Stadium site culvert reinforced over collapse fears

A culvert carrying Opoho Stream under the Forsyth Barr Stadium construction site in Dunedin is to be reinforced because of fears it could collapse under the weight of giant machinery at the site.

Dunedin City Council staff contacted yesterday said they were seeking confirmation from contractors at the site about steps to be taken to protect the culvert from collapse.

However, Carisbrook Stadium Trust spokesman Gary Johnson said the need to protect the culvert had been identified early in planning for the stadium's construction, and "exceptional measures" would be taken.

The 337m-long culvert begins at Logan Park and runs underneath State Highway 88 before crossing under the stadium site and emptying into the Water of Leith.

Mr Johnson said a temporary brace would be built inside the culvert to allow a heavy pile-driving rig to drive over it in the next few weeks.

The rig, which has so far been used to drive piles for the stadium's south stand, would need to cross the culvert before beginning work on the north stand piles, which was scheduled to start in September, he said.

Vibration monitoring equipment would also be installed, and the weight of machinery crossing the culvert reduced where possible to minimise stress on the structure, he said.

As construction of the north stand progressed, piles would be drilled either side of the culvert, with a concrete pad over the top, to keep weight off the culvert permanently, he said.

"They [contractors] are starting to do the planning around that," he said.

Earlier yesterday, council water and waste services manager John Mackie said when contacted he had concerns about moving an "enormous crane" over the culvert.

"We are certainly concerned about the structural integrity of the culvert and wanted some assurance from the contractor it wouldn't fail under the load," he said.

Council water and waste services network manager Rezaul Haque said the culvert ran between 800mm and 1m below the surface, which was "not very deep".

He was seeking further information about plans to reinforce the culvert yesterday.

Mr Johnson said the culvert, along with the rest of the site, had been surveyed and the subject of engineering reports early in the planning stages of the stadium project, and reinforcing work was covered by existing resource consents.

Otago Regional Council director of resource management Selva Selvarajah said work to repair or maintain the culvert would be a permitted activity, as long as no permanent change to the waterway resulted.

- chris.morris@odt.co.nz