Severn-Trent sand: a kinematic hardening constitutive model for sands: the q-p formulation

A simple model is described which is able to represent the mechanical behaviour of granular soils over a wide range of void ratios and mean stresses (neglecting grain crushing). The model combines Mohr–Coulomb failure, critical states, dependence of strength and stiffness on the state parameter, a hyperbolic law for plastic stiffness degradation and a flow rule similar to that of Cam Clay. The model is formulated within the framework of kinematic hardening and bounding-surface plasticity. The model requires two elastic and eight plastic parameters which are linked to clear physical features of the mechanical response. The formulation and numerical implementation are eased by making use of a 'normalized' stress space in which the stress– strain response shows no strain softening. The model is validated by comparison with experimental results obtained from triaxial tests on Hostun sand covering a wide range of density and stress level. Some proposals are made for possible future developments of the model within the same underlying framework.