Numerical simulation on roof and floor blasting rock burst prevention for nearly vertical coal seams
Due to roof and floor extrusion and prying of nearly vertical coal seams,the rock bursts prevention is challenging.Based on Wudong Coal Mine's southern mining area,we investigate roof and floor rock body blasting and pressure relief methods for nearly vertical coal seams.In terms of case study,numerical simulation,and onsite validation,we analyze the effectiveness of deep hole blasting to release pressure during rock burst occurrences in nearly vertical coal seams.Although deep hole blasting reduces the dynamic loads caused by roof and floor extrusion and prying,it is less effective in weakening the nearby rock mass at the working face and reducing static loads.To solve this problem,we employ the combination of deep and shallow hole blasting to release pressure,which mitigates the dynamic loads from prying actions,and effectively weakens the working face rock mass as well as the concentration of static loads.The new technique includes deep and shallow hole alternative blasting and deep and shallow hole simultaneous blasting.Compared to single deep hole blasting,the new technique will further reduce the horizontal stress peak in surrounding rocks of the roadway.The simultaneous blasting is more efficient than alternative blasting,but it is at a higher engineering cost.In the southern mining area of Wudong Coal Mine,deep and shallow hole alternative blasting has been applied.Microseismic monitoring results indicate that,compared to deep hole blasting,the implementation of deep and shallow hole blasting will significantly reduce the occurrence of high-energy events(greater than 104 J)from 9.3%to 0.2%,and gently release the microseismic energy from"low-frequency high-energy"to"high-frequency low-energy,"which effectively mitigating the risk of rock bursts.These findings provide a significant support for preventing rock bursts in nearly vertical coal seams.
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