The occurrence of a new landslide in the sedimentary layer is so abrupt that the heavy rainfall involved at the moment seems largely responsible for it. This phenomenon, however, is really more attributable to various factors and occasion that have combined to produce a chain of shearing fissures (slide surface) in a weathered sedimentary layer. This process of forming a slide surface can help to predict the outbreak of a new landslide.
The movement of the earth crust accompanied by lateral earth pressure leads to the forming of the weathered sedimentary layer that contains many discontinuous fissures. This fissure belt is composed of the destructive part and the non-destructive part of 0.15-0.25 per unit length of the belt.
The non-destructive part is put under concentrated stress of thrust force which the pore water pressure has brought about. The action of failure being of creep failure, it is a function of elapsed. The parts still non-destructive, yielding to the pressure at length, burst forth into fresh fissures, and thus the whole range presents a stretch of shearing failure in an unbroken line, this is, a landslide surface.
In the process of the creep failure, the passive and active zones of ground surface continue either the rising or sinking motion for a period of several years. We can make a conclusion from this that the constant measurement of those deformations will make it possible to predict the occurrence of a new landslide.

View full abstract

Many studies on the mechanical phenomena of soil in box shear test have been done, but few studies on the structures of the shear layers in the test have been done.
The structures gradually change with proceeding of the test. The author prepared three types of the shear layer at different three stages of the test (1st: stress of about three fourths of shear strength, 2nd: shear failure, 3rd: creep). And in order to take X-ray stereoradiographs of the structures, contrast media were pulled into the voides in the soil samples. The results of this study are shown bellow.
The shear layers at the 2nd and the 3rd stage have fully developed and the layers are formed with very many small shear planes which link together in chains. And the chains crowd together like branches of tree. The shear layers at the 1st stage have not yet developed in many cases.

View full abstract

The Kanehanatoge slide in September 1972 took place in the lower part of an ancient slide morphology. The ancient and recent slides were a so-called detritus and clayey soil slide and a so-called clayey soil slide, respectively. Their slide clays are composed principally of large amounts of montmorillonite, which were derived probably from a hydrothermally argillized zone, that is, a veined montmorillonite-kaolinite zone along the joint planes in rhyolite lava (bedrock) of the Upper Miocene Ikutahara Formation . It is suggested, therefore, that the slides related very well to modes of occurrence and properties of hydrothermal alteration zones in the vicinity of the slide area.

View full abstract

There are numerous factors which affect slope Stability analysis. These main factors include: fluctuation of seepage line, variation of density and shearing strength of soil, tention cracks and slope shape . We try to replace these factors with physical elements or mechanical elements, and also, try to incorporate into the stability analysis of stratified slopes with these replaced elements. By applying this stability analysis of stratified slopes, we have tried to simulate a slope failure which occured at Murakuniyama Takefu city in Fukui prefecture. In this paper, we have made a report, a method of the stability analysis of stratified slopes and the camparing the result of the simulation with the field observation.

View full abstract

Timing and intensity of melt water, which is closely related to the landslide occurrence, was measured using snow lysimeters and other meteorological observations including snow depth and water equivalent of snow in a landslide area of a heavy snow district. Results of four winter seasons' (1989 to 1992) observation showed that rain on snow events frequently occurred early in the season. During snowmelt season, melt water was mainly generated in the surface layer of snow cover by solar radiation and high air temperature. Therefore, most melt water was produced during the daytime of almost every day. In years with small snowpacks, melt water was generated intermittently by occasional rainfall and higher temperatures even in January and February. It was estimated that quantity and intensity of the melt water would be highest in the later stage of the snowmelt season because a large amount of precipitaion was stored as a snow cover up until April and May for heavy snow years.

View full abstract

In this paper, it was studied on improving of warning criterion for landslide. For improving of warning criterion, it was investigated on some actual criteria and landslide movement data. As the result, every landslides have different time to fracture, if they move at same velocity. Therefore, an adequate criterion has to decide for each landslide. It was proposed a forecasting method of time to fracture using some factors of landslide configuration.

View full abstract

[in Japanese]

View full abstract