| Summary: | The Longwall Top Coal Caving (LTCC) method has greatly improved the production of ultra-thick underground coal resources. However, face fall and support closure have been becoming highly frequent accidents at the working face, and seriously threaten the safety of miners. The key to avoiding these problems is to reveal the structural evolution of the roof strata and then choose a reasonable working resistance for the hydraulic supports. According to physical modeling, theoretical analysis and field observation of the LTCC panel, four kinds of structural models can be found and defined, in consideration of the coincident movement of key strata (KS) and the mining activities of upper face in overburden strata. The KS are performed as cantilever structures, hinged structures and voussoir beam structures at three different positions in roof strata. The structural characteristics of the KS and its movement laws are shown in the four structural modes. The loads acting on the support in the four typical structural models are also analyzed. The structural instability of the broken roof strata on the upper caving panel caused by the lower ultra-thick coal seam mining is considered to be the main reason for its face’s falls and support failures. Consequently, a method is proposed for calculating the working resistance of the support in the LTCC face, which is verified by the mining pressure monitoring in practice.
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