In this paper we describe an experimental study on the inclination-angle of the spillway-crown, which the sediment overflowing a Sabo-Dam are letten fly away maximum distance. 1. It seems to be quite all right to consider that the sediment which leave the spillway-crown, falling in the parabolic motion. 2. In figure-1, the relation of the falling distance (X) and other factors may be formularized following equation: X=-υs2⋅g-1⋅sinα⋅cosα+υs⋅g-1⋅cosα[υs2⋅sin2α+2⋅g(Y-S⋅sinα]1/2+S⋅cosα where υs is the velocity of the object on the point B, S is the length of slope (from A to B), α is the angle of slope, g is the acceleration of gravity, Y is the height of Dam. Then, We are able to rewrite this equation as follows: υs′=L/[2⋅g-1⋅cosα(H⋅cosα-L⋅sinα)]1/2, L=X-S⋅cosα, H=Y-S⋅sinα where υs′ means the caluclated velocity by the experimental datd. 3. The velocity of the spherical objects which are roll down at the slope on the point B is estimated byfollowing equation: υs=[υ20+10⋅7-1⋅g⋅S⋅sinα]1/2 where υ0 is the velosity on the point A and this υs is the theoretical value. 4. Useing several materials and sizes experiments were done and obtained the velocity ratio υs′/υs such as following: Steel ball: 89-98% average 96% Porcelain ball and Glass ball: 80-95% average 91% Cobbles in the river bed: 69-89% average 79% 5. We tryed same experiments which several sizescobbles were throwed into the flow of overflowing the Sabo-Dam in practice and made observation the same phenomena, above-mentioned. From the results of our experiments, it may be conclude that the optimum angle of inclination for spillway-crown of the Steel-Dam seemes to be suitable for 25-35 degree.
The purpose of this study is to forecast the mean time of landslide occurring caused a heavy storm.The time series of landslide occurring ratio ηt was calculated by the next gamma distribution model. ηt=F(C, rt)-F(C, rt-1)/F(C, rτ), F(C, rt)=1-∑e-1j=0(λr)j/j!e-λr Function F is the probability that an unit slope will slide under the condition of resistance index C, shock rate λ and total precipitation at time t since a rain starts. Consequently F means the landslide area ratio of a watershed. Monte Carlo simulation based upon the stated above model was carried out by an electro mini-computer according to the next procedure. The probability λΔrt was calculated following hourly precipitation Δrt. The judgment whether a shock would happen or not was decided at random by the next inequality, ζt≤λΔrt :happen, ζtλΔrt :not happen where ζt was a uniform random unmber ih the range(0, 1). These operation ware repeated through a series of hourly precipitation at a thousand unit slopes. Consequently an unit slope where many shock, for example j in above equation, were accumulated over the resistance index C was consider as the occurence of a landslide. In this simulation, if the value C is small, the time series of landslide occurring ratio is influenced immeadiately by the pattern of hyetograph. Conversely if the value C is big, the response from rainfall to landslide occurring slows down and a single sharp peak appears behind the maximum hourly precipitation. Meanwhile the time when landslides had broken out was searched by questioning and time series of landslide occurring ratio was got at Fujioka, Kuno and Minami Izu region. At the results of the comparison with these series of landslides by questioning, calculation and simulation, the tendancy of these series are agree under the adequate resistance index C. Therefore, the gamma distribution model and its simulation are effective significantly to forecast the mean time of landslide occurring at some arbitrary region. But the estimation on the resistance index C is difficult and controls the accuracy of a forecast.
Nuta and Yo-une landslide areas located in the northern part of Kouchi prefecture and belong to the Mikabu geological zone. The Mikabu zone is formed of socalled Mikabu green rocks which is composed chlolite, actinolite, epidote, felspar, calcite and quartz. The landslides of the Mikabu zone are characterized by slope inclination, land-use and slide moving type. It seems that those characterestics are caused by Montmorillonite contained in landslide debris. Samples which were surface, subsurface soils and weathered rocks were collected in study area. Laboratry analysis of sampled soils were performed on the measurment of soil suspention apH nd X-ray diffraction for clay particle(2μ). The resulst are as follows: 1) surface soils which wrs yellowish brown contained organic matter, were commonly contained Vermiculite, Kaolinite and Chlolite expect for Montmorillonite. Soil pH value is about 5-6. 2) Subsurface soil about lm depth which was graysh green, contained Montmorillonite and Chlolite. Vermiculite was not existed in this layer. It seemed that the Vermiculite decrease with depth. Soil pH value indicated abut 7-8. These facts are used to estimate the formative enviroment of Montmorillonite. 3) Montmorillonite was not only in subsurface soils, but in weathered rocks.
The large scale debris flow that occurred at Hora-dani in Gifu prefectere in August, 1979, gave a good chance to the case study on the mechanism of debris flow. Application of writer's theory to the processes of occurrence, flowage, and deposition fitted rather well in actual phenomena. Thus, the writer's mechanical method for the delineation of debris flow hazardous area was demonstrated as one of the promising approachs.