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Historic Wharf

Repair Derby Wharf, Salem, Massachusetts

Salem Maritime, the first National Historic Site in the National Park System, was established to preserve the maritime history of the United States. The site consists of about nine acres of land and twelve historic structures along the waterfront in Salem, Massachusetts.  A central feature of the maritime is Derby Wharf, which was constructed in 1762.  Extending nearly a half-mile into Salem Harbor, Derby Wharf was initially lined with warehouses that held exotic goods from all over the world.  The photograph at right from about 1880 shows the working shops and warehouses that still lined the wharf at the end of the nineteenth century. Railroad tracks were laid in the center of the wharf in order to help move cargo from the warehouses.

A 1992 archaeology dig revealed that the portion of Derby Wharf was constructed simply by laying up timber bulkhead walls directly in the mud at low tide, then filling between the walls with dirt and stones.  Over the centuries, the wharf deteriorated, so in 1998, the Department of Interior entered into contract with Triton Marine Construction Corporation for the renovation of the wharf.  Work included dredging and control of contaminants, operating cranes on or near a public area, installation of site utilities, earthwork, stonework, concrete work, timber pile and dock building, and a controlled archeological excavation, all undertaken at a very small work site listed in the National Historic Register.
Triton retained Bath to assist in the development of a value engineering proposal for an alternate means of underpinning the wharf that allowed the preservation of significant archaeological and historic features.  The VE proposal led to the conversion of the contract to the design/build delivery system.

The design team, working under Bath Engineering as the prime design consultant, developed an approach that included large-diameter underwater rock drilling for the installation of king piles in rock sockets, tied back with pressure grouted, and post tensioned soil anchors. The originally specified sheet-pile cellular structure could not be constructed due to large boulders in the glacial till. The steel sheets could not reach the required in-bed due to the boulders. This difficulty was overcome by drilling twenty-four inch diameter rock sockets through the boulders and into bedrock for sheet pile anchoring.