Study Of Strainburst Process Under Rockbolt Support Condition

Strainburst is a dynamic rock failure phenomenon under high stress region companied with sudden release of elastic energy,which frequently occurs in the underground engineering construction process.It not only threatens personnel/mechanical safety,but also restricts economic development and social construction,which has become one of the most prominent geological disasters in deep underground engineering.Presently,rockbolt is widely used to control strainburst,but the effect is not ideal,many tunnels which have been supported by rockbolts were still destroyed by strong strainburst.Therefore,it’s urgent to carry out the corresponding research to explore the mechanism and process of strainburst under rockbolt support.Two methods including physical strainburst test and numerical simulation test were used in this paper to illustrate the process of strainburst under the condition of rockbolt support.In physical test,the strainburst test was carried out by changing the number and location of rockbolt on white granite sample.The new rigid true-triaxial rockburst testing machine is used to reproduce the process of strainburst under rockbolt support and high stress condition.In addition,with the help of high-speed camera system,digital image motion analysis software,and other test equipment,the strainburst process is recorded.In the simulation test,the UDEC(two-dimensional discrete element software)is used to simulate the strainburst of granite samples and a tunnel in Jinping II hydropower station under different spacing rockbolt support condition.The research results indicate that:1.Strainburst process with rockbolt support is similar to the non-support condition in the macroscopic view.This process includes small grain ejections,spalling,shearing rock into fragments and fragments ejection.But there are differences in the microscopic view.For the strainburst with rockbolt,rock failure firstly occurs between rockbolts in the form of particles ejection,and then micro cracks develop into the deep and gradually penetrated through the rock mass,which finally causes the ejection of rock blocks,destroys the integrity of the supporting system,and further resulting in rock mass being loosen and the rapid decrease in the normal stress of rockbolts.Consequently,the reinforcement effect was reduced,the anchored area also finally failed.2.The rock mass between rockbolts becomes the weak zone under the condition of rockbolt support in the strainburst process.Once the strainburst happened,the dynamic rock failure was more serious than that under non-support condition,which indicates that rockbolts does not work insufficiently.3.Under high stress level,increasing density of rockbolts cannot prevent strainburst effectively,whereas the characteristics of strainburst are different.When the rockbolt is too dense,strainburst cause ejection of the whole rock surface,both anchored and non-anchored area are destroyed;when the density of rockbolt support is relatively small,fragments ejection start between rockbolts,and the damage decreases with the increasing of the rockbolt density.