Services · Deep foundations · CFA piles
CFA Piles: Continuous Flight Auger Piling
CFA piles are cast-in-place piles: we drill with a continuous auger and pump concrete through it as we withdraw it. The bore is never open, so the method moves fast in wet and loose ground.
Method
Continuous auger, pumped concrete
Suitable ground
Clay, silt, sand; wet ground
Reinforcement
Placed after the concrete
Vibration
Low; no hammering or driving
Standard
EN 1536
Region
Türkiye and Central Asia
What are CFA piles?
CFA stands for continuous flight auger. The auger is a hollow stem as long as the pile, with a continuous spiral flight around it. In the United States the same pile is also called an auger cast-in-place (ACIP) pile.
First we screw the auger down to the pile toe in a single pass. Then, while we slowly withdraw it, the pump pushes concrete down through the hollow stem. The concrete leaves at the auger tip and fills the space from the base upwards. Finally, we push the reinforcement cage into the fresh concrete.
The key difference from bored piles is the order of work. In a bored pile the bore stays open, the cage goes in and the concrete comes last. With CFA piles, by contrast, the bore is never open while the auger is in the ground.
When do CFA piles suit a site?
- The ground is clay, silt or sand and there is no rock along the pile
- Groundwater is high and an open bore could collapse
- Many piles of similar length need finishing in a short time
- Neighbouring buildings call for low vibration and noise
- There is no room on site for a bentonite plant or casing stacks
On the other hand, sound rock, boulders or very dense gravel stall the auger. On such sites we recommend bored piles instead.
CFA piles or bored piles?
Both methods produce cast-in-place reinforced concrete piles. However, the order of work, the ground they suit and the quality records differ. We make the choice with you after reading the site investigation.
| Topic | CFA pile | Bored pile |
|---|---|---|
| Bore support | Soil on the auger flights holds the bore | Casing or bentonite |
| Order of work | Drilling, concrete, then cage | Drilling, cage, then concrete |
| Rock and boulders | Not suitable | Drilled with a rock core barrel |
| Groundwater | No problem; the bore always stays full | Handled with casing or bentonite |
| Speed | Usually faster for similar piles | Slower, depending on ground and method |
| Cage length | Pushed into fresh concrete; length is limited | A full-length cage goes in easily |
| Diameter and length | Limited by auger length and rig power | Reaches very large diameters and lengths |
| Quality records | Rig log: depth, pressure, concrete volume | Drilling log, base check, tremie |
In short, CFA piles bring speed and a clean site when the ground suits them. When there is rock, a heavy load or a long cage, bored piles are the safer choice. The two can also work side by side on the same project.
Where do we use CFA piles?
We mostly use CFA piles for building foundations. In suitable ground they also work well in pile walls.
Building foundations
Carry loads through soft, wet ground to a firm layer. Where needed, they work together with a raft.
Industrial and energy plants
Factories, warehouses and power plants need many piles, and CFA finishes them quickly.
Infrastructure
Foundations for retaining walls, noise barriers and bridge approach structures.
Contiguous and secant walls
In suitable ground, a row of CFA piles forms a wall that holds an excavation.
In the city, CFA piling has one more advantage. The spoil comes up neatly on the auger and there is no bentonite slurry. As a result, the site stays cleaner.
How do we build CFA piles?
Each pile takes five steps. The most critical point is the balance between the auger withdrawal rate and the concrete flow.
- Setting out: We survey and mark the pile centres from the approved setting-out plan.
- Drilling: We centre the auger on the mark and screw it down to design depth. The bore never empties during this step.
- Concrete: The pump pushes concrete down the stem. Once pressure builds, we withdraw the auger slowly while it turns.
- Cage: We clear the spoil from the pile head and push the cage straight into the fresh concrete. For long cages we use a vibrator.
- Pile head: We break off the weak concrete at the top down to cut-off level and prepare the pile for the cap.
The most common mistake we see on site: pulling the auger faster than the concrete pressure allows. The pile then necks or forms a void. That is why we match the withdrawal rate to the concrete pressure and volume.
