Research on roof structure and support resistance during periodic weighting in shallow group coal seams mining face

Field investigation shows that when the thickness of interval layers is always between 15 -45 m in many shallow seam mining areas,the single key stratum structure is easily to be found. Taking the shallow-buried coal seam group in Shenfu mining area as an example,the periodic weighting of coal seam group mining has some basic charac-teristics identified by field measurement:short roof weighting step,high strength,serious rib fall of coal wall,dynamic load,step sinking and large and small cycle pressure phenomenon. The physical analogue experiments reveal the move-ments and “beam-arch-shell” structure of key stratum behind the goaf and over the mining seam with the broken key stratum by up-seam mining,the differentiation method of the broken key stratum over goaf,and the three basic roof structures of shallow buried coal seam with periodic breaking including the upper and lower step rock beams,the upper masonry beam-the lower step rock beam and the upper masonry beam-the lower masonry beam. Based on the periodic fracture structure and mechanical model of interval rock formation in shallow coal seam mining,this paper provides the calculation method of working resistance of support under static and dynamic loads which has been successful used. The conclusions are helpful for the control of periodical roof pressure shallow coal seam mining.