3 Sept 2001

The new bridge over the Avon River will soon be in use after being officially opened on 19 September.

The building of the 50m-long bridge, four lanes in three spans, ran parallel with the completion of the road works from the New Brighton Road roundabout through to Wainoni Road.

The official opening of this stage of the joint Christchurch City Council-Transit NZ-$16 million expressway will be on Wednesday 19 September.

The next and final stage - Stage Two - from Eureka Street to Birch Street is being designed at present and will be constructed next year.

The new bridge is no ordinary bridge with many unusual characteristics. One is that it has been designed to meet earthquake liquefaction problems and others include special pier frames to enhance its appearance, caissons specially designed to resist seismic forces and cycle-pedestrian ways built partly below the tide level.

The two-pier frames that support the bridge deck are also unusual in that they are made from pre-cast elements bolted together using innovative steel knee joints.

When construction started with the driving of the pier-frame support caissons it was found that ancient totara logs blocked progress. The original site investigation did not show the timber, says the City Council’s structural engineer, Lloyd Greenfield.

The timber was smashed through eventually but the vibration from this set off ground liquefaction that led to lateral spreading of the riverbanks.

This pushed the top of the caissons in towards the river.

The bridge is designed to cope with liquefaction but the lateral spreading caused by the vibration during construction was new problem for the engineers.

The cycleway underpasses partly descend below water level and special jointing and sealing systems are used to maintain water tightness.

The underpass foundations are different, too, as they are designed to resist uplift from flotation and to support the full weight of the water should the underpasses become inundated and the tide then recede below the base.

The first stage of the Expressway - Anzac Drive - has been open since last August.

Eventually the expressway will be taken over by Transit NZ as a state highway, says the City Council Project Manager, Jeanette Ward.