Evaluation on the rock burst risks of roadway using critical stress index method

Rock burst hazard evaluation refers to the confirmation of the rock burst hazard grades and dangerous areas, which is the foundation of rock burst prevention. The “stress-surrounding rock-support” model for roadway rock burst was established. Based on the rock burst theory of disturbance response instability,the internal relationships among the critical stress,the depth of critical resistance zone,the uniaxial compressive strength of coal mass,the support strength of roadway,the geometric parameters of roadway and the impact energy index were found. The impact energy index directly affects the size of the critical stress and critical resistance zone of the roadway surrounding rock system. The increase of the depth of the resistance zone leads to the increase of the critical load of the rock burst. The actual depth of the resistance zone and the stress environment are the important factors affecting the rock burst. The calculation method of the critical stress index considering the in-situ stress environment,the outburst proneness of the coal mass,the struc- tural property of the roadway and the actual surrounding rock state was given. The critical stress index at the area where the rock burst occurred with similar conditions was taken as the rock burst occurrence index Kfcr of the area to be evaluated,and the critical stress index is divided into four nu-merical intervals with 0. 25 Kfcr as the interval in0, Kfcr ,corresponding to the four risk grades of no hazard,weak hazard,medium hazard and strong hazard,respectively. The rock burst hazard of the area to be evaluated is determined according to the distribution of the critical stress index in the four intervals. Taking the 303 working face of a mine as an example,this paper introduces the process of rock burst hazard evaluation which includes 10 steps. The evaluation result shows that there are 5 areas with medium hazard and 7 areas with strong hazard in this working face. Compared with the comprehensive index method,the evaluation results of critical stress index method tend to be more quantitative,and the monitoring data of the drilling bits method show that the evaluation results are consistent with the results of field monitoring.