Continuous Flight Augering (CFA), also known as auger cast piling, is a technique used to create a concrete piled foundation solution.
The CFA process is virtually vibration free and one of the quietest forms of piling, making it ideal for environmentally sensitive areas. The method enables piles to be formed in water-bearing strata, without the need for casing or bentonite. It is suitable for constructing piles in most strata, including; gravels, sands, silts, clays and soft rocks and in mixtures of strata. CFA is the only acceptable piling method approved by the Environment Agency that does not allow cross contamination of underlying acquifers by contaminated upper soils.
CFA piles are formed by drilling to the required depth using a hollow stem continuous flight auger. After reaching the designed depth, a high slump concrete is then pumped through the hollow stem. While the concrete is being pumped, the auger is withdrawn at a controlled rate, removing the soil and forming a shaft of fluid concrete extending to ground level. A reinforcing cage is then inserted into the fluid concrete. Reinforcing cages with lengths up to 12 metres are common; greater lengths can be installed with the assistance of cage vibrators.
Temporary and permanent bored pile walls can be constructed using the CFA technique. They can be designed to function as a simple or a propped cantilever and can also support considerable vertical loadings. The three main types of bored pile walls which are commonly constructed are: Contiguous, Interlocking and Secant. The selection of a particular type of bored pile will depend on the soil and loading conditions.
State-of-the-art Monitoring Technology
To maintain the highest level of efficiency, our rigs are equipped with sophisticated computerised technology designed to monitor, control and record the CFA pile installation process. During the drilling phase, the depth of the auger, speed of rotation and penetration rates are displayed. This information is used to compare with specific target values which enables the integrity of each pile to be monitored as well as managing the overall programme performance.
The CFA technique is one of the quietest piling solutions available and is virtually vibration free, making it ideal for working in close proximity to existing buildings in both residential and environmentally sensitive areas.
Key Benefits & Advantages of Continuous Flight Auger (CFA) Piling
- Construction of piles without significant vibration or excessive noise being produced
- Speed of installation compared to conventional bored piling solutions, therefore offering economic and commercial benefits
- This type of pile does not require temporary casing in unstable soils
- High load-bearing, shear and moment capacities
- Piling rigs can be adapted to operate in conditions with low headroom and confined space
- Fully instrumented piling rigs with computerised equipment, guaranteeing tight quality control.