A basic constitutive model for sands

The modified Cam-clay model has been widely adopted as the theoretical framework for constitutive modelling of clays. However, there is so far no such model for sands on the basis of which further development can be carried out. Based on the main differences in the behaviours exhibited during isotropic compression and shear processes between sands and clays, a basic constitutive model for sands is proposed by introducing the compressive hardening parameter p_s and the critical state parameter χ into the formulations of normal compression line and elliptic yield surface of the modified Cam-clay model respectively. When the new compressive hardening parameter and critical state parameter both equal 0, the normal compression line and yield surface of the proposed model for sands can degrade into the corresponding ones of the modified Cam-clay model for clays. The comparison between test data and the model prediction indicates that the proposed model can predict the stress–strain relationship of normally compressed sands (i.e. the loosest sands without structure) well. The proposed model can be considered as the basic framework for further research on constitutive modelling of sands due to its clearly defined assumption, simple structure and good capability in model prediction.