Experimental And Numerical Simulation Of Fracture Sandstone Failure Mechanics

In recent years,China has vigorously developed underground engineering construction.In actual underground engineering,cracks,holes and other defects are distributed inside the rock mass.The existence of cracks reduces the stability of the rock mass,especially under the superposition of loads such as structural stress and blasting.Fissures will further develop and expand,and the stress and failure modes of surrounding rocks will change and its failure path prediction becomes extremely difficult.Therefore,studying the mechanical properties and fracture modes of fractured rocks is an important reference for guiding field engineering practice and significance.First,the author takes standard cylindrical single-fractured red sandstone as the research object,and conducts uniaxial and triaxial compression experiments to study its mechanical characteristics and failure laws.Then,through uniaxial and biaxial compression experiments on the fracture-cavity composite sample,the mechanical characteristics and fracture evolution characteristics of the fractured surrounding rock under load are further revealed.The PFC2D calculation and analysis program was used to explore the crack propagation law of fractured sandstone.The main research contents and results are as follows:(1)Based on uniaxial compression experiments,the effects of different prefabricated fracture inclination angles on the mechanical properties of sandstone are analyzed.Showing that the peak strength,peak strain,and elastic modulus parameters increase with increasing fracture inclination angles.Based on fracture mechanics theory,the maximum circumferential tensile stress criterion was used to analyze the fractured rock under uniaxial compression,and it was found that the fracture angle of the fractured rock sample increased with the increase of the prefabricated fracture dip angle.According to the conventional triaxial compression experiments,analysis of the effect of confining pressure on the mechanical properties of fractured sandstone under the same prefabricated inclination angle.Showing that the peak strength,peak strain,and elastic modulus parameters increase with increasing confining pressure,and the unevenness of rock sample failure with increasing confining pressure.The weakening of the fracture surface makes the form of the fracture surface simpler.Analyzing the influence of different prefabricated fracture inclination angles on the mechanical properties of fractured sandstone under the same confining pressure,showing that the peak strength,peak strain,and elastic modulus parameters increase with the increase of the fracture inclination;The failure modes of fractured sandstone under different variables in three types of experiments were explored respectively.(2)Based on the triaxial compression test results of fractured sandstone under different confining pressures,Mohr-Coulomb,generalized Hoek-Brown,exponential strength,and Rocker strength criteria were used to fit the data,and the generalized Hoek-Brown strength criterion fits well.The degree R2 is the highest;according to the triaxial compression experiments of different prefabricated dip angles and fractured sandstones,it is found that the peak strength and peak strain increase slowly between 0°and 60°,and increase faster between 60°and 90°.The elastic modulus is between The increase speed is slow between 0°?45°,the increase speed is fast between 45°?75°,and the increase speed is slow again between 75°?90°.The S-type function logistic regression analysis is used to fit the data.(3)Based on the particle flow discrete element theory and PFC2D calculation and analysis program,the macro parameters of the rock samples are measured according to the laboratory experiments,and the parameters are calibrated to obtain the corresponding meso parameters.Through PFC2D,the crack propagation law,force chain changes,structural analysis,and displacement field of fractured sandstone are studied,and compared with laboratory experiments to verify the fracture evolution process and failure mechanism of fractured sandstone.(4)Define the initial macro and meso damage,introduce the initial macro and meso damage characterization coefficient K_D,and establish a constitutive model for non-closed fractured rock coupled with macro and meso damage.Combined with triaxial compression experimental data of fractured sandstone under different confining pressures The verification analysis shows that the error of the theoretical data is small compared with the measured data,which indicates that the theoretical model has strong practicability.(5)Uniaxial and biaxial compression experiments were performed on the fracture-cavity specimens to investigate the effect of the inclination of the fractures on the arch shoulders on the mechanical characteristics and failure modes of the specimens.The fracture process of the fracture-cavity specimens in the uniaxial compression experiment was divided into Four stages,and the reasons for the chipping of the specimen surface during loading were obtained.The influence of confining pressure on the mechanical characteristics and failure mode of the specimen was investigated.The progressive instability failure process of the crack-hole specimen was simulated by PFC2D.The tensile circle,shear crack,and energy evolution characteristics were monitored using the measurement circle.Finally,the evolution process of meso-to-macro fracture and the mechanism of instability and fracture of fracture-cavity samples were obtained.