EVALUATION OF A CONSTITUTIVE MODEL FOR OVERCONSOLIDATED CLAYS

This Paper evaluates the performance of a generalized effective stress soil model for predicting the rate-independent behaviour of K0 normally to moderately overconsolidated clays. The model formulation comprises three components: an elastoplastic model for normally consolidated clay including anisotropic and strain softening behaviour, equations to describe the small strain nonlinearity and hysteretic response in unloading and reloading, and bounding surface plasticity for irrecoverable, anisotropic and path-dependent behaviour of overconsolidated clays. Model complexity is controlled through the use of input parameters which can be obtained from a relatively small number of standard soil tests. The Paper illustrates the selection of model input parameters for a low plasticity, moderately sensitive clay and compares the selected values for different types of clay. Extensive comparisons with measured data from undrained shear tests performed in different modes of shearing and with overconsolidation ratios of up to 8, show that the model gives excellent predictions of conditions at maximum shear stress and describes accurately the non-linear shear stress-strain behaviour. However, it becomes less reliable at OCR > 4, where it tends to overestimate the shear strength in compression and underestimate that in extension. Further comparisons with test data from the directional shear cell demonstrate model capabilities for describing anisotropic properties of Boston blue clay due to a one-dimensional consolidation stress history. The overall high quality of the predictions reported has provided the basis for implementing the model in a general non-linear finite element analysis.