In this study, drainage basins with landslides in the Akaishi Mountains are estimated using the decision tree technique which is a kind of data mining technique. Decision tree technique is characterized by the estimation processes which are explicitly and quantitatively represented by Tree-structures. The purpose of this study is to clarify the relationship between landslide and topography/lithology using Tree-structure. To estimate drainage basins with landslides, topographic characteristics (elevation, slope, profile curvature, plan curvature, dissection and undissection) and geological data were used as explanatory variables. Topographic characteristics were calculated from the DEMs (Digital Elevation Models) of EOS-Terra/ASTER. Objective variable is landslide area data. Correctness of the estimation is 71.2%. The estimation processes quantitatively indicate that the lithology, plan curvature and the slope angle play important roles for estimating drainage basins with landslides. In addition, drainage basins where landslides occur frequently tend to have concave terrain and lower slope angle. While in the Setogawa group, distribution of landslides is not uniform, and landslides are concentrated in the drainage basins where slope angles are relatively small. It is concluded that the decision tree technique can indicate the order of important explanatory variables clearly. This technique can also indicate the quantitative relationship between landslides and topography/lithology.
The changes in pore-pressure, effective mean stress, and deviator stress in the undrained triaxial-compression tests on sands have been numerically analyzed by means of three dimensional Distinct Element Method (DEM) . The value of pore-pressure was assigned to the measurement sphere, the cnetre of which was coincided with the one of each ball element and the diameter of which was twice as much as the ball element. The volumetric changes in those measurement spheres due to the deformation of the cylindrical shaped specimen were calculated and the changes in pore-pressure was obtained by the products of volumetric strain and modulus of compressibility of water. The fluid flow was given based on the Darcy's law. The effective mean stress negatively proportional to the initial void ratio after consolidation was obtained, that is the steady state line was observed, and the loose specimens produced quasi-liquefaction behaviour, in which effective mean stress at steady state was reduced to no more than 25% of the initial confining stress. The medium-dense specimens produced the positive pore-pressure at the beginning of the test and then it reduced its values to remain negative, which successively reproduced the phase transformation that was typical characteristics of the granular materials.
A risk evaluation of old landslides in the Hachimantai area, in northern Japan, was performed to determine a priority rating for effective countermeasures. The evaluation was based on the slope stability analysis where circular slip surface and constant soil strength for all landslides were assumed. From this study, a color-coded map of landslide hazard were obtained, in which the potential for dangerous landslides was easily recognized. It was found that large landslides had generally lower probability of reactivation compared to small-sized landslides and that the safety factor was more dependent on the gradient of the slope than the scale of the landslide.
This paper presents a relation between the effective friction angle and the shear rate. Tests were carried out by means of a ring shear apparatus under undrained condition using artificially mixed silica sand and bentonite specimen. As a result, the relations between shear rates and effective friction angles were recognized. Based on the values of effective friction angles, authors indicated the change in shear mode with shear rate.
Mid Niigata Prefecture earthquake has induced numerous landslides, and hence it has become at most importance to study the mechanisms of these earthquake-induced landslides. Among many landslides, the soil mass of the landslide in Higashi-Takezawa area traveled long distance and consequently caused clogging of the Imo River. A particular emphasis has been placed on the study of the mechanisms of this landslide to examine whether rise in the pore pressure has been one of the controlling mechanisms of the failure. However, no conclusive results have been reported so far to clarify the effects of the pore pressure. In this study, FEA has been performed with analysis code LIQCA to assess the potential mechanism of landslide deformation due to excess pore water pressure. The results of the simulation suggest that rise in pore pressure may be one of the potential mechanisms of this particular landslide.