Design Programs for Highwall Mining Operations

Highwall mining is a hybrid of surface mining and underground mining methods, and is often the only feasible method to recover the coal reserves in the central Appalachian coalfields due to the steep terrain and the closely spaced multiple thin coal seams. Compared to the mountain-top-removal, contour, auger, and underground mining methods, application of the highwall mining method can reduce the environmental impacts, increase the recovery ratio of coal reserves, and enhance mine safety as well as productivity. Therefore, it is probable that highwall mining will be a dominant method for extracting the high-value coal resources in the Appalachian coalfields. By far, the greatest ground control safety concerns in highwall mining operations are rock falls from the highwall and mining equipment entrapment underground. These hazards are most likely caused by the instability of the highwall mine system due to insufficient mine design and difficulties encountered during mining operations.;Most of this thesis emphasizes the mine design concepts and methods to maintain the stability of mine structures. With the purpose of evaluating the stability of the entry roof, the beam theory is applied. After comparing the deflection, stress, and strain profiles of 0.05 ft sandstone and mudstone roof layers, it can be concluded that the existence of relatively thin and weak layer in the immediate roof could cause potential stability problems for the entry roof. Therefore, for highwall mining operations to be conducted in coal seams with thinly bedded roof strata, a correct decision to cut some of the thin weak roof rock layers with the main coal seam can be greatly beneficial to mining operations. The pressure arch concept is applied for the systematic design of the highwall mining operation. Within this concept, an optimization design process is developed to improve the recovery ratio of coal resources to a reasonably high level. For multi-seam highwall mining operations, the largest web and barrier pillar sizes should be selected and vertically aligned into seams. Two numerical programs, Examine2D and FLAC, are used to analyze the stability of highwall structures and to find the stable interburden thickness where no interaction between the two coal seams is expected. Numerical results show that, under given geology and mining conditions in the thesis, the stable interburden thickness is 20 ft and there are no stability issues. In the end, three spreadsheet programs are developed for the assessment of highwall mine structures, for the design of the web and barrier pillars, and for the optimization design process, based on the proposed design concepts and methodologies