Geotechnical Engineer Declines to Name Crack Cause in Reservoir Dam Trial
By all accounts, Dr. David Carrier III is an eminent geotechnical expert on soil science. A paper he co-wrote won a medal from the American Society of Civil Engineers, and he has written about building conditions on the moon.
However, when it comes to identifying the cause of the cracking at Tampa Bay Water's C.W. "Bill" Young Regional Reservoir, Carrier says he is unable to make a definitive diagnosis.
With nearly $100 million on the line, the final verdict likely will be made by a jury of the U.S. District Court in Tampa. Tampa Bay Water and HDR Engineering, Omaha, are asking the jurors in the trial, which started on March 12, to decide if cracking at the utility's six-year-old reservoir is due to design error or construction defects.
Tampa Bay Water recently stated it is seeking as much as $97 million from HDR, which was the engineer-of-record for the 15.5-billion-gallon reservoir. At trial, attorneys for the utility mentioned $92 million as a possible claim amount.
Attorneys for HDR are arguing that TBW is falsely claiming the problem is a design error in an effort to obtain a large damage award that could fund much of the pending $162.4-million rebuild. In Florida, designer's liability is unlimited.
The cracking at the reservoir is occurring in two different sections that, witnesses say, equals about 10% of the facility's embankment. TBW attorneys argue that, due to HDR's faulty design, water within the embankment is getting trapped upon drawdown, leading to a condition of excess pore pressure that ultimately results in cracking. In one instance, Carrier testified that the level of water in the embankment remained as much as eight feet higher than the reservoir's pool.
The trial's first witness, Tampa Bay Water General Manager Gerald Seeber, cited a report from the utility's system engineer, Black & Veatch, that backed the pore-pressure theory and recommended a fix of the entire embankment, which measures five miles in circumference.
Looking for quick answers on construction and engineering topics?
Try Ask ENR, our new smart AI search tool.
Ask ENR →
HDR attorneys attempted to undermine Black & Veatch's recommendation with documents indicating the firm voiced this opinion only after it confirmed that TBW's "ultimate goal was to obtain a permit modification that will allow a withdrawal rate of up to 135 MGD." The original design for the reservoir allows for a 66-MGD drawdown rate; HDR contends the embankment's original design won't accommodate the higher rate.
HDR investigated the pore-pressure theory and, for a period of time, considered it the most likely cause. However, after being fired by Tampa Bay Water as the utility announced plans to sue, the engineering firm discovered construction photos that seemed to indicate the possibility of improper soil placement techniques. One Black & Veatch official who viewed the photos raised the theory that poorly compacted soil could form voids and then collapse after getting wet. In court, HDR is contending this scenario is the most likely cause.
Carrier oversaw the reservoir project for the Florida Dept. of Environmental Protection during the permitting stage and was the first person to investigate the cracking, in January 2007. He is a central character in the legal drama.
Carrier testified that, early on, he deemed pore pressure the "most likely cause" of the cracking. However, after failing to find data indicating pore pressure was occurring and "having trouble reconciling [that] just those two areas" were experiencing cracking, Carrier no longer believes this theory, he testified.
Asked by Tampa Bay Water attorneys whether he currently has an opinion about the cause of the cracking that he could defend with "engineering certainty," Carrier said he did not.
Meanwhile, TBW is pushing forward with a $162.4-million project to repair and expand the reservoir. HDR says the work is rebuilding, not repairs.
