Analysis of overburden structure and support working resistance of working face in fully-mechanized top coal caving with large mining height in ultra thick coal seam

In order to grasp the overburden structure and support working resistance of working face in fully-mechanized top coal caving with large mining height in ultra thick coal seam,this paper study the ultra thick coal seam in Tongxin coal mine.The fracture and combining form of the overburden strata in working face was researched using the methods of theoretical analysis and in-situ observation,and the mechanical model of overburden strata was also established,then the formula of support working resistance in 8107 working face was obtained.The results show that:In the period of normal mining,the immediate roof in working face of full-mechanized top coal caving with large height can easily form“reverse step combination cantilever beam”which was a global body and the fracture and rotary of the“cantilever beams”was the main source of pressure in the mutual feedback between the support and the surrounding rock.In the period of periodic weighting the up“masonry beam”and the down“cantilever beams ”coupled with each other and formed new structure called“masonry beam - cantilever beam”,and the sliding instability of masonry beam resulted in the rotary of the“cantilever beams ”which was the reason that the intensive impact pressure appeared in working face in fully-mechanized top coal caving with large mining height.The actual measurement of support working resistance in 8107 working face were respectively 26 MPa（9750kN）in normal mining period and 40 MPa（15000kN）in periodic weighting period,which tallied with the theoretical calculation results.The ZF15000/27.5/42 four bars low caving coal hydraulic support in 8107 working face can meet the production requirements.