This NYSDOT project featured the replacement ofan existing two-span bridge located immediately at the intersection with NYSRoute 417. The existing bridge crossed Tuscarora Creek at a 90-degree bend in the stream. This severe angle of attack coupled with the high stream velocities (14 fps) led to significant scour of the erodible rock formations below the existing pier and north abutment.
During preliminary design for the new bridge,the existing bridge pier settled more than 3 feet due to scour, forcing the closure of the bridge. Under a separate contract Bergmann prepared the contract documents for a temporary bridge at the site allowing CR85 to be re-opened to traffic 12 weeks after closure. The project schedule for the new bridge was then accelerated to 10 months so that the new bridge could be constructed a full season earlier than planned. The new bridge consists of adjacent prestressed box beams on tall cantilever concrete abutments. The abutments are supported on a single row of large diameter (54") drilled shafts socketed into rock for scour protection. The new bridge is located on a horizontal alignment and raised vertical profile shifted 80-ft downstream of the existing bridge requiring 1,300-ft of full depth roadway and embankment construction.
Traffic was maintained on-site with the temporary bridge. Scour protection is provided by armoring the approach stream banks with extra-heavy stone fill and the installation of 5 quarried-stone rock spurs located in the stream bankwhere Tuscarora Creek parallels County Route 85.