Mobile Terrestrial LiDAR Survey for Rockfall Risk Management along a Highway

In the alpine stretch, from Brenner to Bolzano (Northern Italy), the Highway A22 is exposed to rockfalls and protection structures must be progressively extended as new detachments are identified. This paper defines a procedure to manage the rockfall risk through periodic Mobile Terrestrial LiDAR surveys from a vehicle travelling along the highway. This type of survey requires the adoption of specific precautions to work safely without interrupting traffic on the highway, such as escorting the surveyors’ vehicle using specific vehicles for mobile road works. Prior to a field trial, the potential effectiveness of a Mobile Terrestrial LiDAR survey was demonstrated through a GIS-based simulation. The simulation was performed for the most critical cliffs in a GRASS GIS environment with the support of Python scripts and the results were compared with those from a simulation of a static survey. Still working in a GIS environment, eight cliffs were identified as the most susceptible to rockfalls that may interfere with the infrastructures. The survey simulation revealed that a Mobile Terrestrial LiDAR survey has the potential to sense over 85% of the cliff area with a point density greater than 100 pts/m2. Given these promising results, a trial survey was then carried out in April 2023 using the innovative mobile mapping system Trimble MX9. Half a day was sufficient to sense the rock slopes along a 30 km stretch of the motorway with a point density of up to 900 pts/m2 for distances up to 150 m.