CFA Continuous-flight auger piles
The continuous Flight Auger Piles or CFA piles are constructed using a hollow-shafted continuous-flight auger with diameter varying from 300mm to 650mm and depths of up to 30 meters. The system works well in most soil formations, also in the presence of shallow water table. The Continuous Flight Auger is rotated and pressed into the ground to reach the design pile depth. The soil gradually fills the space between the auger stem and the hole’s wall, The build-up of soil within the blades of the continuous auger compressing the soil laterally. the soil filling the auger prevents water from the water table to enter the augered hole. The bottom of the hollow auger’s stem is plugged with a disposable (sacrificial) plug, usually made of cast iron, which is made to drop off when pouring of the auger pile begins. Concrete, usually made with small aggregates or coarse sand (to allow insertion of reinforcing bars cages) is pumped into the hollow auger stem thru the swivel mounted on the stem's top, is conveyed to the auger bottom and into the hole created by the continuous flight auger, which is gradually lifted. A pressure gauge mounted on the top swivel monitors the poring of concrete and lifting of the auger, to prevent the creation of joints in the pile’s concrete shaft. In reality the use of an efficient concrete pump will pump the concrete with sufficient pressure to cause the concrete to push the auger upwards, thus preventing water from the water table to enter the excavation and preventing the creation of joints along the pile shaft.. The "Pros" of this system are the rapidity of installation, and low cost of installation. However the system require the installation of the reinforcing bars cages after the pouring of concrete, which limits the length of the reinforcing bar cage that can be installed, to a maximum of 15 to 16 meters, making the system unsuitable for piles longer that 15 to 16 meters to be employed in seismic areas where the reinforcing bars are required to be installed thru the full pile’s length.