The effects of normal stress and soil water conditions on soil strength and the process of shear deformation were estimated with a simple shear test using Toyoura standard sand. The simple shear test was able to depict shear deformation and was executed under low normal stress conditions that reproduce shallow landslides. This paper proposes an equation that describes the relationship between shear stress and shear strain. The equation corresponds well with the results of shear tests.
The effects of normal stress and soil suction on the shear deformation process between shear stress and shear strain were explained by variation of the equation parameters. A response analysis of the equation parameters clearly separated and explained two suction effects due to effective stress and another not due to effective stress.

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In order to find out the physical parameters which are useful to the prediction of steep sandy slope failure due to rainfall, behavior of physical parameters such as degree of saturation within the slope, pore water pressure at the bottom, and surface displacement were examined by the slope failure experiments and the numerical simulations. In the numerical simulations, mechanical model for slope deformation due to rainfall proposed by the author was used. These examinations bring the results as follows.
1) In the case of lower inclination of the slope, the degree of saturation in the slope starts increase earlier and is larger than in the case of higher inclination. And pore water pressure is often generated and follows the increase of degree of saturation at the lower layer of the slope. Surface displacement only increases remarkably after the generation of pore water pressure. So the degree of saturation at the lower layer can be a useful parameter for the prediction in the case of lower inclination of the slope.
2) In the case of higher inclination of the slope, surface displacement starts remarkable increase much earlier than in the case of the lower inclination while there is no generation of pore water pressure. So surface displacement is a useful parameter for the prediction in the case of higher inclination of the slope.

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Up to this time, public works was enforced regarding social foundation preparation as the last goal. A main purpose of public works was showing of those functions. In case of Sabo works, it was the most important task, to defend human life and properties from sediment-related disaster. Recently, a citizen life got rich and social requests was diversified. Therefore, it is the present state that interests of citizen starts being assembled into various effects brought about by Sabo works, for example natural environment conservation effects. As natural environment is conserved by Sabo works, our citizen can enjoy an opportunity of recreation. However, because judgments of these effects depend on mentality and sensibility of a human being, evaluation method against these effects isn't established. On the other hand, recently, studies that do to evaluate environment goods by means of sociological knowledge are put into practice. Then, many examples are accumulated. In this study, evaluation of environment conservation effects brought about by Sabo works in Rokko mountain region was carried out, by means of Travel cost method and Contingent valuation method. For the results of this investigation, though a big disparity was confirmed in appraised value depending on both method, an appraised value for natural environment in Rokko mountain region understood to be a range of 30-1, 200 hundred million-yen.

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A debris flow has occurred at torrent Nishinogaito-gawa, in Fujiwara-cho in Mie prefecture on August 19 th, 1999. Heavy rainfall of more than 50mm/h was the most effective factor for the occurrence of the debris flow. There was no damage by the debris flow according to the existence of check dam just constructed and the warning system. A small scale debris flow at the same torrent in 1998 has forced to construct this facilities and it has fully functioned.

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As we have constructed closed type of sediment control dams in devastated watershed, sediment trap capacity of the dam has been decreased in a short period. It is necessary to think out efficient methods to increase a function of sediment control dam and groundsel. The sediment control dam with sediment control trap gate has been planned in upper reaches of Koshibu River. In this study, a slit was cut in Ogawara groundsel and effects of sediment control of slit type dam were investigated by the variation of channel bed survey, to examine sediment outflow from sediment trap gate. Furthermore, relationship between scale of runoff and sediment outflow from slit was discussed. As the result of this investigation, it was confirmed that effects on sediment control of groundsel increased by providing a slit of width of a few 3m for overflow section of width more than 100m.

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Mt. Usu, one of the most active volcanoes in Japan, has been erupting since March 31, 2000. A lot of refugees had to leave their home for a long period because of risk by volcanic activities. The authors made research to know the refugees' thoughts about rehabilitation and recovering of their home and town. The results were as follows; most people answered that the damage of houses were not so heavy, but those who lived in the district seriously damaged by hot muddy water recognized the damages were heavier. Regarding living, around 40 percent people want to live in the same home, and more over the half residents have intention to resettlement. Regarding employment, around 30 percent people were retired their jobs during the refuge. Also about income, 36 percent residents claimed that their incomes were decreased and 27 percent people feared that the incomes would be decreased. Regarding measures, around 60 percent people thought that constructed sabo dams were effective. More over 50 percent people fear that mudflows recur in future. The authors propose that the houses in extremely dangerous district may be moved; required sabo facilities should be constructed in order to secure more safety of the area; the people exploit the property of active volcano as tourism resources.

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An earthquake measuring 6.4 in Magnitude (M) on the Richter scale occurred at 16:02 on July 1, 2000, with an epicenter in the sea near Niijima and Kozushima Islands in the Izu island chain. It was followed by torrential rainfall caused by typhoon No.3 in July 7 and 8, and another earthquake measuring M 6.0 at 3:57 on July 9, with a hypocenter near the previous earthquake. They triggered many slope failures in Kozushima Island. The slope failures damaged some houses, and also produced a large amount of sediments on the beds of many streams.
In order to assess the risk of sediment-related disasters, the team of Erosion and Sediment Control Department in Public Works Research Institute has surveyed the state of slope failure deposits and erosion and sediment control facilities. The results of the surveys from July 4 to 6 and July 10 to 11 are as follows. 1) Slope failure sediments on the streambeds increase danger of debris flow disasters, because these streams have few erosion and sediment control facilities, except for Kozusawa. 2) Many slope failures and a few landslides were recognized in the surveyed area. Many of these failures occurred in the area of pyroclastic deposits. 3) The torrential rainfall by typhoon No.3 and the earthquake in July 9 widen the area of slope failure caused by the earthquake in July hand also caused new failures. It suggests that additional rainfall or earthquake will cause new failures and area extention of the failures which already occurred.

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