Alternative Piling Methods - Chances for Technical and Economical Solutions-Paper

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The paper examines Continuous Flight Auger (CFA), Cased Continuous Flight Auger (CCFA), and Full Displacement Piles (FDP) as faster alternatives to conventional Kelly drilling. These “single-pass” methods drill to final depth in one operation, then pump concrete through the hollow tool as it is withdrawn.<br /><br />CFA is suited to cohesive and sufficiently cohesive granular soils, generally without boulders. It is mainly used for foundations. CCFA drills an auger and casing simultaneously and is especially useful for secant or tangent pile walls; the casing helps maintain pile verticality. FDP displaces rather than removes soil, making it suitable for foundations and rigid inclusions, but not pile walls. Soil displacement can densify surrounding ground and increase pile capacity, while producing very little spoil.<br /><br />All three methods can reduce installation time and costs, but their use depends on ground conditions, equipment capacity, pile dimensions, and site constraints. Typical maximum depths are about 30 m for CFA, 25–30 m for CCFA, and 35 m for FDP, though these vary. Successful work also requires appropriate concrete and reinforcement design, sufficient rig torque and extraction force, reliable concrete supply, and trained, coordinated crews. Electronic drilling and concreting controls can help prevent poor installation practices, concrete overuse, and ground instability.<br /><br />Project examples demonstrate the potential benefits. CFA installation at a Polish refinery exceeded 200 linear metres per day. In Padua, an FDP alternative reduced estimated construction time from 74 to 47 days and greatly reduced spoil and eliminated micropiles. CCFA projects in the UK and Italy achieved high production rates, including a peak of 14 piles per day.<br /><br />The paper concludes that single-pass methods should be considered where soil and site conditions permit. Their benefits depend on proper method selection, preparation, monitoring, and crew training.

Keywords

Continuous Flight Auger

Cased Continuous Flight Auger

Full Displacement Piles

single-pass methods

concrete pumping

soil displacement

foundation piling

secant pile walls

pile installation

ground conditions