| There are 43#and 45#steeply inclined and extremely thick coal seams with an average dip angle of 45° in the northern mining area of Wudong coal mine.both coal seams are mined by high-stage horizontal sublevel fully mechanized caving.Due to the complexity of the occurrence environment and mining technology,the top coal caving ability is poor and the recovery rate is low.Therefore,it is of great practical significance to carry out the research on the pre-cracking technology of hard top coal in fully mechanized caving mining of steeply inclined and extremely thick coal seam in the northern mining area of Wudong coal mine.Taking the+575 horizontal 43#,45#steeply inclined coal seam fully mechanized caving face in the north mining area of Wudong coal mine as the background,the pre splitting technology of steeply inclined hard top coal was systematically studied by using the methods of site conditions investigation,indoor rock mechanics experiment,theoretical calculation,numerical simulation and industrial test application.Firstly,based on the analyse and investigate of geological occurrence and mining technical conditions,of steeply inclined and extremely thick coal seam,the influencing factors of caving ability of top coal are mastered,and the coupling crack weakening measures of top coal were determined.Next,considering the combination method of rock mechanics experiment and numerical calculation simulation,the strength degradation rate of coal sample under the ’waterforce ’ coupling action and the stress distribution law of coal body under the water degradation were studied from the macro and meso scales.the results show that the strength of coal sample and the internal stress level of top coal are significantly reduced after water treatment,and the top coal is fully weakened by water injection.Then,according to the rock mechanics experimental results,the blasting models with different charge diameters are established,and the laws of shock wave propagation,effective stress and damage evolution range of blasting models with different charge diameters are studied.By comparing the results of theoretical calculation and numerical calculation,the distribution characteristics of coal blasting crushed zone and fractured zone are analyzed,and the optimal charge diameter is determined.Finally,based on the above research results,the engineering practice is carried out in the fully mechanized top coal caving face in the north mining area of Wudong coal mine,the on-site water injection and blasting schemes were designed,and the weakening effect of water injection and blasting measures were analyzed and evaluated.after the top coal adopted the ’ water injection-blasting ’coupling fracturing measures,the stress of coal body decreased significantly,and the degree of top coal fragmentation increased,reaching the expected purpose.The research results of this paper give the top coal pre splitting method suitable for the northern mining area of Wudong coal mine,and reduce the dynamic disaster caused by the top coal caving in the goaf.It has practical significance for the safe and efficient mining of the coal mine,and also provides reference for the weakening problems of hard top coal pre splitting in the horizontal section fully mechanized caving mining of steep inclined coal seam under similar conditions in the future. |
