Three-dimensional FE analysis of twin-tunnels excavation in green-field conditions

The construction of the Line C of Rome underground entailed the use of two earth-pressure balance machines (EPBMs) to excavate the twin tunnels within the historic city centre. The objective was to minimise any potentially detrimental interferences with existing monuments and buildings of historical value. This resulted in the implementation of an extensive monitoring programme, the objective of which was to evaluate the impact of the Line C on the surrounding monuments. Furthermore, this programme provided invaluable opportunities for field investigation of the ground response. This paper presents the results of a three-dimensional finite element (FE) analysis conducted to simulate the excavation of the Line C twin tunnels beneath a green-field instrumented research site close to the Basilica of San Giovanni. A constitutive model capable of describing the non-linear and inelastic soil behaviour since the beginning of the loading paths was adopted, using the same set of constitutive model parameters which were calibrated on the results of a detailed geotechnical characterisation of the site and which have been shown to successfully simulate the observed behaviour of deep excavations carried out in the same area. The results of the analyses were found to reproduce satisfactorily the observed displacement field induced by the excavation of the twin tunnels. The comparison between the observed and predicted behaviour highlighted the potential for numerical analyses, despite being performed with widely used tools, to be profitably used to predict the performance of complex geotechnical problems, provided that the adopted constitutive model is carefully calibrated on laboratory and site investigations.