We have tried to make geologic division based on landslide inventory maps in which we have recognized 12, 843 landslides throughout Hokkaido by interpretation through aerophotographs of 1: 40, 000 in scale. As the results, we have recognized 19 geologic regions, and then summarized up the following four zones; 1) Volcanic Rock Zone, 2) “Green Tuff” Zone, 3) Mudstone Zone, 4) Serpentinite- “Green Rock” Zone.

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The land development in mountainous area here in Japan is geared towards being wild driven by recent high demands for land use. In this context, a lot of hillside and mountain side has been developed these days as inhabited districts or mountain resorts which may end up with a ruin in sediment disaster. Therefore, landslide susceptible area is increasing, and landslide which occures suddenly without any signes as well as can be found only by their unique topographies seems to be extremely important in order to predict susceptible area. On this point of view, the standards to pick up the landslide susceptible area based on stability analysis for this kind of landslide is considered here.
A risk assessment method by stability analysis and some standards factor of safety (F_c) derived from a probability density distribution of pseudofactor of safety gained by the Critical Slip Surface analysis by Dynamic Programming (CSSDP) is established.
Since this CSSDP can search automatically a critical slip surface that corresponds to the boundary between the moving zone and the stable one by the dynamic programming theory, although underground geological and/or geostructural condition is unknown. Needless to say, it can treat not only impact factor triggers landslide but slope nature.
Thus, the method gained in this study must be useful to estimate or evaluate the landslide susceptibility.

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A monitoring method for landslide activity by using acoustic emission (AE) was developed. This technique was applied to an insitu slope failure test, where AE was observed with the aid of newly developed wave guides during the ground movement. Using high frequency waves, background noise is effectively eliminated, and the ground movement can be monitored by this method. Results of the test show that AE event rate can be used for monitoring the small deformation of the ground.

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One of the major problems to be clarified in landslide study is the mechanism of the formation of the slip surface in the colluvial soils derived from mudstone. For this purpose, the samples were taken at, above and below the slip surface of a landslide, and analyzed by physical, chemical and mineralogical techniques. The residual strength of them was also measured by a ring shear apparatus.
The total clay content of the colluvial-soil samples tended to be highest at the slip surface, and their main clay mineral was mica followed by kaolinite and vermiculite. The water-dispersive clay was near 30% at the slip surface and its content was clearly higher than the contents for above and below the slip surface.
At the slip surface disintegration into clay-sized particles is accelerated under the concentration of shear stress and by the supply of water through heavy rainfall. Under this condition, the reorientation of platy mica particles along the slip surface is facilitated, and the shear strength of the slip surface falls to the residual strength. The residual angle of shearing resistance of the slip-surface soil was measured to be 11° and this value was at the same level as the value expected for clay mica.

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In order to investigate the influence of hydrogen-ion concentration exponent on engineering properties of bentonites, unconfined compression tests and oedometer tests have been performed on bentonites with different hydrogen-ion concentration exponent and consolidation time.
As a result, a different pattern of consolidation curves was produced for a variation of hydrogen-ion concentration exponent. In addition, strength and deformation characteristics of the samples depend on the hydrogen-ion concentration exponent and consolidation time. The reason for this may be considered that different soil structures were developed with different hydrogen-ion concentration exponent and consolidation time. Hydrogen-ion, concentration exponent, therefore, is one of the most important factors in considering engineering properties of bentonites.

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In this report, it was shown the test result about the measurement precision of GPS survey and an example applied to landslide investigations.
As the result, the horizontal angle and horizontal movement quantity were precision that is same as conventional survey by survey network average calculation. But precision was worse than transit and level about leveling.

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