Retaining walls in mountainous regions are subjected to demanding conditions. What specific challenges are encountered when carrying out repairs on these structures?
Major retaining walls in mountainous regions are subjected to a number of factors which can damage them: extreme weather conditions, earth slides and natural wear resulting from the age of the infrastructure. Managing this infrastructure requires technical solutions that are appropriate for the local geology (which is often complex) and for difficult access conditions. Furthermore, when conducting repairs on these structures, the provisional phase is sometimes more demanding in terms of the resistance of the elements involved than once the repairs have been completed. This is a critical aspect which needs to be factored in, with specific studies for these site phases in particular.. Finally, specific phasing is required so that traffic can continue to flow, but without compromising the safety of users or people working at the site. The provisional phase of the works, however, is particularly critical. During this phase, the infrastructure's stability is severely tested – particularly when it has to remain functional and secure. We need to ensure that reliable temporary support is provided so as to prevent any risk of accidents.
View of the Charmaix viaduct during reinforcement work
Let's take the Charmaix viaduct (on the Fréjus tunnel access road) as an example. This viaduct, built in 1976 on an unstable slope, needed to be reinforced to cope with landslides. We used techniques such as nailed walls, semi-deep foundations and jet grouting to reinforce the soil. We worked on the project between 2016 and 2019, and the result was a “drifting” viaduct, able to keep pace with soil movements, which has a planned service life of 100 years.
