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Symposium on Geotechnical Methods for Mine Mapping Verifications Charleston, West Virginia October 29, 2002 <br />the sedimentary sequences that include the coal and theses oils severely restrict the effec- <br />tive penetration of the radar waves. Nevertheless, GPR has been applied successfully to <br />map mine voids and this paper offers one case history as an example. <br />Magnetics—Coal has a low magnetics us ceptibility when compared to most other rocks. A <br />void in a coal seam, therefore, will not produce a significant disturbance to the earth's <br />natural magnetic field. Collapse structures above a coal seam, however, might produce <br />measurable changes and it is likely that, barring other cultural interference, a modem <br />magnetometer could detect old mine rails at a depth of several tens of feet. The main dis- <br />advantage to the magnetometer is the likely presence of other cultural interference, espe- <br />ciallymetal, commonly encountered in areas disturbed byman. <br />Most geophysical techniques have been around for many years and the physics of detect- <br />ing underground mines hasn't changed. Basic interpretation strategies also haven't <br />changed, as interpretations are based on an understanding of the physics involved. What <br />has changed is the ability of the geophysicist to gather data rapidly. Also, better com- <br />puters and improved software have revolutionized the means by which data can be proc- <br />essed and presented, resulting in improved interpretations. This paper presents five re- <br />cent case histories where modern data acquisition and processing systems have been ap- <br />plied in the detection of coal mine voids. <br />Case Histories <br />Case History No. 1 — Locating Mine Workings at the Regency Park Subdivision, <br />Plum Borough, Pennsylvania <br />The Regency Park subdivision is located over shallow mine workings associated with the <br />Plum Creek Mine operated in the late 1gth and early 20rh century. The subdivision has <br />been the location of numerous foundation failures over the past several decades since the <br />homes were constructed. This is not surprising, as many of the homes were constructed <br />with 25 feet or less of overburden above the Pittsburgh Coal seam. This site is currently <br />being remediated under the Abandoned Mine Land Reclamation Program directed by the <br />Pennsylvania Department of Environmental Protection (PADEP). <br />A portion of the subdivision was surveyed with the DC resistivity technique using the pole - <br />dipole configuration with a multi -electrode automated measurement system manufactured <br />by Iris Instruments. Apole-dipole survey is a type of DC resistivity measurement that uses <br />three mobile electrodes and normally has one current electrode placed far enough from <br />the others such that it can be considered to be at an "infinite" distance. In this case the "in- <br />finite" electrode was located several hundred feetfrom the profile line. <br />The results shown on the attached figures define a series of resistivity lows that bottom out <br />at an elevation of 1140 feet MSL, consistent with the bottom of the Pittsburgh Coal seam <br />as known from available mine maps and the results of borings drilled along the profile. <br />Where borings were drilled within 5 feet of the profile, the resistivity lows were found to <br />correspond to mine voids (partially collapsed) and the zones of relatively high resistivity <br />between the lows was found to contain coal. The anomaly pattern and the results of the <br />borings indicate that the resistivity lows and highs above an elevation of 1140 feet MSL <br />5 <br />