Abstract: The Unified Hardening (UH) model can characterize many aspects of clay stressstrain behaviors, such as, straining hardening and softening, stress dilatancy, as well as the stress path dependent. A users defined material subroutine implementing the UH model was developed using the return mapping algorithm in the commercial finite element analysis software ABAQUS. The UH model was validated by simulating the loadingunloading process in the triaxial compression and other stress paths on a testing element. The results indicated that this constitutive model can reasonably characterize the soil behavior under different stress paths and overconsolidation ratio. This UH model was then applied to simulate a deep excavation of a subway station in cohesive soils. The numerical simulated deformation of the excavated area and the stress in the supporting structures were compared with the measured values. A satisfactory agreement was found between the measured and predicted values.

Key words: UH constitutive model, return mapping algorithm, deep excavation, overconsolidated soil, users defined subroutine