Unified hardening (UH) model for clays and sands

A unified model for clays and sands, referred to as CSUH model, is proposed. The CSUH model develops the following aspects based on the unified hardening (UH) model: (a) a curved normal compression line in the e-lnp plane is proposed by introducing a parameter to describe the isotropic compression of sands; (b) a drop-shaped yield function, involving a critical state parameter, is adopted to get a better prediction of the shear yield and the critical state of sands; (c) a dilatancy parameter is introduced into the dilatancy equation to consider the density-dependent dilatancy of sands; and (d) different CSLs of sands with different lode's angles in the e-p plane are considered. The CSUH model can degrade into the UH model to describe the behaviors of overconsolidated clays and can further degrade into the modified Cam-clay model to simulate the behaviors of normally consolidated clays. Finally, comparisons with the test data indicate that, the CSUH model cannot only predict the stress-strain relations of both clays and sands in a wide range of overconsolidation ratios or densities and stresses, but also is capable of describing triaxial compression, triaxial extension and three-dimensional behavior.