Predictions and observations of convergence in shallow tunnels: case histories in Greece

Convergence of shallow tunnels (30–120 m overburden thickness) constructed in Greece in different types of rock masses has been assessed as a function of the Geological Strength Index (GSI classification). Predictions of maximum vertical and horizontal convergence, during or shortly after tunnel excavation, were made using Finite Element Modeling (FEM) and the ‘characteristic line’ theory, and were found to be in good agreement with geodetic observations of convergence collected during a period of approximately 2 months after the section excavation. The results from FEM were found to adequately and reliably predict the expected deformation during tunnel excavation. The theory of the ‘characteristic line’, on the other hand, seems to offer a realistic and reliable upper-bound estimate of the convergence.