Eurocode 7-based design of SCL tunnels by means of numerical analyses

Although the design of tunnels is not explicitly covered in Eurocode 7 (EC7), a tendency in practice towards EC7-compatible design can be observed, at least for shallow tunnels in soil. However, there is no experience available to indicate which of the design approaches defined in the current version of EC7 is the most suitable for the analysis of shallow tunnels, in particular when it comes to numerical models. This paper presents the results of numerical calculations assessing ultimate limit state conditions of a shallow tunnel constructed using a sprayed concrete lining in overconsolidated soil, comparing different design approaches. It is shown that all the design approaches defined in EC7 can be easily accommodated when the shotcrete lining is modelled as linear elastic. When a non-linear material model for the shotcrete lining is employed the situation is less clear; a so-called implicit design, taking into account partial factors for the time-dependent shotcrete strength, is discussed.