Sydney Harbour Tunnel
The Sydney Harbour Tunnel was completed in August 1992 to provide a second vehicular crossing of Sydney Harbour to alleviate congestion on the Sydney Harbour Bridge.
The tunnel is made up of three sections: twin 900 m land tunnels on the north shore, twin 400 m land tunnels on the south shore and a 960 m immersed tube (IMT) structure.
The IMT structure consists of eight precast concrete units. The units were constructed over 100 km away in a dry dock at Port Kembla and then towed to Sydney Harbour. A trench was dredged prior to the arrival of the IMTs and then the IMTs were lowered into the trench by a system of pontoons and control towers. After the IMTs were in place the trenches were backfilled and then a rock armour was placed over the top to protect the units against marine hazards, such as anchors or sinking vessels.
The land tunnels were constructed by a combination of driving and cut-and-cover techniques.
The cost of the project in 1988 was approximately AU$100 million.
References
Pratley, Juliet (1993) Sydney Harbour Tunnel, Concrete International 15 (7) 19-23.
