QLD Maritime Museum – New Dock Gate
Contract Value: $2.6M
The project, for The Department of Public Works, was to replace the existing caisson gate at the Queensland Maritime Museum at Southbank. The existing caisson was badly damaged and had been leaking for a number of years, posing a risk to the decommissioned WW2 frigate HMAS Diamantina (1420t) on low tides.
The condition of the existing caisson was worse than originally expected, which required revision of the demolition and construction methodology for the project. Temporary gates were installed on either side to form a cofferdam which enabled demolition to occur in the dry. Localised speed restrictions on the Brisbane River were negotiated to avoid bow wave damage to the temporary gates. The first section of replacement gate was precast on site and lifted in place to avoid durability issues with salt water ingress. The balance of the replacement gate was poured in-situ prior to removal of the temporary gates.
Key features of this project include:
- Gate was designed as a symmetrical structure with a hull similar to that of a ship. Shape provided stability while floating and strength to the gate while allowing rotation for maintenance from the dry side.
- Above water sections were removed by oxy cutting and lifting out. Below water sections were removed by placing Bailey bridge sections across the dock, bolting lifting frames to the solid strakes at each end of the caisson and lifting with jacks onto the bailey bridges. After lifting clear of the water, further sections were removed and the remainder lowered onto a barge
- Use of divers for underwater works; ie. installation of temporary gates to dam the dry dock
- Negotiated speed restrictions in the Brisbane River near the works zone to reduce wave impacts on the temporary structure
- Dry dock is a heritage listed structure, parts of existing caisson had to be retained