What is the real impact of instabilities and ageing infrastructure along roads and railways ? Analysis of an event inventory in the Western Alps, Switzerland

The effects of climate change on ageing infrastructures, due to temperature variations, insolation, and especially increased runoff due to extreme precipitations, are not insignificant. In addition,  expected changes in land use and increased impact of anthropic activity, as well as  the degradation of infrastructures due to age, will potentially impact the utility lifespan of a great variety of works. Whether it be retention walls for vineyards, near roads or next to railroad tracks, it is important to determine to what extent climate change and anthropic activity will accentuate the hazard of failure of protective or retaining infrastructures and their backfills. Especially when these are located along busy routes (pedestrian, automobile, railroad, etc.) and can potentially impact moving objects (for example trains with passengers). Even though these events are not so rare, and  the damages caused are easily repaired or managed, their global costs and impacts are very seldom quantified. In order to gain a better overview on the global cost of these types of events and the associated impacts, in particular in areas where maintenance is not so frequent, an inventory of events for the Western Alpine Switzerland was carried out. The associated costs were ascertained either in prevention and maintenance work or in emergency measures and reparation. Examples of events having a significant impact, include those of La Conversion (2021), Châtillens Ecublens-Rue (2013), Col de la Croix (2021), L’Etivaz (2018), La Forclaz (2018, 2022), Col des Mosses (2015), route d'Oron (2014, 2021), Ollon (2021), and Belmont-sur-Lausanne (2021); which were studied in more detail. Information on these events were gathered from various sources including newspaper articles, official reports, and interviews with witnesses and experts. And the conditions leading to such events, such as antecedent precipitation, age of the structure and structural condition, were investigated and analyzed. The results of the analysis were then used to identify a few sites susceptible to this kind rupture in the future, via reports, aerial images, and fieldwork, and subsequently mapped and communicated to the corresponding authorities.