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Landslides are gravitational mass movements of rock, debris or earth. Some move very slowly, thus conforming to the field of statics, but some move rapidly. Study of the initiation and motion of rapid landslides needs to develop "Landslide Dynamics" involving dynamic loading and dynamic generation/dissipation of excess pore-water pressure. New developments in science can be facilitated by new technological advances. This study aimed to develop a new apparatus that can geotechnically simulate the formation of the shear zone and the following long and rapid shear displacement that occurs in high-velocity landslides. Professor K. Sassa and his colleagues at DPRI (Disaster Prevention Research Institute), Kyoto University, have worked to develop an undrained dynamic-loading ring-shear apparatus for this purpose. A series of different types of apparatus (DPRI-3, 4, 5, 6, 7) have been developed from 1992 to the present. This paper describes the development of this apparatus and its application to the study of earthquake-induced landslides and the latest landslide-triggered debris flow in Japan. Also, tests of the latest version (DPRI-7) with a transparent shear box for direct observation of the shear zone during a rapid shearing are described.

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A typhoon (Typhoon No. 10) attacked Shikoku Island and the Tyugoku area of Japan in 2004. This typhoon produced a new daily precipitation record of 1317 mm on Shikoku Island and triggered hundreds of landslides in Tokushima Prefecture. One catastrophic landslide was triggered in the Shiraishi area of Kisawa village, and destroyed more than 10 houses while also leaving an unstable block high on the slope. The unstable block kept moving after the event, showing accelerating and decelerating movement during and after rainfall and reaching a displacement of several meters before countermeasures were put into place. To examine the mechanism for this landsliding characteristic, samples (weathered serpentinite) were taken from the fi eld, and their shear behaviours examined using ring shear tests. The test results revealed that the residual shear strength of the samples is positively dependent on the shear rate, which may provide an explanation for the continuous acceleratingdecelerating process of the landsliding. The roughness of the shear surface and the microstructure of the shear zone were measured and observed by laser microscope and SEM techniques in an attempt to clarify the mechanism of shear rate effect on the residual shear strength.

Largely unknown mechanisms restrain motion of clay‐rich, slow‐moving landslides that are widespread worldwide and rarely accelerate catastrophically. We studied a clayey, slow‐moving landslide typical of thousands in Northern California, USA, to decipher hydrologic‐mechanical interactions that modulate landslide dynamics. Similar to some other studies, observed pore‐water pressures correlated poorly with landslide reactivation and speed. In situ and laboratory measurements strongly suggested that variable pressure along the landslide's lateral shear boundaries resulting from seasonal soil expansion and contraction modulated its reactivation and speed. Slope‐stability modeling suggested that the landslide's observed behavior could be predicted by including transient swell pressure as a resistance term, whereas modeling considering only transient hydrologic conditions predicted movement five to six months prior to when it was observed. All clayey soils swell to some degree; hence, our findings suggest that swell pressure likely modulates motion of many landslides and should be considered to improve forecasts of clayey landslide initiation and mobility.

In recent years, landslide hazard assessment has played an important role in developing land utilization regulations aimed at minimizing the loss of lives and damage to property. A variety of approaches has been used in landslide assessment and these can be classified into qualitative factor overlay, statistical models, geotechnical process models, etc. However, there is little work on the satisfactory integration of these models with geographic information systems (GIS) to support slope management and landslide hazard mitigation. This paper deals with several aspects of landslide hazard assessment by presenting a focused review of GIS-based landslide hazard assessment: it starts with a framework for GIS-based assessment of landslide hazard; continues with a critical review of the state of the art in using GIS and digital elevation models (DEM) for mapping and modelling landslide hazards; and concludes with a description of an integrated system for effective landslide hazard assessment and zonation incorporating artificial intelligence and data mining technology in a GIS-based framework of knowledge discovery.