Loading–unloading judgement for advanced plastic UH model

The unified hardening (UH) model proposed by Yao et al. (Geotechnique 2009) is the constitutive model which can consider the influence of the complex stress path and stress history on the deformation and strength of clays reasonably. Firstly, the loading–unloading criterion of material model is defined as the change law of the intersection of current yield surface and the p axis, which makes the loading–unloading in the process of hardening and softening can be unified considered in UH model. Then, the Newton–Raphson method is adopted to attain the nonlinear problems solution in the finite element method of UH model, and the semi-implicit return mapping method is adopted to update stress. The application of the UH model in the finite element is realized. And then, the analyses of triaxial test are performed using the unit prediction and finite element method. The results of the unit prediction method are compared with the experimental results to illustrate the rationality of the UH model. Comparing the results with the unit prediction method and the finite element method, the correctness of the finite element program of the UH model is illustrated. Further, the three-dimensional finite element analysis of embankment on soft soil is performed by the program. The comparison between the results calculated by the UH model and the modified Cam-clay (MCC) model and the experimental data shows that the UH model is rational in analyzing the actual embankment engineering on soft soil.