Technology News From the Bureau of Mines, United States Department of the Interior

Techndogy news describer tasted developrnsnts f r m Burmau of Minna prwrams. It is published +n Bnmurage the transfer of this information to the minetala lndusuy and Its applimtlon in commercial prdw. Msntlon af mmpeny or praduM names is lor documentation only snd does nM imply O~dbrlpemBnt of a specific firm or product

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Design Practices for Multiple-Seam Room-and-Pillar Mines

Objective Provide room-and-pillar operators with practical in-

formation and guidelines concerning multiple-seam mine design to reduce ground problems associated with the interaction of adjacent working.

Background Interactions of multiple-seam operations can cause

ground problems resulting from the transfer of stress, strata displacement, and caving due to subsidence. Such interactions are a common occurrence, resulting in loss of coal reserves and incseased operating costs. Studies estimate that 140 biion metric tons of coal, representing MI percent of the rninablc reserves in the United Stateq are subject to mdtiple-seam mining. In many instances, mining sequence k based primarily on availability and economics, with littIe rcgard for the effects mining would have on coalbcds above and below the one being mined. These practices could have strong implications for resource conservation. For instance, West Virginia, Vugioia, and Kenlucky have over 90 minable coalbeds, many of which are dasszed as "low sulfur." Many coal analysts speculate that the 1992 Clean Air Act and new compliance coal standards may shift future mining to these reserves. But without compctcnt design strategies, interactions between vcrticaily adjacent operations will increase the difticulty and expense of mining.

Efiedve mine planning and design are essential for avoiding ground problemsrelated lo multiple-seam mining. To avoid higher mining costs, operators should focus on adopting practices and procedurcs that prevent and con- trol interactions in multiple seams. The U.S. Bureau of

Mines (USBM), in an effort to improve mine plan* is investigating multiple-seam room-and-pillar design and development.

Approach Factors that influence interactions between opcratiws

can be classified as either "geologic' or "mine de&d pa- rameters. The geologic parameters include the depth, in- terburdcn thickness and physical characteristics, coalbed thickness and physical characteristia, immediate rwf-and- floor stratigraphy, and in situ stress fields. The mine dosign parameters indude the seam scqucna, pillar size and strength, entry widths and roof spans. percent extrac- tion, m i n i height, geometric layout of the workins sup- port methods, and the h c delay between mining seams. Optimization of mine design factors is the primary means for controlling interactions between operations.

Of the design factors, three are considered primary and have signifid influence in seam interaction. These factors are very closely related and should be weighed equally for effedve mine planning First, the sequence or order in wbich the seams will be mined will determine tbe type of interadion. Second, the design of pillars and entries will determine the magu'tude of interaction. Third, the geometric layout of the workings will determine the Iocntion of interaction. Other parameters Gxed by the ge- ologic environmen& such as depth and interburden thick- ness, will innuenre interaction magnitude and location and must also be considered in the design process.

Empirical investigations involving case study docu- mentation and analysis have constituted mast of the USBM research and have provided important infoma- tion in &e development of design procedures. +However, computer-based numerical models are gaimng more

This document wa prepared by the U.S. Bureau of Mines. Neither the United Slalcs Government nor any person aning an behalf of the U~ted States G c v m m e n t Mume any liability resulting Imm thc of the information contained in this documcnk orwarrants that such us? bt f~ from privately m e d rights.