Experimental And Numerical Simulation Study On Fracture Evolution And Failure Characteristics Of Rocks With Cross Fractures

There are various scale and shape defects(such as microcracks,micropores,etc.)in the rock in nature.Under the action of external forces,the microcracks in the rock will crack,expand,penetrate and even destroy,causing engineering accidents such as slope landslide,tunnel collapse,stope roof fall,etc.,causing huge economic losses and adverse social impact.Therefore,the study of rock fracture evolution and its failure characteristics is of great significance to prevent and control the stability of engineering rock structure.In this paper,according to the similarity theory,the rock like samples with cross cracks are made by using fine sand,white cement and water in a certain proportion,and the rock mechanical test machine RMT-150 B is used for uniaxial compression test.Based on the results of laboratory tests,the PFC numerical simulation model of rock samples with pre fabricated cross cracks is established,and the evolution law,failure mechanism and acoustic emission characteristics of crack initiation,propagation and penetration of rock samples with cross cracks are analyzed.The main research results and conclusions are as follows:(1)Using RMT-150 B rock mechanics testing machine,the uniaxial compression test was carried out on the rock samples with cross fracture,and therelationship among the fracture angle,fracture length and peak strength was obtained.The results show that the peak strength increases first and then decreases with the increase of the fracture angle,and reaches the maximum value when the fracture angle is 45 °.The peak strength increases with the decrease of the length of the primary and secondary fractures.(2)Using high-speed camera and acoustic emission equipment,the fracture evolution law and acoustic emission characteristic parameters of rock samples with cross fracture during loading were recorded.Research and analysis show that when the fracture angle is less than 45 °,most of the rock samples with cross fracture occur shear failure along the diagonal of the sub fracture expansion;when the fracture angle is greater than 45 °,the expansion of rock samples with cross fracture mainly depends on the length of the sub fracture and the main fracture;when the main fracture length is greater than the sub fracture length,most of the rock samples are along the main fracture When the length of the main fracture is less than the length of the secondary fracture,all the specimens are sheared along the diagonal of the secondary fracture.When the length of the main fracture is equal to the length of the secondary fracture,when the inclination of the fracture is 0 ° and 30 °,the specimens are sheared along the diagonal of the secondary fracture.When the inclination of the fracture is45 ° and 60 °,the specimens are sheared along the diagonal of the secondary fracture Shear failure occurs along the diagonal of the main fracture.(3)Based on the results of laboratory tests,the numerical simulation software PFC2 D is used to calculate the cross crack.The influence of differentdip angles on the mechanical properties and crack evolution law of the cross crack specimen is analyzed.The evolution of cracks,the number of microcracks and the failure behavior of the cross crack specimen are studied from the micro and macro aspects.It is found that 0 ° is from the primary and secondary cracks The microcrack number curve can be divided into four stages,and the growth rate of the latter stage is always higher than that of the former stage;The failure modes of specimens with 0 °,30 °,45 ° and 60 ° fracture obliquity are all diagonal shear failure.