Modelling of reinforced concrete framed structures interacting with a shallow tunnel

The construction of tunnels in urban areas inevitably entails the interaction with existing structures. Current design approaches for the evaluation of tunnelling induced damage on buildings are based on the semi-empirical evaluation of the deflection ratios and horizontal tensile strains at foundation level, assuming that the structure will conform to the greenfield displacements. If the stiffness of the structure is deemed significant, coupled numerical analyses have to be performed including a model of the building. The latter can be simulated using either an equivalent solid (e.g. Potts and Addenbrooke, 1997; Losacco et al., 2014), for which appropriate equivalence criteria have to be defined, or a detailed structural model (e.g. Burd et al., 2000; Amorosi et al., 2014; Fargnoli et al., 2015). This paper focuses on the phenomenon of soil-structure interaction due to mechanised tunnel excavation, with special reference to reinforced concrete framed buildings. The study aims at identifying those cases in which the building significantly alters the settlement trough induced by the excavation with respect to greenfield one. In such cases the relative contribution of the foundations and of the structural members to the global stiffness of the building is assessed, seeking for the optimal level of simplification of the structural model. The research is carried out by performing three-dimensional parametric finite element analyses of the problem at hand, adopting the geotechnical conditions and the tunnel characteristics of the Milan metro-line 5 (Fargnoli et al., 2015).