Roof structure characteristics in fully mechanized coalface with large mining height and reasonable loading of support

In this paper, to determine the reasonable working resistance of support during fully mechanized mining with large mining height (FMMLMH), the roof structure characteristics of FMMLMH and reasonable support ability were studied by methods of theoretical analysis and in-situ measurement. The concept and discriminate method of key stratum in the immediate roof (KSIR) were put forward, according to the fact that the existence of hard strata with medium or thick thickness has vital influence on the collapse of overlying strata. Thus, the immediate roof can be classified into two types, type I without KSIR and type II with KSIR, and the support working resistances of two types can be determined respectively as well. The results show that the main roof of Type I without KSIR falls with a single-layer of voussoir-beam structure, and the support working resistance can be calculated by the weight of rock pillar with 6 to 8 times of mining height. Meanwhile, the main roof of Type II with KSIR falls with a double-layer of voussoir-beam and cantilever beam structure, which is formed with the break of KSIR and the main roof, and the support working resistance can be calculated with the thickness, hardness and layer horizon of the KSIR taken into account. With the increase of KSIR's thickness or its hardness, or the lower horizon of KSIR, the support working resistance will increase. The research results have been successfully used in the determination of support working resistance in representative FMMLMH.