ABSTRACT
In recent times (2004) the tunnel required rehabilitation works aimed at strengthening the original structure (particularly the invert), controlling the water leakage and enlarging the tunnel clearance profile. During the execution of the invert reconstruction, a serious disruption took place: a sudden ingress of water and, then, water and soil occurred from the invert excavation. The water inflow (up to 100 l/s) could not be stopped easily and the tunnel was flooded. The amount of mud which accumulated into the tunnel was about 5000 m3. Despite the significant overburden (60 m) (Fig. 1), the event had repercussions on the surface with settlements up to several hundreds of millimetres.
