Throughout the Southeast, as elsewhere in the country, state transportation agencies are spotlighting bridge maintenance. Tennessee's Department of Transportation is no exception, and one of TDOT's recent bridge stabilization projects focused on bridges on Interstate 75.
In Norris, TN, contractor Mid-State Construction of Livingston, TN, recently took on the challenge of stabilizing the I-75 bridge over Hinds Creek in Anderson County. The piers were being undercut by the creek's current, and stabilization work was necessary.
But the piers were submerged beneath the waters of Hinds Creek.
Frequently, either sandbags or sheet piles are used to hold back creek waters while such work is done. But on this project the contractor used a portable cofferdam system from Portadam. The system consists of a relocatable steel frame structure supporting an impermeable fabric liner at a 45-degree angle to form a wall capable of holding back standing or running water up to 10 feet deep.
In addition to being as much as 50 percent less expensive than traditional sheet piling, noted Portadam CEO Bob Gatta, the portable dam system can be installed by a small crew without heavy equipment. It is also environmentally friendly.
“The beauty of the system is that it is easy to install, easy to remove, and environmentally friendly,” says Gatta. “Everything that goes in the water before the project begins comes out of the water once the project is complete.”
Work on stabilizing the Hinds Creek bridge began in mid-July, and the work has been completed in multiple phases with approximately 100 feet of Portadam utilized during each phase.
Installation was straightforward. First, a crew of three divers installed the steel frame. Since each section of the 10-foot frame is light enough to be moved by hand, the frame could be assembled without the need for heavy equipment.
“Assembling the frame requires only socket wrenches and work gloves,” Gatta says.
On this project, owing to the steep slopes along the creek banks, the contractor used a crane to initially set the frame sections in the creek. The crane, working from a temporarily closed lane on the interstate, lowered the frame sections in pairs to the waiting divers. The frame sections were installed at a spacing of 28 inches.
After the frame was assembled, the team went to work installing the impervious liner. The top of each section of the liner was first tied to the top of each section of the support frame. Each section was then unrolled into the creek, with its bottom (underwater) edge allowed to sink to the bottom, where it was anchored to the streambed with sandbags. Water pressure did the rest, sealing the joints between the liner sections as well as the area where the liner contacted the stream bottom. Gatta notes that the liner conformed well to the stream bed on this project, so no work had to be done to the streambed to provide a good seal.
The dam quickly took shape, wrapping around the creek side of the first row of footings and anchoring on shore on each end. Next, with the dam complete, the enclosed work area was pumped down. Pumped-out water passed through a bag filter before being returned to the creek. The dive team stayed on site throughout the pump-down phase. Then, with the dam in operation, the team moved on to its next job and returned when it was time to relocate the dam to the next work area.
Once work on the first phase of the project was completed, the Portadam divers returned to the site to relocate the entire structure to the next set of piers. They removed the sandbags, then rolled up and removed the liner sections. The frame was then repositioned, the liner sections were reinstalled, and – with the relocated dam complete – work began on the next phase of the operation.
Relocation of the dam went every bit as smoothly as the initial installation. The result was another safe and creek-free work area in which footing stabilization could continue – good news for the motorists passing overhead as they cross Hinds Creek.