Study On The Control Of Thick And Hard Roof Of Wongawilli Face In Mining Shallow Coal Seam

Wongawilli mining method was a high yield and efficiency method, which was widely applied. In result of shallow thick-hard roof and bug of Wongawilli production practice, the gob roof of Wongawilli mining face in Shendong mining area generated hanging roof and roof collapse over large area easily, which resulted in death and damage to equipment. For solving the problem, theory study and actual measurement were combined to apply in this paper, the control of thick and hard roof of Wongawilli face in mining shallow coal seam was studied.Through the field measurement, the rule of ground behavior and roof movement in shallow Wongawilli mining face were analyzed and summarized, on condition of the pillar width of 0.5m, irregular pillars in gob were almost damaged, but the roof hadn't yet fallen, which resulted in large area hanging arch. And besides, the numerical simulation indicated that all of the irregular pillars were destroyed as a result of shear stress, and immediate roof was mainly destroyed on account of tensile stress, partly shear stress. Pillars for protecting branch way always kept elastic stable state, besides peripheral part of pillars appeared plastic failure.Based on elastic mechanics theory, combined with actual measurement rules, worked out hypothesis in reason, regarded gob hanging roof as elastic thin plate, and gob hanging roof movement as small deflection bending deformation, the formula of high-point hanging area was got, then the laws of high-point falling step and high-point hanging area were analyzed in the case of different pillar width and different face length.For the problem of hanging roof over large area, The association scheme of forced caving through deep hole blasting and anti-shock bulkhead was advanced. Two problems of the association scheme were studied, one of them was the time difference from crack birth to roof collapse, the other was the forming process of impact wave and the strength of anti-shock bulkhead.Based on fracture mechanics theory, aiming to the automatic collapse of roof, the time difference formula from the hanging roof cracking to collapse was got. Based on hydrodynamic theory, the impact wave was studied, which resulted from thick-hard roof collapse over large area, the different three stages in the process of the formation of shock gas were analyzed. Based on gas dynamic theory, viewed gob gas as no-glutinosity compressible gas, and the gob gas flow as adiabatic flow, the shock gas was analyzed and computed on the condition of the instantaneous failure of big area roof in gob, then the formula of pressure acting on anti-shock bulkhead was obtained. Through analyzing the influencing factors of pressure acting on anti-shock bulkhead, combined with the field condition of Wongawilli mining face, the anti-shock bulkhead was designed, and the scheme by using anti-shock bulkhead were proposed.