Continuous Flight Auger (CFA) Piles
Continuous Flight Auger (CFA) piles are formed by drilling a continuous hollow-stem auger to depth and pumping concrete through the stem as the auger is withdrawn. The reinforcement cage is then pushed into the fresh concrete. The soil is supported by the auger throughout, so no casing or support fluid is needed.
Suitable ground conditions and applications
Can be considered where…
- Medium structural loads in a wide range of soils, including water-bearing sands.
- Projects that need high production rates.
- Work next to existing buildings, where low noise and vibration are needed.
Limitations
- Reinforcement cage length is limited because it is pushed into wet concrete.
- Diameter and depth are limited by the rig.
- Hard layers and boulders make drilling difficult.
- Quality depends on careful control of concrete pressure and extraction rate.
Suitability is confirmed from the site investigation and the performance requirement.
How it works
The auger is screwed into the ground to the design depth, with the soil held on its flights.
Concrete is pumped through the hollow stem while the auger is withdrawn at a controlled rate, keeping the hole filled. The cage is then pushed into the fresh concrete.
Design inputs
- Site investigation and groundwater.
- Loads and pile capacity design.
- Pile diameter and length.
- Concrete mix suitable for pumping.
- Reinforcement design.
Trial and calibration
- Preliminary test piles, where specified.
- Rig parameters confirmed on the first piles.
Execution controls
- Rig instrumentation: depth, rotation, extraction rate, concrete pressure and volume.
- Avoiding over-rotation, which loosens the soil.
- Concrete volume against theoretical volume.
- Cage installation level.
- Concrete samples and pile records.
Verification and acceptance
Design intent, production control and acceptance verification are kept separate, so it is always clear what was required, what was done and what was proven.
What is required
Design loads and settlement criteria agreed with the consultant.
What was done
Rig records for every pile.
What was proven
Static or dynamic load tests, integrity tests and concrete strength tests.
Deliverables
- Method statement and risk assessment
- Pile layout drawings
- Rig records for every pile
- Concrete test results
- Load and integrity test reports
- As-built records
Common questions
What is a CFA pile?
A pile formed by drilling a continuous hollow-stem auger to depth and pumping concrete through the stem as the auger is withdrawn. The reinforcement cage is then pushed into the fresh concrete.
What is the difference between CFA and bored piles?
CFA piles are faster and quieter and need no casing or support fluid. Bored piles reach larger diameters and depths and allow full-length cages and rock sockets.
How is CFA pile quality controlled?
The rig records depth, rotation, extraction rate, and concrete pressure and volume for every pile.
Discuss whether Continuous Flight Auger Piles (CFA) fits your ground conditions.
Share the site location, the investigation report and the performance requirement.