Model simulation study of coal mining under river beds in India

Abstract

Over 80% coal reserve of Bihar coalfield and substantial portion of Ranigunj coalfield of India is within Damodar river basin. Mahanadi-brahmani basin is the coal resource of Orissa region. Total coal of Nagpur area is under the HFL of Kanhan river. The methods of mining thick seams under these water bodies and depth cover of 50 m to 500 m required planning such that thick strata band in between the subsiding mass and the floor of the water body remained free from tensile strain, cracks, bed separation or open joints. For these studies, the high flood level of rivers was taken as catastrophic danger in view of their perennial water resource.

With a view to evolving suitable mining geometry under Indian geomining conditions, an indirect technique-Equivalent Material Mine Modelling was used. The studies conducted under idealised laboratory condition covered the scope of mining 7 m thick seam under river Damodar at Sudamdih Incline mine, 2–4 m thick seam under Damodar at Chinakuri and Seetalpur mines, 3 m thick seam under HFL of river Brahmani at Deulbera, and 5 seams of 40 m total thickness under Kanhan river High Flood Level (HFL) at Kamptee colliery. The problem of mining different seams of Sudamdih, Chasnalla and Chapui Khas underneath subsurface water was also studied in models. Indian coal measure formation contained an average 60–80% medium grained calcareous/arenaceous brittle sandstone which developed open cracks when the strain exceeded 5 mm/m. It was, therefore, essential to devise mining methods/goaf treatment so that the surface subsidence and strain remained within the safe limit.