Pāuanui bridge to close while repair work carried out

Duck Creek Bridge on Hikuai Settlement Rd, Pāuanui, pictured on Wednesday morning, the sinkhole is pictured centre.

A bridge that connects Pāuanui with the outside world will close overnight as authorities say a defect, common in similar bridges across New Zealand, is behind its failure.

Thames-Coromandel District Council has issued warnings in recent days, initially advising heavy vehicles to stay off the one-lane Duck Creek Bridge on Hikuai Settlement Rd, Pāuanui, until further notice, due to a “tomo” that appeared near the bridge approach on Sunday.

Initial investigations and repairs are planned for today with an overnight road closure between 7pm Thursday and 6am on Friday.

Pedestrian and cyclist access will be available under escort during the closure and provisions will be in place to allow emergency services through the site if circumstances arise.

Commercial operations in the coastal settlement have been affected with Cabana Kitchen and Bar forced to close its doors due to 95% of its staff living on the western side of the bridge.

Pāuanui Village Centre manager Tracey Salkeld said she was aware of the situation but did not wish to add comment.

Tairua-Pāuanui Community Board chairman Warwick Brooks said he didn’t know much about the situation, but confirmed he had been made aware the bridge would be closed overnight on Thursday.

“It is a delicate matter, anything to do with our ratepayers is delicate,” he said.

Duck Creek Bridge on Hikuai Settlement Rd, Pāuanui, where a sinkhole has appeared. Speed limits have been in place since Monday.

A Thames-Coromandel District Council spokesman said the hole appeared to have been caused by a migration of fill materials behind the bridge abutment.

“The failure is a known defect with the construction process of this type of bridge and is common across the country.

“When the bridge was constructed, a wooden pile retaining wall was built along the riverbank and infilled behind to create a working platform so that the deep concrete piles and a pile cap beam for the bridge could be constructed,” the spokesman said.

“The bridge was installed, and fill material placed behind the pile cap beam to bring the approach to the bridge up to the level of the new road.

“Over time the fill material moves, and voids form under the bridge approaches; if the river erodes the base of the wooden pile wall and exposes the base of the fill material, this will accelerate the process and fill material will gradually move under the pile cap beam and between the piles into the river.”

The tomo is situated about halfway along on Hikuai Settlement Rd, between Pāuanui and State Highway 25.

It was confirmed the concrete pile structure of the bridge was not affected and the structural integrity of the bridge remained intact.

“In this case we believe that the high tides over the weekend coupled with isolated heavy rainfall events in the area caused the protection to the toe of the wooden retaining wall under the bridge to collapse, removing the base of the fill and creating the void.

“As the toe of the wall is normally below water level and behind the river revetment it is impossible to inspect.

“Similarly, we cannot locate voids forming in the approach until a hole appears. The only way to determine if there are issues is through the use of ground penetrating radar, relatively new to New Zealand, and something that we could consider as a specialist inspection process in the future.”

Heavy vehicles, specifically forestry trucks, have been increasingly present on the main artery to the Coromandel town in recent months due to large sections of forestry being cleared near Duck Creek and further towards the coast, on land neighbouring the township.

The council spokesman said it was unlikely increased heavy traffic movements were related to the failure.

On Tuesday, the council advised all vehicles, including heavy ones, should now keep their speed under 30km/h driving over Duck Creek Bridge on Hikuai Settlement Rd, Pāuanui, until further notice, as the tomo had been temporarily filled.

It followed council warnings on Monday advising all heavy vehicles not to travel over Duck Creek Bridge due to urgent safety concerns.

An estimated cost for repairs had not yet been established, it was still being calculated as part of scoping the proposed remedial works.

Remedial works had been split into two stages.

• Excavate the bridge approach to determine the depth and size of any void, replace missing material and reinstate the road surface (planned for Thursday between 7pm and 6am Friday).
• Investigate methods to protect the toe of the wooden retaining wall in the river and carry out repairs (to be confirmed).

On Thursday morning, Hauraki-Coromandel Post visited the site. Roading contractors were present, and road cones and speed restrictions were in place.

The bridge piles appeared to look stable while the tomo appeared to be located at a connection point between the bridge and land. The tomo appeared to be temporarily filled.