What we Build

May/June 2008

Skanska Fast-Tracks Georgia Highway Expansion

Crews working on the largest of five projects designed to increase capacity of Interstate 95 near Brunswick, GA., are making steady progress on the highly choreographed, $199-million job.

By Debra Wood

(Photo courtesy of Skanska)

Skanska USA Civil Southeast, Virginia Beach, Va., began the 5.72-mile Georgia Dept. of Transportation project in 2006 and is on track for on-time delivery on Oct. 31, 2009. Skanska subcontracted with R.B. Baker, Garden City, Ga., for the earthwork, base and road paving to expand the highway from four to six lanes. Skanska is self-performing the widening of four twin bridges to eight lanes. “To date, we have leaped some major hills and are anticipating meeting the contract completion date,” says Jack Liles, project manager for Skanska. The contract includes a $2,100 penalty for each day the company misses the deadline.

This project is one of the larger ones funded by the state’s six-year, $15.5-billion Fast Forward Congestion Relief Program, established in April 2004 by Gov. Sonny Perdue (R). The program will allow the state to complete projects in six years that otherwise would have taken 18 years without any additional funding, and is designed to relieve congestion and spur economic growth.

Skanska broke the project into two sections, each run by its own superintendent: the expansion of the Turtle River Bridge, and the rest of the work, all being built at the same time.

Turtle River Bridge

Crews place tremie concrete at one of the Turtle River Bridge drilled shafts. (Photo courtesy of Skanska)

Work on the north and southbound Turtle River Bridge is progressing concurrently, starting with a 24-ft-wide extension to the outer lanes. Once that is completed, traffic shifts to the outer lanes and crews will add 17 ft to the inner portion.

In the end, this section of I-95 will have “three 12-ft travel lanes with 12-ft to 14-ft paved shoulders, in and out, for both northbound and southbound travel,” says Bryan Czech, Georgia Dept. of Transportation District 5 area engineer. “Right now, we are experiencing more than 50,000 vehicles per day along I-95 in the Brunswick area. The third lane in each direction will ease the congestion and essentially make I-95 safer to commute.”

The widening of the Turtle River Bridge represents $100 million of work, Liles says. The marine project calls for installation of 424 54-in. and 60-in.-dia., heavily reinforced and drilled caissons, ranging from 100 ft to 150 ft deep. Subcontractor Coastal Caisson, Odessa, Fla., is placing the steel-reinforced drilled shafts. Coastal’s workers access the area between the existing bridges and over the sand bars using a trestle with a hydraulic rotary drill rig. In other sections, workers use a barge with a crawler crane and drill attachment, says Bobby Smith, senior project manager for Coastal.

Crews excavate about 4 ft of the caissons at a time. The spoil material is loaded on a barge that can hold about 160 cu yd of material, the typical amount from two shafts. Skanska stockpiles about 600 cu yd of material onshore until it dries and then hauls it to a disposal area. The job involves removing 34,000 cu yd of spoil material.

Skanska crews build new lanes on the inside and outside portions of Turtle River Bridge. (Photo courtesy of Skanska)

Bentonite slurry is mixed on another barge. The shafts will be installed using permanent casings approximately 50 ft long and drilled under Bentonite slurry, says Smith. As the spoil material comes out, the slurry is pumped into the casing to 4 ft above the water level to maintain hydrostatic pressure and solidify the wall. Drilling stirs up sand. When drilling is complete, crews remove the sand so they can recycle the slurry.

“We’re pumping good slurry in, bad slurry out until we get to slurry with less than 2% content sand,” Liles says. “Once that’s done, we install the reinforcing steel cage,” which strengthens the caissons.

Skanska prefabricates the 25-ton reinforcing steel cages with No. 11 bars in two sections. Once the shaft is drilled and the sand removed, crews install the cage in the casing. Concrete placement follows, with equipment to prevent the slurry from entering the concrete pipe.

The tide is extreme in this area, varying by 7 ft. Pours were done at low tide because because about 50% of the footers are below water at high tide. Side forms also are bolted to the seal slabs at low tide.

Some concrete pours had to be done at low tide because the tidal range was 7 ft. (Photo courtesy of Skanska)

There are 43 bents on the outside of the northbound and southbound lanes. Czech says work was not tidal influenced except for the end bents, and the contractor adjusted the schedule there by pursuing work at other intermediate bents while waiting for the proper tide elevation.

Skanska also used precast field slabs atop the shafts to avoid tidal challenges. Each 20-ft-square, 9-in.-thick, reinforced-concrete slabs was cast onshore and placed atop four drill shafts. Columns and caps sit atop the seal slab, and steel girders span the 200-ft channel. The remainder of the girders are concrete. In all, Turtle River will consume 85,000 cu yd of concrete and 9,000 tons of steel.

Gibson Creek Bridge

Three-quarters of a mile from Turtle River, Skanska is also widening the 844-ft Gibson Creek Bridge, but it does not require marine work. Fourteen-in. to 24-in. prestressed concrete piles support the bridge. They are topped with trestle pile caps and type-two and type-three prestressed concrete girders, ranging from 56 ft to 80 ft long. “There is limited space working between the two [existing] bridges for driving piles,” Liles says.

The U.S. Route 341 bridge

Skanska is using different phasing for the 158.4-ft U.S. Route 341 bridge, which passes above a six-lane, undivided highway. It is about one mile from Gibson Creek.

During the first phase, crews completed substructure work, driving 14-in. to 16-in. prestressed concrete piles to a depth of 25 ft to 75 ft. They poured 4-ft-deep footers, 30-in. square columns and hammerhead pile caps on bents one and two on the south side of the bridge and bents four and five on the north side. Traffic on U.S. 341 was shifted to two lanes and pushed to the inside. The company then moved traffic to the outside two lanes of U.S. 341 and closed off the inside, northbound and southbound, to build bent three.

The steel girders range from 33 ft to 57 ft long. Again, crews will install stay-in-place forms, reinforcing the mat and concrete deck.

CSX and State Road 586 Bridge

Skanska crews are widening the I-95 Bridge over U.S. 341 in Brunswick. (Photo courtesy of Skanska)

A half mile from U.S. 341, the 422.4-ft CSX bridge sits on 14-in., 16-in. and 18-in. prestressed concrete piles, ranging from 30 ft to 60 ft in length, topped with hammerhead bent caps. The structural-steel girders range from 47 ft to 80 ft long. “The difficult part is working around two active railroads,” Liles says. “The Norfolk Southern and CSX railroads intersect at the project limits, so we are dealing with traffic on the Old Jessup Road and the two heavily used tracks. There are about four to six trains per track per day. We have flagmen with both companies to deal with.” The intersection is within GDOT’s right-of-way, but all work stops when a train comes through.

Earthwork and Paving

Baker is moving 140,000 cu yd of dirt for roadbeds and ramps. “They have hauled in and placed approximately 80,000 cu yd on the project,” GDOT’s Czech says. “We were able to use the 60,000 cu yd of surplus dirt material in the median to construct the outside roadbed.”

Baker has begun asphalt paving south of U.S. 341. APAC-Southeast Ballenger Division in Taylors, S.C., will place concrete paving north of U.S. 341 and on the ramps. Pavement will be about 12 in. on top of a graded aggregate subbase, placed in two 6-in. lifts.

Skanska also will run about 30,000 ft of 3-in. conduit for future use in a transportation information system, should GDOT decide to install cameras, changeable message signs, weather stations or fog monitoring equipment, and 150,000 sq ft of shadow-box-style sound wall, ranging from 8 ft to 15 ft tall.