Jet Grouting for Deep Excavation Support at Re-entrant CornersÂ-PPT Presentation

PPT Presentation

Pdf Summary

The presentation describes jet grouting used to support re-entrant corners at Entrance 3 and Ancillary 2 of the 96th Street Station, a deep cut-and-cover excavation for New York City’s Second Avenue Subway. The station is approximately 1,800 feet long, 60 feet wide, and 60–70 feet deep, in ground containing varved silt, silty sand, and organic soils.<br /><br />Two construction approaches were compared. Method 1 used separate passes with fixed jetting parameters, conservatively designed for the most challenging soil conditions. Method 2 used a single pass with parameters varied by soil layer. The presentation outlines how nozzle size, grout pressure and flow, air pressure, grout density, lift time, and rotation speed were adjusted.<br /><br />Quality control considered both input parameters and recovered spoils, including grout and spoil specific gravity, soil variability, entrained air, and shadowing. Specific Gravity Ratio (SGR) was used to assess treatment; an SGR of 1.0 was identified as the successful-treatment benchmark. Verification cores confirmed treated material strengths of 470 psi in organics, 1,250 psi in silty sand, and 2,480 psi in varved silt.<br /><br />The fixed-parameter, multiple-pass method was simpler, provided better control, and produced more consistent SGR results. The single-pass, variable-parameter method optimized treatment by soil layer but was more complex and showed greater SGR variation.

Keywords

jet grouting

re-entrant corners

Second Avenue Subway

96th Street Station

deep excavation

varved silt

quality control

specific gravity ratio

soil variability

verification cores