The shallow slab slides which occurred in the area around the Mineoka uplift zone in chiba prefecture were detaily described and discussed on the mechanism of generation and corrective design.
The slab slides in this area are recognized to have been formed by the repeated slidings. Repeated slow slides are interpreted to have been mainly caused by the generation of small caves (so-called bora) and successive connection of caves (so-called bora-sawa). The each moving mass has the unit thickness of about 3-5m and is mostly composed of cohesive soil with N≤20, Nsw≤100.
Corrective design of surface and trenches was used for the portection of the slides. As a results, the lowering of water level was expected to be 0.5 m and the safeness for the sliding rose 10%.

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Landform and geological structure of a landslide slope are deformed from those of original slope by landslide movement. Slope evolution processes of the Choja landslide which have been active for more than five hundred years are examined geologically.
Owing to the comparison of the present location of Serpentine in the sliding mass with the original one, the landslide slope was formed retrogressive landslides of three stages (Figs. 9, 13). The movement of the first stage was originated in the middle part of the present landslide slope. The second stage was originated from the boundary between middle and upper part of the slope along the present slip surface, and mass of two retrogressive landslides entered into the landslide slope from. the side slopes. The upper part of the landslide slope began to move in the third stage. Total displacement of the latter two stages are around 300m.
The present landslide has correspondent movement to the retrogressive slope evolution, mentioned above. The velocity of surface displacement of the upper slope is larger than that of middle and lower slope. Wide and thin distribution of Serpentine layers in the sliding mass is thought to be formed by ductile deformation around the slip surface, which is shown in the displacement data by borehole inclinometers.

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The landslide observation system has been operating at Hiramaru landslide area since 1988 . The system consists of the ground electric potential meters, the groundwater gauges, the rain gauge and the tiltmeters. The method of observation is carrying out remote sensing in Nigata city of 100km distance from Hiramaru landslide area.
As the analized results of measured the ground electric potential, three patterns have been found . They are the effect of streaming potential caused by interflow in rainy day, the effect of streaming potential caused by flow of groundwater and the complex effects of potential caused by rainfall and changes of groundwater level.
The observation of ground electric potential will be useful for the study of flow of groundwater at the landslide area.

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We don't understand enough communication mechanism of pore water pressure on slip surface.
In the present paper, we shall try to make a few new theoretical models of complicated mechanism of ground water level fluctuation in landslide areas.
By the modeling of mechanism, we shall be able to catch both timelags between rainfall and ground water level fluctuation and the fluctuation size is a match for rainfall.
We design two theoretical models, tank model and Ψ function model. After that, we explain theory of each model. And we set standards of modeles for valuation. Therefore we provided two models that is effective to understand properties of ground water level fluctuation in landslide areas.

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The authors proposed an estimation model of groundwater level which is able to be used when the basal groundwater level is already clarified and duration of precipitation is longer than ti. This model definition is as follows:
γ= (κ·i·β/l) ·Δh+α where t₁ is concentration time of groundwater from top of the catchment area to the observation point, γ is the precipitation density, κ is coefficient of permeability, i is hydraulic gradient, β is effective porosity, l is length of the catchment area, Δh is groundwater ascent volume, α is invalid precipitation density.
Moreover, for the purpose of making to be sure the propriety of this model, we examined this model through the Taninouchi landslide, Kochi prefecture and Kuchisakamoto landslide, Shizuoka prefecture.

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