Stacking of Electrical Potential Gradient (EPG): A New Technique to Detect Abandoned Mining Galeries

Past mining activities, specially in coal mines of southern Brazil have been recognised as problematic due to the risk they represent for areas in development (construction sites, roads, etc). The lack of precise location of abandoned galleries represents a serious risk of accident by inundation or gas leakage, where intercepted by new galleries. It is also important when there is a need to re-evaluate the re-opening of a mine. Although it is possible to detect the presence of sub-surface empty spaces by drilling, the high prices and technical problems of procedures such as these are not economically viable. Geophysical methods are the best alternative and have been applyed with considerable success. In general terms electroresistivity with variable arrangements present the best results. However, dificulties increase with the progressive depth of the empty spaces. Peters and Burdick (1983) have shown that it is possible to detect with confidence empty space with rates of depth/diameter of 10:1, with the use of the pole-dipole array together with special techniques of correction of values obtained.