Abstract

ZHAO, T. et al. Ground control in mining steeply dipping coal seams by backfilling with waste rock. J. S. Afr. Inst. Min. Metall. [online]. 2018, vol.118, n.1, pp.15-26. ISSN 2411-9717.  http://dx.doi.org/10.17159/2411-9717/2018/v118n1a3.

The mining of steeply dipping coal seams involves significant safety risks because of instability caused by the weak nature of surrounding rocks and their movement after excavation. Physical and numerical models were developed to determine an optimum backfill approach to ground control in steeply dipping coal seams. Physical modelling showed that for mining without backfill, the thickness of the largest roof collapse was approximately twice that of the mined seam, the movement of roof strata tended to be asymmetrical, and there was a relatively large empty zone in the upper gob area. For mining with backfill, roof conditions were significantly improved; only slight roof separation appeared 1.5 m above the mined seam. The largest cumulative displacements occurred 5-15 m from the first cut of mining. With backfill, the levels of mining-induced stress release and concentration were significantly reduced, and the vertical range of mining disturbance was shortened by 18%. Numerical modelling showed that floor strata mainly undergo nearly horizontal displacements, while roof strata mainly undergo vertical subsidence, both with and without backfill. The integrity of roof strata improved as the extent of backfill increased, and the range of displacement direction increased. The conclusions are confirmed by results from a field trial.

Keywords : Steeply dipping coal seam; backfill; ground control; strata mechanics; waste rock.

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