Evaluation of Jet Grout Column Formation based on Undrained Shear Strength-Paper

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The paper evaluates whether an analytical model of soil erosion by high-velocity jets can predict jet-grout column diameters in layered soils. The model treats jet advance as a series of bearing failures under undrained conditions. It was tested against three full-scale columns, 25–28 m deep, installed through fill, organic soil, silty sand, and varved silt in Manhattan. Column dimensions were measured using the CYLJET electrical-resistivity method, then compared with predictions based on different estimates of soil strength from cone penetration tests (CPTs).<br /><br />Using conventional CPT cone resistance to estimate undrained shear strength substantially under-predicted measured column diameters. Predictions were more reasonable when the model used an undrained strength equal to half the CPT sleeve friction, or when soil bearing resistance was assumed directly equal to sleeve friction. For anisotropic soils, the authors therefore recommend approximating the strength relevant to vertical jetting as \(s_u \approx 0.5f_s\), with \(q_{bu} \approx f_s\) as a practical alternative for estimating column diameter.<br /><br />The findings support using undrained soil response to model jet grouting in both cohesive and cohesionless soils, despite uncertainty in defining undrained strength for cohesionless deposits. The results are based on a limited field-trial program, and the proposed relationships should be treated as practical estimates rather than universal values.

Keywords

jet grouting

soil erosion

high-velocity jets

analytical model

bearing failure

undrained shear strength

cone penetration test

CYLJET method

layered soils

column diameter