The Study Of Inoculation Mechanism Of Delayed Rock Burst Based On Rock Creep Test

Rock burst is a dynamic instability phenomenon which is caused by the sudden release of inner elastic strain energy because of construction disturbance and may cause the loosening,spalling and throwing of rocks.Rock burst can be divided into delayed ruck burst and instant rock burst according to the time of happen.The delayed rock burst may cause bigger danger to people and equipment because of it happens several hours to several decades after the excavation.We choose the new granite of underground workshop of pumped storage power station to test.Firstly,we decide the way to judge the unloading point and judge the rock burst proneness of the granite.Then we study the creep characters of granite and the creep test was carried out by using the generalized Kelvin model and Poyting-Thomson model for parameter inversion analysis in the way of bacterial foraging optimization(BFO).At last,we study the inoculation mechanism of delayed rock burst.The concrete results are as follows:(1)Rock burst proneness index needs to loading near to the peak stress and then unloading.But the peak stress is hard to know before the test,so the unloading point is hard to judge.According to this problem,we compare the crack damage stress and the stress of the last period of acoustic emission quiet period through uniaxial compression test.The results show,both of them are in the plastic deformation stage and near to 80%of the peak stress.But the crack damage stress is hard to show and monitor automatically,so the acoustic emission monitoring can be used to judge the unloading points.According to the test result and the field monitoring,the rock has weak rock burst proneness.At the same time,the judgement of Kidybinski is narrow to hard rock,while the judgement of Singh is suitable.(2)The creep properties of granite were studied using the uniaxial loading and triaxial unloading confining creep test.The results show that after the first stage load was applied,the rock was subjected to stress redistribution in a short time,and the rock deformation was slightly improved.In the subsequent creep process,the deformation of the rock was mainly concentrated in the period of load change,but the change in the holding period was not obvious.At this stage,the deformation parallel to the excavation direction continued to increase,while the deformation perpendicular to the direction didnot increase much.At the same time,in this stage,the rock was peeled off and the deformation was increased.After reaching the critical load,the rock experienced initial creep,constant velocity creep and accelerated creep in a short period of time,resulting in large deformation and damage.At last,using the method of bacterial foraging optimization,the creep test was carried out by using the generalized Kelvin model and Poyting-Thomson model for parameter inversion analysis.The creep equations of the two models were obtained.The results show that the two models could reflect the creep characteristics of the initial and the constant velocity creep stage of the granite,and the error was small.(3)Using the means of acoustic emission monitoring in the creep test to study the law of energy dissipation and the law of micro-cracks diffusion in the process of creep of granite.Then further study the inoculation mechanism of delayed rock burst.The results show that before the excavation was completed,there were already micro-cracks in the rock accompanied by energy dissipation,and the rock was peeled off,the main cracks produced and the rock burst body produced.After the excavation was completed,due to the construction disturbance,the rock was subjected to stress redistribution,and the acoustic emission activity and energy dissipation were proliferated.In this stage,the origin micro-cracks expansion and a few new micro-cracks produced.After that,the rock entered a stage of steady development,and the number of acoustic emissions and energy dissipation were maintained at a low level,that was when the acoustic emission quiet period occurred.In this stage,although there was micro-crack formation,the expansion speed was slow,and the rock accumulates energy before the destruction.Since this stage was close to the final destruction of the rock,it could be used as a key monitoring stage for rock burst warning.In the destruction stage,the rock had a large energy dissipation in a short time,the micro-cracks rapidly expanded and eventually penetrated,and the rock was destroyed,then the rock burst phenomenon occurred.In a word,acoustic emission monitoring can be used to judge the unloading point.Meanwhile,the granite have creep characteristics and both the generalized Kelvin model and Poyting-Thomson model can reflect the creep characteristics of the initial and the constant velocity creep stage of granite.At the same time,after the excavation,the rock through the stage of previous accumulation,the stage of stress adjustment,the stage of stable development,the delayed rock burst become happen.