Eurocode 7 and new design challenges using numerical methods with different soil models

According to Eurocode 7, soil strength factoring can be achieved by applying the material partial factors to the effective stress parameters c’ and φ’ or to the undrained shear strength cu. Thus, in numerical analyses, material factoring is straightforward for constitutive models with c’, φ’ or cu as input parameters. While designers often use simple elastic-perfectly plastic soil models for ULS checks, the use of more advanced constitutive models allows real soil behaviour to be simulated more realistically and can have significant advantages. In this paper, the feasible use of different soil models for ULS design, increasing in sophistication, such as the Mohr-Coulomb (MC), the Hardening Soil (HS), the Hardening Small Strain (HSS) and the Soft Soil (SS) models, is highlighted and better understood in the context of the EC7 requirements using deep supported excavation examples in stiff clay. The challenges of factoring undrained shear strength when using effective stress model parameters are also discussed and the effect of the soil model is investigated.