Continuous Flight Auger (CFA) or augercast piles System

CFA process

Since their introduction some fifty years ago in North America, continuous flight auger (CFA) piles, also known as augercast piles, have become increasingly popular, as they can be considerably cheaper than alternative pile types. With proper planning and design, efficient equipment and experienced personnel, high production rates can be achieved.

The CFA equipment comprisesa base machine with a fixed,swinging or hanging lead, an auger drive unit (hydraulic or mechanic) and a continuous flight auger equipped with auger cutting heads. For more info about the installation process, placing of reinforcement, etc, please, clic here:

– Installation process
– Casting of pile base and shaft
– Placing of reinforcement
– Advantages
– Limitations
– Soil decompression during augering

Source: Pile info

Drilled piles: Augercast pile CFA

An augercast pile, often known as a CFA pile, is formed by drilling into the ground with a hollow stemmed continuous flight auger to the required depth or degree of resistance. No casing is required. A cement grout mix is then pumped down the stem of the auger. While the cement grout is pumped, the auger is slowly withdrawn, conveying the soil upward along the flights. A shaft of fluid cement grout is formed to ground level. Reinforcement can be installed. Recent innovations in addition to stringent quality control allows reinforcing cages to be placed up to the full length of a pile when required. A typical reinforcing cage will consist of 4 to 8 bars from #5 to #8 bars typically 1/3 the length of the pile with longitudinal circular ties spaced along the length of the cage. Where tension loads are present it is typical to see a single full length bar placed at the center of each pile.

Augercast piles cause minimal disturbance, and are often used for noise and environmentally sensitive sites. Augercast piles are not generally suited for use in contaminated soils, due to expensive waste disposal costs. In cases such as these however a displacement pile may provide the cost efficiency of an augercast pile and minimal environmental impact. In ground containing obstructions or cobbles and boulders, augercast piles are less suitable as refusal above the design pile tip elevation may be encountered. In certain cases drill motors that produce more torque and horsepower may be able to mitigate these events.

Auger Cast Piles can be used :

• As friction piles – the superstructure load is transferred to the soil through friction between the pile surface and the soil.

• As an end-bearing pile – the superstructure load is transferred through the pile tip into a hard stratum of soil or rock.

• As an anchor pile – hydrostatic or other uplift forces are resisted though a full length tendon embedded in the grout column.

• As a vertical component of a continuous auger cast curtain wall in temporary or permanent shoring systems and below grade walls.

• As a temporary or permanent diagonal tie-back in auger cast curtain walls, beam and lagging walls, and sheet pile walls.

Source: Wikipedia and clic here.