With the help of special skids and common soap, an Oregon contractor has replaced two bridges in two weekends as part of a $46-million design-build project for the Oregon Dept. of Transportation. Slayden Construction Group Inc., Stayton, broke ground on the project in June 2007 and wrapped it up in January, replacing a total of five 80-year-old bridges along Highway 38 between the towns of Elkton and Drain.

Photo: Slayden

Mammoet’s system allows new span in Oregon to slide sideways into place atop new bents.

The project’s biggest challenge arose on two bridges known as Crossing 3 and Crossing 4. Crossing 3 is a three-span, two-lane, 325-ft-long steel structure with steel-plate girders and cast-in-place high-performance concrete deck. Crossing 4 is a two-span, two-lane, 225-ft-long concrete structure using precast, prestressed bulb T-girders and a cast-in-place high- performance concrete deck.

The bridges are located within 38 ft and 180 ft of the portals of the 1,000-ft-long Elk Creek tunnel. Crews had no room to build temporary bridges. “To try and set a detour up and get traffic back in the tunnel portal in a 38-ft section would be nearly impossible,” says Larry Gescher, Slayden project manager.

Slayden hired Mammoet Inc., Rosharon, Texas, to bring in its proprietary system of hydraulic jacks and skids. The replacement bridges, designed by T.Y. Lin International, San Francisco, were built next to the existing structures, which consisted of cast-in-place concrete approach spans and main-span steel trusses of approximately 100 ft.

Crossing 4 was replaced in the spring of last year and Crossing 3 in September. Slayden built new substructures beneath the existing bridges, consisting of bents founded on driven piles, solid rock and drilled shafts. Workers had to chip away at existing rock by hand so that the old beams could be removed, says Gescher. Once each old bridge was demolished, the new one was lifted and slid into place using Mammoet’s system.

“We shut down the bridges on Friday, and by Monday they were ready for traffic,” says Carlos Jaimes, Mammoet project manager. The shoes on the skid system were coated in Teflon and lubricated with dish soap to protect against spillage into a pristine stream 50 ft below the bridges.

Jaimes estimates the skid method cut six months off the bridge replacements. The project’s other three crossings, replaced more conventionally, include two bulb-T prestressed girders and an 80-ft-long prestressed slab girder, says Gescher. “The contract was originally set up for the slab bridge; we were allowed to use Mammoet’s system there,” he notes.

But Slayden opted to rebuild the slab bridge conventionally and negotiated with ODOT to use the Mammoet system on bridges near the tunnel. “We had 10 nighttime closures in the original contract for the crossings,” he says. “We said, ‘We just need a couple of weekends.’ ”

The method helped Slayden earn a bonus. “The contractor was allowed only six months for long-term, single-lane closure,” says Steve Narkiewicz, ODOT project manager. “The incentive paid up to $600,000 if the contractor kept the single-lane closure to less than five months. The disincentive penalized the same amount if the contractor took up to seven months of the single-lane closure.”

Narkiewicz says the decision to go with rapid replacement cost about $900,000 more; the cost was offset by time saved and fewer flagmen.