I-10 Twin Spans Speed Relief Over Lake Pontchartrain
When traffic flows on all six lanes of the new $803-million Interstate-10 Twin Spans in New Orleans this September, the region that was devastated by Hurricane Katrina in 2005 will receive a much-needed symbol of recovery.
While relief can't come soon enough for area residents, the Twin Spans' build team worked diligently to fast track the project, which is scheduled to open almost a year ahead of schedule.
The bridge connects east-west I-10 traffic over Lake Pontchartrain. Katrina's 30-ft storm surge on Aug. 29, 2005, tore apart the 1960s-era crossing with uplift and wind, bashing decks off 58 segments and misaligning 473 others. About 40% of the structure was destroyed.
Up and over
Fully funded by the Federal Highway Administration, the new bridge is 300 ft south of the old one. At 30 ft high, the low deck will be 21 ft higher than the original. The bridge meets ship impact standards of the American Association of State Highway and Transportation Officials. It incorporates larger foundations, more redundant pilings and more reinforcement to engage the piles with the caps, making them more resilient to lateral impact, says Arthur D'Andrea, project manager for the Louisiana Dept. of Transportation and Development (DOTD).
The hurricane-resilient 100-year bridge was built with higher-performance, high-strength (10,000-psi) concrete that is very resistant to saltwater corrosion and wind and water loads. Lower-level connections between super- and sub-structure are strong. Beams are connected by means of dowels placed at angles to the cap to resist uplift. Shear keys have been added to restrain the girders against lateral displacement. Each of the 60-ft-wide spans will feature three 12-ft-wide lanes of traffic with two 12-ft-wide shoulders.
When the spans open this fall, Boh Bros. Construction, New Orleans, will have completed its $379-million contract to construct two 4.5-mile-long, low-level runs of the east-west artery well ahead of schedule. TKM, a joint venture of Traylor Bros., Evansville, Ind., Kiewit Southern, Atlanta, and Massman Construction, Kansas City, Mo., completed its $171-million contract 178 days early. It constructed the “hump,” which is made up of 200-ft-wide by 80-ft-high spans that cross a shipping channel.
“It's a real repetitive structure, so we were able to fine-tune work practices to be more efficient,” says G.J. Schexnayder, Boh's project manager. Skylar Lee, project manager for the TKM joint venture, agrees that the bridge was “typical construction on both the approach and high-level main span,” which contributed to the fast pace of the project and made the tie-in between the two projects proceed smoothly.
Quick Thinking
Improving the request for information process was key to speeding progress, Schexnayder says. “On the repair job, no one had time [to wait for responses]," he says. "Everyone had guys who could make decisions in the field 24 hours a day. Our design engineer on site, Dennis Gowins with HNTB, would design and get approvals right away.” Schexnayder points out that “it didn't feel like we were working for an owner. It felt like everybody was on the same team.”
The Boh Bros. project manager credits Mobile, Ala.-based Volkert Inc., DOTD project manager for construction services, with helping to improve the process. “We coordinated with DOTD and Volkert to come up with solutions to problems in the field and obtained approvals in a matter of hours,” Schexnayder says. “To play a part in what was, at the time, the biggest project in Louisiana, and the biggest project Boh Bros. has done to date, was very rewarding.”
Weather and Louisiana's wildly variant soil conditions created some of the project's biggest challenges. “Because the lake is so wide open, shallow and close to the Gulf of Mexico, weather comes in quickly, and winds from different directions cause the lake to become rough really quickly,” says TKM's Lee.
TKM's portion of the project was in the middle of the lake, so the contractor barged material and people from a remote staging area to perform most of the work from the water. The contractor used tandem cranes to lift the 650-ft-long steel girder spans across the main navigation channel in 2008 and 2009. The pre-assembled pairs of steel girders that comprise the two 200-ft-length spans on either bridge weigh about 120 tons per pair. TKM used ringer cranes of both 300-ton and 650-ton capacities to make the lifts in order to compensate for the cumbersome length, required reach and water movement.
Variation in Subsurfaces
Pile-driving was a significant project challenge due to the amount of variation in subsurfaces, probably because of two fault lines in the lake, says John Horn, project manager for Volkert. “In some areas the sand was shallow enough to put in end-bearing piles,” he says. “In others, we had to put in skin-friction piles. Sometimes we had both in the same bent.”
Also daunting was having two separate contracts sharing resources and a work area on such a fast-paced project, Horn says. The project includes 63 miles of girders, 78 miles of piles, 38,563 tons of steel and 48,537 truckloads of concrete. “It was challenging making sure we had the right pile lengths at the right time,” he says. “Everybody really had their head in the game and wanted to do what was best for the project.”
Despite the hectic pace, the team remained keenly aware of the project's historical significance and its symbolism. “As a company, Traylor and the joint venture partners certainly have a sense of pride in being part of restoring a major lifeline to the city,” Lee says. Adds Schexnayder: “This will probably go down as the most memorable project of my career.”
