Identifying Potential Collapse Zones Under Highways

Subsidence of abandoned coal mines is a problem in many places, e.g., the opening of a large hole in Interstate 70 in eastern Ohio. With the support of the Ohio DOT we are looking for geophysical methods to economically determine locations where potential coliapse may threaten highways. The goal is a reconnaissance survey method to identify areas that need detailed investigation. We have completed the first phase study at a site with collapsing coal mines. The techniques tested were: 1. P-wave refraction, 2. S-wave refraction, 3. Gravity, 4. 2D resistivity, 5. Ground penetrating radar (GPR), 6. Surface waves a) spectral analysis (SASW) b) profiling. The data were acquired along a 480 ft (146 m) section of Ohio Route 32 in Jackson County. The data were interpreted and several test borings were made to verify the geophysical results. We found that P-wave refraction, 2D resistivity, and surface wave profiling provided the best correlation with the boring results. S-wave refraction was useful. Gravity and SASW did not have adequate horizontal resolution to be worthwhile additions to the interpretation. GPR signals were too attenuated by the clay-rich soil.