GYPSUM, Ohio — Two years after stringing sensors under a part of State Rt. 2 that passes over an abandoned gypsum mine, the Ohio Department of Transportation plans to start a more permanent cure for the risk that the old tunnel might collapse someday.
A department contractor is to pump grout through holes drilled from the surface into the mine, first to plug it on either side of the right-of-way and then to fill up the area in between. When the grout — a mixture of sand, water, and cement — hardens, it will shore up the tunnel.
The work will require lane closings on State Rt. 2 for the better part of at least two years, but state officials have promised that will be scheduled to avoid the peak tourism season in the area.
“The benefit of filling the mines under SR 2 is to assure the safety of the traveling public,” said Theresa Pollick, a transportation department spokesman in Bowling Green. “ODOT is having this work performed to eliminate any future settlement.”
That benefit will cost $20,668,621.89, the value of the state’s contract with Beaver Construction Co. of Canton.
The contractor last month began building crossovers to shift traffic onto one side of the freeway while work is done on the other side, requiring lane closings in both directions. Route 2’s shoulders also will be beefed up to handle the two-way traffic.
That initial work is supposed to be wrapped up by Memorial Day, if not sooner, Ms. Pollick said. The mine work itself is scheduled to start Sept. 15 and take two years to complete, with lane closings suspended from May 15 through Sept. 15, 2014.
If any more work remains to be done after May 15, 2015, the contractor will wait until the following September to do that.
ODOT spent about $260,000 two years ago to run coaxial cables through the area to detect any shifting that might happen beneath State Rt. 2 where it passes over the old mine tunnels near the prosaically named community just east of Port Clinton in eastern Ottawa County.
It also performed a pilot test that year of the grouting process, which was found to be successful, Ms. Pollick said.
Abandoned in the 1970s when U.S. Gypsum Corp. switched to processing synthetic gypsum for the manufacture of drywall and other products, the mine eventually flooded. Water dissolving some of the underground gypsum rock — primarily calcium sulfate — was later blamed for depressions and sinkholes in the area.
Bill St. Leger, the Ohio plant manager for U.S. Gypsum, said in 2011 that filling part of the mine would not affect the company, which no longer mined the area. Synthetic gypsum — calcium sulfate produced when limestone is used to “scrub” sulfur out of the smoke from coal-fired power plants — is shipped to the Ottawa County plant from outside the area.
U.S. Gypsum is not contributing to the cost of stabilizing the mine.
An estimated 115,107 cubic yards of grout will be pumped into the tunnel, Ms. Pollick said — enough to fill everything beneath State Rt. 2 but no more than necessary. Work will be done on the westbound side first, with all traffic using the eastbound lanes, with the traffic pattern reversed during the project’s second year.
“Confirmation borings” will be drilled after the project’s completion to confirm its effectiveness, the ODOT spokesman said.
Contact David Patch at: email@example.com or 419-724-6094.