DD3 COFFERDAM – Newport News, VA
The primary goal of the Newport News Shipyard Dry Dock 3 Cofferdam project was to construct a robust cofferdam system to facilitate underwater construction and maintenance activities at Dry Dock 3.
Precon has completed all requisite work activities, which included the demolition of existing underwater obstructions and utilities, as well as conducting a dive survey to ensure the removal of all obstructions. The team transported, stored, and installed owner-supplied PZC27 sheet piles, each measuring 90 feet in length, utilizing a 300-ton crane barge to construct 11 square coffer cells. Additionally, Precon continued the installation of sheet piles on the southern side to encompass an additional 50 feet of the existing bulkhead. The company also installed structural steel water stops with the assistance of divers and poured reinforced concrete using tremie methods. Precon also formed and placed pile caps and the deck slab to connect the northern and southern banks. Coffer cells were filled with VDOT #57 stone in five-foot layers up to the top. Furthermore, underwater dredging and cleaning of the dry dock apron and sill were conducted using a clamshell, while additional sediment and debris were cleared through the utilization of divers and hydraulic dredge pumps. An apron drainage system was established utilizing filter fabric, sand, and perforated pipes, along with a secondary filtration layer comprised of filter fabric and #78 stone. To construct a stability berm standing 27 feet tall, approximately 4,500 tons of VDOT #57 stone were placed. For cleaning and filling, the dry dock was dewatered, with asphalt subsequently placed to create access ramps from the land to the deck. Lastly, Precon installed handrails and cleats on the deck for stability.
The completion of this project was critical for ensuring structural integrity and stability, allowing for future dewatering activities at Dry Dock 3.
