ABSTRACT
The Mont-Blanc Tunnel is an infrastructure of strategic importance for Europe, linking France and Italy under the highest summit of the Alps. The tunnel was opened in 1965 and is a 11.6 km long single tube structure with 8.6m diameter. The road inside the tunnel is carried by a reinforced concrete slab, which is supported by two concrete linear walls, separating three service ducts. In the general scheme of preventive maintenance for this asset, this concrete slab is undergoing replacement works to build it new after nearly 60 years of operation. Before and during these works, planned over a few years, an exhaustive Structural Health Monitoring (SHM) system based on strain measurements on the lower face of the slab has been in operation. This paper describes the SHM strategy implemented since 2016 and its results for the asset manager. A first phase was achieved from 2016 to 2018 before the beginning of the slab works with 56 wireless optical strand sensors on a 555m long zone. Then, from 2019 to 2022, the SHM system was removed from the initial zone undergoing replacement works, and extended to next zones before and after, with a total of 117 sensors on 1200m along the tunnel. Starting from 2022, the wireless system has been replaced by a fully integrated wired solution, allowing the gathering of more volume of relevant data and an instantaneous dataflow while the works are going on. Long-term evolutions reflecting the effect of ageing, as well as short records at 100 Hz sampling rate for assessing the effect of the traffic loads on the concrete slab, are combined to give a synthetic stability index of each monitored location on the slab and check the health of the structure in real time throughout the duration of the works.
