CONTINUOUS FLIGHT AUGER PILE (CFA)

Continuous Flight Auger Pile (CFA)



Continuous Flight Auger Pile (CFA)

Continuous Flight Auger Pile (CFA) was developed in the United States in the 1960's and originally licensed in the UK as a grout injected system for piles up to 450 mm by a company called Prepact Inc. At that time a small Yorkshire company had this franchise and although It was used nationally it did not come into the main stream of piling till the mid seventies with the introduction of pumped concrete replacing grout in almost all cases.

This method generally requires piles to be bored in soft to hard clays or well weathered, very weak rock or well graded granular soils overlying a suitable founding strata. The system has undergone many changes since its inception, most important of these is the use of concrete in place of the grout and better purpose built equipment. Ironically although the grouted system is still in wide use in the U.S. they are now re-adopting the method with European equipment using concrete and this is through a largely British influence over there. (Vipulanandan and McClelland 2007 15-19)

CFA piles are formed by drilling a continuous flight auger into the ground. The sides of the hole are supported at all times by the soil-filled auger, eliminating the need for temporary casing or bentonite slurry. Upon reaching the required depth, sand-cement grout or concrete is pumped down the hollow stem as the auger is steadily withdrawn. Reinforcement is placed immediately after withdrawal of the auger.

The bearing capacity and settlement behavior of CFA piles is to a large extent influenced by the equipment used and the experience of the operator. The significance of these two aspects is often underestimate or overlooked at the design stage, but plays an important role for the performance of CFA piles. (Vipulanandan and Kaulgud 2005 290-308)

Because the ground is supported throughout the piling process, initially by the auger boring the pile out and then by the concrete injected through the hollow central stem as it is extracted there is no need to use casings or drilling fluids to support the excavation. This makes it suitable for use in deep unstable and water bearing strata and this combined with the negligible level of vibration and the low level of noise has contributed to the growth of this piling method to be one of the most common in use in the ...