Landslide-risk zonation along mountainous highway considering rock mass classification.

Landslide and especially rockfall hazard widely occurs along cut slopes in mountainous regions. The risk assessment of mass movements is still one of most challenging problems in slope engineering geology. We propose a routine method to assess rock slide and rockfall risk of cut slopes essentially based on slope properties and rock mass structure. The method is a lean low-cost path to a risk estimate. Rock block size is simplified into two classes, {small} with a volume less than 1.0 m and {large}, greater than 1.0 m. Studies indicate that for a slope with n small-medium rock blocks, the possibility of rockfalls can be estimated by 1 − (1 − P), in which P is the likelihood of one {small} rock block fall. The possibility of other types of mass movement can be determined by the first-order second-moment (FOSM) method. Based on this, an exponent equation was adopted to evaluate the consequence and the risk. The methodology is demonstrated by a case study from the mountains of Mentougou district, Beijing, China. Based on the investigations of geological conditions (i.e., lithology, weathering and rock mass structure) and some historical mass movement data of the cut slopes, a zonation map for rockfall and rock slide risk along a 17-km section of a road is presented. The result is supported by mass movement event observations in the recent 2 years. [ABSTRACT FROM AUTHOR]