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| Highwall mining system extracting a 13 ft thick seam in Wyoming |
Description of Problem
The use of highwall mining systems has increased substantially in open-pit coal mines where overburden depth exceeds economical recovery. Highwall stability is a major concern during highwall mining. The Mine Safety and Health Administration requires highwall miner operators to follow ground control plans that specify the web and barrier pillar sizes necessary to prevent a pillar collapse that would threaten highwall stability. Other safety concerns arise when a highwall miner is trapped underground and it becomes necessary to tunnel in to retrieve it.
Research and Development Activities
NIOSH has developed a number of design tools that are relevant to improving ground control during highwall mining operations. The Analysis of Retreat Mining Pillar Stability (ARMPS) computer program is considered particularly useful. It uses the Mark-Bieniawski formula to estimate the strength of long strip pillars. The NIOSH guidelines for preventing massive pillar collapses and the Coal Mine Roof Rating (CMRR) are also applicable to highwall mining. Most recently, NIOSH has developed simple design charts for selecting web and barrier pillar widths, together with guidelines for highwall mining in areas containing old auger holes or two seams in close proximity.
R&D Outputs and Transfer Activities
NIOSH has transferred the ARMPS program to the general mining community through open industry briefings, publications, and computer training workshops. A short course specifically devoted to highwall mining ground control was held for Massey Energy, the largest single user of highwall mining equipment, in 2004. A series of three professional papers on the topic was recently published. Perhaps most importantly, over the past decade, NIOSH ground control experts have responded to more than 50 requests for information about using ARMPS and other NIOSH products to develop safe highwall mining designs.
Description of Intermediate Outcome
A recent survey showed that several MSHA-approved ground control plans for highwall mining specifically mention the ARMPS program. In fact, as evidenced through discussions and training sessions held at open industry briefings, Massey Energy, Fola Coal, and several leading highwall mining consultants routinely use ARMPS or the new design charts for their highwall mining designs.