Overconsolidated (OC) clays are commonly encountered in geotechnical engineering and are subjected to threedimensional (3D) stress conditions. This study proposes a unified plastic potential function for triaxial and 3D general stress conditions, by incorporating the overconsolidation parameter and intermediate principal stress parameter. This function can effectively capture the coupling influence of the overconsolidation degree and intermediate principal stress on the dilatancy characteristics of OC clay. Additionally, it possesses a simple form and clear physical significance, making it easily applicable in constitutive models. Then, a simple bounding surface model in triaxial stress conditions is established by adopting the dilatancy relation and the model is extended to general 3D stress conditions by the transformed method based on spatially mobilized plane (SMP) strength criterion. Finally, the performance of the proposed model is validated through various triaxial shearing tests under a wide range of overconsolidation ration (OCR) and the simulation results of the proposed model are compared with those of the SANICLAY model. The comparative analysis indicates that the proposed model effectively describes the complex characteristics of OC clays by simple theory and it demonstrates significant advantages in deformation and pore water pressure simulation due to the advanced dilatancy relation.

This paper presents a semi-analytical solution for calculating soil stresses and pore pressures in the vicinity of an expanding cylindrical cavity. The main features of the solution are: i) realistic modelling of time-dependent soil behaviour, by means of an elastic-viscoplastic constitutive model, and ii) accurate prediction of soil strength under the stress path followed during plane-strain undrained cavity expansion, by using the transformed stress method to formulate the solution in the three-dimensional stress space and adopting an appropriate failure criterion. Predictions of the presented solution are benchmarked against a published solution, and are comprehensively analysed to identify the effect of the failure criterion and of the cavity expansion rate on the soil stresses and pore pressures developing in the vicinity of the cavity, and the associated stress paths.