INFLUENCE OF ANTECEDENT PRECIPITATION ON SLOPE FAILURES AT THE YOKOGAKI-TOGE PASS

The heritage of many cultures of the world consists of buildings, including shrines, temples, and ruins; only two such heritages have places of pilgrimage that incorporate roads. One of these is the Kumano pilgrimage route, along which there is a risk of sediment disasters. In 2011, Typhoon Talas caused collapses at Yokogaki-toge, which is part of the Kumano pilgrimage route. Two studies examining the localized characteristics of the rainfall, and how the rainfall contributed to slope failures at Yokogaki-toge, are described in this paper. Seepage flow analysis was carried out based on two types of rainfall, which enabled us to identify the characteristics of the rainfall event which triggered the collapse. Our results indicate that the characteristics of antecedent precipitation affect the infiltration characteristics, and the formation of a saturated zone. Localized rainfall was observed at multiple locations within Yokogaki-toge, with regional variations in the amount of rainfall. North-facing slopes are subjected to more rainfall than south-facing slopes, which may cause more weathering of these north-facing slopes.