A Method for Depillaring of Thick Seams Standing on Pillars with Cable Bolt Support

Abstract

The studies were undertaken to maximise the safe recovery from the thick seam of Chirimiri area at NCPH mine, standing on pillars and improve production and productivity by way of modified method of mining. Under the geo-mining conditions of the mine, several options were reviewed in depth for their suitability and the final choice was put to depillaring with cable bolt as high

roof support. The roof coal band of 3.5 to 5.0 m thickness was reinforced such that the bolt remained anchored at least 1.5 m within the sandstone roof. The top section coal was thereafter recovered by systematic slicing in one or two passes, with recovery around 75 per cent. The hanging type support helped in keeping the floor free of obstruction for the movement and maneuvering of SDL.

The efficacy of the roof support was studied in the mine, wherein 19-22 mm diam old haulage ropes of 5.0 to 6.5 m length were used as cable bolts. The experiment was repeated in 4 panels of 22-52 pillars and under 33-256 m depth cover. The method first of its kind , facilitated depillaring of seams of 6 to 8 m thickness, improved the strata condition , safety, and achievement in respect of

conservation, production, and productivity. The method improved the level of recovery from 40 to 75 per cent, productivity from 1.4 to 2.8, and production from 5000 to 13000 t/month while the cost of production decreased from Rs. 443 to 417 with margin al investment towards mechanisation for coal loading, drilling, and grouting of the cable bolts. The cable bolts installed with over

8 t anchorage to the immediate roof served as support to the exposed roof and ensured the safety of the workers and the workings.