INTERSTATE 77 ABANDONED UNDERGROUND MINE REMEDIATION PROJECT

During 2001, the Ohio Department of Transportation (ODOT) completed a significant project for the purpose of remediating unstable surface and subgrade conditions related to an abandoned underground coal mine lying beneath Interstate 77 in northeastern Ohio. This project was located within the glaciated boundary of Summit County. An ODOT district engineer identified surface subsidence features related to mine subsidence in late March 2001. An abandoned underground mine map indicated that 800 ft of the interstate highway was underlain by coal mine workings. This mine extracted the Brookville #4 coal within the Allegheny Formation. An ODOT subsurface investigation found mine workings at a depth of 25 to 35 ft below the road surface. The overburden consisted of 3 to 4 ft of highly broken and jointed limestone overlain with thick interbedded deposits of sand and/or clay containing a high groundwater table. An ODOT Abandoned Underground Mine Inventory and Risk Assessment of the location determined it to be a high risk site requiring immediate mine stabilization work. An emergency contract was established and construction began in May 2001. Drilling program modifications were required to address the sand formations and the high groundwater table. Time Domain Reflectometry instrumentation was installed to monitor the roadway which continued to carry the 75,000 average daily traffic. The resulting emergency project construction included air rotary and sonic drilling, and placement of cement flyash grout in mine workings beneath 2,000 ft of roadway. This project required 25,000 cu yd of grout and was completed in October 2001 at a cost of $8.4 million.