The first of 3400 stone columns are being installed for the Baypark to Bayfair Link, marking a milestone for the project.
The columns will improve the ground conditions throughout the site so it can eventually take the weight of the two flyovers.
Installing stone columns involves putting vertical columns of gravel into the ground and using vibration to move the sand to make way for the stone.
This will be done using an 80-tonne crawler crane with a 3.2-tonne "vibroflot" attached - the vibrating element that carries out the compaction and delivers the stone.
New Zealand Transport Agency project manager John McCarthy said the installation of the columns is a significant milestone for the project.
"The stone columns will cover more than two rugby fields and use enough gravel to fill eight Olympic-size swimming pools," he said.
"They push against the surrounding ground, increasing its density and enabling the ground to support the weight of the on and off ramps that will be built on top. It will also protect the ground from the risks of liquefaction during an earthquake."
McCarthy said each stone column is "relatively small" - up to 16.5m deep and 1.1m in diameter - and installation will take 20 to 40 minutes each to complete.
The stone column work has started on SH2 Maunganui Rd near the Te Maunga roundabout.
A second stone column rig will arrive in a few weeks. Construction of the 3400 stone columns is expected to take about 10 months.
McCarthy said while nearby residents can expect some vibration during the stone column works, every effort will be made to minimise the impact of noise and vibration during the project.
The Baypark to Bayfair Link is designed to reduce congestion and improve safety by separating local and state highway traffic and providing walking and cycling connections.
The key features include the construction of two flyovers and improvements to the SH29A and Truman Lane roundabout, and the SH2 Maunganui-Girven roads roundabout.
People can also expect to see some changes at the Bayfair roundabout this week, with traffic switching to new lanes from October 24.
The traffic switch will allow for earthworks to begin and utility services to be relocated on Maunganui Rd between Girven Rd and Exeter St, in preparation for construction of the Pāpāmoa-bound on and off ramps.
City-bound traffic will use the new lanes from Wednesday morning, and from Friday morning, October 26, traffic travelling towards Pāpāmoa and Baypark will move onto the old city-bound lanes.
Access onto Maunganui Rd from Exeter St will also be temporarily closed on Friday and there will be no right turn option from Bayfair carpark onto Girven Rd near the roundabout.
The agency thanked people for their patience while this work is carried out, and reminded drivers to stick to the temporary speed limits throughout the construction site.
• If you put all the stone columns end to end from the project site they would reach Waihi Beach (about 40km)
• The stone columns will cover more than two rugby fields and use enough gravel to fill eight Olympic-size swimming pools
• The stone column method, which uses gravity and vibration, was invented in Germany in 1958
• Stone columns are well suited for sandy soils and help limit the consequences of future liquefaction during an earthquake.