3D numerical modelling of soil-structure interaction during EPB tunnelling

The paper illustrates a three-dimensional finite-element analysis aimed at back-predicting the response of a multi-storey reinforced concrete building underpassed by a metro tunnel. The study refers to the case of the Milan metro line 5, recently built in coarse-grained materials using an earth pressure balance machine, for which settlement measurements along ground and building sections were available. The soil behaviour is modelled using an advanced constitutive model that, when combined with a proper simulation of the excavation process, proves to realistically reproduce the subsidence profiles recorded in free-field conditions. The building is found to modify the deformative pattern at the ground surface in relation to its stiffness and weight, reducing the differential settlements as compared to those calculated under free-field conditions. Results of the numerical simulation carried out, including the model of the building schematised in detail, are found to be in good agreement with the monitoring data. They thus indirectly confirm the satisfactory performance of the adopted numerical approach, which takes into account a unique model of the soil, the tunnel and the building - that is, the key ingredients of this interaction problem. Further analyses are also carried out modelling the building, adopting different levels of detail. The results highlight that, for the case under study, the simplified approach based on the equivalent plate schematisation is inadequate to capture the real displacement field. The overall behaviour of the system proves to be mainly influenced by the buried portion of the building, including its foundation elements, which plays an essential role in the interaction mechanism.