Ground movements induced by TBM excavation under an historic church in Napoli

A recently completed railway tunnel of the underground network of the city of Napoli underpasses one of the corners of an old church, built in the 16th century. The tunnel with an external diameter of 8.15 m runs at a depth of approximately 10 metres beneath the church foundations. It has been excavated by means of an EPB tunnel boring machine. For its relevance the church underwent an accurate monitoring during construction. At the design stage the presence of the church was carefully taken into account, with settlement predictions based on cautious range of expected volume loss during tunnelling. 3D finite element analyses modelling stiffness strain dependency at small to medium strain levels have been performed. The paper describes the monitoring system and compares the measured displacements with those predicted by 3D FEA in the greenfield sections located in the public gardens in front of the church. The influence of the stiffness of the structure and of the relative position of the underground line with respect to the plan section of the church is also discussed