Project Detail

Dry Dock Caisson Replacement


Scope of Work

Cianbro is replacing the existing dry dock caisson and conducting repairs to the inner and outer seats of the caisson at an existing naval shipyard facility. Repairs include maintenance dredging up to 1,078 cubic yards of silt and sand at the entrance to the dry dock with upland disposal, concrete repairs within the dry dock, replacement of gates, a trash rack, concrete stairs, and interior framing.

Project Details

  • Cianbro will:
    • Replace an existing caisson
    • Repair the concrete of the outer caisson seat
    • Repair the concrete of the inner caisson seat
    • Repair the concrete of the dry dock floor and walls
    • Replace the existing dry dock stair system
    • Replace the existing sluice gate
    • Replace existing conduit grates
    • Reroute existing capstan and fire pump feed conduits

Lean, Innovative, and Unique Project Solutions

Unique challenges include the construction taking place inside a controlled industrial area while the dry dock is active and servicing vessels. The team has had to work around the numerous schedule changes due to boats coming in and out of the dock. Cianbro has also had to coordinate with the boat project teams working in the same area to allow for a safe work environment for both teams. While completing demolition of the North and South walls in the dry dock, the team had to create a barrier of netting to prevent any debris from entering the work area of the submarine. A limpet cofferdam was designed and installed in order to keep the dry dock functioning while working on the outer seat. 

Team members at the Portsmouth Naval Shipyard successfully executed a technically and logistically challenging offload of a new dry dock caisson. After two years of construction, months of planning, and a 600-mile trip by barge, the project team offloaded the new caisson, assembled and rigged 20 tons of rigging to pick the 700-ton caisson, and after a 48-hour operation, the Chesapeake 1000 crane barge successfully set the caisson without any complications.