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Cofferdams Create Dry Conditions for Culvert Extension in Asheville

Thu January 19, 2006 - Southeast Edition
Gwenyth Laird Pernie

Innovative methods of cofferdam construction allowed for two 70-ft. (21.3 m) culverts running under Long Shoals Road in Asheville, NC, to be extended 40 ft. (12.2 m).

According to Chris Byers, project manager of Taylor and Murphy, the $13-million project’s prime contractor, extension of the culverts required the building of cofferdams at the four openings of the culverts. Cofferdams allow a submerged construction area to be temporarily drained, so that work can progress in a semi-dry environment.

Sheet metal cofferdams were used around the 10-by 7-ft. (3 by 2.16 m) box culvert extending from Lake Julian to a swampy area adjacent to Long Shoals Road.

On the lakeside of the box culvert, a solid sheet of metal was placed into the ground down stream of the culvert to block the water; the area around the culvert was then sandbagged. On the swampy side, sheet metal was set into the ground in a semicircle around the work area near the opening of the culvert. Prior to both areas being pump drained to a semi-dry state, and the sheet metal was secured with steel piles.

A new cofferdam technique was used around the pipe culvert that extends from Lake Julian to a 2acre (.8 ha) pond.

“This cofferdam method was a first for us,” Byers said. “Initially, a diver was sent down 10 feet to the culvert opening on the lakeside. The diver placed a balloon bulb in the pipe opening, which stopped the water from flowing from the lake to the pond, pressure sealing off the lake water. The two acre pond was then drained using two eight-inch and one 12-inch pumps.”

The water was transferred from the pond to Lake Julian.

“Once the pond drained, a plastic lining was pushed into the pipe until it reached the balloon on the lakeside,” Byers continued. “This was done to keep the pipe from collapsing in the future.”

Immediately after the pond was drained, state workers spent a full day netting approximately 400 fish from the muddy pond floor and transferring them to the Lake Julian.

Extension of the box culvert and pipe culvert have been completed and the cofferdams have all been removed, allowing the water to flow.

According to Ronny Clark, resident engineer of the North Carolina Department of Transportation (NCDOT), the need to widen Long Shoals Road was due to safety and traffic issues.

A total of 1.8 mi. (2.9 km) of Long Shoals Road (NC146) which runs east of I-26 to U.S. 25 (Hendersonville Road) will be widened from two to five lanes.

“Extensive new development along Long Shoals Road, including new homes, apartment complexes and businesses, along with the Volvo International headquarters, and three schools have created continual traffic delays and back ups,” Clark said.

Approximately 33,000 cu. yds. (25,000 cu m) of unclassified excavation and 93,000 cu. yds. (71,000 cu m) of barrow excavation were required for site preparation during the project.

According to Clark, some of the existing pavement will be saved and some will be removed. In total, the project will require 47,000 tons (43,000 t) of asphalt. APAC Carolina Inc.’s Asheville Division was subcontracted for the paving work.

“Paving will begin next spring or summer. However, some temporary paving has been done to accommodate traffic while the grades are lowered,” Clark said.

According to Clark, there will be seven new signal lights at the intersections which will be interconnected and progress with the traffic in the hopes of tightening up the traffic flow.

The project requires extensive utility work.

“To accommodate the five lanes of traffic all the utilities along Long Shoals Road had to be relocated; including Progress Energy, Bell South, public gas lines, water and sewer and Charter Cable lines,” Clark said.

“To plan for relocation of the utilities, while allowing the contractor to continue their work, meetings began one and half years before construction,” Clark said.

“If the utilities are on a DOT right of way, then the utility owner must pay for the relocation. If they have their own valid right of way then the DOT will pay to have the utility relocated.”

Water lines are being upgraded from 6 and 8 in. (15 and 20 cm) pipes to 24-in. (61 cm) pipes.

Buckeye Construction Co. Inc. of Canton, NC, is responsible for all the water and sewer work, which is subcontracted for $2.6 million and associated with the Metropolitan Sewerage District of Buncombe County, NC.

According to Gary Mease, owner of Buckeye, the project will require installing 10,000 ft. (3,000 m) of 24 in. (60 cm) water lines and 3,000 ft. (914 m) of 16-in. (40 cm) sewer lines.

Mease said approximately 35 percent of the work is being done at night and estimates the work is approximately 40 percent complete.

“The utility work is all in progress,” Clark said. “It is being done in sections in order to allow the road work to progress simultaneously.“

According to Clark, coordination between the utility companies and contractors has gone well, due largely to the years of planning that ensured the work would progress in an orderly matter.

Because of the schools and the rush hour traffic along Long Shoals, the contractors are restricted to the hours that lanes can be closed.

“Lanes can not be closed between the hours of 6 and 9 a.m. and 2 and 8 p.m. Monday through Friday” Clark said. “Consequently, some work has had to be done at night, including laying storm drainage pipes. We wanted to minimize the inconvenience to this busy travel route, but because of the tremendous necessity to widen the road, the public has been very understanding.”

According to Byers, construction is moving along on schedule.

“There have been several unique challenges to this project,“ Byers stated, “including the extension of the culverts and coordinating the utility companies, all while maintaining a tight work schedule with intermediate completion times. So far the work is successfully progressing as planned.”

Construction began in April 2005 and set to be complete by November 2007. CEG

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