Sewer Bridge Rehabilitation
When a gravity sewer collection main crosses a low swampy area or ravine aerially, the pipeline is installed on a sewer bridge. There are currently about 50 sewer bridges of varying size, configuration, and construction material interspersed throughout James City County. Sewer bridges are typically constructed of timber piles driven in the ground on each side of the pipeline about 10 to 20 feet apart, with wooden supports and bracing bolted to the piles. JCSA recently selected five sewer bridges that were significantly deteriorated and scheduled them for rehabilitation. The selected bridges are in swampy areas where access is difficult and working space is limited.
JCSA elected to rehabilitate the sewer bridges using an innovative approach requiring only a mini-excavator and a few skilled laborers. Replacing the timber piles in kind would have required large pile driving equipment, matting in the swamps to keep the equipment from sinking, and potentially additional temporary easements and clearing to access and perform the work (JCSA’s typical easement is only 20 feet wide). Timber piles and wooden supports are being replaced with galvanized steel helical auger piles and steel pipe roller supports. Helical piles have been used for years in the building industry to support foundations in poor soils. The helical piles can be carried into the swamps and augured into the ground using a special adaptor on a common mini-excavator. As the helical pile is installed the operator monitors the torque being applied to the hydraulic auger. When a specified torque is attained the operator knows the desired bearing capacity is provided. The pipe roller supports are then assembled and attached to the piles to complete the support replacement. When the height of the sewer bridge is greater than 4 feet above the ground, the auger pile shaft can be encased with high strength concrete to provide greater stabilization.
Cost
- Five sewer bridge replacement projects (approximately 46 total piles) - $50,645
Project Schedule
- Project completed – 8/2006
Project Team
- JCSA – Danny W. Poe, P.E. Project Manager (757) 253-6810
- Construction Contract – Foundation Systems, Inc., John Jarrell (757) 259-0790
Pictures
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