What Is CFA Piling?
What Is CFA Piling?
Continuous flight auger (CFA) piling, or auger piling is a common, in-situ foundation method, used in the UK since the 1960s. Due to its low level of vibration, this method of piling is particularly suited for soft or water-bearing strata where casings or bentonite would otherwise be necessary. [1]
It involves drilling a contiguous flight auger into the ground. The auger holds the soil surrounding the hole, eliminating the need for temporary casings and support fluids. CFA piling is often known as one of the quietest piling methods available, making it an ideal solution for environmentally sensitive sites.
What Are CFA Piles?
When the CFA piling process is completed, it leaves behind a column of concrete, creating a continuous CFA pile. It is also referred to as auger piles. These piles can be achieved with depths up to 35m and in various dimensions between 300mm and 1200mm based on the ground conditions. [2] This means that CFA piles are effective for low to mid-range loading. They can be constructed as single piles or used in the installation of Contiguous Pile Walls or Secant Pile Walls.
How Are CFA Piles Constructed?
The CFA piling method contains the following general steps:
- A hollow stem continuous flight auger is drilled and rotated into the ground to the specified depth.
- Once the desired depth has been met, the concrete mix is pumped through the hollow stem with controlled pressure and volume whilst the auger is slowly extracted from the ground.
- After the concrete is added, a steel reinforcement cage is inserted through the fluid concrete to enhance its structural capacity.
- After the pile has been constructed, the ground around the top of the pile is cleared and prepared for further construction activities.
- Rigorous testing is carried out to monitor and manage the structural integrity and load capacity of the pile.
How Much Does CFA Piling Cost?
CFA piles cost varies widely from project to project, typically a couple of hundred pounds per linear metre. The cost reflects the high productivity for projects where large numbers of piles are required. Ground conditions, pile depth and diameter, site accessibility, material and labour costs are some factors that can influence CFA pile cost.
What Is the Difference Between CFA Piles and Bored Piles?
CFA and bored piles are both installed using augers and both involve cast in-situ concrete. When installing bored piles, the auger is removed once the channel has been dug, with the reinforcement added prior to the concrete pour. Bored piles are larger in diameter than augered piles, and are often used for larger loads and greater depths. CFA piling is quicker to install, due to the auguring and concreting being part of the same motion.
How Many CFA Piles Can Be Installed per Day?
For private projects installing CFA piles with a diameter of 300 to 450mm and under 20m in length, around 300 to 450m can be installed per day. These rates are achievable on private projects, such as large buildings, where most of the piles are relatively close together, reducing the rig’s movement between piles.
Lower production rates, such as 60 to 150m (200 to 500 ft) per day, should be expected for transportation projects where pile groups supporting bridge bents are spread across a large project area.
Advantages of CFA Piling
The advantages of CFA piling include:
- High production rates mean that piles are commercially attractive
- Minimal noise produced during the CFA piling process
- Virtually vibration free
- Suitable for a wide range of soils and challenging ground conditions
- There is no requirement for a casing when piling, reducing both cost and time
- Fully monitored pile production
- Quick to install
- Economical solution
- Can be constructed in close proximity to other structures and buildings
Sources
- Designing Buildings. (20222). Continuous Flight Auger Piles. Retrieved 6th January 2025, from:
https://www.designingbuildings.co.uk/wiki/Continuous_flight_auger_piles - The Constructor. (n.d). Continuous Flight Auger Piles: Constructions and Applications. Retrieved 6th January 2025, from:
https://theconstructor.org/geotechnical/continuous-flight-auger-piles/9123/
Written by Aarsleff UK
14 January 2025
Aarsleff Ground Engineering is a leading sheet piling supplier and contractor. We specialise in designing and delivering sheet piling solutions across the UK.
Reviewed by Mark Fuller, Piling Director
14 January 2025
Mark Fuller is the Piling Director at Aarsleff Ground Engineering. He has amassed a wealth of experience and knowledge within the specialist piling and ground engineering industry throughout his 20 years of experience in the industry. Mark is directly responsible for the overall driven piling within the business, including technical and operational management of awarded contracts, development of strategic long-term plans and planning of recruitment and resource.
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