Rib/snook design in mechanised depillaring of rectangular/square pillars

• Scope of conventional methods to design an irregular shaped rib/snook are discussed.
• Site conditions and field performances of different mechanised depillaring operations in India are briefly presented.
• Taking help of the field studies, numerical simulations is done to visualise the effect of geo-mining conditions on the rib/snook performance.
• A relationship is attempted to design the area of the rib/snook under varying site conditions.

A field study at different mechanised depillaring (MD) operations in Indian coalfields (with depth ranging from 60–377 m and caveability Index variation from 2300–10500) found mixed performances of adopted sizes of the ribs/snooks. Formation of an irregular shaped rib/snook during MD of the existing square/rectangular pillars by a continuous miner and uniqueness of the existing geo-mining conditions also limit scope of application of the conventional rib/snook design approaches. Taking guidance from the field studies, a parametric investigation is conducted in laboratory on the calibrated simulated models using FLAC3D. An analysis of stress redistribution for different stages of the MD in simulated models provided a different characteristic of an irregular shaped ribs/snooks failure. Presence of moderate roof strata is found to be, relatively, more significant for the rib/snook design. Based on the simulation results, an attempt is made to provide a model for the rib/snook design in MD.