What Is Continuous Flight Auger (CFA) Piling?

What Is Continuous Flight Auger (CFA) Piling?

What Is Continuous Flight Auger (CFA) Piling?

Continuous Flight Auger (CFA) piles are a type of bored cast-in-place replacement pile. They are constructed by rotating a hollow stem continuous flight auger into the soil to a designed depth.

Concrete or grout is pumped through the hollow stem, maintaining static head pressure. Compared to bored piles, construction is very quick as temporary casings or support systems are not required.

CFA piles are suitable for most soil types but are particularly suited to collapsible soils with high water tables.

What Is A Continuous Flight Auger Vs Bored Piles?

Continuous Flight Auger (CFA) piles and Rotary Bored Piles are two different types of piling techniques used in construction.

CFA piles are constructed by rotating a hollow stem continuous flight auger into the soil to a designed depth and pumping concrete or grout through the hollow stem, maintaining static head pressure.

This technique requires no additional ground support, such as casing or drilling fluids, because the bore is self-supporting as the auger is rotated into the ground and the concrete supports the bore.

CFA piles are suitable for lighter loads and can be installed quickly, making them an efficient solution for lightly-loaded structures.

In contrast, Rotary Bored Piles are built by rotating an encasing into the ground. Once the required depth is reached, the auger is removed, reinforcement is added and concrete is poured.

This technique requires temporary casing to provide support during the boring and concreting process through unstable ground.

Rotary Bored Piles have a larger diameter than CFA piles and can support greater loads. They can also be used in the ground that is too hard for a CFA pile or to bypass underground impediments.

What Are The Advantages Of A Continuous Flight Auger?

Continuous Flight Auger (CFA) piles are constructed by drilling a continuous flight hollow stem auger into the ground to a specified depth. CFA piles offer several advantages over other types of piling, such as driven piles or Franki Piles.

These advantages include lower noise and vibration levels, higher load capacities on larger-diameter piles, and minimal levels of vibration. Additionally, CFA piles can be installed in very long lengths and are suitable for cohesive soils.

However, there are also some disadvantages to using CFA piles. These include a higher waste of concrete as a percentage than traditional bored piles, the need for strict quality control and thorough supervision during installation, and limitations in length due to lifting forces required to withdraw casing.

What Is The Depth Limit Of Continuous Flight Auger Piles?

The depth limit of continuous flight auger piles is typically up to 29 metres. The diameters of these piles generally range from 450mm to 1200mm.

It is possible to drill piles with a diameter of 40-140cm and a length of 31m. However, for depths greater than 9m (30ft), other piling techniques may be required.

What Are The Continuous Flight Auger Piles Disadvantages?

The disadvantages of continuous flight auger piles include the need for longer piles than driven piles, the removal and disposal of spoil material generated from the pile, drilling through large obstructions, and strict quality control requirements.

The process also involves more construction traffic to accommodate the delivery of steel and concrete and to remove any arising’s, as well as requiring cranes for installation.

Additionally, extensive testing and monitoring are required to ensure quality control and structural integrity of piles such as monitoring during drilling and grouting including auger rotation speed and torque.

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