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.