Abstract
Large-scale collapses are often observed in rock slopes called “dip slope of type II” by author. In this type, the angle of geological separation is larger than it's sliding friction angle, and is smaller than that of the rock slope. When the angle of separation exceeds the angle of the rock slope, the slope is classified into the “dip slope of type III”. In this case, even if the cohesion becomes zero, the rock will never slide as long as the basement of slope is destroyed because the sliding is occurred in the direction that the basement resists against sliding movement.
This angle of dip slope corresponds to the maximum limit of danger for sliding to occur, and is called “critical factor of danger”. Ratio of a factor and the critical factor is defined as “hazard index”, and provides us a criterion to judge the danger of sliding collapse.
When the index is applied to a hill behind of Asagishi railway station and to rock slopes in the vicinity of this station, it was proved that the index provides us with a rough criterion of sliding danger.
