Pillar design and coal burst experience in Utah Book Cliffs longwall operations

Abstract

Longwall mining has existed in Utah for more than half a century. Much of this mining occurred at depths of cover that significantly exceed those encountered by most other US longwall operations. Deep cover causes high ground stress, which can combine with geology to create a coal burst hazard. Nearly every longwall mine operating within the Utah’s Book Cliffs coalfield has been affected by coal bursts. Pillar design has been a key component in the burst control strategies employed by mines in the Book Cliffs. Historically, most longwall mines employed double-use two-entry yield pillar gates. Double-use signifies that the gate system serves first as the headgate, and then later serves as the tailgate for the adjacent panel. After the 1996 burst fatality at the Aberdeen Mine, the inter-panel barrier design was introduced. In this layout, a wide barrier pillar protects each longwall panel from the previously mined panel, and each gate system is used just once. This paper documents the deep cover longwall mining conducted with each type of pillar design, together with the associated coal burst experience. Each of the six longwall mining complexes in the Book Cliffs having a coal burst history is described on a panel-by-panel basis. The analysis shows that where the mining depth exceeded 450 m, each design has been employed for about 38000 total m of longwall panel extraction. The double-use yield pillar design has been used primarily at depths less than 600 m, however, while the inter-panel barrier design has been used mainly at depths exceeding 600 m. Despite its greater depth of use, the inter-panel barrier gate design has been associated with about one-third as much face region burst activity as the double-use yield pillar design.