Sectional Flight Auger (SFA) pile

The "Sectional Flight Auger" or SFA is an auger bored 'replacement' pile with soil extraction and pumping of concrete under pressure. The piles is formed by means of helical screw (auger) with a hollow stem bored into the ground to design depth. Concreting is achieved by pumping fluid concrete through the hollow stem of the auger, delivering concrete to the bottom of the pile bore. Pile arisings are brought to the surface during the drilling and concrete phase.

Construction Sequence

1. Position the SFA rig over proposed pile position.

2. Commence augering into ground to design depth. The auger and soil held within the flights supports the sides of the pile bore during this phase. An expendable cap or flap on the bottom of the lead-flight prevents soil entering the hollow stem auger. 

3. Once design depth it reached, concrete or group is pumped to the base of the pile bore through the SFA system and through the hollow stem of the flights. As the auger is extracted, the pumped concrete maintains stability of the pile bore. No voids are created during this process. 

4. Once concrete is placed and arisings removed from the pile position, the pile cage is lowered into the wet concrete.

Fields of application

  • Able to construct piles into highly stratified layers of soil comprising very resistant layers.
  • As a single pile or as an element of a piled wall (contiguous and secant piled walls)
  • Housing, infrastructure and industrial projects

Environmental impact

  • In vibration sensitive areas: no vibration is induced as the pile is formed by a hydraulic boring technique as opposed to a percussive element.
  • In a noise-sensitive environment: low noise level generated compared to other methods of piling.
  • The concrete used to form the pile has a high energy input to make the cement, but this can be offset by the use of ground blast furnace slag as a cement replacement (which would otherwise be a waste product).
  • Removal of soil from the job site (SFA piling is a 'replacement' technique and creates pile spoil which will require disposal).

Technical Specifications

  • Wide range of diameters: from 250mm up to 900mm
  • Depth: up to 25m
  • Reinforcement is placed after the concreting phase with can limit the pile cage specification (with respect to depth).
  • High lateral load capacities enable contiguous and secant piled walls to be constructed.

Related projects for this technique

Franki Foundations UK

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