This method combines all major piling operations in a single process and hence it provides for a highly productive, cost-effective solution that facilitates fast, noise and vibration free piling installation. CFA is implemented in soft to medium strength rock and in sand, gravel or slit land with ample adhesion and end-bearing strength.
A continuous flight auger with a hollow stem at its center is utilized for the drilling process. The end of the hollow stem is sealed with an expendable cap to prevent contamination. During the drilling process, drilled matter rests at the top of the auger flights maintaining positive pressure at the shaft walls and thus providing it with lateral support and stability. After reaching the desired drilling depth, concrete is pumped at a controlled rate through the hollow stem blowing off the expendable cap.
The auger is simultaneously withdrawn at a rate synchronized with the concrete pumping process such that the pumped concrete promptly occupies the displaced volume exerting a positive pressure, which assists in the extraction process whilst maintaining lateral support to the surrounding soils. The steel reinforcing cage (if required), is then immersed into the wet concrete.
Typical CFA applications are for pile depth of 14m and 600mm diameter. However, larger pile dimensions maybe achieved. The size limitations on CFA piles is related to machine capabilities and also to the fact that the reinforcement must be placed into the fluid concrete and verticality of the piles can be difficult to maintain for long piles.