True Triaxial Test On Rockburst Of Granites With Different Water Saturation

Rockburst is a phenomenon in which the elastic strain energy in the rock mass is suddenly released and the rock looses and violently ejects due to excavation or other disturbances under high stress conditions.It is a common geological hazard in deep underground engineering disaster.Due to the complex and diverse engineering conditions and geological conditions,the mechanism of rockburst is not yet fully understood,and the prediction and prevention of rockburst is facing huge challenges.Based on practical experience that the water bearing state of rock has a significant influence on rock burst,rock burst prevention and control measures such as surrounding rock watering and high-pressure water injection have been made and achieved certain results.However,the internal mechanism of water prevention and control of rock burst is not completely clear,and most of the studies on the relations between rock moisture and rock burst intensity remain in the qualitative analysis stage.Therefore,the in-depth study of the intrinsic rockburst mechanism of different water-saturated granites and the establishment of a quantitative relationship between the moisture condition of the granites and the rockburst intensity are of great significance for revealing the mechanism of the impact of water on granite rockburst,and playing an important role for guiding the prevention of rockburst in deep underground engineering scientifically.The true triaxial rockburst test system was used to carry out true triaxial rockburst tests for red coarse grain granites in Cenxi County,Wuzhou,Guangxi with four different degrees of water saturation,and the characteristics of the rockburst failure process,stress-strain curve,failure mode,particle-size of rockburst fragments,acoustic emission,kinetic energy of specimens have been synthesized to analyze and discuss the mechanism of different rockburst granite rockburst.The main conclusions are as follows:(1)The higher the degree of saturation,the smaller the kinetic energy of ejection,showing a linear negative correlation between the two.That is,the intensity of rockburst decreases monotonously with the increase of the water saturation,with a maximum decrease of 74%.The quantitative relationship between water and rock burst is established,which has important guiding significance for the prevention and control measures of rock burst such as surrounding rock watering and high-pressure water injection.(2)Compared with natural specimen,the peak stress and yield stress of specimen with water saturation greater than 0.3 are obviously lower,the time of the beginning of small particle ejection to rock burst increased significantly.With the increasing of water saturation,during the process of rockburst,the ejection of small particles ejected decrease and the spalling of small rock slices increase,the spliting characteristics of rock plates increase,and the bulging behavior of rock plates weaken,the rockburst pit volume decreases,and the shear characteristics and the penetration of the main rock enhanced,the fragments are more broken and the distribution of particle size is more uniform.(3)With the increasing of water saturation,AE impact time at the rockburst moment increase,and accumulated absolute energy and absolute energy rate decline,AE impact time fractal dimension is from single peak to multiple,reflecting the enhancement of specimen plasticity.The decrease in the rise time of the AE signal indicates that the micro-fracture and fracture activity of the specimen is promoted.(4)The effect of water on rocks is mainly "softening" and "water wedge".The "softening" effect causes the rock strength to decrease and the ability to store strain energy to diminish.The "water wedge" effect caused the rock plates on the free surface to be quickly pulled and split.The rock shearing activity behind the rock plates has not yet been fully carried out.The thin rock plate has already undergone flexion fracture and the rockburst has occurred immediately.In addition,the viscosity of water will also have an impact on the ejection of the fragments.This is a further analysis of the internal mechanism of "water control rock burst" engineering measures.