Rockfall and Debris Flow Hazards After Summer Wildfires in Cerreto Sannita, Benevento, Italy

摘要

Wildfires transform large areas on highly dangerous slopes and create unsustainable risks where roads, railroads, or buildings are at the foot of such slopes. The casual relationship between summer wildfires and rockfall and the efforts to mitigate the resulting hazards was carried out. In order to minimize these hazards a stabilization system was put in place along a main road in the Province of Benevento, Southern Italy, connecting Cerreto Sannita to Cusano Mutri. After summer wildfires, it became apparent that continuous rockfall from the slopes was becoming increasingly dangerous. This rockfall frequency was brought about by the lack of vegetation in the form of medium to tall trees acting as natural barriers and of surface grass serving to control erosion. Sections of slopes were left bare after the fires meaning that the roots of the former vegetation could no longer help to maintain soil in place. As such, a variety of factors could easily have triggered the frequently jointed limestone outcropping to collapse, including seismic forces, heavy rain, wind, wild animals, evolving from simple rockfalls to debris flow along main gullies, from the crest of the cliff to the road underneath. Furthermore, it is likely that the high temperatures reached in the fires induced a change of stress state itself, increasing the likelihood of single blocks falling. The adopted solution to restoring conditions of basic safety along the road was implemented in two different steps. Firstly, climbers walked all along the slope marking and counting all the unstable rocky boulders, and cleaning any block bigger than 0.30 m. During this step, road traffic was periodically stopped. Larger blocks in inaccessible areas were treated with high resistance steel mesh and rock anchors, with the aim of actively reinforcing the surface. In a second step, in areas where the joints were so frequent that the drilling was a danger to the workers themselves, a passive protection measure was adopted consisting of highly specialised and well performing rockfall barriers. Once safety was ensured by means of the above solutions, further potential points of instability were directly treated with standard techniques, with environmental impact given constant consideration. For instance, allowing vegetation growth alongside the aesthetic perspective from the vantage point of the road. Consequences of further wildfires were considered when choosing the type of coating designed to prevent the corrosion of the adopted measures’ steel components. In the future, new fires in the cliffs are not expected to lead to further rockfall hazard in the sites where the project has been implemented.