CFA pile diameters and concrete volume
Load, ground and rig together set the diameter and length. On most projects CFA piles range from 40 to 100 cm in diameter. The mast and auger length of the rig limit the pile length. So on jobs that need long piles, we settle the rig choice before work starts.
| Diameter | 1 m of pile, theoretical concrete | 15 m pile, theoretical concrete |
|---|---|---|
| Ø40 cm | 0.126 m³ | 1.88 m³ |
| Ø50 cm | 0.196 m³ | 2.95 m³ |
| Ø60 cm | 0.283 m³ | 4.24 m³ |
| Ø65 cm | 0.332 m³ | 4.98 m³ |
| Ø80 cm | 0.503 m³ | 7.54 m³ |
| Ø100 cm | 0.785 m³ | 11.78 m³ |
We worked out the volumes with V = π × D² / 4 × L. On site, concrete use comes out a little above the theoretical volume. This is because pumped concrete also fills voids in loose layers.
CFA pile quantity and concrete calculator
You can work out the total drilled length and theoretical concrete volume for your project below. The result is for an early budget; the design sets the final quantities.
Optional: rough budget with your own unit rates
Rough budget: —
Theoretical geometric volume. Concrete use on site is usually slightly higher. Reinforcement, mobilisation and taxes are not included.
Quality control and testing of CFA piles
Nobody can see the concrete inside the ground. For this reason, the rig’s monitoring system shows most of the quality of CFA piles. For example, the log gives depth, concrete pressure and concrete volume along the full length of every pile.
| Check | What it shows | What it does not show |
|---|---|---|
| Rig log (pile profile) | Concrete pressure and volume with depth; possible necking | Where the cage sits |
| PIT (integrity test) | Changes in section and signs of defects along the pile | How many tonnes the pile can carry |
| Static load test | Settlement under load and bearing capacity | The quality of the other piles on its own |
The client usually asks for PIT testing, and most specifications include it. When asked, our testing partner carries out the test. We also check the concrete and the steel together once we cut down the pile heads.
Our experience with CFA piles
Our founder, Abdullah Çetintaş, also worked on CFA piling in earlier roles. For example, in 2021 that work included the piles for the Aksa Enerji 240 MW combined-cycle gas power plant in Uzbekistan. See our founder’s earlier projects with photos.
We look at CFA and bored piles with the same engineering eye. First we read the site investigation, then we propose the method that suits the site best. You can find quantities and site photos on our bored piles page and in our projects.
What does the price of CFA piles depend on?
We price CFA piles per metre. However, no single rate fits every job. That is why we do not publish rates and quote from the quantities instead.
- Diameter, length and total quantity
- Ground: dense layers and coarse gravel slow the drilling
- Cage length and weight
- Steady delivery of concrete and the pump (supplied by the client)
- Site access, working hours and the working platform
- Mobilisation distance and the tests you need
What to send for a quote
- Site investigation report and borehole logs
- Pile layout plan and a list of diameters, lengths and numbers
- Reinforcement details and concrete class (structural design)
- Site address, access width and target programme
If you have no site investigation yet, we can arrange one with our drilling partner. We also tell you at quote stage whether the method suits your site. If it does not, we propose bored piles or another solution.
Frequently asked questions about CFA piles
We have grouped the questions we receive by who asks them. If yours is not here, call us or write through the quote form.
Buying and cost
How much do CFA piles cost per metre?
We do not publish a fixed rate, because the price depends on the ground, the diameter and the quantity. Send the borehole logs and the pile list and we will quote from the quantities. Our quote shows drilling, cage placing and mobilisation on separate lines.
Are CFA piles cheaper than bored piles?
When the ground suits them and there are many piles, CFA piles often come out cheaper. Drilling and concreting happen in one pass, and there is no need for casing or bentonite. With rock or large diameters, however, bored piles are the better choice.
Who supplies the concrete and the steel?
On most jobs the client buys the concrete and the reinforcing steel. We assemble the cages on site with our partner. This way the cages are ready to push in as soon as the concrete is in place.
Is the concrete pump included in the quote?
No, the client supplies the concrete pump. Still, the pump is part of the process, because the concrete travels down the auger stem. So we plan pump arrival and pour times together with the client and the batching plant.
Why do quotes from different firms differ so much?
Usually the scope differs. For example, one quote may leave out cage placing, the pump or testing. Line up the items first, then compare the unit rates.
Project managers and contractors
Are CFA piles faster than bored piles?
