The Otago Daily Times watched two of the about 18m-long solid concrete piles being hoisted by crane and then punched into the ground by a hydraulically activated pile-driver yesterday afternoon.
In each case, the piles appeared to drop silently about 10m straight down into the ground in a matter of moments, before the pile-driver was needed to ram them the rest of the way down over 30 minutes.
However,a construction source - who did not want to be named - said, despite them appearing to drop, the piles were actually being driven into the ground by their 12-tonne weight and the force of the 14-tonne pile-driver.
Each pile was cutting through a layer of soft marine silt initially, before reaching firmer ground beginning about 12m down.
Five hundred and thirty piles are to be driven into the site to support the weight of the stadium, which is being built on reclaimed land beside the Water of Leith.
The piles were expected to reach an average depth of 18m, with some as shallow as 15m and others as deep as 25m.
The piling work is being carried out by Daniel Smith Industries, of Christchurch, overseen by main contractor Hawkins Construction.
