JET GROUTED FOUNDATION FOR 57-STORY TOWER-Paper

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The paper describes the design and construction of a jet-grouted foundation for a 57-story tower in lower Manhattan, where deep bedrock, shallow groundwater, and highly variable soils made conventional foundations challenging. The site contained up to 28 ft of uncontrolled fill, soft organic clay, and approximately 130 ft of dense sand over bedrock. The building’s high loads could not be safely supported by the near-surface soils, while deep piles or caissons were considered costly or impractical.<br /><br />The selected solution was a 10-ft-thick mat supported by jet-grouted soilcrete columns that improved the fill and clay and transferred loads to the underlying dense sand. Pre-stressed rock anchors were included to address wind-related uplift. Finite-element analyses estimated settlements of approximately 2–3 in. under dead and live loads, most of which were expected during construction.<br /><br />Construction involved field trials, production grouting, and verification. Testing established suitable grout mix and operating parameters, while monitoring grout specific gravity and laboratory testing of samples from drilled holes helped assess quality. Core drilling evaluated the extent and continuity of the treated ground. Production testing generally showed soilcrete compressive strengths and elastic moduli at or above design values. However, cores revealed potential weak zones, likely caused by debris obstructing grout distribution. These areas were strengthened with additional grouting, and steel bypass elements were installed at selected locations.<br /><br />The authors conclude that jet grouting can make poor near-surface soils suitable for high-rise foundations when the properties of the improved soil and settlement potential are carefully considered. Site-specific field trials, rigorous quality control, verification coring, and corrective measures are essential to achieving the design performance.

Keywords

jet grouting

foundation design

high-rise tower

soil stabilization

soilcrete columns

lower Manhattan

mat foundation

rock anchors

settlement analysis

quality control