Research Of Floor Burst Prevention In Gob-side Entry In Full-mechanized Caving Mining Field

For deep wells with fully-mechanized caving face that has a rock burst tendency, mining is usually performed along the goaf. However, the goaf has the risk of floor rock burst. The conventional pressure-relief measures have the defects of large engineering load, complex procedures and the insufficiency to effectively prevent rock burst. Based on the geological conditions and mining conditions of Huafeng Coal Mine of Xinwen Orefield, theoretical analysis, numerical simulation and field measurement were carried out. The influence factors and mechanism of rock burst induction along the goaf were analyzed for the fully-mechanized caving face in thick coal seam. Moreover, the rock-burst prevention effect was examined. On this basis, the measures for preventing floor rock burst were proposed, and were applied to coal mine to verify the prevention effect. The research contents were as follows:(1) On the basis of a assessment of rock burst risk of coal seam, the method for assessing the rock burst risk of the mining field was discussed. By summarization, and analysis of the methods for assessing the rock burst risk, the relationship between the field dynamic monitoring data (vibration field, stress field, drill cuttings) and the rock burst was identified. A combined static-dynamic assessment method was established based on the influence factors of pre-mining rock burst and the vibration field-stress field-coal dust quantity, namely, delineation of risk areas by monitoring of microquakes and underground sound. The close-range monitoring of coal-rock stress can help prevent the expansion of anti-burst scope, therefore improving assessment of anti-burst effect. Verification was performed by drilling method. The new method for assessing the anti-burst effect was further tested. This method can achieve the narrowing of monitoring scope, the assessment of rock burst risk from long distance to short distance, and the assessment accurate to points.(2) According to the theory of material mechanics and elastic mechanics, the mechanism of induction of floor rock burst was analyzed through microseismic monitoring. Based on the stress on roof and floor, the mechanical model of rock burst-induced instability on the goaf floor was constructed for fully-mechanized caving face. The influence of each parameter on the stress and energy conditions of floor damage was discussed; the relationship between each parameter and the risk of floor burst was analyzed. Thus the mechanism for controlling floor rock burst along the goaf was revealed. By changing the stress environment of the floor, the contribution of strong dynamic pressure to the floor is reduced. Therefore, the risk of floor burst can be relieved.(3) The scheme of floor rock-burst prevention along the goaf and the prevention effect were studied by mechanical analysis and numerical simulation. It was found that the surrounding rock stress in scheme2for anti-burst mining field was lower than that in scheme1. The area of plastic zone of roadway floor was large and the ability of buffering the rock burst was strong. This was favorable for floor rock-burst prevention.(4) Based on the above analysis, scheme2was chosen for floor rock-burst prevention. Experimental study on anti-burst effect was then carried out for Huafeng Coal Mine of Xinwen Orefield. The results of assessment based on "vibration field-stress field-coal dust quantity" showed that the design of anti-burst mining field (scheme2) can reduce the risk of floor rock burst.Engineering application was carried out for No.1412working face of Huafeng Coal Mine that had a risk of floor rock burst. Satisfactory effect was qbtained, which verified that there was no rock burst risk along the goaf.