It is very difficult to confirm in the way of field measurements whether landslips on the ground water surface can take place without the piping phenomenon or not, because it is difficult to predict the place where a landslip will take place and nearly impossible to set the instruments to detect the ground water surface and the slip surface in prior to the slip.Therefore, model experiments of landslips will be one of the best ways to resolve the authors' suspicion that all of landslips in homogeneous sand layers could not be explained by the piping phenomenon. The results of model experiments have proved the existence of landslips on the ground water surface with out the piping phenomenon in homogeneous sand layers, regardless of slope angle (in the range of 20°-40°) and void ratio (in the range of 0.59-0.85). The following papers “Landslips on the ground water surface and its mechanism-II&III”will report the interpretation of vane tests in model sand layers and the mechanism of the slips on the ground water surface estimated from the measured in-situ shear strengths.

View full abstract

The main problem on the application of vane tests to sand is that the effective stress on the shear plane is changed by the force transmitted from the vane blades because of the drained condition.(A minor problem on the application of vane tests to sand is that the void ratio at failure is usually different from the initial void ratio under the drained condition, but the void ratio at failure can not be measured in vane tests. However, since slips themselves are estimated to take place under the drained condition in sand layers and the influence of void ratio is not so great as shown in Fig. 3, it will be unnecessary to be so sensitive for this problem.)
The equation proposed by Farrent and the equation rededuced here are the corrections for this main problem. The equation deduced here is considered to be fundamentally right from the process to lead it and the examination of it in Fig. 5 indicates that it is numerically appropriate, though it will not be said that it has been verified enough. The corrective equation of vane tests includes the angle of internal friction in it. Therefore, when attempting the measurement of the variation of shear strength in the sand layer by vane tests, the variation of the angle of internal friction is also needed. However, the measurement of void ratio in the model sand layers and the relation between void ratio and the angle of internal friction by H. Inoue and the examina tion of the influence of saturation on the angle of internal friction have demonstrated that the tangent of the angle of internal friction (tanφ) can be regarded to be constant with 1-4%error in the model layers of the Toyoura standard sand (void ratio 0.78-0.85).Now it will be possible to say that the necessary means to measure the variation of in-situ shear strength in the model sand layer has been established.
Finally the authors acknowledge Mr. Marui H. who is a post-graduate student in our laboratory and helped us in the direct shear tests and also acknowledge the assistant professor of our laboratory Kobashi S. for his advice and encouragement.

View full abstract

In order to clarify the sub-surface structure of landslide areas, we usually carry out boring investigation and seismic prospecting. As the sub-surface structure obtained by a seismic prospecting is one based on elastic properties of rock bodies, so it does not always agree with the geological structure of a landslide mass obtained by visual inspection of boring cores. The difference is important problem in landslide investigation.
In order to clarify the sub-surface structure of landslide areas, we usually carry out boring investigation and seismic prospecting. As the sub-surface structure obtained by a seismic prospecting is one based on elastic properties of rock bodies, so it does not always agree with the geological structure of a landslide mass obtained by visual inspection of boring cores. The difference is important problem in landslide investigation.
Main results are collected in Fig. 5 to 7. By the figures, it is clear that the depths of the bedrocks of which V_p exceed 3.0km/s are in approximate agreement with the depths of boundaries between soft and hard rock masses. By the data of the boring cores, these soft rock masses are usually composed of debris deposits or weathered crystalline schists, and are considered as sliding masses. On the other hand, the hard rock masses are the basement and are stable.
Conclusionally, seismic prospecting is effective for the determination of the depth of landslide masses and the bottom of boring should be in hard rocks.

View full abstract

It is a very difficult problem to predict landslide and slope-rupture.
It cannot he denied that various predictions of these means have their own merits and demerits.
But, at present, the best way for the prediction of slope-rupture is, I think, to make a quantity analysis through a precise and rigid grasp of some factors in slope-rupture.
In the analysis multiple regression analysis of multivariate analysis is used.
An unknown field of this learning is considered here.
In the dissertation, a theoretical study for the establishment of this means in the scientific field concerned is taken into consideration.
The theoretical method of this investigation is, first of all, briefed in “Construction of predict technology of slope-rupture”.(Fig. 1)
Fig. 1 shows, especially, that, for an appropriate selection of factors for each phenomenon, we should always return from the column of the selection of each factor in each natural phenomenon to the column of the setting up of construction factors of slope-rupture.
Therefore, this is a feedback circuit in the systematization of predict technology of slope-rupture.
How to grasp construction factors of slope-rupture and their functions is an important condition in the establishment of predict theory. This is briefed in Fig. 2.
By the following expression, the answer can be got.
R=R₀X₁^r1X₂^r2X₃^r3X₄^r4 I
logR=logR₀+r₁logX₁+r₂logX₂+r₃logX₃+r₄logX₄ II
This is an expression which shows a model for predict decision value of slope-rupture.
Fig. 3 shows related situations of coefficient factors.
As primary factors in the occurence slop-rupture are subsurfacegeology, “Key to the classification of the subsur facegeology” is indicated in Table 1.

View full abstract

In this paper, characteristics of weathering in black mudstone of Neogene Tertiary are discussed and a classification of the weathering is proposed. As the result of this study it is also found that weathering rate changes regularly through the process of weathering.

View full abstract