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U.S. 70 Bypass Work Comes With Strict Environmental Standards

Tue August 29, 2006 - Southeast Edition
Gwenyth Laird Pernie



Extensive erosion control plans will ensure the integrity of the wetlands and creeks surrounding the future U.S. 70 Clayton Bypass in eastern North Carolina.

The general contractor for the bypass is the S.T. Wooten Corporation of Wilson, NC.

According to Corey McLamb, assistant resident engineer of the North Carolina Department of Transportation (NCDOT), environmental concerns for the blue-line streams and wetlands in the area required the development of special erosion and sedimentation designs that would protect the ecology of the water systems at a cost of $7.3 million.

“Vital to the project’s design was maintaining the habitat of the dwarf wedge mussel, an endangered species found in the Swift Creek Watershed. Essentially the entire project is within this watershed,” McLamb said. “To protect the mussel’s habitat, the whole project was designed to meet high quality water erosion and sedimentation control standards.”

Typically, NCDOT projects are planned to accommodate 10-year storm events for erosion and sedimentation control measures. However, this project was planned to accommodate 25-year storm events.

“The most notable difference with the 25-year storm design is the size of storage basins, which are constructed to accumulate maximum storm water runoff,” McLamb explained.

According to Mark LeGrand, senior project manager of S.T. Wooten, regulating the flow of water leaving the storage basins is essential to preventing the erosion of the wetlands and creeks.

Erosion Control Plans

Erosion control plans for the clearing and grubbing phase of the project include constructing basins positioned to control runoff according to the original topography of the land. Most of the pre-construction basins will phase out during the life of the project, especially once ground cover is established. Some, however will be converted to hazardous spill retention ponds.

As the construction progresses, and the shape of the land changes, construction erosion control plans will be implemented. These plans call for 60 skimmer basins with Coir fiber baffles and 22 Faircloth skimmers.

The baffles, which look like rows of fencing across the basin, reduce the energy of the water as it flows across the basin and allow the larger sediment and silt particles to fall out of suspension. Approximately 112,300 ft. (34.220 m) of silt fence and 688,000 sq. yds. (575,355 sq m) of matting will be installed throughout the project.

The Faircloth skimmer functions like a settling pool; essentially, it is a dewatering device. It floats in the basin along the water surface and dewaters the basin from the top of the water surface at a designed flow rate. The purpose is to allow the sediment and silt particles time to settle to the bottom of the basin and thus allow cleaner water to flow off-site.

An additional tool used to assist in settlement is polyacrylamide (PAM). PAM works through the introduction of an anionic material to the turbid or muddy runoff entering the basin. As the runoff and PAM are mixed together the smaller silt particles are attracted to one another causing them to become heavier and eventually settling to the bottom.

In addition, 47 preformed scour holes (PSH) will be installed. The PSHs are used at pipe and ditch outlets in environmentally-sensitive areas and are basically a rock-lined hole with a small grass-lined swell around the perimeter. As runoff exits the pipe and enters the scour hole, the energy of the water is reduced and spread out to discharge in a diffused manner prior to leaving the right of way or entering an environmentally sensitive area. Approximately 77,000 tons of stone will be used on the project.

Level spreaders also are a permanent part of the project. They are placed at pipe outlets and are either concrete- or grass-lined. They are level ditches that allow the water to flow around the perimeter and reduce erosion.

There also will be two stream relocations, in which rock cross vanes, a-vanes, j-hook vanes and boulder walls have been used. These devices help create pools and riffle sections along the stream channel.

Finally, to further prevent extreme run-off, new vegetation will be planted to replace that which is removed during the clearing. Seeding subcontractors include Lineberry Inc. of Climax, NC, and Parrish Co. Inc. of Middlesex, NC.

“To ensure the project remains environmentally sound, NCDOT’s inspection staff is working closely, including weekly meetings, with S.T. Wooten and [its] subcontractors. In addition, monthly meetings are held with the environmental agencies,” McLamb said.

“The most challenging aspect of this project has been working within the constraints of all the permitted and buffered areas and assuring that the erosion control plans are carried out in the approved manner. However, because of the cooperation of the coordinating agencies, the project is moving along on schedule and as planned,” LeGrand said.

The Clayton Bypass

U.S. 70 Clayton Bypass, the largest road construction project in Johnston County since the construction of I-40, will alleviate traffic congestion on existing U.S. 70 and save commuters a considerable amount of time.

NCDOT began constructing the $123 million roadway in June 2005. The 10.8 mi. (17.4 km) of new four-lane, divided highway will connect I-40 near NC 42 to U.S. 70 at the business-bypass split just west of Smithfield, NC. It will include 22 bridges with four interchanges and 11 culverts.

According to LeGrand, site preparation will include excavation, grading, cut and filling, clearing and grubbing 185 acres (74.9 ha) and some building demolition. It is approximately 65 percent complete at this time.

Grading and excavation of the project is divided into three sections, which are being worked on simultaneously by three subcontractors.

PLT Construction Co. Inc. of Wilson, NC, is responsible for grading the I-40 portion of the project; Thompson Contracting of Raleigh, NC, is responsible for the middle section near NC 42 and, Wooten is handling the grading of the 70 interchanges.

“In total there will be 3,370,400 cubic meters of unclassified excavation,” McLamb said. “Most of the dirt is being relocated within the project as fill dirt and also in the building of noise berms.”

Bridge Work

Bridges will be built by the cast and build method and constructed with concrete decks and steel and concrete girders. Approximately 383,018 sq. yds. (320,252 sq m) of reinforced concrete deck along with 6,540 cu. yds. (5,000 cu m) of concrete for the substructure will be required for the 22 bridges.

Wooten will handle a portion of the work, along with several subcontractors. Sanford Contractors Inc. of Sanford, NC, is responsible for building the bridge structures on the I-40 crossings; Smith-Rowe Inc. of Mount Airy, NC, is responsible for the Corbett road bridge and four others; and United Contractors is responsible for two bridges that cross over the Swift Creek tributary and two bridges that cross over the Austin Pond — both environmentally sensitive areas. Wooten will handle the construction of all remaining bridges.

According to LeGrand, of the 22 bridges, six are close to completion, 12 are in various stages of construction, and four have not yet been started. Most of the bridge work will be completed before paving begins.

Wooten will be responsible for all the paving work. Approximately 385,309 tons (350,000 t) of asphalt will be used on the project.

The new bypass, with a speed limit of 70 mph, is expected to save commuters traveling U.S. 70 to eastern North Carolina 15 to 20 minutes, and should relieve traffic congestion on existing U.S. 70, which NCDOT projects will more than double in the next 20 years. In addition, planners anticipate the new bypass will bring opportunities for growth and development into Johnston County.

According to McLamb the project is running 15 percent ahead of schedule. Completion is expected by June 19, 2009. CEG