DEM simulation of progressive damage and permeability evolution of sandstone during direct-shearing
In order to investigate progressive damage and permeability evolution of sandstone under direct-shearing conditions,a group of numerical models based on physical experiments are established using the particle flow code in two-dimension(PFC2D).Four different levels of normal stresses are set to discuss meso-crack propagation features,energy dissipation mechanism,and permeability evolution characteristics of sandstone in the process of direct-shearing.The results show that the mesoscopic cracks gradually expanding,merging,connecting,nucleating,and finally forming an obvious macroscopic shear band,and the total number of cracks after failure increases with the increase of the normal stress.In addition,the total energy input in the pre-peak stage is mainly stored in the form of the strain energy of interparticle bonding bonds,and the dissipated energy increases rapidly in the post-peak stage.The dissipated energy is close to 40％of the total energy when the numerical rock samples fail completely.Furthermore,the permeability variation is governed by the preferred seepage channels in the rock sample,and the sudden increase of permeability is the manifestation of the transformation of"pore flow"into"fracture flow"during direct shearing process.
rock mechanicsdirect-shear testprogressive damagepermeability evolutionparticle flow codediscrete element method
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