Mathematical modelling of monotonic and cyclic undrained clay behaviour

The proposed general analytical model describes the anisotropic, elasto‐plastic, path‐dependent, stress‐strain‐strength properties of inviscid saturated clays under undrained loading conditions. The model combines properties of isotropic and kinematic plasticity by introducing the concept of a field of plastic moduli which is defined in stress space by the relative configuration of yield surfaces. For any loading (or unloading) history, the instantaneous configuration is determined by calculating the translation and contraction (or expansion) of each yield surface. The stress‐strain behaviour of clays can thus be determined for complex loading paths and in particular for cyclic loadings. The stress‐strain relationships are provided for use in finite element analyses. The model parameters required to characterize the behaviour of any given clay can be derived entirely from conventional triaxial or simple shear soil test results. The model's extreme versatility is demonstrated by using it to formulate the behaviour of the Drammen clay under both monotonic and cyclic loading conditions. The parameters are determined by using solely the results from monotonic and cyclic strain‐controlled simple shear experimental tests, and the model's accuracy is evaluated by applying it to predict the results of other tests such as (1) cyclic stress‐controlled simple shear tests, (2) monotonic triaxial loading compression and unloading extension tests, and (3) cyclic stress‐ and strain‐controlled triaxial tests on, this same clay. The theoretical predictions are found to agree extremely well with the experimental test results.