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88娱乐城
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Highwall mining is estimated to account for about 4% of US coal production, and its use 鈥� often in areas where the overburden makes surface mining an uneconomical option 鈥� is only continuing to grow. That, paired with a recent rash of failures, was the impetus for the computer program.
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鈥淲e have learned a lot about pillar mechanics and design over the past 20 years,鈥� pointed out NIOSH rock mechanics chief Chris Mark from the Pittsburgh Research Laboratory. 鈥淭his new knowledge provides a framework within which solutions to specific pillar design problems can be developed.鈥�
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The program, entitled ARMPS-HWM (Analysis of Retreat Mining Pillar Stability 鈥� Highwall Mining), was developed by examining various factors of both highwall and underground room and pillar mining and the pillar design factors involved in both.
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Included in the development was an investigation of likely failure modes, from which two alternative strategies were established: , which is achieved by increasing the web pillar鈥檚 dimensions and stability factor (SF), and , achieved through limiting the number of holes between barrier pillars. Appropriate panel widths for both scenarios were researched and realized as the project progressed.
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The research also encompassed web pillar strength and load determinations as well as defining a minimum SF for web pillars. For example, Mark said a web pillar SF should be at least 1.3 when the panel width excluding the barrier is up to 200 feet. Over 200ft, the SF should be a minimum of 1.6.
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Additionally, if a barrier鈥檚 width-to-height ratio is 4.0 or less, the barrier pillar鈥檚 SF should be at least 2.0. For larger barrier pillars, with w/h ratios that exceed 4.0, the SF can be 1.5.
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Mark said both barrier pillar spacing and w/h ratio were vital factors when compiling the case history data and developing the guidelines for design. The w/h ratio, for example, was of major importance because of the need for the barrier pillar to maintain integrity by keeping a possible pillar collapse contained within one panel and not creating a domino effect.
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When all of the research and computations were complete, the final step in the development process was to examine case history data from more than 3000 successful highwall mining holes in southern West Virginia over a three-year period. Mark noted collapse experience could not be incorporated because the available data was considered to be insufficient.
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The existence of the ALPS (Analysis of Longwall Pillar Stability) and ARMPS (Analysis of Retreat Mining Pillar Stability) programs as blueprints for the development of ARMPS-HWM was very valuable, and their accuracy, comprehensive nature and positive reputation in the industry were key to the new program鈥檚 success. The modern advances made in numerical modeling, he added, combined with those empirical methods have helped move the science of pillar design forward and made a project like this one possible.
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The software package, released last year, is available for download through the NIOSH web site. In the meantime, Mark noted that he and the entire rock mechanics team at the Pittsburgh Research Laboratory will continue studying what he calls 鈥渢he age-old questions of pillar design鈥� and keep all their programs as accurate as possible.
