What Is Continuous Flight Auger (CFA) Piling?

In this article we examine the various aspects of CFA piling, from what it is, to its key benefits, how it compares to traditional piling methods, and some of the processes involved in its construction.

What is Continuous Flight Auger (CFA) piling?

CFA piling is a construction method used for creating deep foundation piles. It involves drilling into the ground a continuous flight auger, which is a large rotating tool.

The process is suited for wet or granular ground conditions that might otherwise necessitate temporary casings to support the excavation. As the auger drills into the soil, it reaches the required depth, and concrete is pumped through the hollow stem of the auger under pressure.

This method allows for the simultaneous removal of soil and filling with concrete, streamlining the piling process. After reaching the desired depth and while concrete is still being pumped, the auger is withdrawn, leaving a reinforced concrete pile in place. A reinforcement cage is added immediately after drilling, ensuring the pile's integrity before the concrete sets.

CFA piling is noted for its efficiency and effectiveness in various ground conditions.

Key benefits of using CFA piling in construction

CFA piling is primarily valued for its speed and economy, making it a highly efficient technique for construction projects. It is particularly advantageous in wet or granular ground conditions where other methods might require temporary casings to stabilise the soil.

This method reduces the need for such casings, streamlining the construction process and reducing costs associated with additional materials and time. This not only ensures a smoother and faster construction process but also significantly reduces the risk of soil collapse during the drilling, making it a safe and reliable method in challenging environments.

Moreover, the ability to reach significant depths of up to 32 metres with various auger sizes enhances its versatility for different project scales and soil types.

Environmental benefits of CFA piling

We observe several environmental benefits of the CFA piling method as below, making it a favourable choice for sustainable construction projects.

• Reduced noise and vibration: CFA piling is notably quieter compared to traditional piling methods. It also produces less vibration, which is crucial in urban or sensitive environments where noise and ground disturbance can be problematic.
• Minimal waste production: The method is designed to minimise waste during the drilling and concreting processes. By managing materials efficiently and reducing excess, CFA piling contributes to lower environmental impact.
• Faster construction: Efficiency comes from the continuous nature of its process, where drilling and concreting are done simultaneously, minimising the time required for setting up and completing each pile. As a result, CFA reduces the overall time construction equipment is operational, which in turn decreases the carbon footprint associated with prolonged machinery use.

These environmental advantages make CFA piling not only an efficient but also an environmentally friendly choice for modern construction, aligning with growing ecological concerns and regulations in the industry.

Comparing CFA piling to conventional piling methods

In addition to the above environmental benefits, we also observe that CFA piling has the below features and benefits compared to traditional methods:

• Installation of reinforcement: In conventional bored piling, the reinforcement cage is typically placed before the concreting. In contrast, CFA piling allows for the reinforcement cage to be inserted after the concreting, which can improve the structural integrity and reduce the risk of displacement during the piling process.
• Soil displacement: CFA piling involves augering into the ground and filling the void with concrete as the auger is withdrawn, which minimises soil displacement. In contrast, certain traditional methods such as driven piling forces the pile into the soil, displacing more ground material, which can be an issue in certain soil types or near existing structures.
• Versatility: CFA piling can be adapted to a variety of soil conditions and is particularly beneficial where there are concerns about ground stability during construction.

How the reinforcement cage is installed in CFA piling

The CFA piling process involves a unique approach to installing the reinforcement cage, which differs from traditional methods:

• Post-concreting installation: Unlike open bored piles where the reinforcement cage is typically installed before concreting, in the CFA method, the cage is inserted after the concrete is poured. This method ensures that the pile maintains its integrity and alignment during the initial drilling and concreting stages.
• Use of hydraulic vibrating hammer: To insert the reinforcement cage into the freshly poured concrete pile, a hydraulic vibrating hammer is used. This tool helps lower the cage accurately and efficiently to the predetermined depth within the pile.
• Precision and depth control: The process is carefully controlled to ensure that the cage reaches the exact required depth, which is critical for the structural performance of the pile.

This method of installing the reinforcement cage post-concreting enhances the overall quality and durability of the pile, making it a robust foundation for various structures.

The importance of concrete mix design in CFA piling

We want to note that special attention to concrete mix design is critical in CFA piling. This importance stems from the need to maintain the concrete's workability throughout the drilling and piling process.

A well-designed concrete mix ensures that it remains fluid enough to be pumped under pressure and to accommodate the insertion of a reinforcement cage to the required depth efficiently. Proper mix design is crucial for achieving the desired strength and integrity of the pile, as it must support structural loads once it sets, especially in challenging soil conditions.

Electronic monitoring during the CFA piling process

Electronic monitoring is a crucial component in CFA piling, with data visible in the operator cabin. It ensures the drilling and concreting processes are conducted efficiently and with high precision. The key improvements brought by electronic monitoring include:

• Real-time data: Operators receive real-time data on various crucial aspects like pile inclinations, drilling pressure, and concrete pressure. This visibility allows for immediate adjustments to maintain the quality and accuracy of the piling.
• Quality control: The system helps monitor the entire process, which is essential for maintaining the structural integrity of the pile. It ensures that the parameters stay within safe and effective ranges, preventing potential issues during construction.
• Operational efficiency: By having data directly visible in the operator cabin, the process becomes more streamlined, reducing downtime and errors, leading to faster and more reliable piling operations.

Electronic monitoring, therefore, enhances the overall effectiveness and safety of the CFA piling process, making it a preferred method for various construction projects.

Conclusion

CFA drilling is recognised as a fast, economical, and environmentally friendly method for piling construction, suitable for various structures. At the start of a project, we highly recommend you consult with an experienced team of construction experts and geotechnical engineers to ensure the CFA pile foundation meets the needs of the structure requirements.