Analysis of convergence data and 3D numerical modelling of tunnels excavated in fine-grained soils

This paper focuses on the convergence measurements of twin motorway tunnels under excavation in a Pliocene formation in the South of Italy. The tunnels are driven full face, with a cross-section of 120 m(2), by means of a conventional excavation method, up to a maximum depth of 120 m. The primary lining is an open arch made up of shotcrete and steel sets; the definitive lining consists of concrete cast in three different stages. Convergence measurements were analyzed on the basis of the curve-fitting technique proposed by Sulem et al. (1987). Then, the influence on tunnel deformation of overburden and lining construction sequence is investigated. Finally, the role of the primary and final linings in reducing tunnel convergence is investigated by means of a three-dimensional stress-strain analysis, performed with FLAC3D code.