Ultimate limit state design of deep excavation problems according to EC7 using numerical methods

For complex geotechnical problems, the finite element method (FEM) can be considered state-of-the-art with respect to the prediction of deformations and stresses for serviceability limit states (SLS). The verification of the ultimate limit
state (ULS), on the other hand, is usually done using conventional methods. However, numerical methods are gaining relevance in the ULS design of geotechnical structures, which will also be reflected in the next generation of Eurocode 7 (EC7). Therefore, the design approaches used in EC7 require a detailed investigation on the factors influencing the design with numerical methods.
In this paper, the design approaches DA2* and DA3 of EC7 are applied to a multi-strutted deep excavation problem using the Hardening Soil Small (HSS) and Mohr-Coulomb (MC) constitutive models. The differences resulting from the various design approaches and constitutive soil models are discussed. Since soil stiffness is known to play an important role in numerical analyses and its parameters are subject to a higher degree of uncertainty compared to strength parameters, it is shown that soil stiffness can have a major impact on the ULS design and the variation of its parameters can lead to significantly different result