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Precast Counterfort Seawall Simplifies Road Widening Project in USVI
The U.S. Virgin Islands (USVI) Department of Transportation is executing a multiphase Federal Highway Administration (FHWA)-funded reconstruction of Veterans Drive (Route 30) in the city of Charlotte Amalie, St. Thomas. The first phase involves widening and reconstruction of about 2,500 linear feet (760 meters) of roadway and includes provisions for a people friendly sidewalk and recreational features along the waterfront. The gravity seawall placed along the offshore face will retain fill soils varying in height from 8 to 14 feet (2.4 to 4.3 meters). The paper describes the design and construction aspects of the modular precast concrete counterfort units forming the seawall for the project.
The original bid design had envisioned the use of a stacked modular block system for the seawall. However, construction of this option required significant underwater work and was deemed difficult to construct by the winning contractor. The design-build team adopted a system consisting of modular precast concrete counterfort wall units placed on the prepared seabed and connected together by a cast-in-place concrete tie beam. Precast concrete coping units and bollards/lights were placed over the wall to provide a pleasing finish. All reinforcing bars were made of Grade 60 stainless steel to provide a 50-year design life. All the precast elements were fabricated in Virginia and barged to the island. The modular precast wall concept allowed the contractor to achieve very good placement control for the mostly curved alignment (with three outlooks) and met the stringent architectural finish required by the client.