Sand in Dallas levees could delay Trinity River bridge

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by By MICHAEL A. LINDENBERGER and RUDOLPH BUSH / The Dallas Morning News

wfaa.com

Posted on March 11, 2009 at 3:52 PM

Updated Monday, Oct 19 at 4:56 PM

The first Calatrava bridge over the Trinity River could be significantly delayed by a deep layer of sand in the east levees near downtown Dallas, a problem that has sent engineers working on the city's massive Trinity River project scrambling.

The 40-story suspension bridge, with its soaring arches and specially fabricated Italian steel, is slated to open by 2011. But it might lack some access ramps - becoming literally a bridge to nowhere - unless engineers for the state and city can persuade the U.S. Army Corps of Engineers to allow fresh holes to be dug in the east levees, near where the sand was found.

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The latest hitch for the already delayed bridge comes as city leaders anxiously await delivery of the steel, which is steaming across the Atlantic Ocean on its way to Houston, and then to Dallas. Designed by famed architect Santiago Calatrava, the bridge has emerged as a powerful symbol of both the promise and the headaches associated with the Trinity River Corridor project, which voters first approved in 1998.

A larger question

It is the effect of the sand on that larger project - on the nearly $2 billion toll road, the lakes and other major features of the multibillion-dollar development - that poses the most vexing questions. Not a single person in City Hall, at the Texas Department of Transportation, or the North Texas Tollway Authority can say for sure how much time and money the sand will add to the Trinity Parkway toll road or other aspects of the Trinity project.

"I don't have one God-blessed answer," Dallas City Manager Mary Suhm said. "I don't know, and it's not in our control to know."

And they won't know until two things happen: Engineers analyze how big a risk the layer of sand could pose to the levees and - equally important - determine how widespread the seam of sand is along the 22-mile levee system. The state transportation engineer leading the bridge project said the sand layer was found throughout the footprint of the bridge and its sprawling infrastructure.

To help answer whether the sand extends beyond that area up and down the levees, the North Texas Tollway Authority is taking soil samples at some 300 spots along six miles of the levees.

If the sand layer turns out to run for miles, the fixes could get extraordinarily complex - and extraordinarily expensive.

Expensive solution

One possible solution floated by the city and by transportation officials would be to build concrete barriers - called diaphragm walls - along the levees where sand is discovered. They would have to be built deep below the ground, in the sand layer, and doing so along the length of the levees could cost more than $1 billion, officials have said.

"What you fear is that you find on the back side of a dam a soft spot where water can percolate up," said Bill Hale, the top engineer in Dallas for the state transportation department, which is overseeing construction of the bridge and is closely involved with planning for the toll road.

It could take weeks or months before officials can assess the sand's full effect on the Trinity project. But the problems it is posing already for the Margaret Hunt Hill Bridge, which is intended to extend Woodall Rodgers Freeway across the river to Singleton Boulevard, are fast coming into focus.

Crews dug dozens of columns for the bridge between the levees last year, and they will begin working on the span itself once the steel arrives from Italy, probably sometime later this spring. But work on the $67 million access ramps to connect the bridge to roads on either side of the river could soon come to a halt, thanks to concerns raised by the corps.

Oncor must first move utility lines from the path of the new ramps. But the corps has said no new holes can be dug into the levees, not even for something as relatively minor as a transmission tower, until engineers can devise a way to offset the risk posed to the aging, earthen dike.

Hale said teams have submitted possible solutions several times to the corps, but each has been deemed unacceptable. "They are saying, 'Try again,' " he said.

"We're trying to find a fix," Hale said. "There are utility poles dug all up and down the levees, and they've been there for years. So we thought we were OK.

Corps tougher now

"But after what happened down in New Orleans, things have changed. The corps thought they had a solution down there and found out later they didn't. They are afraid the same thing could happen here, and they can't afford to have another catastrophe in a city the size of New Orleans or Dallas."

Hale said he needs to know how to proceed within 60 days, or else taxpayers will have to begin paying compensation to the contractor building the access ramps.

"Within one to two months, this has to be resolved or I am going to have problems with our contractors," he said. "They could file a claim, saying we have impeded their work. My biggest way of losing money or causing problems is by delaying contractors."

David Lott, the transportation department engineer overseeing the bridge project, said work on the access ramps will take less time than construction of the span, so crews could make up some lost time and still meet the opening day deadline in 2011. "But if it is delayed more ... then the bridge will be impacted. You can't open a bridge without ramps to get on or off."

Moving the utility tower is probably the least of the problems worrying city officials. The levees have failed a five-year inspection by the corps, and only after its final report is issued later this month will the city begin in earnest to test just how serious the barriers' shortcomings are.

Those levee concerns come even as the corps is also being asked to review a first-of-its-kind plan to put a toll road - in this case 10 miles long - inside a river corridor, for which the agency has formed a special nationwide team of experts to evaluate. Approval rests in the hands of the corps' commander and chief of engineers, a three-star Army general for whom local political pressure is not likely to weigh especially heavily.

"The tollway project is a pretty massive project, and it's challenging from an engineering point of view," said Eric Halpin, the corps' top expert on levee safety.

Complicating all that has been the rigor with which the corps now reviews the thousands of levees for which it is responsible, thanks to the levee failures in New Orleans during Hurricane Katrina. In communities across the country - including along the Rio Grande in Texas near New Mexico and New Orleans itself - sandy soil has complicated levee repairs and made them more expensive.

For supporters of the controversial toll road and other aspects of the Trinity project, the corps' meticulousness has been frustrating.

"We had one set of rules; [now] we have a new set of rules," said Suhm. "Our first question was what in the Sam-hell is going on here. That's my description. Their description is they have raised the bar. What I hear is new rules, new template, new application, new policy."

For Hale, the concern over the relocation of the utilities has been especially troubling. Utilities have been dug into the levees for generations. And for the past 80 years, the levees - sand and all - have worked fine, he said.

Still both officials said they respect the corps' focus on safety and are working overtime to keep all aspects of the project intact and, they hope, on time. It has not been easy, Suhm said, but then nothing about the Trinity River Corridor has been.

"We've worked through problems in the past," she said. "This is not easy. It never has been easy, [and] it's not going to be easy in the future. But it's a project I think is well worth doing and I think possible to do. But sometimes it's like pushing a rock up the hill, and I hope I live long enough to stand someday on a bank and say to myself, I knew this would work."

Q&A: The sand problem

Why is the corps concerned about sand?

The presence of sand alone isn't the worry. But digging a structure - a bridge pier, for instance, or support for a toll road - into the sand can be. The man-made material will contract and expand with the weather, creating gaps between it and the sand. "That provides a potential avenue for water to move up and down within that gap," said Kevin Craig, Trinity project manager for the corps. "That sand layer acts as a way for the water to move down under the levee system. If enough water moves through the seam along with the sand, that creates a potential for a failure. ... Our goal is not to have any water infiltrate the levee system or the foundation of the levee system."

What is the fix?

A typical fix is a wall built down to the bedrock to block water's passage. Very rough estimates peg the cost of a concrete wall at about $10,000 per running foot.

Why has relocating the utility transmission tower been delayed?

Craig says that until the soil analysis can determine how big a problem the sand layers pose, no disturbance of the ground beneath the levees can be permitted. He said it will be weeks before all the data is gathered, and weeks or more beyond that to conduct a lab analysis and devise a mitigation plan.

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