Particle flow analysis of crack propagation characteristics of hole-type tridental crack sandstone

In order to study the influence of joints and holes on the mechanical properties of rock mass,this paper selects a group of reasonable micro parameters by comparing and analyzing the elastic modulus,peak strength and the final failure mode of the intact sandstone and the sandstone samples with prefabricated single fracture in the laboratory uniaxial compression test and the PFC2D simulation test.The micro parameters are used to carry out the uniaxial compression simulation test on the holetype trident crack sandstone.The results show that the uniaxial compression strength and uniaxial compression strain of the fracture specimens are nonlinear with the change of the crack angle α,the crack angle β,the hole diameter dand the crack length 2a,and they are significantly lower than those of the intact specimens,and the crack length 2a has the greatest influence on the uniaxial compression strength of the specimens.Tensile and shear failure occurs during loading,and the main failure mode is tensile failure.The wing cracks generally originate at the outer tip of prefabricated trident cracks or near the junction of refabricated trident cracks and hole,while the secondary cracks generally originate at a certain location during the growth of wing cracks.The crack angle α mainly affects the damage extent of the specimen,the crack angle β mainly affects the propagation mode of the crack,the hole diameter d mainly affects the initiation position of the secondary crack,and the crack length 2a mainly affects the initiation position of the wing crack.Through the discussion of the crack growth mechanism of the holetype trident fracture sandstone,in the initial crack initiation stage,the stress concentration region of the specimen generally occurs near the tip of prefabricated trident crack and the edge of the hole,with the acoustic emission events in the specimen,and finally,with the continuous increase of stress and the evolution of stress field,the continuous propagation of the macrocracks formed by the gradual convergence of microcracks eventually leads to the instability and failure of the specimen.