Key construction milestone on Bay Link project

4 MinutesBy NZ Trucking magazineDecember 7, 2020

Significant ground improvement works are underway at the Bayfair roundabout. This is a key milestone for the Bay Link project to move forward with construction of the new underpass and the State Highway 2 flyover bridge.

NZ Transport Agency portfolio delivery manager Jo Wilton says after the uncertainty created with the unresponsive pumice layer, it is great for the project to reach this point with a plan and progress.

“The design for the ground improvements needed altering after the pumice layer in the area was not performing as we expected. The lattice piling framework will provide further stability and limit liquefaction during an earthquake,” says Wilton.

Due to the sandy soils and high-water table in the area, around 5600 stone columns have already been installed throughout the site.

Two giant drilling rigs, weighing approximately 72 tonnes each and up to 25 metres high, will be located on-site for around six months. The lattice piles will be installed around each of the five supports for the flyover bridge.

“Installing the lattice framework involves overlapping concrete columns to create a sealed wall. It is estimated 9000m3 of concrete will be poured – equalling more than 21600 tonne, which will be delivered by around 1800 truck movements,” says Wilton.

Undertaking the works and operating the rigs safely in such a confined area presents some logistical challenges.

“We have worked closely with Tauranga Airport to ensure the height of the rigs‘ masts don‘t intrude on the flight path. Working alongside live traffic lanes also means the safety of motorists, members of the public and road workers is paramount. As part of this, the size of the Bayfair roundabout will increase to accommodate a larger construction zone.

“We have a better understanding of the issue and have designed an appropriate solution. The pile contractors and on-site team continue to conduct ongoing tests to ensure the new design is constructed and performing as required,” says Wilton. 

The first of two changes to the Bayfair roundabout is anticipated to take place this week. This work will involve a partial closure of the roundabout. Motorists are encouraged to visit the Journey planner website for more information.

The piling works will mainly occur during the day and while NZTA endeavours to minimise any disturbance to local residents and businesses, the ground improvements work may generate some noise and vibration.

More information: The lattice framework

This approach involves constructing a network of overlapping concrete columns arranged in a square lattice. The primary piles are augured (drilled) into the earth. Concrete is then pumped through the auger and the auger slowly extracted, replacing the displaced ground with concrete. At completion of the primary piles, secondary piles will be installed that overlap the two adjacent piles, creating a sealed wall.

To install the lattice piles, two giant Continuous Flight Auger drilling rigs will be located onsite for around six months while the works are underway. The first rig is already operating next to the former underpass while the second rig will soon begin work within the Bayfair roundabout.