Macro-micro Mechanical Properties Study On Cracked Rock Mass Under Loading And Unloading Based On DEM

In the construction of all projects,excavation must be carried out first.Excavation is actually a complicated process of loading and unloading.In recent years,a large number of researches have been conducted on the macro-mechanical properties,deformation characteristics,constitutive equations,and fracture mechanisms of rock masses for unloading and unloading,and satisfactory results have been obtained.However,from a microscopic point of view,the cracking mechanism of rock mass loading and unloading has only just begun.Therefore,in this paper,brittle sandstone is simulated by similar materials(mortar),based on the uniaxial compression test of indoor PFC2 D meso-parameters,prefabricated cracks of numerical model are completed by self-compiled FISH function,and loading and unloading of samples is achieved by self-programming.Simulation test.At the macroscopic level,the mechanical characteristics and deformation characteristics of the simulation are analyzed,and the microscopic crack propagation,mesoscopic field,displacement field,and energy field are analyzed,and the breakdown time,rupture mode,and rupture mechanism are analyzed.A comparative analysis of the simulated loading and unloading tests was carried out.To provide a basis for understanding the macro-mechanism of rock mass instability fracture under loading and unloading conditions.Through the above research work of this article,some useful conclusions have been obtained,mainly obtained the following preliminary research results.First,PFC meso and macro contact: In the role of external forces to promote the internal particle movement of the sample,particle movement caused by the contact force between the particles is greater than the parallel bond strength,parallel bond fractures produce micro-cracks,micro-cracks expand and make the stress with The strain changes.Specifically,when the number of microcracks increases more significantly,the stress-strain curve corresponds to a more significant drop.Second,based on the PFC energy: The meso-scopic energy consumption rules of the specimens with different stress paths and cracks at different inclination angles are basically similar,but there are obvious differences in magnitude.Obviously,the energy absorbed by the specimen during biaxial compression(boundary work)is the largest.Italso causes correspondingly more energy.By comparing the energy between different stress paths and cracks at different angles,the authors found that the total strain energy-strain curve and the stress-strain curve maintain a high degree of agreement.Since the friction energy is mainly generated after the fracture after sliding between particles,the friction energy The number of cracks remains highly consistent;Third,based on the PFC simulation of the unloading failure mechanism: By comparing the ratios of shear cracking and tensioning cracking during biaxial compression and unloading,it is found that the ratio of shear cracking and tensioning cracks in specimens suddenly decreases during sudden unloading.At a certain value,a large number of tensile cracks suddenly occur,tensile failure occurs,and then the ratio of shear cracks to tensile cracks stabilizes at a certain value,that is,the tensile failure of the specimen occurs.