CONSTITUTIVE MODELLING FOR TROPICAL RESIDUAL SOILS WITH MODIFIED ROTATIONAL HARDENING PARAMETER

The proposed constitutive model is a generalized model to explain the stress-strain behaviour of soils encompassing unsaturated and saturated states of natural soils and also soft clays. The previously proposed models had treated the unsaturated and saturated states separately. The model is intended for tropical residual soils. The explicit nature of the stress-strain response of tropical residual soil mostly depends on the fabric and nature of cement bonding in addition to the usual factors such as current state, stress history, stress path, and drainage conditions. Despite the availability of quite a good number of constitutive relations concerning the behaviour of clays, the strain softening behaviour of tropical residual soils during the deformation process has not been satisfactorily tackled. The model is proposed within the framework of hardening plasticity. The rotational hardening parameter of modified Wheeler’s model is modified in the proposed model. The method allows for calibrating model parameters adopted in the model in addition to being an independent method to model the strain softening behaviour. This approach has the twin advantages of combining the conventional hyperbolic approach to the critical state concept and calibrating the model parameters adopted in the model for use in other stress paths. The model was validated by the analysis of data available in the literature to reproduce quantitatively, the observed behavior. The concordance between observed and computed results is regarded as satisfactory and supports the likelihood of duplicating the key characteristics of soils found in many states using a simple general framework. After formulation of the model for isotropic and triaxial stress states, typical predictions are provided and compared qualitatively with typical trends of tropical soil behaviour.