The impact of groundwater on the excavation of tunnels in two different hydrogeological settings in central Italy

Abstract

To double the capacity of the Orte-Falconara railway line (central Italy), the Santa Croce tunnel was constructed (1985-1995), which runs between the Nera Montoro and Narni stations. In the same period, to double the capacity of the Ancona-Bari railway line, the Moro, Cintioni, S. Giovanni and Diavolo tunnels were con- structed between the Ortona and Casalbordino stations. The high likelihood of intercepting a significant volume of groundwater in calcareous rocks of the Santa Croce tunnel led to a shift in the layout of the tunnel, which allowed construction of the tunnel by more rapid and less expensive means. Groundwater along the Moro tunnel layout, in a sandy aquifer, has been drained by the excavation of a preliminary tunnel, which allowed a discharge of up to 0.080m 3 /s. In the S. Giovanni and Diavolo tunnels, a particular hydrogeological setting was found to exist in the form of lens-shaped bodies of fine grey sand-and-silt aquitards intercalated between the bottom muddy-sandy deposits (very low permeability) and the sandy aquifer; this caused sudden groundwater inflow and tunnel collapse. The S. Giovanni tunnnel, excavation was completed using the HydroShield system, whereas in the Diavolo tunnel, a well-point system was adopted, which avoided any environmental hazards.