Gannon’s Narrows Causeway Bridge Rehabilitation

The Challenge

The Gannon’s Narrows Causeway bridge required extensive rehabilitation, including upgrades to its structural frame, gussets, and bearing piers. With the busy tourist season ahead, the project owner wished to keep disruption to both road and waterway users to a minimum. The majority of pier repairs were located underwater and therefore needed to be carried out by experienced divers. This added a new level of complexity to the project, therefore, ease of handling and assembly was a priority for material selection and design.

The Solution

Armtec’s engineering team recommended a 4m diameter heavy galvanized 6.0mm Multi Plate ring structure to serve as pier caissons and stay-in-place forms to repair the bridge’s foundation. Underwater divers first repaired the bridge’s steel footing piles before leveling and preparing the riverbed for the Multi Plate forms. Pre-assembled Multi Plate rings were lowered from the bridge deck to the river bottom, where divers guided each partial ring into place before completing underwater bolting and assembly. After the rings were fully assembled and set in place, the 4.6m tall Multi Plate structures were filled with tremie concrete. Once hardened, they provided vital protection to the bridge footing piles. Divers completed the installation, guiding the placement of heavy granite riprap around the base of the Multi Plate caissons for added scour protection.

Technical Details