Appricability of the quantification method II to the discrimination of landslide-prone areas was examined. Six quantities obtainable from a topographical map and likely to be related to landslides, were treated as representative of the geomorphological information. The six quantities are elevation, slope inclination, depth from the summit level, height above the river level, relative relief, and drainage density. Data were collected from each grid square laid on the topographical maps Shinano-Nakajo and Takafu, in which a large number of landslides have occurred. Accuracy of the discrimination was examined by the following four factors. They are precision of elevation measurement on the map, size of the grid square, categorization of the geomorphological items, and data sampling from the grid considered to be safe from landslide risk. The accuracy was largely affected by the data sampling. A simple improvement of the data sampling raised the accuracy of discrimination from 74% to 95%, as judged from a comparison with the actual landslide data.

View full abstract

Ih the plan of measuring works for landslide, the strength parmeters of soil of slip surface are ordinarily obtained by the back analysis. This reason is that the safety factors obtained from the stability analysis considering the strength parameters by the shear test usually exceed 1.0.
The strength parameters of clay picked up from slip layer of cut slopes agreed approximately with the strength parameters obtained by back analysis. The stability analysis of landslide at fracture zone in Shikoku district were carrid out using the experimental strength parameters. Most of the safety factor of the landslide exceed 1.0. This means that the movement of landslide is the creep phenomenon.

View full abstract

Generally, degree of danger of slope falures is estimated by stability analysis. However, mainly from economical limit, when object site extends very wide area such as for the estimation of slope falure due to earthquake, estimation based on tha factors which is related to slope falure can be effective. For such a judgment, the Fuzzy Set Theory is found to be useful. Therefor, the authors introduce this theory into the estimation and apply it to the estimation of slope falures due to the Chiba-ken Toho-oki earthquake. As a result, good correlation is found betwen the Fuzzy Integral which is the index of the degree of danger and factor of safety calculated from stability analysis.

View full abstract

This report presents the methods of quantitative assessment for the function decrease of ground drainage facilities with the progress of time after completion of them by using data of pore water pressure and drain water volume which change depending on time series.
For development of the methods, we used data which were observed at Sarukuyoji Landslide area. Two methods are considered in this study. At the tension zone where has sliding mass of high permeability, the method involves estimating the value of rain sensitive pore water pressure and drain water from horizontal drainage boring by using equation (2), (3), and comparing to this with the value of the reference period. At the compression zone water has sliding mass of low permeability, the method is to evaluate yearly changes of the observed data of pore water pressure just before the snowfoll.

View full abstract

[in Japanese]

View full abstract