In suitable ground, usually yes. Drilling and concreting happen in one pass, and nobody waits for casing or bentonite. Even so, the ground, concrete supply and cage preparation set the daily output.
How many CFA piles can one rig install per day?
A single number would mislead you. Pile length, ground, rig power and timely concrete all affect the pace directly. So we build the programme from the borehole logs and site conditions.
Can you install CFA piles where there is groundwater?
Yes, and they have an advantage there. While the auger stays in the ground, the bore never opens and water cannot flow in. Also, the concrete arrives from the base under pressure and pushes the water up.
Can you install CFA piles in rock?
Usually not. A continuous auger cannot advance through sound rock and boulders, or it slows down a great deal. On such sites we recommend bored piles, which use a rock core barrel.
Do you work outside Türkiye?
Yes. We work in every province of Türkiye and have also worked in Uzbekistan. For distant sites we fix the rig and crew plan before work starts.
Site engineers
What do we need to prepare on site for the rig?
The rig needs a level, firm working platform that can carry its track loads. Also mark out positions for the pump, truck mixers and cage stacks in advance. We plan the platform with you for the rig and the ground.
What kind of concrete do CFA piles need?
The concrete has to be pumpable and flowable, with a small maximum aggregate size. It passes through a narrow stem, and then a cage goes into it. The design sets the concrete class; we agree the mix with the batching plant in advance.
How do you push the cage into fresh concrete?
As soon as the pour ends, we push the cage in vertically with the crane or the rig. For long cages we also use a vibrator. Cover spacers keep the steel in the middle of the concrete.
What happens if the concrete supply stops mid-pour?
Each pile needs a continuous supply of concrete; otherwise a weak zone can form. That is why we plan for truck mixers to arrive one after another. If the delay grows long, we may need to redrill that pile.
Supervising engineers and inspectors
What records do you keep for CFA piles?
The rig’s monitoring system logs depth, concrete pressure and volume for each pile. We also record the pile number, length, pour time and concrete quantity. These records form the basis for payment and for reading test results.
What does it mean if a pile took more concrete than expected?
A small overrun is normal, because pumped concrete fills voids in the ground. A clear overrun, however, can point to a loose layer or a collapse. In that case we review the log and the cause together.
What should we do if a pile took less concrete than expected?
This is a more serious warning, because the pile may have a neck or a void. First we review the rig log. If needed, we arrange a test and decide with the designer.
Structural and geotechnical designers
Which standard do you follow for CFA piles?
For construction we follow EN 1536, which also covers continuous flight auger piles; Türkiye adopts it as TS EN 1536. Designers use TBDY 2018 and Eurocode 7. On public works we also follow the client’s technical specification.
Can you place full-length reinforcement?
It is possible, but pushing a cage into fresh concrete gets harder as the cage gets longer. So the cage should be as long as the load and seismic demand require, and no longer. If the design needs a full-length cage, we review buildability with you at design stage.
Can you build a retaining wall with CFA piles?
In suitable ground, yes; CFA piles can form a contiguous or secant wall. In deep excavations, however, cage length and anchor connections become decisive. For deep shoring we therefore often recommend bored piles.
Owners and neighbours
Are CFA piles right for my building?
The site investigation and the structural design decide this. CFA piles are a good option in clay, silt and sand, especially with high groundwater. We can arrange the site investigation with our drilling partner.
Is CFA piling noisy?
It is much quieter than pile driving. Most of the noise comes from the rig engine and the concrete pump. In the city, therefore, we plan working hours around local rules and the neighbours.
Academics and students
Why does the cage go in after the concrete?
The auger keeps the bore closed until the concrete fills it, so the bore is never empty. As a result, there is no open hole to lower a cage into. The cage goes into the concrete while it is still fluid.
How do CFA piles differ from displacement auger piles?
In CFA piling the auger carries the soil up and out of the bore. In a displacement pile, a special drilling head pushes the soil sideways and compacts it. Because of this, displacement piles produce very little spoil.
What affects CFA pile quality the most?
The biggest factor is the balance between auger withdrawal and concrete flow. For example, if the auger rises too fast, the concrete cannot fill the space and the pile necks. That is why the pressure and volume data in the rig log are so valuable.
Sources
Request a quote for your CFA piles
Send us your site investigation and pile list. We will confirm whether the method suits your site and prepare a quantity-based quote.