The Nonlinear Constitutive Behaviour of Coode Island Silt-Paper

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The study develops and validates parameters for the Hardening Soil (HS) constitutive model to represent the nonlinear, stress-dependent behaviour of Coode Island Silt (CIS), a soft, compressible deposit beneath much of central Melbourne. Accurate modelling is important for predicting deformation and designing foundations and ground improvements in this challenging soil.<br /><br />Remoulded CIS samples were tested in consolidated-undrained triaxial compression at effective confining pressures of 75, 100 and 125 kPa. The tests indicated a friction angle of approximately 21°, cohesion of 10 kPa, and peak deviatoric stresses of 56–88 kPa. The authors calibrated the HS model using these results and numerical simulations in PLAXIS. The resulting parameters include a drained reference secant stiffness of 6.3 MPa, an unloading/reloading stiffness of 39.9 MPa, an oedometer stiffness of 3.5 MPa, and a stress-dependency exponent of 0.95. Model predictions agreed well with measured stress–strain and excess pore-pressure responses.<br /><br />To validate the calibration independently, the researchers used spherical cavity-expansion analysis to predict cone penetration test (CPT) tip resistance and excess pore pressure. The calculated profiles showed good agreement with field measurements.<br /><br />The findings demonstrate that the HS model can capture key nonlinear and stress-dependent features of CIS behaviour. The proposed parameters can support more realistic finite-element analyses of foundations and other geotechnical structures in the Coode Island area, improving deformation predictions and potentially enabling safer, more cost-effective designs.

Keywords

Hardening Soil model

Coode Island Silt

geotechnical modeling

stress-dependent behavior

triaxial compression

PLAXIS calibration

cone penetration test

cavity expansion analysis

foundation design

pore pressure