Jet Grouting in Stratified Soils

Video Transcription

Video Summary

The presentation reviews jet grouting used to support the N32 building excavation for New York City’s Second Avenue Subway. The design combined a six-foot-thick jet-grouted slab for a stepped excavation with a jet-grouted gravity wall to retain a soil berm and limit movement of nearby historic buildings. Jet-grout columns also sealed potential gaps beneath secant piles.<br /><br />Trials and production monitoring showed that borehole stability—especially deeper casing—was important for consistent columns. Specific gravity of grout and returned spoils helped assess installation and soil cutting, though results varied with soil layers, grout parameters, air entrainment, and column sequence. Single-fluid grouting generally produced better cutting indicators and stronger, more recoverable cores than double-fluid grouting. Strength increased between 14 and 28 days, but varied substantially by soil type. Silty sand tended to produce brittle behavior, while variable silt showed a wider range of strengths and behavior. Overall, jet grouting was effective, but quality depended on careful control and verification.

Keywords

jet grouting

Second Avenue Subway

N32 building excavation

jet-grouted slab

gravity wall

borehole stability