2008 年 15 巻 p. 23-31
This study describes method to determine risk due to landslide and applies Certainty Factor (CF) model to determine landslide susceptible area along the most important highway in Bhutan. The quantification of the risk in terms of total duration of road blockages was done based on the data collected from eleven years eight months period Kuensel (weekly newspaper of central government). The total traffic and passenger losses determined with freight and passenger transport value losses in terms of dollar values indicated that the road operation risk would have significant impact in terms of economic value for the country. The certainty factor model that used 149 cases of the existing landslide with its affecting parameters indicated that the landslide certainty factor increases with the increase of slope value above 30° for the slopes facing towards the south. The rainfall parameter showed the increase in certainty value from the rainfall intensity of 7.76 mm/day. The lithological and land use parameters used indicated the certainty of landslides in phyllite areas and barren area with grasses. Application of the certainty factor model along the most important highway in Bhutan could delineate the susceptible areas similar to the existing landslides.