ABSTRACT
The Mena twin tunnel, located along the A23 Motorway linking Palmanova to Tarvisio, was excavated during the 1970s in limestone by sequential excavation method, system-atically installing steel ribs temporary support. During the construction, the worksite suffered several rock mass failures from the top of the excavation face and two severe seismic events, occurred in May and September 1976 after the crowns were built up, related to the majors earth-quakes that Italy can remember in its recent history. The effects were amplified by the presence of a capable fault crossing the tunnel alignment, and a rock falling was activated at the Tarvisio side of the tunnel. A series of notable damages affected the tunnel lining, compromising the wa-terproofing capacity of the concrete to such an extent that a hydraulic protection system, combined with wire mesh reinforced shotcrete, was installed along the tunnel seven years after the construc-tion site closure, to guarantee safety conditions to the transit of vehicles. The complete covering of the inner part of the tunnel creates an obstacle to the visual inspections of the following years and make fake safety knowledge up to the present day when Tecne, Autostrade per l’Italia engi-neering company, focus on designing the best retrofit solution to extend the infrastructure life. The paper is the opportunity to show how historical inspections and as-built analysis help to re-construct the dynamic evolutions of the defects induced by the seismic events. The effect of the horizontal compression induced by seismic loadings, as pointed out by Japanese references from historical experiences of tunnel damages, is proposed to explain the presence of many longitudinal fractures in different parts of the tunnel crown. Considering all the boundary conditions, in this paper the authors show how the Tunnel Renewable Strategy is applied to solve all vulnerabilities affecting the tunnel.
