Study on prevention technology of rock burst by break-tip blasting and its effect estimation

Break-tip blasting is widely used in the prevention and control of rock burst under the condition of hard roof.Based on the mechanism of rock burst induced by static and dynamic loading,the mechanism of break-tip blasting to prevent rock burst is analyzed.Based on the analysis of the pre-assessment and dynamic evolution characteristics of the rock burst,the time-space-level division characteristics of rock burst is revealed,a technology system of time-space-level division break-tip blasting to prevent rock burst is proposed,which is applied to the engineering practice of rock burst prevention with hard roof,and it through theoretical calculation,drilling cuttings monitoring and microseismic monitoring to evaluation of break-tip blasting effect.The results show that the continuous weak surface consisted of fracture zone is the most important area to control the rock burst,the break-tip blasting can reduce the dynamic load strength released by the instantaneous breaking or collapsing of the roof,reduce the static load level imposed by suspended roof in coal,and promote the peak stress of the coal to transfer to the front of the working face,which can reduce the risk of rock burst.Based on the characteristics of "three parts" of time-space-level division of rock burst,a time-space-level division technology system for prevention and control of rock burst is established,which includes inclined break-tip blasting in cutting hole,strike break-tip blasting in coal pillar,pre-splitting blasting in working face and breaking-tip blasting in time.The system is applied to engineering practice and the effect of breaking-tip is evaluated,in which the flexural elasticity of roof decreases by 72% and 76% respectively in the initial weighting and periodic weighting after inclined break-tip blasting in cutting hole; the average amount of drilling cuttings decreases by 0.55 kg/m after strike break-tip blasting in coal pillar; the total energy and the maximum energy per day of microseisms in the presplitting blasting area of the working face are obviously reduced and the frequency of microseisms is significantly increased during the mining period.The effectiveness of time-space-level division break-tip blasting technology system to prevent rock burst is verified.