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Letter to the editor

Second sinking column means more tests, delays

By JEAN HELLER
Published July 15, 2004

	[Times photo: Joseph Garnett Jr.]
	Behind the white vehicle, column No. 99 has settled 1.3 inches. Extensive testing of supports for the elevated lanes of the Crosstown Expressway in Tampa is planned. The problem is expected to delay the opening up to three months and add millions to the cost.
	View related 10 News video: Crosstown construction workers remove segment of elevated highway

TAMPA - A second column supporting elevated lanes of the Lee Roy Selmon Crosstown Expressway has sunk because of unstable ground, forcing more repairs, delays and tests to check the safety of other supports.

The second failure, discovered July 6, was not nearly as severe as the April collapse that dropped a column 11 feet into the ground and took a span of roadway with it. Still, the latest problem is expected to delay the opening of the $300-million project by up to three months and add up to $4-million to its price tag.

The settling discovered last week involved column No. 99, two to the west of No. 97, which collapsed April 13. Column No. 99, also referred to as a pier, settled 1.3 inches, a third of an inch more than the project's tolerance.

"Settlement happens during construction," said Pat McCue, executive director of the Tampa-Hillsborough Expressway Authority. "Settlement up to 1 inch is acceptable. When you put all that weight on top of a pier, it's going to settle a little."

Other columns have settled from 1/8 to 3/4 of an inch, McCue said, and present no danger to the project.

Seismic testing around No. 99 found that while it is anchored in hard limestone, it is two-thirds surrounded by muck, which does not provide adequate support.

The latest setback has raised questions about the project and has officials at the Expressway Authority worrying whether drivers will ever completely trust the new road enough to use it.

"We have to regain our credibility with the public, and we will do everything in our power to do that," McCue said. "We have the time; we have the money. We will do whatever is necessary."

The two supports sank under similar circumstances. Each was loaded with a 175-ton construction girder, or truss, plus segments of roadbed being put into place, which officials say is far more weight than the columns would have to support once the road opens to traffic.

According to William McDaniel Jr. of URS Construction Services, the general engineering consultant on the Crosstown project, the 6-mile road has 197 supports, 82 of which have already been subjected to the weight stress that affected Nos. 97 and 99. None of the others was affected adversely.

McCue said extensive testing is planned for the remaining supports, especially in the area of the two that sank, to make sure they have ample subterranean support. The columns already topped by roadway will not be retested, he said, because they have proved themselves safe.

Manjriker Gunaratne, a professor of civil engineering and a geotechnical engineering specialist at the University of South Florida, said McCue is correct, up to a point.

"For the moment, they're safe," Gunaratne said. "But if any of those other piers are built in muck, problems could show up years from now. Water is pressed out of muck very slowly. Even if piers didn't settle immediately, they could over time. But if they have tested, and know that those other piers are set in good rock, then they're fine."

No. 99's settling was gradual and, unlike the April incident, caused no damage.

"We actually stopped work and watched it," McCue said. Today, crews will begin removing sections of roadbed atop the column. "Once the weight is taken off, we expect it to spring back a little, though maybe not to where it was."

The road segments can be used again, but officials won't risk using the affected column again to support the road.

Ross McGillivray of Ardaman & Associates, who is serving as the forensics engineer on the two support failures, said muck around No. 99 wasn't discovered earlier because the only preconstruction soil boring done at the site was in the exact middle of the column's footprint, which is the state standard for such construction.

"In boring, you know everything about where you drilled, but you can't tell anything about the soils 1 inch beyond that spot," McGillivray said.

McCue said that given the experience along the Crosstown, the state standard might need to be revised.

Additional soil borings done at the site show there is solid rock all around No. 99, but it is 12 to 15 feet below the bottom of the column's foundation.

To salvage the structure, two more foundations will be sunk into the good rock below and to either side of No. 99, and the column will then be attached to its "sister foundations." The downward pressure on the column will be distributed to its siblings.

A similar solution is in the works for No. 97, though officials are not yet certain what caused its precipitous plunge in April. (Officials revised an initial estimate that the column sank 20 feet and now say it fell 11 feet.) Speculation has focused on a sinkhole. Debris from the incident was only recently cleared away, and the support was sawed off at ground level.

Engineers then drilled through the center of the concrete and determined that neither the column nor its foundation had broken. But they haven't done any seismic testing there yet.

Are the failures of the two columns related? Officials aren't positive, but they think it's possible. McCue said he suspected an "intermittent ground problem" had hit columns 97 and 99 but not affected No. 98.

He said the repairs at column No. 97 will cost about $9-million, most of which will be covered by insurance. Neither of the incidents will require an increase in tolls on the road.

Tolls might be the least of the Expressway Authority's troubles. The latest problems only added to users' concerns about the road that is meant to alleviate commuter traffic between Brandon and Tampa by going one-way west in the morning and one-way east in the afternoon.

Bob Minthorn, a retired Hillsborough County School District official who lives in Gibsonton, still takes the Crosstown two or three times a week. He said he has been worried about safety since the first collapse.

"It really is spooky to think what could happen," said Minthorn, 56. "The one that did collapse, if that had been on a Monday morning at 7:30, there would have been considerable loss of life."

Whether he'll drive on the elevated portion next summer, he said, remains to be seen.

"I probably will not use that part of the Crosstown when it is open," Minthorn said. "I'll let it go for a year or so and see what happens."

Jack Merriam, who commutes from Bradenton to downtown Tampa, said the members of his regular vanpool have a "lack of comfort" about the road.

"I can speak for most of the folks in the van to say that we've discussed it and have some concerns about it," said Merriam, a Hillsborough County environmental scientist. "We obviously don't know what we're going to do."

- Times staff writer Jay Cridlin contributed to this report.

[Last modified July 15, 2004, 01:00:38]