Four Years Monitoring Experience of Displacements induced by a Large Landslide in a Tunnel Serving a National Road

n Passo della Morte, UD (46° 23%39;49 "N, 12° 42%39;51" E), in North East Italy, the National Route SS52 across a mountain ridge through a 2200 m long tunnel. However, the presence of a 24*106 m3 block-slide that is intersected by the tunnel, causes problems to the infrastructure management since its first stages of construction (1992-2008). This work describes the Structural Health Monitoring system that controls since 2014 the crack pattern of the portion of the gallery mainly affected by landslide's slip surface activity. The monitoring system within the tunnel encompasses 4 bi-axial clinometers, 24 crackmeters, and a low-cost plastic optical fiber sensor plastic. Along, two thin plate weirs allow to measure the discharge of the internal drainage system of the tunnel while outside, on the surface, GNS benchmarks, in-place inclinometers and piezometers gather realtime data on the landslide dynamic. On the base of the four years monitoring experience, a simplified static scheme that accounts for the evolution of the crack with respect of the landslide displacements and allows defining a damage prognosis (DP) for the tunnel, is presented. The results will be used for the design of the most appropriate and effective mitigation measures to reduce the progression of damage within the tunnel. Meanwhile, the monitoring system acts like a non-structural mitigation measure assessing in real-time the structural status of the tunnel, supporting the infrastructure management in assessing each day the safety for road transit and giving indications for the drafting of maintenance protocols.