The Influence of Stiffness Anisotropy on the Behaviour of a Stiff Natural Clay

Abstract

The stress–strain response of stiff plastic clays is known to be highly non-linear and anisotropic. However, whilst there have been many investigations on the non-linearity of stiff plastic clays, this is not the case for stiffness anisotropy. It is generally believed that, at least at small strains, soil stiffness is anisotropic and can be interpreted within the framework of cross-anisotropic elasticity. However, very few measurements of all cross-anisotropic stiffness parameters have been reported in the literature. Recent research on stiff plastic London Clay, from London’s Heathrow Airport Terminal 5 (T5), is one of the few examples where these independent stiffness parameters have been quantified. On the basis of these research findings, this paper uses a cross-anisotropic non-linear elasto-plastic model to simulate the behaviour of London Clay. The model is used to simulate a number of laboratory tests and the predictions are compared with available experimental data from the T5 investigation. The predictions of the cross-anisotropic non-linear elasto-plastic model for the laboratory tests are also compared with those of an isotropic model, which has been used successfully in the past to simulate the behaviour of stiff plastic clays. Predictions obtained with the two models are then compared in the numerical analyses of a tunnel constructed within the London Clay. Both short-term undrained and long-term drained conditions are examined in fully coupled analyses.