Parameter Calibration and Numerical Analysis of Twin Shallow Tunnels

Prediction of displacements and lining stresses in underground openings represents a challenging task. The main reason is primarily related to the complexity of this ground–structure interaction problem and secondly to the difficulties in obtaining a reliable geotechnical characterisation of the soil or the rock. In any case, especially when class A predictions fail in forecasting the system behaviour, performing class B or C predictions, which rely on a higher level of knowledge of the surrounding ground, can represent a useful resource for identifying and reducing model deficiencies. The case study presented in this paper deals with the construction works of twin-tube shallow tunnels excavated in a stiff and fine-grained deposit. The work initially focuses on the ground parameter calibration against experimental data, which together with the choice of an appropriate constitutive model plays a major role in the assessment of tunnelling-induced deformations. Since two-dimensional analyses imply initial assumptions to take into account the effect of the 3D excavation, three-dimensional finite element analyses were preferred. Comparisons between monitoring data and results of numerical simulations are provided. The available field data include displacements and deformation measurements regarding both the ground and tunnel lining.