Gully builders muddle up dirt

The consortium behind the $850 million Transmission Gully motorway project north of Wellington has miscalculated the amount of earth it needs to shift by as much as 50 per cent.

Wellington Gateway Partnership (WGP) has confirmed that it is seeking new resource consents for an extra 3 million cubic metres of earthworks – but says the road will still open in April 2020.

WGP originally applied for consents for about 6m cubic metres of earthworks.

The extra consenting costs are expected to total about $50,000, which was within the project’s budget, chief executive Sergio Mejia said yesterday.

‘‘We’re working closely with relevant consenting authorities and the New Zealand Transport Agency to ensure there are no impacts on project timeframes.’’

The underestimation of the earthworks required for the 27-kilometre-long motorway from MacKays Crossing to Linden was not uncommon in big roading projects, Mejia said.

‘‘It’s not unusual for volume increases of this scale once detailed design and specifications are finalised. It is common for contractors to need to seek additional consents to account for those changes in scope.’’

Fifteen of the 20 extra consents had been approved by Greater Wellington Regional Council and associated local councils, he said.

The regional council’s environment committee has called for an update on the project after learning of the consent issues.

Committee chairwoman Sue Kedgley said it defied belief that the project estimates had so badly undershot.

‘‘I can’t imagine how you can get it so wrong that you underestimate the earthworks by that amount,’’ she said.

‘‘It really stretches credulity and doesn’t inspire confidence in the project.’’

Project director Boyd Knights admitted last month that wet winter weather had slowed construction, but said he still expected the project to be completed on time.

WGP, a private group of financiers and contractors, holds the contract to maintain the fourlane motorway for 25 years after construction.

Together with the $630m Kapiti Expressway further north, and a project under way to solve congestion in Wellington central, it is hoped the motorway will make the journey in and out of the capital safer and faster.