Eglinton Crosstown, a New Step in Toronto's Subway System-Paper

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The paper examines three single-pass piling methods—Continuous Flight Auger (CFA), Cased CFA (CCFA), and Full Displacement Piles (FDP)—as faster alternatives to conventional Kelly drilling. In each method, the drilling tool advances to full depth in one pass, then concrete is pumped through its hollow stem as the tool is withdrawn.<br /><br />CFA is mainly used for foundations in suitable cohesive or granular soils. CCFA combines an auger with a casing and is particularly effective for secant and tangent pile walls; the casing helps maintain pile verticality. FDP displaces rather than removes soil, making it useful for foundations and rigid inclusions. Soil displacement can densify surrounding ground, increase pile capacity, and greatly reduce spoil.<br /><br />The methods can reduce installation time and cost, but their suitability depends on ground conditions, pile dimensions, equipment capacity, and site constraints. Boulder-containing or unsuitable soils can prevent their use, and each method has practical depth and diameter limits. Successful installation also requires adequate rig torque and extraction force, suitable concrete and reinforcement, reliable concrete supply, experienced crews, and careful process monitoring. Electronic drilling and concreting controls can help prevent over-drilling, excess spoil, concrete overuse, and blockages.<br /><br />Project examples demonstrate the potential: CFA work achieved more than 200 linear metres of piles per day; an FDP alternative reduced estimated construction time from 74 to 47 days and substantially cut spoil; and CCFA projects recorded high daily production rates.<br /><br />The paper concludes that single-pass methods should be considered where site and soil conditions allow, especially when schedule savings are important. Their benefits depend on proper design, preparation, training, and coordination.

Keywords

Continuous Flight Auger

Cased CFA

Full Displacement Piles

single-pass piling

Kelly drilling

soil displacement

pile foundations

secant pile walls

construction efficiency

pile installation