Lateral thinking saves five months on SH20B project

Cutting the ribbon: Fulton Hogan CEO Graeme Johnson; Auckland Mayor Hon. Phil Goff; Minister of Transport Hon. Michael Wood; Auckland International Airport CEO Adrian Littlewood and Kaumātua, David Wilson – Te Ākitai Waiohua.

‘Timely’ is a word to describe the new $73 million State Highway 20B (SH20B) project to Auckland Airport, that was officially opened on Friday 16 April.

The team brought it on time, achieving the original 31 March 2021 date despite an unplanned five-month resource consent delay. (A project that was to span two summers and a winter, became a two winter, one summer job).

Timely, too, because it coincided with the trans-Tasman bubble – an early sign that traffic on SH20B is about to return to its 30,000 vehicle-per-day pre-Covid levels.

Project Director Richard Anthony says the team rose to the challenge of completing an already tight programme – 3.5 km of two additional lanes for public transport and vehicles with three or more people, and a new shared use path – in five fewer months than envisaged.

“This was probably the most collaborative project I’ve been involved on. We did what we said we’d do, and that’s a source of pride for everyone involved.”

North Island General Manager Simon Dyne paid the project the ultimate compliment.

“SH20B is the best delivery job I’ve seen – day and night delivering for three key clients involving more than a dozen parts of the business,” he says.

To make up time, the team focused on ground improvements and the paving system. This included introducing 800 wick drains to the ground improvement areas and increasing the amount of material used to load these areas to 20,000 tonnes, reducing the settlement period by approximately two months. The aggregate used to load these areas was then reused to bring the road up to its final level, approximately 1.5m above.

In collaboration with the Fulton Hogan paving team and Aurecon, they changed the road design by replacing the aggregate layers with AC28 asphalt after site trials showed they could use the asphalt as a subgrade improvement layer in the existing road, on top of the existing clay. This enabled them to carry out the full depth reconstruction of the existing road using a night-time mill and mix approach.

By using machine control on both the 2m Mill and the asphalt paver they were able to control the levels in the centre of the new road with no external reference. Richard describes it as “working from the inside out”. Rather than operating in three zones – either side and the middle of the road – they used a two-stage approach, with the median pavement works carried out at night using mill and mix. This shaved a further three months off the programme.

The project team identified a number of sustainable options to re-use as much of the material from the existing road corridor as possible, including the successful re-use of the basalt aggregate milled out as part of the pavement operations as subgrade improvement for both the road and the new shared use path. In addition to a cost saving, this avoided more than 100 truck and trailer movements on Auckland’s roads.







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