Electrical resistivity surveys were completed at two sites along State Route 32 in Jackson and Vinton Counties, Ohio. The surveys were done to determine whether the electrical resistivity method could identify areas where coal was mined, leaving air- or water-filled voids. These voids can be local sources of potable water or acid mine drainage. They could also result in potentially dangerous collap se of roads or buildings that overlie the voids. The resistivity response of air- or water-filled voids compared to the surrounding bedrock may allow electrical resistivity surveys to delineate areas underlain by such voids. Surface deformation along State Route 32 in Jackson County led to a site investigation, which included electrical resistivity surveys. Several highly resistive areas were identified using axial dipole-dipole and Wenner resistivity surveys. Subsequent drilling and excavation led to the discovery of several air-filled abandoned underground mine tunnels. A site along State Route 32 in Vinton County, Ohio, was drilled as part of a mining permit application process. A mine void under the highway was instrumented with a pressure transducer to monitor water levels. During a period of high water level, electrical resistivity surveys were completed. The electrical response was dominated by a thin, low-resistivity layer of iron ore above where the coal was mined out. Nearby overhead powerlines also affected the results.

This project was a natural extension of the 1996-1997 void detection work completed by the USGS for ODOT. This earlier project was entitled "Detection of Underground Mine Voids in Ohio by Use of Geophysical Methods" and was published as U.S. Geological Survey (USGS) Water-Resources Investigations Report # 97-4221. This report discussed several possible geophysical techniques that might be successful at detecting mine voids. The only geophysical technique tested during this earlier research project was ground penetrating radar. The report indicated that the likelihood of detecting variations in electrical resistivity due to the presence of abandoned underground mine voids was sufficient to warrant further investigation. The approach for the current research project reflects the proposed completion of the investigation of electrical resistivity measurements for this purpose. This proposed research approach would benefit the Office of Geotechnical Engineering as a continuation of research related to finding effective.

Results of ground-penetrating radar surveys at three highway sites indicate that subsurface penetration varies widely with geologic material type and amount of cultural interference. Two highway sites were chosen over abandoned underground coal mines in eastern Ohio. A third site in western Ohio was chosen in an area known to be underlain by naturally occurring voids in limestone.