.Then,the crack initiation,propagation and coalescence of prefabricated double-flaw tips under uniaxial and biaxial loading conditions are analyzed.The main contents of this paper are as follows:(1)Based on the indoor test results of gypsum samples,the improved PBM three-dimensional contact model and FJM model were verified to match the physical and mechanical properties of brittle rock materials,especially the ratio of uniaxial compressive strength to tensile strength;(2)Based on the improved PBM contact model,the uniaxial compression and biaxial compression test simulation were carried out on the gypsum sample with two flaws.The three-dimensional numerical model was used to directly reflect the process of crack propagation.The influence of crack angle,rock bridge angle,rock bridge length and confining pressure on the crack propagation mode was studied.By analyzing the development of microcracks,the distribution of contact force chain and the displacement mode of particles,the essence of crack development was revealed from the meso level;(3)By comparing the crack propagation test results of the improved PBM contact model and FJM model,it was found that the crack development mode and the crack growth stress of the two models are similar,but the improved PBM model has better applicability in the study of crack propagation due to its unique meso contact parameters;(4)Through the sensitivity analysis,the influence of the micro parameters on the macro crack growth law was discussed.It was proposed that the characteristics of crack development should be included in the process of calibration and verification.