Jet Grouting in Stratified Soils - A Case Study-PPT Presentation

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The case study describes jet grouting for Ancillary Building No. 2 at New York City’s Second Avenue Subway. The structure required deep excavation in stratified ground—fill, organic soils, silty sand, and varved silt—with jet-grouted elements used to form an excavation-support slab and gravity wall.<br /><br />A trial program tested different grouting parameters and column configurations before production work. The trials showed that casing needed to extend through the fill and organic layers into silty sand or varved silt to maintain borehole stability. Production parameters were then selected for the slab, gravity wall, and closure columns.<br /><br />Spoil specific gravity varied with the properties of the grout actually supplied, changes in soil stratification, installation sequence, nearby columns or obstructions, and use of compressed air. The study used a specific gravity ratio (SGR) of 1.0 as an indicator of successful treatment. It also found that 28-day spoil compressive strength provides an indication of the lower-bound strength of hardened grout cores.<br /><br />Coring and strength tests highlighted differences between treated soils: grouted varved silt exhibited brittle-to-ductile behavior, while grouted silty sand failed in a brittle manner. Grouted varved silt was more sensitive to drilling disturbance, and total core recovery was lower when coring took place within 91 days of jetting.<br /><br />The findings emphasize the importance of adapting jet-grouting procedures to soil layering, monitoring grout and spoil properties, and accounting for installation and coring effects when verifying treatment quality.

Keywords

jet grouting

Second Avenue Subway

New York City

deep excavation

ancillary building

varved silt

silty sand

gravity wall

spoil specific gravity

grout strength