Engineers are using radar and seismic equipment to search for more problems where a sinkhole ate part of an elevated highway's support pier.
By JEAN HELLER
Published April 16, 2004
10 news video: Governor Bush calls for investigation into Crosstown collapse
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TAMPA - The soil beneath the elevated lanes of Lee Roy Selmon Crosstown Expressway will undergo additional testing to search for other subterranean surprises that could threaten the project.
Tampa-Hillsborough Expressway Authority officials and their contractors said Thursday that they used ground-penetrating radar Wednesday night to gather soil information where a sinkhole swallowed 20 feet of a road support pier, causing two segments of the highway to collapse and damaging a third.
They also plan to use seismic equipment along with the radar, which could find additional soil instabilities if they exist. And they will do additional borings to take soil samples where there are any doubts about what lies beneath the 6-mile, $120-million elevated road project.
Engineers also plan to bore a vertical hole in the pier that collapsed Tuesday to determine how it withstood the collapse. It will be replaced when that section of road is rebuilt.
Results of the initial testing won't be known until next week, said Tom Mullin, vice president of URS, the project's design consultant. He said it could be 10 weeks or longer before there are answers about what caused the pier to sink.
Pat McCue, executive director of the Tampa-Hillsborough Expressway Authority, said he does not want to rush the analysis.
"We're going to be building the bridge elsewhere, and if we wind up finishing that (segment) last, that's fine with me," McCue said.
Officials have not decided how extensive the additional testing will be, but it could involve all 152 of the support piers build so far and the sites for the remaining 60.
"This should not have happened," McCue said. "Everything tells me it was a freak of nature, and I don't want any more freaks. . . . If there's something that we can do that we haven't done that's appropriate, we're going to do it."
He said he did not know what the additional testing will cost.
"It doesn't matter," he said. "We're going to accomplish whatever we have to do to assure ourselves and our customers of the bridge's safety."
Meanwhile, more details emerged about the collapse. Sometime before 7 a.m. workers discovered that Pier 97 was several inches lower than it was supposed to be, McCue said.
"Over some period of time it had shifted," he said. "It was gradual, a very slight problem in the beginning. And then they started to feel vibration, and they all got off the bridge."
Two workers were slightly injured.
McCue said the movement of the pier wasn't obvious, but instruments showed it wasn't where it should be. Since the collapse, the remaining 151 completed piers have been checked, McCue said.
"They're not moving," he said. "They're not a micrometer off. They aren't going to move."
According to a geotechnical report released Thursday, the initial testing along the elevated highway's route involved 181 soil borings ranging from 70 to 90 feet deep. The samples drawn from the ground were 3 inches in diameter and tested to determine the properties of the limestone beneath the project and most of Florida.
No problems were found, but 181 borings is 31 fewer than the number of piers that will hold up the road. McCue said this week that there had been a boring at the center of the site for every pier under the road.
"We did supplemental borings in some spots," said Mullin, "in places where the piers turned out not to be where we had done the initial borings."
He did not say whether all 212 pier locations eventually were checked.
Mullin sidestepped questions about whether the use of alternative testing, such as ground-penetrating radar and seismic methods, might have provided an early warning of a sinkhole beneath Pier 97.
"That's an open-ended question," he said.
The three-lane elevated road will provide an express ride for commuters between east Hillsborough County and downtown Tampa. All lanes will run east-to-west during morning rush hours and west-to-east in the evening. The road will be for the exclusive use of SunPass electronic toll customers.
Meanwhile, work continues to build four temporary ground-level lanes to carry traffic around the site of the collapse, two lanes in each direction. The lanes are expected to be open by 6 a.m. Monday.
In another development Thursday, Gov. Jeb Bush said he favored a state Department of Transportation investigation of PCL, the Canada-based company which is the general contractor on the crack-plagued new Memorial Causeway Bridge in Clearwater and the company which built the support pillars for the Crosstown.
"If there's a chronic problem . . . the Department of Transportation needs to inquire into what the status is," Bush said. "It may be nothing out of the ordinary, but absolutely both the Expressway Authority and the Department of Transportation (have) a duty to determine if contractors or designers of infrastructure have done so in a faulty way.
"And I'm not suggesting that that's the case in this . . . with this particular company, but sure, it should be investigated."
- Staff writer Alisa Ulferts contributed to this report.
10 news video: Governor Bush calls for investigation into Crosstown collapse