Wind throwing and root wedging occur as trees are overthrown by strong winds. Wind pressure on a tree can produce a destabilizing, moment which will cause it to topple over. The uprooting mechanism has not been clarified yet, and a theoretical uprooting model is proposed and the resistance force of root wedging is estimated in this paper.
The uprooting is considered as a phenomenon that a tree with a hemisphere of soil is detached from the ground, generating resistance force due to friction between the root and the ground. Root wedging force depends on tensile strength and pulling resistance of roots.
The pulling down experiment of trees was carried out to prove the proposed uprooting model true. The moment curves versus the rotation angle of the test trees calculated according to the model is verified to be in conformity to the findings of the field experiments.

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On the occasion of designing the anchor works for the purpose of stabilizing the slope, it is necessary to estimate the shape of slip surface, the location of anchor forces and its acting angles. Kondo has showed the designing method as concerns the shape of slip surface. On the other hand, Kawasaki et al., Yamagami et al., Yoshimatu et al. have discussed the location of anchor forces on the condition of the given slip surface such as a landslide. But the location of anchor forces for slope stability has been seldom reported in the condition of the unknown slip surface such as a slope failuer. In this paper, therefore, the authors clarify the design method of the effective anchor force location on the condition of the unknown slip surface by the analytical methods of the model slope. The results of an analysis are obtained from the Slice Spring Method as a slope stability method and Quasi-Newton method which is one of the nonlinear programming as a optimization method for slope stability analysis.

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In order to match Sabo facilities to surroundings and to make them suave to the human sense of vision, surface patterns seem to be as important as the brightness of the surface. In this point of view, here the focus is put on the surface pattern on Sabo structures, and the investigation by means of spatial frequency fluctuation, Fractal dimension, questionnaire, and multi-discriminant analysis are carried out. Natural torrent bed surface is felt as “bland surface pattern” in the sense of vision, therefore they are supposed to have “bland fluctuation i.e. 1/f fluctuation (f : frequency)”. Consequently, it is found that the surface pattern with 1/f fluctuation have suave vision and the handmade structure like stone-made dam has 1/f fluctuation that means “the human touch bland pattern.” But simple pattern with a keen peak in its spectrum seems to give a good impression, too.

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We developed a new direct shear apparatus with soil water control to evaluate the effect of soil moisture on soil strength under low normal stress. The sample column of the apparatus consists of two poly-vinyl chloride pipes (total size 19.8cm in diameter, 55cm long); one pipe comprises the upper part (5cm) and the other the lower part (50cm). The shear plane lies between these parts. The capillary water pressure, as the negative suction pressure of the soil, is determined at the shear plane to control the water level in the lower part of the apparatus. To evaluate the shear strength obtained by the new direct shear apparatus, we compared it with results of other shear test apparatus using Toyora standard sand. The results of the new direct shear apparatus correspond well with those of other shear test apparatus. Therefore, we concluded that the new direct shear apparatus provides an adequate assessment of the shear strength. Next, the effect of soil moisture on the shear strength was evaluated. Various soil moisture conditions greatly affect the apparent cohesion, but almost independently of the internal friction angle of the Toyera standard sand. In the lower suction level, more than in the critical capillary head (29cm H₂O), the apparent cohesion fluctuation showed a positive linear correlation with the increase in soil suction. The shape of the variation curve of apparent cohesion in this range can be explained by using Bishop's theory (that effective stress expands to an unsaturated zone), but the increase in apparent cohesion was greater than the value estimated by Bishop's theory. These results suggest that soil suction not only influences the effective stress but also the physical properties (elasticity, etc.) of sand.

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Nango Village, Miyazaki Prefecture, suffered a great damage from windfalls caused by Typhoon 13 in 1993. The damage in these areas from slope failures was researched from morphological and soil mechanics aspects. The following results were determined. The percentage of the occurrence of windfalls in valley tracts was 10% higher than in ridge tracts. The great amount of windfalls occurred in areas at 300m-400m in altitude. The diameters of windfalls' butt-swells which are concerned with holding trees in stands on mountain slopes were rather small in comparison with their stem lengths. Therefore, the roots of these trees were not strong enough to fix their stems to the earth, and they were easily blown down by the strong winds of Typhoon 13. There were 3 types of windfalls: breaking, over-bending, and falling trees. Differences among them depended on the magnitude of the critical breaking strength of wood, the cycle of the fluctuation of wind velocity, and the diameters of butt-swells of trees. Crushed soil layers caused by the great shaking of the butts of trees in the hours of the typhoon extended to a depth of only 80 cm from the earth surface. These slopes took about 5% less time to collapse than normal slopes.

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Fishway function of low dams series was studied in Shiretoko Peninsula, Hokkaido. In three sets of the low dams series, pool depth, head (vertical drop between top of a dam and surface of pool formed just below the dam) and total fall (sum of the depth and the head) were measured. Total fall varies in accordance with fluctuation of stream bed elevation nearby. When total fall is constant, pool depth and head greatly fluctuate. Low dams series thereby can be a barrier to upstream passage for fish. Installing a trapezoid notch to a low dam is efficient for reducing head temporarily. However, degradation of the stream bed possibly causes expansion of total fall and head. In order to ensure fish passage, structure of dam should be modified as follows. Fixation of channel course by making a cut with enough width and depth for flood passage is required. Installation of auxiliary dam is still effective where the next downstream dam prevents excessive degradation of the stream bed. Making downstream slope of a dam gentle and extending it into the stream bed would help fish passage.

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Consideration for the ecosystem and landscape in sabo works has become essential, as the consciousness toward environmental conservation has grown. This study has tried to analyze the sense of landscape evaluation to sabo facilities, and clarify its effect on evaluation to sabo facilities. The evaluation was determined by landscape evaluation method: Semantic Differential (SD) method and Fuzzy Analytic Hierarchy Process (Fuzzy AHP) method. Questionnaires with sampled photos were distributed to officers of the sabo work office, (1) research division, (2) engineering works division, (3) general affairs division, and to groups of general public, (4) tourists, (5) amateur cameramen, and (6) undergraduate students. The results of the evaluation by these 6 groups are as follows: (1) Officers in the research and the engineering works division attach greater importance to structure and function of sabo facilities and evaluate them depending on not only the sense of sight but also their informations which have been got already. (2) People in general who have nothing to do with sabo works place greater importance on harmony between sabo facilities and the surrounding environment, and are fond of sabo facilities which harmonize with greenery and old sabo dams. (3) The evaluation by officers in the general affairs division is relatively close to that of general public.

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