Screwpiles: The Forgotten Lighthouses

Advanced Screwpile Designs The development of screw pilings and screw cylinders was one of the most important advances in civil engineering in the nineteenth century. Invented by Alexander Mitchell, the screw pilings and screw cylinders were used throughout the British Isles for piers, lighthouses, and bridges. The foundation system was adopted in the United States to answer the need to build lighthouses over soft subsoil in shallow waters, perfect for the Chesapeake Bay and North Carolina sounds and rivers.

The beautiful adjacent drawing made by the office of Lt. H. Braids, Washington, D.C., in September 1853 shows the screw to be used in all three James River lighthouses. Each point on the drawing is determined by a hand done calculation, the points coming together for the desired curve of the iron flange. Once the lighthouse site was chosen, soil borings were taken. The screw pitch was adjusted depending on the type of soil, shell, sand, and mud encountered at the site.

Deep Water Shoals iron work details, 1867 National Archives RG 26

James River foundation screw, 1853 National Archives RG 26

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