A concrete support pier for an unfinished $350-million reversible-lane elevated toll road in Tampa sank 20 ft April 13 due to an unexpected sinkhole. Two construction workers suffered minor injuries.

At 7:15 a.m., the pier in the median of the Lee Roy Selmon Crosstown Expressway between Interstate 75 near Brandon and downtown Tampa sank 20 ft, causing two 150-ft elevated segments supported by it to buckle in the middle, forming a V, says Trooper Larry Coggins of the Florida Highway Patrol. Traffic on either side of the at-ground median was shut down for two hours, with one lane eventually reopening, says Coggins.

There was speculation that wet weather may have caused the sinkhole, but Coggins says later reports apparently negated that possibility.

PCL Civil Constructors, a division of PCL Enterprises, Edmonton, Alberta, had been ahead of schedule on its $145-million contract for the three-lane, six-mile precast concrete elevated portion, scheduled for completion in 2005. The new road is to provide added capacity to the direction most traveled by morning and evening commuter traffic and double as a research project for intelligent highway systems.

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Phone messages for the owner, the Tampa-Hillsborough County Expressway Authority, and to PCL offices were not returned Tuesday. Coggins says the owner and contractor were conferring with geotechnical engineers to find out if the sinkhole was undetected in previous tests or else how it formed.

The viaduct, designed by Tallahassee-based Figg Engineering Group, uses just 6 ft of the 40-ft median. The precast segments, with hollow cores for information technology, weigh 90 tons each. PCL drilled shafts to 70-ft depths.

PCL experienced another sinking problem two years ago when steel crossbeams rolled as crews were moving concrete forms, causing an 80-ft section of the new Memorial Causeway Bridge in Clearwater, Fla., to sink and twist. The suspended roadway and steel supports were demolished and rebuilt. That was due to engineering error, officials said (ENR 12/30/02, p.11).