I considered the following problems from mathematical view point.
(1) The relation between the practical safety period and the period of landslide happening.
(2) The economical merits and demerits when we apply the forecasting to prevention works.
(3) How to make the research program of landslide reasonably.

View full abstract

Remote sensing have been done its remarkable technological advances during the last 10 years. It is very available to detect the vegetation growth, ocean environments and pollutions, earth resources, transition of land use formations and other many fields. In remote sensing technique, the physical characteristics (spectral reflectance and radiance) and space characteristics (form, distribution and continuity) are detected remotely, then remote sensing data are processed and interpreted. The features of remote sensing are in following points; rapid and spacious data collection, remotely analysis and interpretation of objects and detectability of phenomenas which are not able to catch by the usual techniques.
This paper is intend to comment on the technique of the remote sensing and its availability for the natural resources and environmental quality survey, as followes; basic subjects of remote sensing, classification of the remote sensing and image processingse In addition, a brief comments on the evaluation of the possible usage to furture technique is described.

View full abstract

[in Japanese]

View full abstract

The prospect of permanent measures of a land-slide disaster will be promissing, if it is possible, through reviewing the disclosing process of land-slide phenomenon, to grasp accurately the part of subterranean water, which plays all over a land-slide area. The authors have applied several field experiments to the land-slide district of Kuriyamazawa, pursuing after the uttermost limit of deduction according to the respective definition, i.e. specific discharge, specific electric resistivity of the earth, natural moisture content in a boring core and electric conductivity of water in a well, a spring, a pond and a brook. The proposal of the authors concerning the evaluation technique of water content of any kind of natural phase at the site, appears to prove effective for designating features, such as geology or soil character.

View full abstract

A description is made of landslides occurring in the north part of Nagano Prefecture. The geology of slopes there consists of the Tertiary layers. Most of landslides belong to the shallow layer slide induced by the surface colluvial soil and by weathered rocks in the shallow layers of the slope. But some are the basement rock slide caused by collapsed basement rocks. The basement rock slide, which is rarely seen, is generally large in scale and complicated in structure, involving troublesome problems for its protection work. Since the slide surfaces are formed in the depth affected by the geological structure, the land mass doesn't always slide along the slope of the mountain. In order to investigate the occurrence mechanism and to predict accurately its occurrence time of basement rock slides, it is most important to grasp the movement mechanism of rock masses causing landslides.
This paper reports the movement characteristics and development processes of Chausuyama landslide representative of the basement rock slide. The Chausuyama sliding area sited in the south-west of Nagano-city is 2, 000m in length and 46 ha. in area, having a land mass of 9, 000, 000m³. The depth of slide surfaces reachs 40m in the upper slope. The basement rock of this sliding area consists of the tertiary miocene rhyorite tuff and sandstone-mudstone. Layers of sandstone mudstone wraps in conformity the rhyorite tuff, and the thin layer of mudstone running between the rhyorite tuff and the sandstone-mudstone forms slide surfaces. The strike of the thin layer is N45°W and the gradient has 30°SW. and to the direction of the strike does the rock mass slides. At Chausuyama area the rock mass has slided from the south peak to the south-east direction, but this direction of slide doesn't coincide with that of the lanform slope (the north-east). Hence starting from the Shinano-Echigo earthquake, the Chausuyama landslide has been developed by the weathering of basement rock and the change of veins of groundwater. The apparent change of the mountain is the occurrence of cracks at the south peak in 1884: then the slopes in the east gradually and the slow sliding movement occurred between the south peak and the slope of 800m domnward. The collapsed landmass slided to the east along the stream of the Takizawa-gawa river to form the present landform.
The development process of landslide will be classified into the following five stages.
(1) Preparatory stage: 1847-1883
(2) Fluctuation stage: 1884-1929
(3) Primary heavy sliding movement period: 1930-1943
(4) Secondary heavy sliding movement period: 1944-1964
(5) Stabilized period: 1965-
The slide mechanism of Chausuyama area, ahs been affected by ground structure from the early stage of landslide occurrence. As a result of landside, a special landform, which is not produced by the ordinary weathering as the fluvial erosion, has been formed.

View full abstract

The case-history of a landslide in detritus in the Himalayan region is presented. An attempt is made to determine whether the in-situ shear strength of detritus along the surface of sliding, mobilised at limiting equilibrium, conforms to the shear strength of overall detritus material as such, comprising both the hard roch inclusions and the matrix soil or else by the shear strength of matrix soill alone. The study points out that in the effective stress method of analysis of landslides, which occur for the first time, the peak shear parameters of the matrix material govern stability at limiting equilibrium.

View full abstract