Soil, Steel Issues Slow Bridge Project

Santiago Calatrava’s bridge over the Trinity is still ‘coming along’

More obstacles confront the Margaret Hunt Hill Bridge project in Dallas

By Debra Wood

Contractors working on the Margaret Hunt Hill Bridge over Dallas Trinity River. (Photo: Courtesy of TxDOT.)

Even though the U.S. Army Corps of Engineers has required more soil testing at the site of the future Margaret Hunt Hill Bridge in Dallas, construction continues on other portions of the structure, which is part of the Trinity River Corridor Project.

“It’s coming along,” says Rebecca Dugger, director of the Dallas Trinity River Corridor Project for the city of Dallas. “It’s still moving forward.”

Williams Bros. Construction Co. of Houston received the $69-million contract from the Texas Department of Transportation to build the six-lane, 0.366-mi, cable-stay, suspension bridge, designed by Spanish architect Santiago Calatrava. J.D. Abrams of Austin secured the $47.4-million contract to build the east and west, six-lane approaches to the Trinity River, outside the levees of the Dallas Floodway.

The bridge will extend Spur 366, the Woodall Rodgers Freeway, across the Trinity River. It is one of three bridges planned for the corridor.

The bridge’s official groundbreaking took place in December 2005, but construction did not begin until June 2007 on the span, says TxDOT spokesman Tony Hartzel. At that time, the expected completion date was early 2010. Abrams started work on the approaches in October, and now the new target for the entire project and anticipated finish date of the bridge is mid-2011.

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The bridge underwent a redesign process, after Williams Bros.’ first bid came in significantly higher than estimated, $113 million vs. the $57 million Calatrava projected. The city had raised private funds to pay for the design of a signature bridge, rather than a planned, simple suspension bridge, which was approved as part of a 1998 bond program.

“It’s very dramatic, 400-ft tall, and there will be nothing like it in this country,” Dugger says. The Margaret Hunt Hill Bridge will be the first vehicular bridge designed by Calatrava in the United States. He also has designed a pedestrian bridge in California.

After the initial bid came in high, the city approved changing the seven-side arch and the teardrop-shaped columns to cylinders to save money.

“It was just making shapes easier to fabricate,” Dugger says.

Crews pour the concrete for arch support for the Margaret Hunt Hill Bridge’s cable stay. (Photo: Courtesy TxDOT.)

TxDOT also divided the project into two parts, which Dugger says was done for two reasons: The span was ready for construction before the approaches and could get started sooner, and there was a desire to use foreign steel. But federal regulations preclude foreign steel unless the bid for the entire project is 25% less than what it would cost for domestic steel.

“Since we were ready to go on the signature span and wanted to try the foreign steel angle to get the price lower, we went ahead and bid it [separately],” Dugger adds.

Soil concerns While drilling the support piers, crews hit sand, and one of the excavation areas started caving in, Dugger says. Crews added a casing to the pier. The U.S. Army Corps of Engineers then asked the city of Dallas to perform more soil borings, which was done. In addition, the corps found the levees unacceptable during a periodic inspection, so the federal agency requested further geotechnical borings to identify the soil characteristics and determine if there are seepage or stability issues affecting the levees.

“If those characteristics show there are problems, they will have to identify some solutions to ensure construction of the bridge does not have long-term adverse impact on the levee system,” says Kevin Craig, acting director of the Trinity River Project for the corps.

Crews pour an arch support for the Margaret Hunt Hill Bridge’s cable stay. (Photo: Courtesy of TxDOT.)

Dugger says that remediation could include a slurry wall.

Craig says the corps has no reason to believe the bridge would be structurally affected by the sandy conditions. He says its concerns are related to putting piers into the levees.

“We have to ensure that doesn’t lead to a shorter seepage path for water to get under the levees and potentially erode them,” Craig says.

TxDOT’s geotechnical consultant began working on the evaluation at the end of June. The agency gave Kleinfelder of Fort Worth 3.5 months to take soil borings and produce a seepage analysis.

Hartzel says TxDOT has not set a schedule for submitting the investigation’s results to the corps. Until the issues are resolved, contractors must avoid any construction activity within 50 ft of the toe of the levees.

“Bridge construction is ongoing, except in an area just above the levee template,” Craig says. “They can put up their steel and deck everywhere except right there at the levee.”

Preparing for the arch support for the bridge’s cable stay. (Photo: Courtesy of TxDOT.)

Current activity Neither Williams Bros. nor Abrams returned requests forinformation about the project. Williams Bros. is working its way across the river, Dugger says. Crews poured the identical arch span columns during all-day pours in April and May. The company has started working on temporary shoring, Hartzel says.

Meanwhile, Abrams is setting beams over Interstate 35 on the east side of the levee. Approaches on the west side fall into the 50-ft construction-free zone, waiting geotechnical results.

Steel spans, fabricated by Cimolai Costruzioni Metalliche in Italy, have started to arrive and on-site welding was expected to commence in August .

“We’re still making a lot of progress on the bridge,” Hartzel says. “There will be a couple of bents and decks we cannot do until we have clearance from the corps.”