In the present study, ring shear tests were firstly performed for landslide soils which showed a considerable variation in physical and mineralogical properties. Influences of the mineral compositions on shear behaviors were analyzed, and classification of the stress-displacement curve was discussed. A fall in the strength from the peak to the residual state was clearly observed for the soil containing a large amount of silt and sand particles, and clay fraction below 20%. The variation of the strength reduction versus total contents of preferred-oriented clay minerals was expressed as a convex curve. Stress-displacement curves of landslide soils were classified into 4 types based on the total amount of minerals in soil.

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The stability of slopes stabilized by anchors was analyzed by the three-dimensional elasto-plastic finite element method, and the results were compared with those of Fellenius' method and Bishop's simplified method. The comparison indicates that the threedimensional elasto-plastic finite element method has the ability to evaluate the safety factor of the slopes reinforced with anchors. The safety factor of the three-dimensional elasto-plastic finite element method was almost the same as that of Bishop's simplified method, and was slightly larger than that of Fellenuis' method. Additionally, two simplified approaches are proposed to simulate anchors in slopes, and the results indicate that the safety factor of the proposed approaches was almost identical to that of the three-dimensional elasto-plastic finite element method where anchors and soil-anchor interaction were simulated in details.

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This paper describes both the principles of Slip Surface Direct Shear apparatus (SSDS) that would be able to adjust the position of slip surface to coincide with the shear surface of the apparatus and the results of the test in use of it. The number of tested slip surfaces is124. These were taken from Tertiary strata landslides, shear zone landslides and solfataric landslides. From the test results, a typical stress path on the slip surface is recognized. The results obtained from Tertiary strata landslides clearly show that the residual shear strength is affected by slip surface covered with thin smectitic clay. As for the shear zone landslides, test results show that the residual shear strength is strongly affected by the coarse size grain content in the slip surface clay. Comparing SSDS data with that of ring shear tests, authors have found that if the sample prepared for a ring shear test has the same clay content as the slip surface clay, both results show the same strength parameter.

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Rock color values a* and b* (CIE L*a*b* color measurement system) of borehole cores from the caldera of the Quaternary Shirataka Volcano, Yamagata, Japan, were measured with a colorimeter, and their changes with depth and lithofacies were analyzed to understand weathering environments in volcanic areas. In general, the weathering environment is reflected in oxidative changes to iron minerals in rocks. The correspondence of a* and b* color values to the colors of goethite, which is brownish as a result of low-temperature oxidation, and hematite, which is reddish brown, reflecting high-temperature oxidation, makes it possible to distinguish the spatial distribution of these iron minerals by examining color distribution.
The distribution of a* and b* values in rocks of the caldera indicates that a goethite zone of low-temperature oxidation extends widely, but hematite zones of high-temperature oxidation are localized. b*-values, indicating goethite, were higher at shallow depths and decreased with depth, reaching a constant low value at 50 to 150m depth. Low-temperature (i. e., normal atmospheric temperature) oxidation has thus prevailed in this volcanic region for a long time period, as indicated by the thick weathered zone represented by high b* values.
The thickness of the high-b*-value zone seems to be independent of lithofacies or geologic structures instead, it is almost concordant with the present-day topographic relief in the caldera. The continuity of the weathered zone suggests that the caldera has not been exposed to recent large-scale surface sedimentation or erosion. Therefore, recent large-scale avalanches or sector collapses, which would have caused large-scale sedimentation, probably have not occurred in this area.

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Various laboratory tests such as triaxial test, reversal direct box shear test, swelling pressure test, slaking test were carried out to investigate the mechanical properties of serpentinite using the undisturbed and reconstituted samples originated from the Kamuikotan belt in Hokkaido. From the test results, it was concluded as follows.
The residual angle of shearing resistanceφ'_r as well as the peak angle of shearing resistanceφ'_p were unexpectedly large by showingφ'_r=27-28° and φ'_p=31 ± 2° irrespective of the state of undisturbed or reconstituted. But the undrained strength of the reconstituted specimen was less than one fourth of the undisturbed one due to marked difference of dilatancy characteristics of those specimens. The angle of shearing resistance between the pre-existing foliated flakes of serpentinite exhibited 6.5° at minimum.

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In this paper. a theoretical model is proposed to investigate the behavior of tree roots subjected to mass movement and to determine the reinforcement capacity of tree roots at slip surface of landslide. Tree roots function as a type of reinforcement material to minimize landslide. By modelling a root system as a cluster of root fibers inserted through the unstable soil to the bedrock, the increase in the shear resistance of soil can be reliably estimated. Properties and distribution of the roots are taken from a number of previous field experiments. Roots used in the model are Japanese cedar (Criptomeria japonica) roots, the most popular species in Japan. With the inclined roots classified by inclinations and diameters, the relationship between reinforcement capacity of root fibers and horizontal displacements is analyzed under two main conditions: ultimate stress and pullout resistance. The computed results of the tree root model are used in the prediction of root reinforcement at slip surface of a previous soil-shear test. There is, in general, a reasonable agreement between predicted results and experimental data.

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The Central-ridge large-scaled block of Jinnosuke-dani landslide is well exposed at the left bank of the Betto valley. Accessibility of the exposure is limited to the bottom part along the valley floor, because the exposed wall is nearly vertical and more than 100 m high.
The geological structure of the wall is clarified by both direct observations and analysis of the photographs taken from the opposite ridge. The observable internal structure suggests that the Central-ridge large-scaled block has three major slip surfaces.

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The Hagerman Valley area is the ‘landslide capitol’ of the State of Idaho, United States. Land-use change from sagebrush desert to irrigated cropland has coincided with the development of unnatural groundwater aquifer systems. Snake River water has been pumped up onto the Bruneau Plateau and distributed by canal systems to crops since 1970. Irrigation water percolates down through the unconsolidated sediments and forms human-made unnatural groundwater systems.
These aquifers are the causative agent for six large slope failures since 1979 within the Hagerman Fossil Beds National Monument and two others on Bureau of Land Management property. They are damaging natural resources and private property. In 1987, a million-dollar water diversion facility (pump station) on the edge of the Snake River was obliterated by a landslide and two workers had to run for their lives. not having time to get into their vehicle and drive to safety.
The landslide was likely caused by human intervention with the natural system . Fossil sites, American Indian Cultural sites. rare plant species and endangered Snake River aquatic species have been impacted or imminently threatened . Therefore, numerous studies, research and monitoring programs have been implemented since 1984 to gain an understanding of the dynamic groundwater flow systems and the related massive landslides.

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