Rib/snook competency in mechanised depillaring of the conventionally developed coal seams

The stability of a natural support like pillar, fender, rib/snook is fundamental for the success of a bord and pillar mining. In fact, the stability of these supports becomes more important at the time of depillaring than the development. An application of mechanized depillaring, utilizing continuous miner (CM), provides faster rate of extraction and, therefore, the roof is not supported during the slicing operation. However, the slicing of a existing square or rectangular type pillar provides irregular shaped rib/snook. Available conventional approaches are difficult to be applied for the design of such a rib/snook. Even the scope of application of a foreign design approach for the rib/snook design is limited, mainly, due to the uniqueness of rock mass and site conditions of Indian coalfields. Considering these facts a systematic study on numerical models in laboratory is undertaken to understand the required competency of a rib/snook at different stages of a mechanized depillaring operation. Giving a brief background of different important field trials of the mechanized depillaring in Indian coalfields, this paper describes the modeling approach and presents results of these models to show the effectiveness of different sizes of ribs/snooks at different stages of the depillaring. Considering the scope of strata dynamics at the goaf edges, some practical considerations for rib/snook design are also discussed on the basis of different field experiences