Terrestrial mobile LiDAR survey to manage rockfall risk along a motorway

This work presents the validation of a terrestrial mobile LiDAR survey from a vehicle to provide the A22 motorway operator with a tool for rockfall risk management. The paper focuses on the A22 section between Bolzano Nord and Chiusa (South Tyrol, Italy), where the Isarco River valley morphology features steep rock slopes, and the motorway runs at their toe, primarily on cut-and-fill roads and viaducts. A qualitative rockfall risk assessment has highlighted a significant level of risk affecting a 13 km section of the A22 motorway. As a consequence, the motorway operator is required to develop a management strategy and implement tools—such as periodic LiDAR surveys—to support ongoing validation and updating of the risk assessment over time. Due to the morphology of the site and the characteristics of the infrastructure that locally does not have an emergency lane, managing the rockfall risk and detecting detachment zones through traditional static LiDAR surveys would require traffic closure to ensure safety conditions. In this area, the motorway mostly consists of superficial structures, so a terrestrial mobile LiDAR survey from a vehicle was assumed to be a convenient, innovative methodology. A survey was carried out in April 2023 to test its effectiveness and efficiency in detecting potential detachment zones in wide areas. The effectiveness of the mobile LiDAR survey is evaluated in terms of point density and percentage of detected areas of each potential detachment zone. The efficiency is proved in terms of time since the survey required only half a day and in terms of the safety of the workers without closing the traffic lane. The capabilities and limitations of the mobile LiDAR survey from a vehicle are also addressed in detail for some potential detachment zones of interest.