A cast-in-place pile of a diameter of 1.0m to 3. 5m is used as a rigid dowel pile for landslide control, but the method of design of such a pile is not yet established.
The paper discusses the behavior of the rigid dowel pile used in the landslide area for increasing the shearing resistance at the sliding surface by the dowel force and also the method of design of such a pile .
The basic concept of design is that when a soil mass slides over a sliding surface, the pile tilts to produce subgrade reaction in the soil mass above and below the sliding surface and thus a dowel force at the sliding surface. And it is intended to resolve the equilibrium conditions of the forces loaded on the pile, to calculate the bending moment, shearing force, tilt and subgrade reaction acting on the pile and thus to obtain the basic conditions for design of the pile. This method of analysis is applicable to multi-layered soils . From the result of measurement of the earth pressure on a large diameter pile constructed actually in a landslide area, said me thod of design of the pile is adequate. It is also shown that a method of determining the pile casting position at which the pile will exhibits the dowel force fully from a diagram of distribution of the horizontal internal force obtainable by slope stability analysis.

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The clay layer in the landslide face is about 3mm thick. Accordingly, the constants of shearing strength are as follows;
c'≈0.φ'>0
The reason is that the shearing conditions of sliding face are not consolidated-undrained but consolidateddrained. Therefore, the safety factor of landslide face can be expressed as;
F_s=tanφ'∑ (W cos θ-u_w) /∑W sin θ
The pore water pressure U_w acting on the slide face, has direct effects upon the occurrence of the landslide which is caused by a heavey rain.
When the sliding movement passes a certain value, the c' and φ' are changed by the negative dalatancy etc. So the safety factor F_s is given by the followng formula,
F_s=c'L+tanφ'∑ (W cos θ-u_w+u) /∑ W sin θ
In the formula, U shows excess hydrostatic pressure.
In the sliding, when the safety factor becomes fixed after reaching a certain value, it doesn't increase any more even if the pore water pressuer becomes higher.

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It is generally said that landslide movement relates to variation of . groundwater. But the quantitative analysis of this relation has not been established . If it is analysed the behavior of groundwater by using simple models which are consisted of pipes and tanks, we will be able to know the characteristics of groundwater in land slide area. Especially, if the models were reflected to geological nature of landslide soil mass, we could know the characteristics with the most quantitative accuracy . In this paper, analysis method and its result are discussed.

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In the case of discussing on stability of slopes in landslide areas, investigations and researches from soil engineering point of view are indispensable. However, there are very few reports about those aspects.
In this paper; as a basic study of understanding soil properties at landslide areas in Hokuriku region, the accumulated data obtained at various location in Noto peninsula are analyzed, and physical and mechanical properties and in correlation between soil constants and grain size characteristics of material relevant to landslide are described.
Moreover, comparative studies on soil properties of Noto peninsula, south-western parts of Niigata Prefecture and Tokushima Prefecture are carried out.

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This paper deals with examples of analyses based on theory of “The Metbod of Predict Technology of Slope-rupture”.
This type area was chosen in October to November 1977.
I have been investigating this field in detail since then.
This analyses due to prior paper (I)-Fig. 1, 2, 3 and expression?, the data obtained from the investigation.
The results of this analyses, are shown on Table 1-4.
From this result it is concluded that the best method is the one obtained from this analysis.

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