What is a cast-in-situ pile?
A cast-in-situ pile, also called a cast-in-place pile, is a foundation pile formed in the ground on site: a void is created, reinforcement is usually placed and concrete is poured. The alternative is a precast pile, made in a factory and then driven into the ground in one piece. In Dutch this type is called a stortpaal.
There are several ways to form the void. For a bored pile, soil is drilled out and removed, and the reinforcement cage goes in before the concrete. For a CFA (continuous flight auger) pile, a hollow-stem auger supports the bore while it is drilled, concrete is pumped through the stem as the auger is withdrawn, and the cage is pushed into the wet concrete. Driven cast-in-place piles displace the soil instead: a steel casing is driven, filled with concrete and withdrawn.
| Bored pile | Soil is drilled out and removed. The reinforcement cage goes in before the concrete. |
|---|---|
| CFA (continuous flight auger) pile | A hollow-stem auger supports the bore while drilling. Concrete is pumped through the stem as the auger is withdrawn, then the cage is pushed into the wet concrete. |
| Driven cast-in-place pile | Displaces the soil instead of removing it. A steel casing is driven, filled with concrete and withdrawn. |
One advantage is that the length is decided on site, so there is no cropping of overlong precast piles or extending of short ones. Bored and CFA methods are also low in noise and vibration, which suits built-up areas. The drawback is that, unlike a precast pile, the shaft cannot be inspected before installation, so quality depends heavily on workmanship.
In practice
- Leave the choice of pile to the structural engineer and the site investigation. The right system depends on soil, loads and surroundings.
- Think about the neighbours. Near sensitive buildings, bored or CFA piles are often chosen to keep vibration down.
- Allow for spoil. Bored and CFA piles bring soil to the surface that has to be removed, which costs more if it is contaminated.
- Test the piles. Acoustic integrity testing after casting shows whether the shaft is continuous.
- Keep pile records. Depth and concrete volume per pile reveal a lot about how installation went.
Common mistake: assuming every cast-in-situ pile is vibration-free. With driven cast-in-place piles, the casing is still driven.
Related terms
- Pile foundation
- Driven pile
- Screw displacement pile
- Grouted pile
- Acoustic pile testing
- Cast-in-situ construction
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