Toward the end of the year, a spectacle will begin to unfold in full sight of Kanawha Valley motorists. Travelers will witness the three-year construction of a new Interstate 64 bridge over the Kanawha River between South Charleston and Dunbar. It will be noteworthy in both design and construction method.
The bridge, badly needed to alleviate congestion in a dangerous stretch of interstate, will carry eastbound traffic. That will leave the current bridge for only westbound vehicles.
In May construction crews started excavating the area in South Charleston where some of the piers will be erected. Crews have started clearing trees on the Dunbar side. Project Supervisor John Buchanan says the public will notice progress as the piers begin taking form by the end of the year. The planned completion date is Oct. 29, 2010.
The new bridge will cost a projected $83 million, and that's the cheaper version. It will be made of concrete, and Buchanan said the steel alternative would have come in at $112 million. Upon completion, T.Y. Lin International's design will be the longest continuous segmental span in the United States. Its total length will be 2,975 feet and the main span, 760 feet.
But the size isn't the only aspect making history. Crews will erect the bridge using the balanced cantilever construction method. Buchanan says this technique has never been used in the construction of a bridge this large in West Virginia. The cantilevering method is typically used where it is difficult or impossible to erect scaffolding, such as over deep valleys or wide rivers.
"There won't be anything in the Kanawha River," Project Engineer Ahmed Mongi said. "No platforms, towers or anything to support the bridge. Everything will be done from the deck." The bridge will be supported by seven piers, five on flat land and two on the river bank, said Bob Long, construction superintendent for Brayman.
Mongi, who holds a master's degree in civil engineering from West Virginia University, says aesthetics were important in the design process because of the bridge's size and location.
Concrete has tremendous strength when under compression, Buchanan said. In this case, that compression will be achieved through the post-stressing technique. "Each segment is cast (poured), then we have tendons going through that we tighten," Buchanan said. "That is what keeps the bridge up."
He said the concrete superstructure should last as long as a steel version and actually should require less maintenance. However, the use of concrete will be more time-consuming and labor intensive.
Crews will pour one 15-foot concrete segment at a time, and there will be 168 segments, Buchanan said.
The need for improved safety on that stretch of I-64 was a big impetus for the project, Mongi said. The accident rate on the curve at the west end of the existing bridge is 137 per hundred million vehicle miles. That's significantly more than the U.S. urban interstate average of 85 per hundred million vehicle miles.
A large majority, 70 percent, of the accidents, have been rear-end collisions, which are typical of those that occur in congested areas.
More gradual curves at each end of the new bridge will increase eastbound drivers' sight distances, allowing them more time to maneuver, slow down or stop, Mongi says.
The 67-foot-wide deck will include four traffic lanes with shoulders on either side. The three 12-foot through lanes and one 12-foot auxiliary lane will provide eastbound and westbound traffic with more capacity between the interchange ramps leading to MacCorkle Avenue in South Charleston and to Roxalana Road in Dunbar.
By providing an exit lane for Dunbar and South Charleston, the plan will help drivers avoid maneuvering across lanes of fast-moving traffic. The existing ramps also will be improved, said Susie Watkins, a communications representative for the state Department of Transportation.
Mongi predicts traffic will flow as usual during the long construction process.
He says I-64 traffic should not be affected until the end of the project in late 2009 or early 2010, when the new bridge is connected to the existing road. "This type of construction has never been done in West Virginia, so there will be a lot of public interest," Mongi said.
To provide room for field offices on both sides, workers bought and tore down the Red Roof Inn property in South Charleston and two houses on the Dunbar side.
Buchanan says he has attended several seminars to learn more about the very long bridge and is eager to see the results. "Since this is not a new construction, but new to us, my concerns are getting spreadsheets and checklists together so we can get this smoothly done," Buchanan said.