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Case histories of dc resistivity measurements to map shallow coal mine workings

D'Appolonia Engineers, Monroeville, Pennsylvania, U.S.

Corresponding author: wjjohnson@dappolonia.com

The first 20% of the full text of this article appears below.

Two recent events have focused attention on the need for mapping underground mine workings: the failure of the Martin County Coal Corporation tailings impoundment near Inez, Kentucky on 11 October 2000 and the 24 July 2002 Quecreek Mine inundation that trapped nine miners for 77 hours in Somerset County, Pennsylvania. In both cases, unexpected conditions related to abandoned mines were the sources of the accidents. In the first case, the overburden between an abandoned mine and the base of a slurry impoundment was too thin and the slurry broke into the mine. The consequence was that the slurry broke out and flooded two separate watersheds with coal refuse. In the second case, miners accidentally excavated into the flooded workings of the abandoned Saxman Mine, which they thought was hundreds of feet away.

Conditions such as these require that the location of underground workings be defined. This is not easy. Detailed mine maps may be unreliable or missing. Conventional exploration (drilling) can easily miss targets as small as a mine entry. Because of these difficulties, the National Resource Council appointed the Committee on Coal Waste Impoundments to evaluate remote sensing technologies to locate mine workings. In Pennsylvania, a Commission on Abandoned Mine Voids and Mine Safety, convened in September 2002 as a result of the Quecreek inundation, has also identified various geophysical technologies that could be applied to the mapping of mine workings.

Most geophysical techniques have been around for many years and the physics used to detect underground mines hasn't changed. Basic interpretation strategies also haven't changed. What has changed is the ability of the geophysicist to gather data rapidly. Multielectrode systems have greatly improved the efficiency of data acquisition with the dc resistivity method—e.g., measurements can now be made automatically. Until recently, the dc resistivity method was limited by . . . [Full Text of this Article]