Revising the unified hardening model by using a smoothed Hvorslev envelope

The original unified hardening (UH) model, in which a straight Hvorslev envelope was employed to determine the potential peak stress ratio of overconsolidated soils, is revised using a smoothed Hvorslev envelope (Hermite-Hvorslev envelope). The strength at the intersection between the straight Hvorslev envelope and the critical state surface (i.e. Mohr-Coulomb envelope) can be undefined due to the discontinuous change in the slope of the two linear strength envelopes mentioned above. A smoothed Hvorslev envelope is derived through Hermite interpolation to ensure a smooth change between the proposed Hvorslev envelope and the zero-tension surface as well as a smoothed transition between the proposed Hvorslev envelope and the critical state surface. The Hermite-Hvorslev envelope is then integrated into the original UH model, and then the UH models with four different functions of the Hvorslev envelope are compared with each other. The UH model revised by the Hermite-Hvorslev envelope can well predict the mechanical behaviors of normally consolidated and overconsolidated soils in drained and undrained conditions with the same parameters in the modified Cam-Clay model.