It has been estimated that creep movement is caused by underground erosion in the crystalline-schist debrismass landslide. However, it is not sufficient to explain the movement mechanism of landslide.
Then, the authors carried out monitoring of sediment discharge caused by underground erosion, landslide mass deformation and measurement of underground water paths in Zentoku landslide mass, Tokushima prefec-ture, Japan, to clarify the movement mechanism of such type of landslide. From the results of analysis about the factor affected to underground erosion using these monitoring and measurement results, it is considered that (1) water paths are formed along/above the shear zones, where underground erosion is caused (2) sediment discharge caused by under ground erosion is affected by the factors of not only groundwater discharge but also landslide activity (3) high landslide activity makes the debris mass structure subjected to underground erosion in the landslide mass. Consequently, the investigation has made clear that the mechanism of creep movement consists of the link of two processes, one is underground erosion caused by landslide activity, and another islandslide activity caused by underground erosion.

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A method for predicting hazard area of a landslide is proposed by analyzing the landslides triggered by irrigation along the edge of the Heifangtai platform, Gansu, China. A new formula on the relationship between static friction angles and dynamic friction angles is proposed, based on three - dimensional simulation of 20 worldwide landslides.
The influence of loess thickness, ground water, slope gradient, and earthquakes on the shapes of slip surfaces and factor of safety are judged on the basis of calculation on loess slopes in different conditions. Along with the rising of the ground water level, the factor of safety of a slope decreases and its slip surface becomes deeper. Even a small earthquake may trigger landslides in this area.

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The rise of ground water level caused by rainfall is one of the main reasons for which landslides and slope failures take place. In this paper numerical analysis of water flow through unsaturated-saturated soils is performed based on the finite element program in Fortran 90. The rainfall effect on the stability of slopes is predicted by the elasto-plastic shear strength reduction finite element method, in which the water pressure head is obtained from the previous analysis of transient water flow through unsaturated-saturated soils. The calclated results indicate that the patterns and values of the rise of ground water level in slopes due to infiltration of the rainfall are greatly influenced by the hydraulic properties of soils. It is shown that the present method is suit able for evaluating the rainfall effect on the stability of slopes in practice.

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Geological structures are supposed to be a remarkable index of landslide susceptibility. For example, tectonic line and its shattered zone is often found to be the area that has high landslide density. But, from the tectonic point of view, the high density just does not only reduces to shattered level by fault activity, but it also does to quality of the formation, i.e. in this case, material difference (crushed level) due to different geosyncline origin in orogenies explained by the accretion tectonics recently.
Therefore, landslide distribution features are investigated around the Bocono tectonic line, Venezuela Andes. This area has no volcanoes and consists of rather typical structure for that the tectonic theory is easily applicable.
Consequently, landslides tend to locate in the more turbulent formations that are formed from eugeosyncline at a deep sea bottom and make the accretion. This tendency can be found also in the similar geological structure like Chyuo Tectonic Line in Shikoku, Japan. This result is expected to be a valuable knowledge to landslide susceptible investigation.

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The authors prepared shear layers by various shear displacement from 5 mm to 500 mm with a new trial direct shear apparatus, and we observed the surfaces of the layers with an electron microscope . The structures of the surfaces changed correspondingly to the stages of the shear.
In the initial stages of the shear, soil flakes composed with many soil particles were arranged at some angles to the surfaces. In consequence the surfaces were a little flat.
In the creep stages, the soil flakes and the soil particles were flat arranged on the surfaces . In conseqence, the surfaces became so flat and polished as slickenside on which many traces of the displacements of the soil flakes and the soil particles were fromed in parallel with the shear direction.

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Probe into the landslide slip surface which had been formed in the Tertiary stratum is possible, so that the stability analysis on the slip surface seems to be easy. Since theoretical solution of the safety factor for the slip surface is hardly obtained, the following method is used for the approximate calculation of the safety factor.
(1) There are four kinds of the slip surface in the latent zone that is included in landslide area (this area con-sists of the latent, active and passive zones). These shear strength constants, c and φ, are fundamentally different, and each of distribution in the latent zone are not constants. Hence, the shear strength constant (Cohesion c is considered to be zero) that is obtained by the reverse calculation method is applied in the latent zone. while the shear strength constants that are measured by the shearing test can be used in the active zone and the passive zone.
(2) There are two kinds of pore water pressure on the slip surface, one is the pore water pressure which always acts on the slip surface and another is critical pore water pressure that is required to slide. It is very im-portant to determine accurately the pore water pressure in the slip surface.
The safety factor cannot be calculated up two digits below the decimal by the present stage. The safety factor shows the state that balance between thrust and resistance on the slip surface changes depending on the pore water pressure. From this view point it is concluded that the safety factor cannot estimate the preventive construction against landslide whose sliding is interrupted briefly during drop of the pore water pressure.

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