A new bridge over Thurmond Lake along U.S. Hwy. 378 will cost $6 million more than planned and take longer to complete, due in part to problems with support columns anchored in water as much as 80 feet deep.
“As is often the case in a project of this magnitude, there have been issues arise during construction,” said Cissy McNure, a spokeswoman for the Georgia Department of Transportation, in an e-mailed response to questions.
The bridge will cross the Savannah River and link Lincolnton, Ga., with McCormick, S.C. Construction began in April 2010. The new scheduled completion date of June is 11 months later than planned.
The problems are related to possible movement in the bridge supports, known as “bents,” and engineers are working diligently to devise a solution.
“Bridge construction projects, by their very nature, are expensive undertakings,” she said. “And the substructure work on a bridge – a major portion of which occurs underwater – is perhaps the most expensive element of the entire project.”
The problems, McNure added, are due to factors that include the effects of temperature changes on cement placed below the lake’s surface.
“This isn’t a question of anyone making a mistake,” McNure said. “Because substructure work largely takes place underwater, it is difficult, if not impossible, to know definitively what circumstances might be encountered once that work begins. That is what occurred here.”
Engineers believe the deep, cold water – and differences in temperature – affected the curing of the concrete and caused stresses in the seal it was designed to create.
Currently, about 50 percent of the project’s substructure has been completed.
In addition to issues with the submerged concrete, a second issue involves very soft soils discovered beneath the bridge supports.
“We currently are working with the contractor and the Federal Highway Administration to determine the best solutions,” McNure said.
The newest budget for the project is $22.4 million – about $6 million more than the original contract, she said.
The contractor is Alabama-based Scott Bridge Co., which also managed the $192 million construction of the Interstate 20/Bobby Jones Expressway juncture in Augusta.
Once completed, the new concrete bridge will be 1,680 feet long and 44 feet wide to accommodate two travel lanes and two emergency lanes. At its highest point, it will stand 36 yards above the lake at full pool.