Managing car-crunching sinkholes

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

A 4-meter section of the eastbound driving lane of Interstate 70 in Guernsey County, Ohio, suddenly collapsed on March 4, 1995. The collapse was caused by the caving in of an abandoned underground mine. Although no vehicle fell into the sinkhole, four vehicles swerved around, dipping some wheels in the hole. Fortunately, no serious injuries were sustained.

The Ohio Department of Transportation (ODOT) recognized that other mines may exist beneath interstate highways and other roadways and that other significant settling or sinking could occur due to the increasing age of the abandoned mines. Consequently, an effort was initiated to develop and implement an Abandoned Underground Mine Inventory and Risk Assessment process.

This process, as documented in a recently adopted ODOT manual, is a proactive response to the need to locate and assess the risk of all roadway sites beneath which abandoned underground mines exist. The overall purpose of this inventory and risk assessment effort is to enhance the safety of the traveling public by minimizing the possibility of a sudden roadway collapse that could result in fatalities or bodily injuries.

The first reported production of coal in Ohio was in 1800, and since then, various types of recoverable resource mining have occurred in the state.[1] Most of the abandoned underground mines in Ohio range in age from 50 to 150 years. Detailed abandonment maps are available for approximately 4,600 underground mines. However, for an estimated 2,000 mines in Ohio, no detailed maps are available.

The development of an Abandoned Underground Mine Inventory and Risk Assessment process for all state roadways in Ohio is a formidable task. Hundreds of roadway sites may lay atop underground mines. These roadway sites represent an existing, undefined, and yet possibly significant risk to the safety of the traveling public. Counties in 10 of the 12 ODOT districts contain identified mines for which there are available maps.

The Ohio manual was developed with input from the Federal Highway Administration, the U.S. Department of the Interior's Office of Surface Mining, the U.S. Geological Survey, two divisions of the Ohio Department of Natural Resources (Division of Mines and Reclamation and Division of Geological Survey), the Ohio Environmental Protection Agency, the Ohio Mine Subsidence Insurance Underwriting Association, West Virginia University's Department of Mining Engineering, and nine state transportation agencies.

During development of the manual, ODOT examined several roadway sites. These investigations were made in the interest of preventing subsidence (or sinkage) similar to the I-70 collapse from occurring again while the inventory and risk assessment process was being developed.

Remedial Response During Process Development

Including the repair of the I-70 collapse site, three notable mine remediation projects on interstate highways have been undertaken by ODOT in response to roadway conditions suggesting mine-related subsidence activity.

I-70 in Guernsey County

The first of these mine remediation projects was undertaken in the area of I-70 in Guernsey County in eastern Ohio between March and July 1995. After investigations by ODOT revealed possible mine-related subsidence activity, a consultant was retained for the purposes of project investigation, design, and construction management assistance. Unfortunately, in spite of ODOT's monitoring of the site every four hours, a 4-meter-diameter by 3-meter-deep hole suddenly opened in the eastbound travel lane of I-70. Three cars and a truck were damaged when they drove through this hole. Fortunately, no critical injuries resulted from this incident; however, the road was closed for more than three months.

The length of the project area was approximately 610 linear meters. The remedial effort involved the air rotary drilling of approximately 1,800 boreholes down to the mined coal seam interval - a depth of approximately 20 meters. Approximately 13,800 cubic meters of flyash grout were pumped into subsurface void areas. Two land bridges with lengths of 213 meters and 34 meters, respectively, were constructed over areas where the drilling and grouting program encountered high concentrations of caved and broken materials at the mined level. The cost of this project, including land bridge installations and pavement replacement, was approximately $3.6 million.

I-70 and I-77 Interchange in Guernsey County

The second mine remediation project was undertaken at the interchange of I-70 and I-77 in Guernsey County between June and November 1995. The office and field investigations of this site revealed the need to perform remediation work on portions of all mainline lanes and all ramp lanes with the exception of one ramp. Conditions at one ramp necessitated the immediate closure and remediation of the ramp while project investigations and design were completed.

The project entailed approximately 9.2 lane-kilometers of roadway, including the work on all mainline lanes and ramps. The remedial effort involved the air rotary drilling of approximately 2,600 boreholes to the mined coal seam interval at a depth ranging from 3 to 30 meters. Approximately 61,000 cubic meters of flyash grout were pumped into subsurface void areas. The cost of this project was approximately $4.7 million.