Study On Fracture Propagation Mechanism Of Deep Rock Mass Under Loading And Unloading Condition

Natural rock masses have formed various macro and mesoscopic cracks under the action of human activities and natural environment.Due to the existence of these fractured rock masses,many unexpected accidents will occur,which will cause significant loss of life and property to construction personnel and geotechnical engineering.Therefore,it is of great significance to study the mechanical properties of fractured rock masses under true triaxial conditions.This paper prefabricates red sandstone samples with cracks,uses the GCTS RTX-3000 rock mechanics test system to carry out true triaxial loading and unloading tests,combines the acoustic emission system to study the influence of the intermediate principal stress and the prefabricated crack inclination on the mechanical properties of the red sandstone,and uses Ansys simulates the unloading test to study the unloading mechanism.The main research contents are as follows:(1)By setting 5 kinds of prefabricated crack inclination angles and 4 different intermediate principal stresses to explore the law of strength changes under true triaxial compression conditions,and verify the experimental conclusions using the Mogi-Coulomb criterion.The influence of the intermediate principal stress on the deformation in the true triaxial compression test is studied from the two aspects of peak strain and elastic modulus.(2)The influence of the intermediate principal stress on the crack initiation angle is discussed,and the crack propagation characteristics under true triaxial compression are analyzed in combination with the maximum shear stress theory;the fracture process of the specimen in the true triaxial compression test is shown in combination with the acoustic emission system,and The crack classification method on the acoustic emission parameter RA and the average frequency AF is used to verify the main crack type.(3)The true triaxial unloading test of red sandstone with prefabricated cracks under two stress paths was carried out,and the influence of the intermediate principal stress and the prefabricated crack inclination angle under different unloading stress paths on the strength characteristics,deformation characteristics,failure characteristics and acoustic characteristics of the specimens was discussed.The influence of emission characteristics.Ansys modeling completed the unloading test,and analyzed the unloading mechanism from the perspective of the strain energy density changing with the unloading process.