High-Capacity Pressure-Grouted Helical Displacement Piles In Urban Redevelopment-PPT Presentation

PPT Presentation

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The presentation describes the use of pressure-grouted helical displacement piles for a seven-story redevelopment in South Brooklyn. The site’s soft, liquefiable soils made shallow foundations unsuitable. The original design called for 200 micropiles, but the contractor proposed grouted helical piles as a lower-cost alternative.<br /><br />The alternative piles used 7.625-inch steel shafts with a helix near the toe and pressure grouting to form an approximately 18-inch grout column in the bearing layer. They were designed to reach roughly 105–125 feet. Three instrumented test piles were installed; two underwent compression testing, including tests to 480 and 760 kips and an overload test that reached 930 kips before plunging. Measurements indicated substantial shaft resistance in the lower sand and supported the design’s capacity assumptions. Analysis also showed the neutral plane below the highly compressible soils, helping address long-term drag loads.<br /><br />Because this pile type was not pre-approved under the New York City Building Code, the project required a code variance and additional testing, extending approvals and testing time. Testing nevertheless established installation criteria. Production improved from three to four piles per day to five to six after predrilling the upper soils and improving cement quality control.<br /><br />The estimated total cost fell from $4.0 million for micropiles to $1.9 million for the alternative, while the overall schedule was estimated to shrink from 12 months to six. The presenters recommend that designers specify clear loads and deformation criteria, require material quality plans and load testing, encourage accepted testing standards, and account properly for neutral-plane behavior and drag loads.

Keywords

pressure-grouted helical piles

displacement piles

South Brooklyn

micropiles

liquefiable soils

load testing

neutral plane

drag loads

code variance

foundation cost savings