Many sabo structures; dams, groundsills and embankments have been constructed in mountain areas. Some of them are hated because white bright surfaces of new structures dismatch with natural surroundings. To add dyes to concrete and to make ruggedness on the surfaces are examined to reduce the brightness and to hermonize sabo structures to their surroundings. Elements controlling results are picked out and evaluated through experiments. The methods give good results. Darker surfaces and not too much contrast get good reputation. These methods are applid to a sabo dam as an example by a photo montage methods.
“Pseudo Factor of Safety” was calculated by multi-planar sliding surface method using shear strength proposed by Okimura (1982) . Using pseudo factor of safety (fp), following results are obtained in 6 sampled areas. 1) As obtained value of fp is connected with thickness of failure potential layer (Figure 2), effect of the thickness on fp needs to be taken off. Gamma, which is a function of thickness of the layer, is introduced to accomplish this purpose. 2) Discriminant function of slope failure, whose value can be called as critical pseudo factor of safety (fpc), are regressed by using area of catchment (S) and gamma explained above. If fp is less than fpc, slope failure will occur. The result obtained was that 73%-100% of slopes were properly discriminated in sampled areas. 3) The result of discrimination was obtained similarly to that of the previous analysis when 1.3 times as much as value of shear strength is used. If value of fpc-fp of a slope becomes plus, then its solpe will be failure. Average of the absolute value of differences between fpc-fp in previous cash and that in this case is 0.018-0.025. 4) A critical effective precipitation (Pec) can be defined on each slope. If effective precipitation is more than Pec of a slope, slope failure will occur in the slope. Pec is linearly regressed by using logarithm of S, fp, and gamma mentioned above. In one sampled area, relative error of decided Pec is about 8%.
A sediment related disaster occurs frequently in rainy seasons in Japan. In this study, pressure heads in the soil were measured at 10 points on the hillslope consisting of weathered granite to get fundamental data to explain the behaviour of rainwater on a forested hillslope and the mechanism of hillside landslides. The observed suction for natural rainfalls was reproduced by a numerical model that estimates the process of infiltration as a vertical unsaturated seepage and a parallel saturated flow along the slope. Following matters were found by this study. (1) Drying and wetting processes of soils step forward to deeper layers from the surface. (2) The arrival time of rainwater to the bedrock decreases with a decrease of the depth of soils. (3) In the initial stage of rainfall, a large amounts of rainwater are temporally stored in the weathered surface layer that contains organic matters. And, it reaches the bedrock layer gradually as the time goes. (4) Comparison of the observed and calculated soil-moisture content showed that this simulation model is adequate for reproducing the arrival time and the infiltration process, of rainwater.
Sabo dams have not had sediment frash gates. Sediment control functions of ordinary sabo dams snd slit sabo dams are limited. One of the methods to improve sabo dams is to install sediment frash gates to them. The feasibility of the installation is examined from the structural view point. The result is; it is possible. Some specific gate types and locations of the installation are recommended.