How each pile is formed
A bored pile is drilled as an open shaft. Where the ground is unstable, a temporary casing or a support fluid holds the shaft open. The reinforcement cage is lowered in and the concrete is then placed.
A CFA pile is drilled with a continuous hollow-stem auger. The soil on the auger supports the hole. Concrete is pumped through the stem as the auger is withdrawn, and the cage is pushed into the fresh concrete afterwards.
Side-by-side comparison
| Factor | Bored piles | CFA piles |
|---|---|---|
| Support of the hole | Casing or support fluid where needed | Soil on the auger |
| Diameter and depth | Large diameters and great depths | Limited by the rig and auger |
| Rock sockets and hard layers | Yes, with suitable tools | Limited |
| Speed | Slower | Fast |
| Noise and vibration | Low | Low |
| Reinforcement | Full-length heavy cages possible | Cage length limited by insertion |
| Inspection | Shaft and base can be checked | Relies on rig monitoring records |
When bored piles are usually considered
- High loads that need large diameters, long piles or rock sockets.
- Hard layers, boulders or rock that an auger cannot penetrate.
- Piles that need heavy or full-length reinforcement for lateral load or tension.
When CFA piles are usually considered
- Moderate loads in sands, clays or mixed soils without hard obstructions.
- Water-bearing or loose soils where an open shaft would need casing or fluid.
- Sites where speed matters, or where noise and vibration must stay low.
Quality control for each
For a bored pile, the records cover the drilling log, the founding stratum, base cleanliness, the support fluid properties where used, and the concrete volume against depth.
For a CFA pile, the rig instruments record depth, auger rotation, concrete pressure and volume, and the withdrawal rate. These records are the main evidence that the shaft is continuous.
Both types are then checked by integrity tests and by load tests on selected piles.