Extraction of Thick Coal Seams

Abstract

This project presents numerical model studies on stress analysis during depillaring of 5-11m thick coal seams at depth range of 150-900m at an interval of 150m. Finite Difference Code – FLAC (fast Legrangian analysis for continua) was used for understanding the influence of depth and thickness of coal seams on stress distribution over pillars, stooks and ribs at development stage and depillaring stage through parametric studies. 24 numerical models with different configuration representing the parameters in field experimental trials are used. Variables of the parametric studies for stress analysis are: seam thickness in the range of 5 – 11 m at an interval of 2 m and depth cover of 150 m to 900 m at an interval of 150 m.The maximum on pillar was found to be 35 MPa at 900m depth in 5m thick seam and the minimum was 5 MPa at 150 m depth. The maximum stress on stooks and ribs was found to be 70 MPa and 10 MPa in 5 m, 7 m at 900 m and 450 m depth respectively.
From model it was found that thickness of the seam does not have any effect on the stress behaviour of the pillars after development work. Parametric studies through the numerical models indicated decreased vertical stress over the stooks with increasing height of the extraction at the depth covers in the range of 150-900 m. Though the stress coming was less, the stooks were getting yielded very soon due to increase in height of the stook and increase in height to width ratio.