Movement and failure law of overlying strata above fully mechanized mining faces under shallow and thick hard bedrocks
To reveal the characteristics of roof stress and overlying rock movement on the fully mechanized top-coal caving face in shallow and thick coal seams,drilling holes were laid in the auxiliary transportation roadway of the No.15304 working face at Wujiagou Mine to re-probe the distribution of roof rock layers and the key layer position,also to monitor the characteristics of the fissure development and fracture positions at different level,and to analyze the distribution law of working resistance of the support in the working face.The results show that the key layer of the roof controls the movement of the overlying rock above the working face and arises up the mining pressure on the working face.The breaking of the key layer causes severe movement of the overlying rock and intense pressure in the mining area.The overlying rock collapse in the goaf develops in a regular arc shape,gradually decreasing from the middle bottom to the upper part and both ends of the roof.The failure form of the overlying rock is easy to form a"saddle shape".Due to the large thickness and strength of the sub key layer,it is only when the No.15304 working face was pushed 90 meters that the sub key layer will break,causing the first weighting.During the periodic weighting,the water conducting fracture zone gradually develops upwards to near the main key layer,and the thick and hard key layer blocked the continued upward development of roof fractures.The first weighting interval of the working face is 90 meters,and the periodic pressure step is 22 meters;The maximum development height of the overlying rock collapse zone is about 44 meters,and the maximum development height of the water conducting fracture zone is 58 meters.
shallow coal seamoverlying strata movementthick key stratumtwo zones of overburden stratarock pressure monitoring
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