Overcoming Constructability Challenges for Drilled Displacement Pile Installation in Difficult Geology-Paper

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The project involved deep foundations for an office building and parking garage in Queens, New York, where 15–20 ft of uncontrolled urban fill overlay soft organic deposits and glacial soils. Drilled displacement piles (DDPs) were selected over driven piles and auger-cast piles to reduce noise, vibration, and spoils while providing the required capacity with shorter piles.<br /><br />Installation revealed two major challenges: abundant buried debris—including boulders, wood, and steel—made drilling through the fill difficult, while dense glacial soils caused refusal above planned pile-tip elevations. These conditions threatened both constructability and schedule.<br /><br />To address the obstructions, the contractor used rotary-percussion duplex predrilling through the fill before installing every DDP. This broke up and cleared debris, preventing further pile relocations, though it required careful coordination of multiple rigs, hoses, and material deliveries on the increasingly congested site.<br /><br />To assess early refusal in the glacial soils, instrumented test piles were loaded to failure. Strain-gauge data and load-test results allowed the contractor and owner’s engineer to evaluate side resistance and end bearing, then establish acceptable minimum pile-tip elevations for different design loads. Field crews could apply these criteria as piles were installed, avoiding delays and the expense of adding piles.<br /><br />The project demonstrates the value of detailed, instrumented load testing, experienced local contractors, in-house engineering, and close coordination among project participants when subsurface conditions differ from expectations. The authors recommend testing piles to failure when feasible, as the resulting data can support timely, site-specific design adjustments. With aggressive predrilling and responsive engineering, the work was completed within a week of the anticipated schedule.

Keywords

deep foundations

drilled displacement piles

Queens New York

underground debris

glacial soils

rotary-percussion predrilling

pile refusal

instrumented load testing

pile-tip elevations

construction scheduling