Auger cast piles overview
Auger Cast Piles are a quiet and cost-effective process for casting deep foundation piles. Also known as continuous flight augering (CFA), piles are cast in-situ by using a continuous flight auger with a hollow center to inject liquid cement as the auger is removed.
INstalling Auger Cast piles
A flexible tube pipes a cement grout mix into the hollow center, and the auger tip is fitted with a temporary cap to prevent the concrete mix from being expelled. The auger is then drilled into the ground, up to 35 yards deep. Once the auger has reached the correct depth, the auger is slowly withdrawn and the displaced soil is brought to the surface. The liquid Cement mix (also called grout) is pumped under pressure through the hollow stem auger. As the auger is withdrawn the pressurized grout displaces the soil creating the pile from the bottom of the shaft up. When the auger cast pile is complete, it begins to cure. To increase the pile’s strength, reinforcement rebar cages can be inserted into the liquid cement before it becomes hard.
benefits of auger cast piles
The auger cast pile process is very economical for foundations in soft ground, as other techniques would require casings or support fluids to keep the ground in place. Auger cast piles are faster to install than bored piles and cause less noise and vibration during installation than driven piles, ideal for noise and environmentally-sensitive areas. Auger cast piles are also stronger than pre-fabricated piles because of the increased friction of the soil surrounding the pile caused by in-situ casting.
A common use for auger cast piles is to build secant (interlocking) piled retaining walls. It is important that the pressure and volume of liquid concrete is carefully controlled in order to cast a well-formed pile. This process can be used in ground containing clay, water-bearing sands, gravel, and soft rocks, but the soil conditions must be well-understood before drilling begins.