Experiment Study On Rockburst Of Granite Triggered By Dynamic Disturbance Under Biaixal Compression Condition

Rockburst is a severe rock dynamic damage phenomenon.Under high geo-stress conditions,engineering excavation disturbance often cause serious rockburst damage.The occurrence of rockburst is usually accompanied by with a huge amount of energy releasing in the form of rock fragments ejection with a high-speed.It will bring serious threat to workers,construction equipment and the progress of the project.Thus,it is very necessary to study rockburst.Furthermore,in practical engineering,many rockbursts were triggered by dynamic disturbance,such as excavation blasting,mechanical drilling,and the seismic wave.For the special structures,such as the walls between the hydraulic tunnel cavern group,the mine's roof arch and base,granitic mass often suffer a state of biaxial compression.When these special structures encounter dynamic disturbance,the rockburst can be easily triggered.Therefore,it is necessary to carry out an experimental study on rockburst of granite induced by different disturbance under biaxial condition.To simulate the rockburst triggered by dynamic disturbance under biaxial compression condition,the rockburst test on granite specimen subjecting coupling static-dynamic loading was conducted using a self-development testing rockburst system.The influence of dynamic disturbance on rockburst was investigated.Various technical means including deformation test system,acoustic emission system,and high-speed camera system technology are applied to monitor the test process.A comparative analysis on the ejection process and ejection kinetic energy,failure pattern,deformation and damage characteristics,acoustic emission characteristics of rockburst triggered by different dynamic disturbance load was conducted.The main conclusions are drawn as following.(1)Dynamic disturbance shows an important influence on the intensity of rockburst.When the vertical static stress is 110 MPa,the ejection kinetic energy of the rockburst triggered by strong disturbance is 6.6 times higher than that under medium disturbance condition.The weak disturbance load failed to trigger the occurrence of rockburst.When the vertical static stress is 179 MPa,the total ejection kinetic energy of the rockburst triggered by weak disturbance is higher than that of the self-initiated rockburst.This shows that the higher static stress level and dynamic disturbance strength are,the larger the kinetic energy of the rockburst is.(2)The rock failure patter character is significantly influenced by dynamic disturbance.The tested specimen under self-initiated rockburst is relative intact,the cracks are short.Under strong disturbance condition,the tested specimen presents serious shear failure.Under weak disturbance condition,tension cracks on the bottom and thoroughly shear cracks can be observed on the tested specimen.Under medium disturbance condition,the tested specimen shows serious expansion,and tension cracks in the middle and thoroughly shear cracks can be observed.This suggests that the higher dynamic disturbance strength is,the more serious the tested specimen of the rockburst damage is.Furthermore,by comparing the characteristics of the debris,we conclude that the dynamic disturbance load can promote the development of the vertical cracks.(3)Dynamic disturbance has a significant effect on the vertical accumulative strain before the specimen occur rockburst failure.When the vertical static stress is 110 MPa,the specimen's vertical strain of the rockburst triggered by strong disturbance load is bigger than that under weak disturbance condition,but smaller than that under medium disturbance condition.This means that dynamic disturbance strength can affect the accumulative deformation of tested specimen at the moment of overall failure.The greater the dynamic disturbance strength is,the higher the accumulative deformation is.When the vertical static stress is 179 MPa,the vertical strain of rockburst triggered by weak disturbance load was obviously higher than that under 110 MPa vertical static stress condition.This means that the high initial static stress can increases the accumulative deformation.Furthermore,the accumulative deformation during the self-initiated rockburst is smaller than that during the rockburst triggered by weak disturbance.So,we can conclude that the higher static stress level and dynamic disturbance strength are,the easier the rockburst is triggered by dynamic disturbance.(4)The acoustic emission characteristics of rockburst is obviously influenced by different dynamic disturbance.When the vertical static stress is 110 MPa,the maximum accumulative absolute energy of acoustic emission of the tested specimen under strong disturbance is lower than that under medium disturbance condition.This indicates that the internal damage of the tested specimen under strong dynamic disturbance condition is lower than that under medium disturbance condition,further showing that low energy dissipation is one condition of triggering intensive rockburst and the dynamic disturbance strength controlling the intensity of rockburst.When the vertical static stress is 179 MPa,the maximum accumulative absolute energy of acoustic emission of the tested specimen with weak disturbance is apparently higher than that under 110MPa vertical static stress condition or under self-initiated rockburst condition.This suggests that the higher static stress level is,the larger the intensity of the rockburst is.