Experimental Study On Rockburst Of Rock Similar Material Under Different Stress Gradient Loading Paths

Rockburst is a common geological hazard in deep mining.When it occurs,it has a strong destructive force,which will lead to equipment damage and even casualties.Due to the diversity of engineering geology and the complexity of rockburst,the rock burst mechanism has not been fully understood.The engineering practice shows that the stress concentration of surrounding rock has a certain influence on the rockburst after excavation.Therefore,based on the law of stress redistribution of surrounding rock after excavation,rockburst tests with different stress gradient loading paths were carried out in this experiment.Therefore,based on the law of stress redistribution of surrounding rock after excavation,rockburst tests with different stress gradient loading paths were carried out in this experiment.And the relationship between stress gradient and rockburst failure characteristics was established,which has guiding significance for preventing and controlling rockburst in deep mining.Based on an engineering example and previous researches,choose high strength plaster as similar rock material,using YB-A type pneumatic-hydraulic composite rockburst simulation test device,to carry out the three groups of rockburst test under different stress gradient loading paths.And the rockburst failure process,debris size,failure surface morphology,acoustic emission(AE)energy characteristics and acoustic computer tomography characteristics under different stress gradient paths were analyzed.Focusing on the study of the mesoscopic fracture characteristics of rock burst test,including the morphology of debris crystal and fractal characteristics of debris crystal under scanning electron microscope(SEM).The PFC2 D simulation was used to verify and supplement the test,and further analyze the microfracture process of rockburst under different stress gradients.Specific conclusions are as follows:(1)Different stress gradients loading had significant effects on the distribution of rockburst debris.With the increase of the stress gradient,the ratio of sheet debris in the rockburst debris decreased and that of block debris increased,and the rockburst failure mode changed from splitting failure to shear failure.(2)With the increase of stress gradient under the same confining pressure,the AE energy of the specimen in the loading process was relatively more accumulated in the early stage of rockburst.As a result,the more energy released in the rockburst,the farther the debris was thrown during the rockburst,and the higher the rockburst strength grade.(3)Damage areas were close to the unloading surface in the rockburst,with the phenomenon of compaction.The damage in specimen increased with the increase of stress gradient.(4)The microstructure characteristics of rockburst debris varied with different stress gradient loading paths.The larger the stress gradient,the more the number of crystals in short stick shape,and the higher the density of crystals.The crystal profile of debris had fractal characteristics,and the fractal dimension increased with the increase of stress gradient.(5)Numerical simulation was performed to reproduce the rockburst failure process of the specimen.The crack first appeared near the unloading surface of the specimen.As the stress gradient of the specimen increased,the crack propagation and rockburst failure range of the specimen increased during the loading process.In terms of rockburst failure mode and other aspects,the numerical simulation results were almost same as the phenomena and characteristics of laboratory tests,indicating that rockburst tests were effective and reliable.