Pilings were at correct depth
Levee failure still a puzzle
By AMY WOLD
Advocate staff writer
NEW ORLEANS - The sonar tests were wrong, and the U.S. Army Corps of Engineers documents were right.
Sheet piling at the 17th Street Canal levee breach extended 17 feet into the ground, not the 10 feet that sonar tests done by the corps and the state's levee investigation team had showed.
The corps Tuesday pulled up eight sections of sheet piling from each side of the 455-foot breach in the floodwall. Sheet piling is supposed to keep water from flowing through the ground beneath the floodwall and undermining the structures.
Before the work started, Brig. Gen. Robert Crear, commander of the corps' Mississippi Valley Division, talked about the pilings, which quickly became a focus of investigations into why the floodwall failed during Hurricane Katrina.
"We know from our drawings what they should be," Crear said. "The only way you can figure it out is pulling them out. That's what we're doing."
At 8:10 a.m., Crear gave the order to pull out the first sheet piling. Almost 100 people -- former residents, government officials, reporters and scientists -- turned toward the crane and watched as the first one came up.
The floodwall was designed to be built with 23-foot-long sheet pilings. The pilings were supposed to extend 6 feet above ground and 17 feet below ground. A concrete "cap" completes the wall.
When the sheet piling was pulled out, many corps employees smiled -- it looked right.
A few minutes later, Crear announced the results: 23 feet, 6 inches.
In fact, all eight sheet pilings the corps brought up Tuesday topped the 23-foot mark.
Col. Lewis Setliff, commander of Task Force Guardian, the corps group charged with rebuilding damaged levees before the start of hurricane season June 1, said he thought it looked good as soon as it came out of the ground.
But he said he didn't feel relief. Regardless of the sheet piling lengths, the fact remains that the floodwall failed.
"We still have a lot of work ahead of us to find out why this failed," Setliff said.
The discrepancies between what the sonar measured and what was actually found means sonar test itself will need to be worked on, he said.
Team Louisiana, formed by the state to investigate the levee failures, had reported that sonar tests showed the pilings were only 10 feet below sea level. Later corps sonar tests showed the same results.
Paul Kemp, a member of Team Louisiana, said the sonar tests don't always give definitive results. He added that the sheet piling measurements Tuesday were good news.
"So far, we see no evidence that the contractor did something different than the corps called for, so that's reassuring," Kemp said. "The fact exists that a failure occurred."
Fred Young, a structural engineer with the corps, said he saw exactly what he expected to see -- 23-foot sheet pilings. Research into corps documents that included photographs, diagrams and engineering reports showed that would be the case, he said.
"I had no doubt," Young said.
Col. Richard Wagenaar, commander and district engineer for the New Orleans District, said it was important to remove the pilings so the public could see for itself what was actually there.
"It's just not as simple as saying the sheet piles were only 10 feet and they failed," Wagenaar said. "There's still a lot of data collection that needs to go on."
But as the corps finds information that could help in the rebuilding effort, those things are immediately being incorporated into the plans, he added.
For example, at the Inner Harbor Navigation Canal levee breach, the corps found that the I-wall was easily undermined by scouring if overtopped by storm surge.
So now they'll be using a T-wall construction, which will help prevent that by armoring the land behind the floodwall with concrete. In the T-wall design, an inverted "T" of concrete is poured at the base to provide more stability.
"We're applying lessons learned as we go," he said.
One of the next steps will be digging out the portion of the floodwall that actually failed and testing the concrete and pilings, Setliff said. The failed portion of the floodwall is now covered by the emergency levee built shortly after the hurricane.
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