Analysis of Mine Roof Support (AMRS) for US Coal Mines
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Analysis of Mine Roof Support (AMRS) for US Coal Mines Christopher Mark 1 & Ryan C. Stephan 1 & Zach Agioutantis 2 Received: 6 July 2020 / Accepted: 2 September 2020 # This is a U.S. government work and its text is not subject to copyright protection in the United States; however, its text may be subject to foreign copyright protection 2020
Abstract During the past 15 years, roof fall rates have fallen dramatically in US coal mines, particularly in regions where the roof is weakest. The remarkable reduction in the number of roof falls has been accomplished with more effective roof support systems. The purpose of this paper is to present a design methodology that builds on and quantifies the basic roof support concepts that have been successful in the USA. The methodology starts by defining three modes of roof support, based on the roof strength relative to the stress level: (1) suspension, where roof bolts mainly provide skin control for strong roof; (2) beam building, where moderate strength roof can be supported by roof bolts alone; and (3) supplemental support for weak roof. Next, a large database of roof fall histories at a number of mines is used to define the approximate boundaries of these three regimes based on the coal mine roof rating and the depth of cover. Finally, guidelines are presented for site-specific design of support systems within each regime. The new computer package, analysis of mine roof support (AMRS), implements the design methodology. Keywords Ground control . Coal mining . Roof support . Rock bolting
1 Introduction In 2016, the US coal industry recorded its first year ever without a roof fall fatality. This historic achievement was repeated in 2018 and again in 2019. Zero roof fall fatalities is an extraordinary accomplishment, considering that more than 50,000 coal miners died in roof falls during the twentieth century, and nearly 50 were killed as recently as the first decade of the twenty-first century (Fig. 1). Less dramatic, though almost as remarkable, has been the decrease in the number of non-injury roof falls. Nearly all non-injury roof falls involve a collapse of a portion of a mine entry that extends to or above the anchorage zone of the roof bolts. Each one, therefore, represents a failure of the roof support system. Nationwide, the roof fall rate has fallen by * Zach Agioutantis [email protected] Christopher Mark [email protected] Ryan C. Stephan [email protected] 1
Technical Support, Mine Safety and Health Administration, Pittsburgh, PA 15236, USA
2
Department of Mining Engineering, University of Kentucky, Lexington, KY 40506, USA
more than two thirds during the past 15 years, from about 2.3 per 200,000 underground hours worked to about 0.7 in recent years (Fig. 2). The improvement has been most noticeable in the Illinois Basin, which has the weakest roof rock of any US coalfield [11], and once had non-injury roof fall rates that were more than twice the national average (Fig. 2). The impressive reduction in the number of roof falls has been largely a
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