1600-Ton Caisson Tilts On Harbour Bridge Job

Press, Volume XCV, Issue 28269, 6 May 1957, Page 8

1600-Ton Caisson Tilts On Harbour Bridge Job

(New Zealand Press Association/

AUCKLAND, May 5. A setback to work on the Auckland harbour bridge occurred yesterday when a 1600-ton caisson sank on one side and tilted to an angle of 30 degrees. Mr W. Cardno, project supervisor for the contractors, the Cleveland BridgeDorman Long combine, said today the situation was “serious.” The caisson began to tilt slightly yesterday morning, but during the early afternoon it swung suddenly to its present position. There were no men working in it at the time.

Little damage was done to either the caisson or the pontoons surrounding it. Some valuable equipment fell from the caisson top into the water, and a diver went down today to examine it. The sudden movement of the caisson was probably caused by a subsidence of the harbour bed under one of the cutting edges, said Mr Cardno today. It was too early to say how much the project would be delayed. The caisson is the second of three at present in position. It is a huge, prefabricated steel structure which originally weighed 65 tons, and when fully sunk the bottom will be 80 feet below the surface of the water. It has

a working chamber, the walls of which form 7ft 6in high cutting edges. These edges are forced through the strata by the weight of hundreds of tons of reinforced concrete which is added inside and on top of the caisson. Men inside thfc chamber excavate the harbour bed as the caisson sinks, and when it is properly placed this chamber is pumped full of concrete to form a solid base. Workmen Recalled

Yesterday, one of the cutting edges sank lower than the other, tilling the whole structure, and mud from the harbour bed half filled the working chamber. Workmen were recalled hurriedly to begin removing the mud and other material from the chamber. This work is being done with hand buckets, as the normal mechanical gear cannot be used, and Mr Cardno said this would be a “fairly long process.” Mr Cardno said similar trouble had never happened previously in the firm’s experience, although caissons often had a slight lean during sinking. The latest setback is one of many which have delayed work on the bridge since it began in July, 1955. There have been 11 strikes and a number of technical hitches. (Picture on Page 10.)