Holdfast Training Services Trial Blog

A commonly used piling method in Australia is continuous flight augering, with an experienced operator it can be relatively simple to install, cost effective, with limited noise and vibration.

The interesting aspect of CFA piling by AVO is their use of compressed air to stabilise the excavation. Avo use a Bauer BG 24 rig, which has the ability to inject compressed air from the tip of the auger.  Compressed air is injected near the discharge pump at 150kPa increasing by 100kPa for every 10m of depth. The pressure helps maintain the stability of the excavation prior to concrete being introduced through the stem of the auger.

As the soil is excavated from the pile shaft, the horizontal effective stress (σ’3) on a soil particle on the shaft wall reduces to zero. The air pressure applies an equalising horizontal force to the walls of the excavation of about 250kPa, this is larger than the 146kPa which is being exerted by the soil around the shaft near the toe (see table 1). The air pressure helps stabilise the excavation from collapsing by applying a passive force against the active force from the soil around the shaft walls. Excess pressure is forced up the shaft helping lift soil up the flights of the auger.

This method helps increases the pile skin resistance by limiting voids along the pile shaft.