Council gives green light to Albatross Close slip repair work

Porirua Mayor Mike Tana says the Council has agreed to fund slip repairs for Albatross Close.

“It is our responsibility – we must fix it, and fix it well,” says Mayor Tana.

The proposed solution is estimated to cost $1.5 million. Of this, $220,000 will be funded by ratepayers, with the balance coming from an NZTA subsidy and savings from other slip work.

“This is a major slip, caused by an underground water source that has changed course, so it has been difficult to pinpoint the cause of the subsidence. This has affected the road, residents, a preschool and a football club. It requires a substantial, robust and long-term solution,” says Mayor Tana.

“The Council has opted to go with building a palisade wall – installing a series of 25 metre deep concrete reinforced piles to form a retaining wall from the top of the bank. Drainage will be installed in the slip area and the damaged water, stormwater and wastewater infrastructure will be replaced. We will also plant the bank with deep-rooted, water-hungry trees, which will further improve the stability. The road will then be resurfaced,” he says.

Northern Ward Councillor Anita Baker is pleased that the Council has uncovered the source of the problem and has found a robust solution. “It has been unsettling for residents and I’m relieved that we are able to fix the problem. The whole process expected to take 4–6 months.”

The Council’s geotechnical engineers, ENGEO, are working on a design for the palisade wall, based on the latest information available from onsite monitoring equipment.

Background
The stretch of Albatross Close, a cul-de-sac of 76 houses near Endeavour Park in Whitby, has had a history of subsidence, which was first noticed in 2011. There was a major subsidence of the road in front of 4–6 Albatross Close in October 2016, due to high groundwater levels from an unknown source.

After the November 2016 earthquakes, the same section of road subsided. A temporary repair was completed in late 2017, which consisted of adding field drainage at 3 metres deep, remediating and resealing the road, and adding inclinometers to monitor movement.

In June 2018, some cracks appeared at the top of the bank after a period of heavy rain which led to further slumping. The road was closed and the temporary road (which was installed after the 2016 earthquake event) was reopened to give residents of Albatross Close and Seagull Place access to their properties. The water main recently burst and has been temporarily replaced above the ground, with temporary repairs currently underway to both the wastewater and stormwater mains.

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