Road slopes risk assessment of the northern part of Gifu Prefecture, Japan

The road slope hazard, which is the occurrence rate of rock falls along the major roads, in the Northern part of Gifu prefecture, consists of Takayama, Furukawa and Gero areas (total 4,177 km²), is evaluated in this paper. This rock fall rate is estimated in two flods. First, the relative rate of rock falls is estimated by the logistic regression analysis based on the inventory data of slopes along the major roads in the region which includes about 3000 slopes. The inventory data include past events records, as well as topological, geological and geotechnical characteristics of each slope evaluated by the experts in 1996. The slopes are also classified into three categories by the experts as "measures required', "continuous observation" and "no measure required". Based on this classification, the logistic regression analyses are carried out to rank the hazard of the slopes by their attributed characteristics as the explanatory variables. Once relative rate of rock falls are estimated for each slope, this rate is calibrated to the absolute rate by using the actual rock fall event records between 2004 and 2008. By these two folds estimation procedure, the absolute rate of rock fall for each slope along the roads are finally estimated. This study is a part of the development of a methodology for making road maintenance strategies based on risk. Thus, the information gained in this study is combined with other data for damage to propose the strategy for repair and maintenance plan of the road slopes in this region.