Studies estimate that 156 billion tons of coal, representing 68 pct of the minable reserves in the United States, is subject to multiple-seam mining. Historically, room-and-pillar mining has dominated coal production, and this mining method has been the focus of most multiple-seam research. Advances in Longwall Mining Method have made this system more economically attractive because of its efficiency and production potential. The high productivity being achieved by longwall mining demonstrates its potential for being a substantial segment of underground coal production. Longwall mines produce more than 30 pct of all underground coal, up from 5 pct just 15 years ago. The continued growth of longwall mining without appropriate multiple-seam planning may increase the cost and risk of mining. Optimization of the mine design factors is arguably the primary means for controlling interactions between operations. The U.S. Bureau of Mines, in an effort to improve long- wall planning, is investigating multiple-seam longwall design and systems development.
Significant advances have been made in longwall design for single seams in the areas of gate road pillar design, panel layout, powered support selection, and roof control. Multiple-seam designs are less developed, but progress is being made as more longwall operators gain experience. In research,