Experimental And Numerical Study On The Fracture Mechanism Of Brittle Rock Specimens With Open-type Preset Flaw

After decades of industrial development,the depth of mineral resources has gradually increased,which accompanied with frequent rock bursts.In particular,the structural-controlled rock bursts occurring in brittle rock masses are one of the most dangerous and violent phenomena that endanger the stability and safety of artificial underground structures.Therefore,it is very significant for engineering construction and personnel safety to accurately understand the failure principle of rock mass with 3D preset flaw.Results obtained by the specimen with internal 3D filling-type preset flaw have proved that the development process and distribution of secondary failures are different from that shown in the traditional 2D studies.However,there is no suitable preparation method to make the internal 3D open-type preset flaw in rock specimen,thus the results of numerical simulation and theoretical analysis under this condition cannot be verified by experimental phenomenon.Based on this background,the physical mechanics and failure characteristics of brittle rock masses with internal 3D open-type flaws were deeply studied,and the main research contents and results are as follows:(1)Research and development of the preparation method of the rock-like specimen with internal 3D open-type preset flaw.Based on the idea of volume loss,a new method for preparing specimens with internal 3D open-type preset flaw was developed,and the real cavity structures was successfully obtained in gypsum rock-like samples(verified by the CT scanning technology).(2)The uniaxial compression failure test of samples with open-type preset flaw.Taking the inclination angle and strike length of the preset open-type flaw as the independent variables,the physical mechanics,external and internal secondary failure characteristics of fractured rocks under different flaw occurrence conditions were deeply researched,and the temporal and spatial differences of the external and internal secondary destruction processes were compared and analyzed.(3)The uniaxial compression failure test of parallel double-flaw samples under different flaw concealment conditions.Taking the flaw concealment status as the independent variable,the physical mechanics,external and internal secondary failure characteristics of fractured rocks under three types of flaw concealment conditions(double flaws expose on surface,one flaw expose on surface,double flaws conceal inside sample)were deeply studied.In addition,based on the results of single flaw and double flaw tests,the differences between the appearance and real state of fractured rock masses were discussed,and the reasonable safety strength and key failure locations of various fractured rock masses are proposed.(4)Theoretical analysis on the fracture mechanism of surrounding rocks of the open-type preset flaw.Under the condition of uniaxial compression,the 2D and 3D tip stress field models of the open-type flaw were established respectively,and the stress intensity factors and secondary failure modes at different positions of the fracture tip were solved.Besides,based on the theoretical rectangular board model with four fixed sides,the in-plane stress fields in free surface of the roof surrounding rock were figured,which help to obtain the initiation position,development process and final distribution region of secondary failures in this positon.(5)Numerical simulation of the uniaxial compression failure test of samples with internal 3D flaws.Conduct the related experimental studies by the PFC3D software,and the particle displacement trend method was applied in 2D research sections and 3D local research models to analyze the fracture mechanism of secondary failures in different positions,including the influence of the flaw thickness on the initiation and development of secondary failures.(6)Numerical simulation of the uniaxial compression failure test of parallel double-flaw samples with various flaw concealment conditions.Conduct the related experimental studies by the PFC3D software,and the analyses of surface deformation,destruction process,failure initiation mechanism and failure modes were completed in different 2D research sections.