Study On The Failure Characteristics Of Deep Rock And The Mechanism Of Strainburst Under True Triaxial Unloading Condition

There are many difficulties for deep mining. For example, how to improve the complicated stress environment of deep rock mass which contains high in-situ stress, high ground temperature, high hydraulic pressure and dynamic disturbance caused by blasting and mechanical excavation. High in-situ stress means high strain energy stored in deep rock. The high strain energy stored in deep rock mass can be induced to release by excavation unloading engineering. The phenomena of rock burst and zonal disintegration induced by excavation unloading in high depth buried rock mass prove that the release of elastic strain energy can cause rock failure and induce severe disasters.In view of the aforementioned problems, the main purpose of this study is using self-designed true triaxial electro-hydraulic servo-controlled test system to study the failure characteristics of highly-stressed rock mass and the mechanism of strain rock burst under true triaxial unloading condition. The main contents and conclusions are as follows:(1) The true triaxial electro-hydraulic servo-controlled test system can apply load to high stress level independently in three directions (σ1> σ2>σ3≠0, where σ1is the maximum principal stress;σ2is the intermediate principal stress; σ3is the minimum principal stress). It can also impose dynamic load.The studies on the mechanical characteristics of granite, red sandstone and cement mortar cubic samples under true triaxial unloading condition were carried out. When intermediate principal stress is low, the failure mode was shear failure. While intermediate principal stress increased, the failure mode changed into slabbing. The occurrence of slabbing related with lithology and stress state of rock. (2) When intermediate principal stress is low, the peak strength of rock samples is smaller than the calculated strength based on Mohr-Coulomb criterion. This is the further evidence for slabbing failure.(3) The characteristics of slabbing failure were monitored by AE test system and infrared cameras. With the increase of σ2, the shear crack initialed and propagated during the whole compressive progress. But AE count rate of rock specimen with slabbing failure had a catastrophe point and slabbing crack began forming.Under compressive test the temperature of compressed vertebral surface significantly changed and the rock failure mode is shear failure. When σ2is low, the lower part of specimen firstly damaged and overall destruction occurred subsequently, the failure mode is shear failure. When σ2reached a higher level, the failure surface is planar and failure mode turned into slabbing.(4) According to the stress path after engineering excavation and the occurrence condition of slabbing failure, the experimental studies on strain rock burst induced by dynamic load were carried out. Regardless of dynamic load parallel or perpendicular to the direction of the maximum principal stress, rock burst could be induced as long as the load amplitude reaches a certain level.(5) Rock burst induced by perturbation was simulated by PFC3D particle flow code, the conclusions were consistent with the experimental result. When the disturbance load amplitude researched to300,400,500kN, propagation of micro-crack expanded stably but the rock samples did not damaged; while disturbance load amplitude equal to600kN, micro-racks rapid expanded rapid and rock samples failed.