The Rangitata rail bridge is expected to be reopened to trains towards the end of next week once temporary support structures have been put in place.
The bridge, spanning the Rangitata River in south Canterbury, had one of its 34 piers washed out by high flood waters last Friday.
The 610m-long Rangitata rail bridge is an “important part” of the rail connection between Invercargill, Dunedin and Christchurch, with around eight freight trains crossing each weekday and five each weekend.
Footage provided to 1News showed part of the bridge visibly sagging after the pier was washed out by a raging Rangitata River.
KiwiRail chief infrastructure officer André Lovatt said the first phase of work on the bridge has been completed and construction of the temporary supports that will allow the bridge to reopen has begun.
“With lower river levels we were able to undertake a detailed inspection of the damage to the bridge on Sunday. Work began immediately to divert the river flow away from where the pier was.”
Civil contractors have been working to temporarily divert the main river flow and drain water from around the pier site.
Lovatt said there was a “staged process” to go through now.
Focus will first be on ensuring the sagging spans do not collapse into the river and damage the adjacent road bridge which carries State Highway 1, he said.
“We will then install a temporary structure to replace the pier and allow trains to resume running over the bridge.”
Construction on a structure which will bring the sagging spans back into alignment, known as a pigsty, begins today.
From tomorrow, a 250-tonne crane will drive steel caissons into the riverbed which will form part of the temporary support for the bridge, Lovatt said.
“At this stage we expect to have the bridge reopened to trains towards the end of next week, provided the river flows remain at current levels and working conditions remain safe.”
Permanent replacement of the pier will begin once this has been achieved.
“We are also undertaking work to find the missing pier, which could be buried in the river downstream.”
All train movements over the bridge have been suspended due to the damage and rail freight will be managed by road while the bridge is out of action.
