What Is CFA Piling?

When the installation 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 soil conditions. [2] This means that CFA piles are effective for low to mid-range loading.

CFA piles are constructed using the following general steps:

1. A hollow stem continuous flight auger is drilled and rotated into the ground to the required depth.
2. Once the desired depth has been met, the wet concrete mix is pumped through the hollow stem with static head pressure
3. The spoil is removed by an excavator as the auger is slowly extracted from the ground.
4. After the concrete is added and extends to ground level, a steel reinforcement cage is inserted through the freshly placed concrete to enhance its structural capacity. Cages are usually inserted by an excavator or a cage-vibrator for longer cages.
5. After the pile has been constructed, the ground around the top of the pile is cleared and prepared for further construction activities.
6. Rigorous testing is carried out to monitor and manage the structural integrity and load capacity of the pile.

Throughout the pile construction process, CFA rigs fitted with state-of-the-art instrumentation provide rig operators with feedback based on the key parameters such as auger depth, casing depth, drill pressure/auger torque, and penetration speed during the drilling phase. This enables piling contractors with continuous operation monitoring and real-time quality control.

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.

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.