Managing car-crunching sinkholes

Public Roads, July-August, 1999 by L. Rick Ruegsegger, Thomas E. Lefchik

I-470 in Belmont County

The third mine remediation project was undertaken on I-470 in Belmont County in extreme eastern Ohio between September and December 1996. This project area included 518 linear meters of interstate highway just west of the Ohio River bridge connecting Bellaire, Ohio, and Wheeling, W.Va. This project area had exhibited pothole subsidence in ditch and backslope locations. It was designated by ODOT as a study area for the field testing of investigative techniques and site evaluation techniques being drafted for the manual.

Through investigations, it was determined that the overburdened rock was extremely fractured. A large void was found to be migrating toward the surface. Consequently, it was decided to immediately close the roadway and remediate the site by excavating to the base of the mined coal seam and then backfilling.

The resulting mine remediation project involved approximately 306,000 cubic meters of roadway excavation, new pavement, signs, lights, guardrail, striping, and revegetation. The project was completed in 14 weeks at a cost of approximately $3 million.

Long-Term Process Approach

The ODOT Abandoned Underground Mine Inventory and Risk Assessment process is the most logical and practical approach to responsibly monitor the safety of the roadways in areas with abandoned underground mines. Due to the large number of potentially problematic sites, it is not logistically or financially responsible to commit limited resources and funding to random investigation and remediation of sites.

The process comprises four basic activities, as shown in figure 1:

1. Establishment of an inventory of all roadway sites beneath which abandoned underground mines may exist.

2. Assessment of the risk posed by each site to the safety of the traveling public.

3. Remediation of sites, if necessary.

4. Permanent monitoring of sites.

Establishment of an Inventory of Sites

The first step in this process is to establish an inventory of sites. An initial comprehensive site listing is based on: (1) a review of available records, (2) field report forms, (3) follow-up investigation of field report forms, and (4) field visits to all identified potential sites.

Risk Assessment

A large portion of the overall process is the risk assessment of each site on the inventory. The risk assessment portion of the process involves three levels of site evaluation: (1) initial site evaluation, (2) detailed site evaluation, and (3) priority site investigations and recommendations. The risk assessment criteria used for all levels of site evaluation take into account two basic factors: (1) the existing site conditions and (2) the level of the traveling public's exposure to those conditions.

Initial Site Evaluation

This initial site evaluation subdivides the entire inventory of sites into five risk-assessment groups. The groups, listed in order from the highest to the lowest risk level, include: (1) surface deformation, (2) mine opening, (3) high rating, (4) low rating, and (5) eliminated site groups. The first three groups proceed to the detailed site evaluation portion of the process. The low-rating group is placed under a permanent monitoring program and remains as active files in the inventory program. The eliminated site group becomes inactive but is permanently recorded in the files of the inventory program.