McMillan Drilling Ltd have introduced a New Zealand first stone column ground improvement technique following the recent Christchurch Earthquakes.

The method is currently being used to provide ground improvement for an important link road that was significantly damaged due to lateral spreading and liquefaction.

The method provides the following benefits over traditional vibrating stone column installations:

• The method is vibration free (ie it can be used immediately next to sensitive sites or neighbouring buildings).


• The method is fast to set up, and column installation can begin within an hour of the equipment arriving on site depending upon which base machine is used.


• Only two pieces of plant are required at each site. The stone column machine, and a loader. Stone deliveries by truck.


• The equipment involves less high pressure and high wear hydraulic components, and is consequently more reliable with reduced costs.


• The method is best suited for loose collapsing ground conditions (like Christchurch) that require either wet top feed vibroflot (extremely messy) or dry bottom feed vibroflot (more expensive).


• No pre-augering of the columns is required to start the tooling penetration as is frequently required with dry bottom feed vibroflot methods to get through the hard upper crust.

"We've created a new stone column method."