1996 Fiscal Year Final Research Report Summary
Study on the evaluation of hazard against the attack of debris flow in areas of damaged slopes by windfalls
| Project/Area Number |
06660193
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| Research Category |
Grant-in-Aid for Scientific Research (C)
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| Allocation Type | Single-year Grants |
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| Section | 一般 |
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| Research Field |
林学
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| Research Institution | Miyazaki University |
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Principal Investigator |
TANIGUCHI Yoshinobu Miyazaki University, Faculty of Agri., Porfessor, 農学部, 教授 (70041051)
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| Project Period (FY) |
1994 – 1996
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| Keywords | Debris flow with floating logs / Windfalls / Coefficient of slope stability / Index of slope stability / Soil hardness / Coefficient of permeability / Windfalls of broken tree's type / Windfalls of fallen tree's type |
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| Research Abstract |
Relationship between the occurrence of windfalls and morphological factors in areas of Hita District, Oita Prefecture, and Nango Village, Miyazaki Prefecture, were investigated. As a result, some of morphological characteristics were found. The percentage of the occurrence of windfalls had the peak at about 23 degrees in slope gradient. Most of windfalls of fallen tree's type occurred in areas at 300m-700m, and the ones of broken tree's type occurred in areas at 200m-400m in altitude in the district of Hita. However, there are many windfalls of the former type occurred in Nango Village. Most of them were located in areas at 310m-410m in altitude, and these of valley tracts exceeded those of ridge tracts 10-20 in percentage. Type of the windfalls was classified by the magnitude of fluctuation of a gale. Its characteristic was calculated in 0.2 seconds-0.3 seconds in cycle time. The experimental results proved that a number of windfalls of broken tree's type would occur at a site a bit down from the top of a slope. Deterioration of the slope strength by windfalls was discussed using the data of soil hardness and coefficients of its permeability. It was found that the coefficient of slope unstability got 0 at the depth of 60cm-70cm from the earth surface, and the lower soil layrfrom the above was not so much crushed by the typhoon. It was known by the way of kinematic wave that time for the occurence of slope failure in areas of windfalls of Nango Village would become 10%-20% smaller in comparison with non-damaged slopes, and the precipitation for it would take only 15mm/hr in the district of Hita.
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