Cobble Hill Road Bridge Replacement
Swanzey, New Hampshire
Client: Town of Swanzey, NH
Cobble Hill Road is a dead-end road that serves approximately 45 homes as well as an active church. The previous bridge at this site consisted of three corrugated metal pipes which were in poor condition and had inadequate hydraulic capacity. During 10-year storm events, the road was overtopped and the majority of the residents or emergency response vehicles were unable to pass over the bridge, which created life safety response concerns for the Town.
In order to prevent the roadway from becoming impassable during the 100-year storm events, we determined that a much larger bridge was required in addition to raising the profile at the bridge by 5.5′. The design of the bridge was complicated by poor soil conditions which necessitated a large cofferdam system and tremie seal which acts as a mat foundation for the new precast concrete twin cell box culvert. The project included 900′ of roadway improvements including installation of a new, aesthetically pleasing timber guardrail.
Hoyle, Tanner personnel provided bid and construction-phase contract administration services as well as part-time construction observations. One lane of alternating traffic was maintained throughout construction through the use of temporary signals. This project was partially funded through the NHDOT Municipally-Managed State Bridge Aid Program.