Bridge repair work, more closures due

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Work on repairing the dip on the Ashburton bridge is making progress with the main river flow diverted from the affected settled-pier to allow contractors to get close enough to start.

The settlement occurred at a pier about 100 metres from the north end of the bridge when flood flows, concentrated by debris damming, damaged existing scour protection and mobilised bed material around the piles.

The structure has since been proof-loaded and assessed by engineers monitoring the structure closely through multiple surveys, detailed structure inspections and electronic (real time) monitoring.

NZ Transport Agency network manager Jessica McFarlane said all of the measures have shown that the pier had stabilised following the late-May flood event, once the bed material resettled, and the structure was safe for continued use.

“Over the last couple of months, Waka Kotahi and bridge advisors at WSP, and construction companies Downer and Fulton Hogan, have been working together to reinstate the structure to its original position and return the bridge to normal service.”

A diagram showing how the slumped part of the bridge will be repaired.

The bridge superstructure including its beams, concrete deck, footways and services will be lifted off the pier using hydraulic jacks to provide a level driving surface.

“Once this has been done, pier support and restraint to the ends of the beams will be re-built with reinforced concrete to provide a robust connection between the beams and pier to permanently recover the bridge.

“Pier scour protection will also be reinstated, consistent with the rest of the structure.”

The bridge performance will continue to be closely monitored over the months following these works being completed

Major work which will involve an overnight full closure of the bridge is scheduled for this Sunday from 9pm to 5am. A SH1 detour will be well signposted on the night. Emergency Services vehicles will still be able to pass over the bridge but there will be no pedestrian access.

By Daniel Tobin