Relationships between Landslides Phenomena and Road Network: An Example from the Hilly Region of Asti Province (North-Western Italy)

Starting from the study of the geological framework and the historical background for landslides of the Asti province, the research has focused on the causes triggering the landslides directly affecting the road network of the studied area. This kind of instability is common in Asti area and has a strong economic and social impact. 151 landslides have been analyzed; this led to identify some returning structural failure of the roads. In this way some typical situations have been identified: incorrect lateral slope of the road (36% of cases); undersize or absence of the devices for the collection and disposal of rainwater (27%); drainage pipes not adequately extended beyond the road edge towards appropriate receptors (6%); blockage of the water drainage systems (road ditches, fencing, wells, etc.) along the road infrastructure due to landslides affecting the upwards side (4%); leaking water mains or sewer (3%); little or no maintenance of the drainage systems (1%); other causes (23%). The study shows that the incorrect slope of the road together with the undersized or incorrect design of the runoff drainage, represent the main elements of vulnerability, causing over 60% of landslides involving the roadway. The regulation of the rainwater drainage is therefore essential for the sustainable management of road network in hilly regions.