Abstract
This paper describes an occurreNce of trees fallen by storm caused by typhoon 9807 on September 22th, 1998 and the following slope failures in Hichisoucho, Gifu prefecture.
The author investigates geology, vegetation and ground condition from simple penetration test to clarify the characteristics of forest damages and damages of grounds.
The results of this study are summarized as follows;
1) Trees fallen by storm are much in afforested coniferous forest. However they are little in broadleaved forest.
2) Most amount of disaster by fallen trees occurs the slope on the ground conditions where basement rock is shallow in depth, moreover, where do not thin out a forest.
3) Damage of grounds for trees fallen by storm is regarded as Nc≤2 by simple penetration test. The damage is much on the slope afforested by coniferous trees such as white cedar and Japanese cedar. In broadleaved forest, the damage is little.
4) Slope failures on damaged grounds for trees fallen by storm occur along the gentle valley caused on concentration of surface water and ground water.
5) Slope failures on the ground damaged for trees fallen by storm are characterized as many following occurrence of debris flows, because of including many fallen trees.
