Constitutive Modeling of the Cyclic Loading Response of Low Plasticity Fine-Grained Soils

Calibrations of the PM4Silt constitutive model are presented for two low-plasticity fine-grained soils that exhibit significantly different cyclic loading behaviors. The PM4Silt model is a stress-ratio controlled, critical state compatible, bounding surface plasticity model that was recently developed for representing low-plasticity silts and clays in geotechnical earthquake engineering applications. The low-plasticity clayey silt and silty clay examined herein were reconstituted mixtures of silica silt and kaolin with plasticity indices (PIs) of 6 and 20. Undrained monotonic and undrained cyclic direct simple shear (DSS) tests were performed on normally consolidated, slurry deposited specimens. Calibration of the PM4Silt model was based on the monotonic and cyclic DSS test data, plus empirical relationships for strain-dependent secant shear moduli and equivalent damping ratios. The calibration process and performance of the PM4Silt constitutive model are described for each soil. The results illustrate that PM4Silt is capable of reasonably approximating a range of monotonic and cyclic loading behaviors important to many earthquake engineering applications and is relatively easy to calibrate.