For the last several decades, railway freight traffic has increased so much that trains now routinely use double-stacked cars. Century-old tunnels through the Appalachian Mountains along the Heartland Corridor—an important Norfolk Southern Corp. railway line that connects Hampton Roads, Va., and Chicago—were not large enough to accommodate the larger train sizes, causing some trains to be rerouted up to 200 miles out of the way.
Norfolk Southern embarked on a $150 million project to increase the height of 28 of its Appalachian tunnels and ensure that they will be safe and stable for another 100 years. To accommodate the double-stacked trains, the tunnels, which range from 174 to 3302 feet in length, must increase in height by up to 2 feet to achieve the required 20-foot, 9-inch clearance.
Norfolk Southern chose Quikrete, Atlanta, to supply the cement materials for 27 of the tunnels. To complete the expansions, eight tunnels require linear notch work to square rounded corners, 18 require complete roof replacements, and one smaller tunnel will be “daylighted,” meaning that its roof will be completely removed. Between April and December 2008, Quikrete already had provided contractors with 16,950 bags of grout and shotcrete for the project.
Before notch work or replacement begins, workers ensure that tunnel roofs are stable by drilling holes every 4 feet, and filling any voids they find with Quikrete Core Fill Grout. Then they install 18-foot-long roof anchors that secure the tunnel ceilings to the mountains above, and fill in the holes with Quikrete Non-Shrink Precision Grout.
To ensure that ceilings are stable prior to squaring corners, workers also drill holes in the ceiling canopies and fill any voids they find behind them with Core Fill Grout. “It's hard to know exactly what we are up against until workers start testing the canopy and pumping grout into the voids,” says Charles Davis, manager of Quikrete's Pounding Mill, Va., plant, which exclusively serves this project. “For one void, workers pumped 780 bags of grout into the massive hole.”
Roof replacements are completed using Quikrete Fiber-Reinforced Shotcrete MS, eliminating the need for forming. At 9000 psi, this high-density shotcrete provides the tunnels with a strong lining.
One of the major challenges for this project is working around the trains that continue to use the Heartland Corridor during construction. “Norfolk Suffolk cannot close the tunnels to all rail traffic because this is such an important route for freight movement,” says Davis. “That means workers have a limited window in which to work.” The company tries to limit the number of trains that use the line during this time, but it is never completely shut down. To accommodate the train schedule, construction occurs between 2 a.m. and noon from Saturday through Wednesday each week.
Construction is scheduled for completion in 2010, but this project already has been named an Outstanding Underground Project by the American Shotcrete Association, Farmington Hills, Mich.