Paying attention to lessons from Hurricane Katrina has stalled work on a controversial bridge spanning the Trinity River in Dallas. Experts want more time to study the impact piers drilled into the city’s levee system will have on its integrity.
Following an inspection of the levee system in March, the U.S. Army Corps of Engineers recently rescinded environmental clearance it had given earlier for work on the Margaret Hunt Hill Bridge. The bridge will extend SP 366, the Woodall Rodgers Freeway, connecting U.S. 75 and I-35, to Singleton Boulevard.
The Continental Avenue Bridge, the current route into the city from the west, is just north of the new bridge and will be converted to a bike/pedestrian bridge when the project is complete.
Before the work was stopped, crews had “drilled into the levee in a couple of places” to install the two of the bridge’s 14 “bents” that are in the levee, David Lott, Texas Department of Transportation (TxDOT) area engineer for the Dallas district, said. The bents — columns, drill shafts and cap — are in the levees at each end of the span.
The Corps wants further study of the entire levee system before permitting bridge work to continue in the levee area because a layer of sand was found in the levee there, Lott said.
“That’s what they are concerned with,” Lott continued. “If water seeps down in there…you know how sand does when water hits it. That’s what they were concerned with. They want an analysis to see if the levees will be damaged by what’s been done. It has nothing to do with the levy itself. The structure will be fine. It’s sound.”
If the sand had been discovered earlier “we would have just straddled the levee and not put any drill shafts into it,” Lott said. The piers are drilled 85 ft. (26 m) to bedrock “so it’s a sturdy foundation,” he added.
The 1,200-ft. (365 m) long bridge will be the first cable-stayed suspension bridge in North Texas, and one of only three cable-stayed suspension bridges in the state. It will feature six lanes in each direction with a center arch span and cables that rise 450 ft. (137 m) above the pavement.
But the stoppage has not totally halted work on the signature bridge designed by renowned Spanish architect Santiago Calatrava, Lott said. Work is continuing on sections of the bridge that are not in the levee, he added.
Even with the delay, hopes are high the bridge will be completed on schedule.
“We are working in areas where we can and still hope to complete the project by May 2011,” Lott said.
Area leaders are hoping the bridge will be a Dallas icon much as Golden Gate Bridge is to San Francisco, Lott said. He likened the bridge’s arc pylons to St. Louis’ renowned Gateway Arch.
“If you picture the arc pylon, it looks like the St. Louis Arch. You’ll have cables suspended down from the top of it.”
Construction on the $69 million bridge started in June of 2007 with Williams Brothers as the contractor. Work on the approaches, a $47.5 million, .67-mi. (1 km) long project, began in October of 2008. J.D. Abrams is constructing the approaches.
Spokesmen from both companies declined to comment on the projects.
The bridge and the approaches are two separate projects because all the funding wasn’t available at the same time — and possibly because of political considerations, Lott said.
“Originally, everyone wanted to see the steel up,” he said.
Both projects are slated to finish in May 2011.
Originally the bridge completion date was May 2010 but it was pushed back because the steel, which was coming from Italy, was not going to be ready in time, Lott said.
“That [building the structure early on] was a politically driven milestone,” he said. “You wouldn’t be able to ride on the bridge until 2011 anyway because the approaches wouldn’t have been constructed. You would have had a structure up there to look at while we got the approaches built.”
The city of Dallas is sharing in the bridge’s cost because it wanted a bridge that “would be a segue way into Dallas — a signature bridge,” Lott said. “Normally TxDOT would put a conventional bridge there. That’s what we had funding for.”
The work is a little different from the typical TxDOT bridge because it’s a steel bridge instead of the usual concrete structure, he said. Still, the steel bridge doesn’t mean any specialty work is needed aside from the erection of the arc pylon, Lott said.
“That’s really the only difference,” he said. “Expertise needs to be there with suspension cables and the actual welding of the steel to the arc pylon.”
The project’s only challenge is with the levees, Lott said.
“The rest of it is pretty straightforward.”
What’s really helping the project is that it’s an extension, meaning crews don’t have to deal with traffic the way they would if the work was being done on an existing road.
“We don’t have any traffic to contend with,” Lott said.
“Where we have challenges is when we have traffic to contend with. How do you build it and keep traffic moving? We don’t have to worry about that. That’s the good thing. You can just build the whole thing and not have to worry about having to stage certain pieces to keep traffic rolling. It’s almost like a new location because there was no roadway there.”
Concerns about the levee’s integrity stem from the levee failure in New Orleans.
“They [the Corps] have heightened their restrictions on all levees across the United States,” Lott said. “They have to. If you have a flood, you don’t want the levee to break and flood everyone like what happened in New Orleans. I understand their position on that but also I don’t know that there’s anything alarming with the construction we’re doing. But it’s just like anything else — you have to go by the rules. That’s it.”
Lott said he does not know how long the additional study will take but he’s optimistic about what the results will be.
“They could say there’s no significant damage, which I’m expecting it to be,” he said. “Or they can tell us we need to reinforce it with diaphragm walls or something of that nature to protect the sand in that area.”
But the levee issue has actually given the project another challenge — where to put the steel when it arrives.
“To bring the steel in, we can’t put it on the levy,” Lott said. “We can’t run up and down the levy with it. We’re going to have to find a viable route to bring it in and then off-load it down into the flood plain and not touch the levees with it. The Corps does not want the levy damaged.”
Bridge construction equipment includes cranes for setting metal/wood forms, a drill rig for drill shafts, dozers and front loaders for building pads for cranes, Tony Hartzel, public information officer for the Dallas District of TxDOT, said.
“There are going to be some heavy duty cranes out there because the steel is awfully heavy,” Lott said. “It’ll be your typical cranes but they’re just going to have to handle 120 tons of steel.”
Above ground some 4,080 cu. yds. (3,120 cu m) of concrete will be poured for the bridge with 7,570 linear ft. (2,300 m) of drilled shafts and 234,020 sq. ft. (21,740 sq m) of reinforced concrete slab, Hartzel said.
Since the project is new construction in a floodplain “there isn’t a lot of earth work,” he said.
Approximately 18 to 22 crew members are working on the bridge project.
Subcontractors include Scott Derr Painting Co.; Trevcon Inc.; Odum Services, Texas Environmental Management — San Antonio Inc.; Highway Pavement Specialties Inc.; Indus Construction, Costruzioni Cimolai Armando S.P.A.; Mica Corp.; VFC Inc.; Layfield Construction Inc.; and Cosme SRL.
“It’s going to be a nice bridge,” Lott said. “It’s going to be aesthetically pleasing to the eye. We don’t have any bridges like that around here. There’s a bridge down in Austin that’s an ornamental type bridge but it’s not this type of bridge. There’s nothing in the state of Texas that’s going to be like this bridge.”