Geophysical Technologies for Detecting Underground Coal Mine Voids:
An Interactive Forum
Applications of the Electrical Resistivity Method for Detection of Underground Mine Workings
Presenter: William J. Johnson
Firm/Organization: D'Appolonia Engineering
Mailing Address: 275 Center Road
Monroeville, Pennsylvania 15146
Efforts to delineate underground mine workings typically rely on available maps and confirmatory boreholes and the characterization of regions between boreholes is uncertain. Electrical resistivity measurements can be used to supplement the borehole data and reduce the uncertainty of the interpretation. Furthermore, electrical measurements can be used to optimize the number and locations of the boreholes.
Project experience with DC electrical measurements demonstrates that commercially available technology can be effective, especially for the rapid mapping of mine workings at depths up to about 100 feet. For deeper workings, the method has the potential to be effective, but theoretical models and practical experience demonstrate that the target size/depth ratio needs to be favorable and the required length of the resistivity profile to acquire deep images is often limited by surface interference. The method is therefore usually most effective for mine subsidence applications, rather than in evaluating the proximity of relatively deep active mines to abandoned, flooded workings, but local conditions can allow for this technique to be effective for deeper targets.