Fracture Characteristics Of Rock Containing Defects Under Biaxial Loading And Unloading Conditions

During the formation process of rock mass,there exist various primary fractures,joints and holes due to various complex geological environments,and the existence of primary joints fractures and holes in the rock mass affects various strength and deformation damage characteristics of the rock mass.The disturbance of underground excavation breaks the original stress distribution,causing the micro-cracks in the rock to expand and penetrate each other,resulting in unloading failure to the rock,which may even cause destabilization damage,threatening the lives of personnel and production safety,causing various production accidents,and becoming a technical problem faced by the majority of field engineering construction personnel.It is of great significance to study the various mechanical properties and rupture laws of rocks under biaxial loading and unloading conditions to avoid possible destabilization damage in underground construction and ensure the safety of life,property and production.In this paper,numerical simulations of uniaxial compression,biaxial compression and biaxial loading and unloading were performed on granite specimens containing different prefabricated defects.Uniaxial compression experiments were carried out on intact standard cylindrical granite specimens and square granite specimens containing prefabricated defects,and the experimental results were used to calibrate the microscopic parameters in the numerical model.The effects of different stress paths,different shapes of prefabricated defects,different numbers of defects and different distributions of defects on the strength,deformation and crack initiation stress characteristics of the rock specimens were investigated.In addition,the initial cracking and cracking stage distribution,cumulative crack number,ultimate damage mode and crack extension fractal dimension of the specimens with different prefabricated defects under biaxial loading and unloading conditions were analyzed and compared.Three stages were divided into pre-peak,peak and post-peak to analyze the crack evolution mechanism.The results show that most of the cracks appear after the peak strength,and different shapes,the number of defects and the relative positions of the defects have great effects on the crack generation,crack extension and crack coalescence.Uniaxial compression tests were conducted on the prepared rectangular sandstone specimens containing semicircular arch holes with different inclination angles and standard cylindrical specimens to measure their strength and deformation characteristics as well as crack extension and acoustic emission characteristics.The mechanical parameters were calibrated to the numerical model,and the numerical models of semicircular arch holes with different inclination angles were established,and uniaxial compression,biaxial compression and biaxial loading and unloading simulations were performed.The effects of different angles of semicircular arched holes on the strength and deformation of sandstone specimens are studied,and the crack evolution mechanism and the damage process of specimens under uniaxial compression and biaxial loading and unloading are analyzed in detail in three stages: before,at and after the peak strength.The experimental results show that different angles of semicircular arch holes and different stress conditions have significant effects on the fracture behavior of sandstone specimens.Through field measurements and data collection in the Maluping mine area of Guiyang city,the thickness of the EDZ data of 18 monitoring holes were obtained,and the rupture range of mineral rocks in the measured area was divided,and in addition.