Replacement of this 86-foot single-span bridge along the scenic Cohasset coastline presented several challenges. Construction would be subjected to the significant tidal currents generated in “the cut”, as this inlet into Little Harbor is known locally. The roadway could not be closed during the summer tourist season, so the construction would need to be performed quickly, and much of the work would need to be performed during the winter months and be subject to the severe cold and wind environment of this shoreline location. The near-surface bedrock would complicate the installation of cofferdams and water control measures for the substructure construction. The project would need to minimize impacts to the adjacent salt marsh. Lastly, the project would need to meet the aesthetic requirements of the local residents and town officials for the appropriateness of both the scenic natural views and the affluent neighborhood.
To meet aesthetic requirements, MassDOT requirements for substructure facades subject to tidal flows, and to reduce construction duration, the abutments were designed with an innovative technique that combined precast and cast-in-place concrete construction. The abutment face was built using precast concrete panels that were cast integrally with a granite veneer. These panels were then set in place and used as one side of the formwork for the cast-in-place concrete that was poured behind the panels to create the abutment stems. This method anchored the granite to the wall face with the most secure method available, eliminated the need to apply granite facing in the field within the cofferdam, reduced the amount of formwork needed to be built within the cofferdam, and minimized the amount of visible joints between panels compared to what would have been required to keep the weight of each piece low had the stems been entirely precast.
The wingwalls were designed using cast-in-place concrete that will be faced with a thick stone veneer using oversized dovetail anchors. The wingwall veneer will consist of stones from the original bridge wingwalls that will be cut to a thickness of 18 inches. Re-use of the existing stones was an important element of the project to area residents.