The occurrence of landslides generally depends on complex interactions among a large number of partially interrelated factors. It is appropriate to use multivariate analysis for predicting landslides from a given set of independent variables. However, the procedure of landslide hazard assessment by regression analysis requires the evaluation of the spatially varying terrain conditions as well as spatial representation of the landslides. In this paper, multivariate regression analysis was applied to predict landslides in the Himi district from independent factors, such as geology, clinal-aspect, slope angle, land use and soil using Geographic Information System (GIS) . Based on GIS, every factor was classified into several categories and then the statistical weight of every cluster was assigned for every factor respectively. By the weights of five factors, the linear regression's coefficients of these input factors in landslide area were extracted and assigned to the whole region, and then the susceptibility for the potential landslide was obtained to make the landslide hazard assessment map. According to the coefficients in the Himi district, geology and clinal-aspect factors are the most important ones. Soil factor is not so notable in this research region, though it may be significant in other regions. Finally, the average susceptibilities map for existing landslides was made for the engineers to do control work.
Stratum water and crack water passing through cracks of bedding planes and joint surfaces significantly influence the amount of displacement of moving mass in a landslide area. Measuring technology using borehole imagers has recently advanced and enabled us to determine crack direction, crack scale, crack frequency and loose zones in the ground. We have developed three-dimensional seepage flow analysis for dealing with aspect cracks and line cracks from joint surface or schistosity planes. In this paper, we accurately modeled structures containing an enormous number of line cracks and conducted three-dimensional seepage flow analysis in the SHIONOYAMA Landslide area. As a result, we found that line cracks tend to decrease the pore water pressure. In addition, the response of water pressure to rainfall was found to be delayed and the profile became sluggish for deep groundwater. We demonstrated that we were able to analyze a three-dimensional seepage flow of ground filled with line cracks.
A simple finite element analysis system to evaluate the seismic slope stability in the mountains area is proposed. The time history of the dynamic ground response during strong earthquake can be estimated by an effective constitutive model of soil with appropriate soil parameters. A comparison of the calculated results with the observed damage distribution in old Yamakoshi village during Mid Niigata Prefecture Earthquake in 2004 is performed to validate the proposed analytical method. As a result, a few important conclusions, that will be useful to develop a more simple and effective method to evaluate the risk of seismic slope failure based on a local topographical and mechanical condition, are provided.
Recently, landslides triggered by heavy rain have occurred widely. This study note was designed to have a good grasp of the relationship between a heavy rain and ground water level in a shear zone landslide area. As a base of the method of prediction of safety factor of slope based on rainfall, the amount of precipitation of agricultural landslide areas and ground water level in a lot of bore holes set in the areas were observed, and the relationship between them were analyzed. As a result, it became enabled to grasp approximately the relationship between them in the area, by determining the half-period of accurate rain based on the change of ground water level cased by rainfall. In addition, from the view point of the relationship of the accurate rain and ground water level, it is considered that there are two kinds of modes there, and that the difference of forms of rainfall causes them to appear.