As a result, compared to more traditional highway bridges, Fort Lauderdale’s runway structures feature decks that are 4 to 7 inches thicker than usual, and precast beams that are up to 4 inches thicker than standard, says Scott Dean, design manager with HNTB Corp., the engineer for the joint venture. Additionally, Dean says, “We have roughly 50% more pile on this project than would be necessary on a highway bridge of similar proportions.”
Tutor Perini/Baker has experienced challenges with the underground conditions during pile driving.
"There's a lot of variability in the subsurface conditions," says Hernandez.
The depths needed for individual piles have differed significantly, for instance, with final depths varying by as much as 40 ft for piles within 10 ft of each other.
"That kind of variability has been challenging," he says, adding that it's slowed production considerably. That work is approximately 86% complete now, Hernandez says, adding that some resequencing of scope and maintenance-of-traffic plans was necessary to keep the contractor on schedule for its original February completion target.
Mounting the Runway
Like Atlanta's elevated structure, this runway was designed by PBS&J, since acquired by Atkins. But unlike Atlanta's runway, this project could not use a conveyor belt to transport the 6.5 million cu yd of material to the site, due to the extensive foundation supports that would be necessary with the site's mucky conditions resulting from its proximity to the ocean, says Murtha.
Odebrecht-Central Florida's roughly 300 trucks are in near constant movement six days a week over two 10-hour shifts, delivering an estimated 2,000 truckloads of material daily, for a total of 40,000 tons.
Roughly 15,000 tons comes in daily via rail, on a spur to the airport property built by Florida East Coast Railway. Once it's arrived, Herzog Contracting, working for FEC, maneuvers its excavators atop the train, where they then offload the material car by car. The setup reduces the number of trucks that would otherwise be necessary, says Murtha.
The embankment consists of two sections: a segment east of U.S. 1 with about 4 million cu yd of material and another west of the highway that's about half that size. Atkins' Larson says the speedy construction of the massive embankment—especially the eastern section, which sits atop considerable pockets of muck—is key to the project's schedule.
"The fact that we're creating an embankment as high as we are in a fairly short period of time" remains a main focus of project officials, he says. Of particular attention is the settlement of that material.
"We're really concerned about making sure that the embankment that's on either side of those structures is sufficiently settled before we construct the runway, so we don't end up with a differential settlement between the structures and the runway," Larson explains.
So far, says Larson: "We're pleased with the results. It's flattening out at a faster rate than we [expected]."
Filling the voids
To the west of U.S. 1, throughout the runway area, layers of fractured limestone—called pinnacle rock—feature widespread existing voids that had to be addressed, since the new runway will handle much larger aircraft than the old one did, Murtha says.
"The old runway didn't handle big aircraft, so what was there was OK," he says. "But it's not sufficient for the beating this runway's going to get."
Odebrecht-Central Florida brought on the Japanese firm Fudo to propose using a method known as mammoth vibratory tamper, or MVT, instead of the traditional deep dynamic compaction that had been originally specified for the project.