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| Typical web and barrier pillar used in highwall mining |
Background
Highwall mining is an important coal mining method in the United States and may account for approximately 4% of the total U.S. coal production. Highwall stability is the major ground-control-related safety concern in highwall mining. Studies have shown that three of the nine fatalities connected with auger and highwall mining in the last 20 years were caused by highwall collapse, and the only fatality in the last 5 years was due to highwall collapse. Thus, ensuring highwall stability through proper ground control engineering is of paramount importance to safe highwall mining operations.
MSHA recognizes the safety concerns associated with highwall mining and requires each portable auger or highwall mining operation to develop and follow an appropriate highwall ground control plan that addresses web spacing and other measures necessary for safe recovery of the resource at high rates of recovery. A proper ground control plan for highwall mining should usually specify web pillar width, barrier pillar width, and number of holes between barriers given site-specific conditions, such as seam thickness, hole width, maximum hole depth, and maximum overburden depth.
Potential Outcome
To help mine operators address the new MSHA requirements, ground control researchers developed design charts and a new software package to specify required web and barrier pillar widths for highwall mining. The design charts have been reproduced in several publications and provide estimates of necessary web and barrier pillar widths. The highwall mining design software, available next year, has a form similar to the successful Analysis of Retreat Mining Pillar Stability (ARMPS) program and is named ARMPS-HWM (High Wall Mining). The interactive software package provides web and barrier pillar widths at given depths of cover and mining heights.
The design tools developed from the project will be widely distributed to stakeholders through classes at the MSHA Academy and open-industry briefings throughout the coal fields.