May 13, 2007

I-40 bridge work speeds along

A dozen bridges demolished, replaced in 14 months

San Bernardino Sun
Andrew Silva, Staff Writer

Twenty-eight days.

A contractor working for Caltrans tore down a bridge and erected a new one on Interstate 40 in less than a month.

And that was only one of 12 bridges demolished and replaced in 14 months on the southern edge of the Mojave National Preserve.

"It's pretty amazing," said John Diskin, chief engineer for Skanska USA, the contractor that did the accelerated work.

The final bit of work is scheduled to be completed this week.

In March 2006, Caltrans engineers discovered the 12 bridges - six in each direction of the divided interstate - were failing along a 17-mile stretch between Kelbaker and Essex roads.

While planning and building road projects usually moves along like a snail with stomach cramps, the state can blaze through a project if it's an emergency.

"When it's a dire situation, the state has the ability to go around normal avenues to get a project done sooner," said Traci Peterson, a spokeswoman for Caltrans.

This time the state required some innovative construction techniques, including the first-ever use of precast bridge abutments, installed on the Marble Wash Bridge about 80 miles east of Barstow.

And all 12 bridges used precast and prestressed girders, dramatically cutting down on the construction time.

On the dozen bridges, built in the early 1970s, the steel rods that secured the bridge decks to the pillars had sheared and the concrete was eroding.

Traffic was reduced to one lane on each bridge and the speed limit was lowered to 45 mph.
After the bridges were temporarily shored up, traffic in both directions was diverted onto the westbound side, and Skanska started demolishing the six eastbound bridges, one a day.

The $35 million project basically became an assembly-line operation, with crews working on all the bridges at once, moving from one to the next as each step was finished.

"We put together a tight schedule and kept to it," Diskin said. "Everybody, including the subcontractors, just bought into the project. It was just one of those things that really clicked."

It took only four months to complete the six eastbound bridges. Then the crews switched to the westbound side.

The precast girders, assembled by Pomeroy Corp. in Perris, meant crews didn't have to build them in place.

The real innovation was bringing in already completed abutments, the beefy ends of the bridge that support the whole thing. Each weighed roughly 180,000 pounds.

It took only a few hours using a 500-ton crane to lift the abutments off flatbed trailers and drop them in place.

That compares to several weeks to set up forms, create the steel mesh of rebar and then pour the concrete and let it set.

Diskin said next time, he'd prefer the abutments perhaps be in two parts, which could then be joined.

"They were definitely big chunks of concrete," he said.

The Marble Wash bridge was demolished in a little more than a day on March 30 and opened to traffic April 26.

"This is an amazing accomplishment when you consider the size of this structure and its remote location," Hector Davila, Caltrans deputy director of construction, said in a written statement.

It's even more impressive if you consider the crews took Sundays off. That means the bridge was actually built in 24 working days.