Moving freight from the Port of Hampton Roads in Virginia to the Midwest is a vital part of the economy, but when a route cannot accommodate the increased freight capacity of today's ...
A Caterpillar 328D outfitted with an Alpine Cutter road grinder sits on top of a flatbed railcar waiting to enter the tunnel. A small excavator sitting inside the rail car will remove the liner material that is designed.
Moving freight from the Port of Hampton Roads in Virginia to the Midwest is a vital part of the economy, but when a route cannot accommodate the increased freight capacity of today's trains, modifications must be made. Norfolk Southern Corporation is modifying 28 railroad tunnels along the Heartland Corridor, a railroad line that runs between the Port of Hampton Roads in Virginia, through western Virginia, southern West Virginia, and through to Columbus, Ohio. Once these 28 tunnels are modified, four distinct benefits will be realized:
Norfolk Southern currently moves freight between Hampton Roads and the Midwest in three different ways:
When tunnel clearance is relatively good and requires only slight modification, Norfolk Southern is notching the tunnel along the entire length of the crown. A road grinder makes several passes in order to remove a strip of the concrete liner to a depth of approximately 1.5 feet. If the notch is deep enough, rock bolts are installed to avoid cracks and stress to the liner and further secure it. This is the fastest and least expensive tunnel modification method.
Lowering the tracks is primarily being done on double-track tunnels along the corridor. To lower the tracks, a large machine with a chainsaw-type blade is placed underneath the tracks, which remain in place. The blade cuts through and pulls out the ballast material, which is either dumped alongside the tracks or placed on a conveyor that dumps it into a rail car that is pulled behind the machine. The machine moves about 11 feet to 13 feet per minute, and one pass of the machine clears about 12 inches of space beneath the tracks.
Once the old material is removed to the required depth, ballast cars come along and dump new ballast material. Another machine carefully lifts the track, and the new ballast material is placed under the ties and tamped down. The track is then carefully lowered into place at its new height.
The primary method of tunnel modification is total replacement of the crown of the tunnel's liner, which is constructed of concrete. This method is being used on the Cowan Tunnel, the longest tunnel on the project at 3,302 feet and located near Roanoke, Virginia. Originally constructed in the late 1800s, it was an open rock tunnel; the concrete liner, which averages 18 inches thick, was added later in the early 1900s.
According to Robert Billingsley, director of Structural Projects for Norfolk Southern, work on the Cowan Tunnel began in October 2007 with geotechnical studies and preparation. Several thousand holes were drilled through the tunnel liner to determine what was behind the liner.
"We needed to know what we were dealing with so we didn't have anything cave in on us," says Billingsley.
Once it was determined that the rock was sturdy limestone, Johnson & Western Gunnite out of Seattle, Washington, drilled holes through the liner and pumped grout behind the liner's side walls. All of the voids behind the liner have been filled with concrete grout up to the spring line, which is where the liner begins to curve upward.
To further stabilize the walls during removal of the liner's crown, two rows of rock bolts have been installed through the liner and back into the native rock. The 8.5-foot-long bolts have been installed every five feet along the top row and every 10 feet along the bottom row.
Before removing the liner, six holes are predrilled every five feet through the crown of the liner, which is then saw cut at the spring line. There are two methods for removing it. Working remotely, crews with R.J. Corman Derailment Services either use a road header to grind away the concrete or they use a hoe ram to break it out.
With the liner removed, crews with Johnson & Western scale any loose rock and install 16.5-foot rock bolts into the predrilled holes to further secure the exposed rock. The crew installs rebar in the side walls and sprays 4 inches of gunnite back onto the roof. This, then, is the final tunnel structure. According to Billingsley, depending on the location of the rock, about 3 feet of clearance is gained on average, though only 1.5 feet is needed.
With a 10-hour work window each day, work is proceeding in sections to maintain production, and work proceeds at a pace of about 35 feet to 40 feet per day.
"If too much material is removed at one time, it would take too long for the rock bolt drilling crew to catch up," explains Billingsley. "By doing smaller 5-foot to 8-foot sections, the rock drilling crew can keep up with the other work in the tunnel."
Work has proceeded smoothly at the tunnel, and Norfolk Southern has been pleased with the material behind the liner. Along other parts of the route, Norfolk Southern has contractors in eight tunnels west of Bluefield, West Virginia, preparing to notch or remove liners, and three tunnels — Eggleston 1, Eggleston 2 and Pembroke — have already had the tracks lowered.
The Cowan Tunnel is expected to be completed by September 2008, and the target date for completion of the entire Heartland Corridor Project is by the end of 2010.
Editor's note: Additional material provided by Norfolk Southern Corporation and the Virginia Department of Rail and Public Transportation.
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