Earth pressure on a vertical wall in a sliding mass changes al ong the sliding surface, and it changes also time to time . An active or passive failure will take place along a slidi ngsurface inthe sliding soil mass. The auther pointed out that this idea might be helpful for designing countermeasures by remov ing a part of soil mass or drainage . The ground surface is extended, and extension cracks are observed in the active pressure region . The ground surface is compressed and swell up in the passive region. Wh ena part of soil mass is removed, the area is extended from the activepressureregion to theinter mediate region, and should not be extended to the passive pressure region.

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Recent methods of instrumentation of underground deformation are discussed concerning accuracy and reliability of observed values. In order to improve the week points of a pipe strain meter of ordinary type, a instrument has been newly designed for the investigation of the underground deformation and the procedures of the instrumentation by use of the new strain meter and the data obtained are examined.
As shown in Fig. 1, this instrument is composed of a vinyle bar of guide and a sensor which has a vinyle plate with two strain gauges and two vinyle pipes. The curve of the vinyle pipe in boring hole accompanied with the deformation of soil mass has been measured by the strain gauges of the sensor part inserted into the pipe. It is ascertained that the underground displacement can be quantita tively measured to an accuracy of 2cm/400cm.

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The soil masses at the lower part of a landslide at Genjigakubo village, Niigata Prefecture, suddenly changed into a mudflow in the thaw of 1969, and the mudflow gradually flowed downward along a valley.
The movement and the soils of the mudflow are mainly discussed in this report.
(1) The mean flow speed from start to stop was about 0.87m/min.
(2) The whole distance of the flow can be divided into several parts. Then the relation between the mean flow speed υ (m/min) and the mean longitudinal inclination of the valley θ (°) in these parts can be shown by a linear formula:
υ=64.8sinθ-3.93
(3) The movement in the bottom layer of the mudflow is assumed to be a Bingham flow; then the coefficient of viscosity η (poise) and the yield value τ₀ (dyne/cm²) of the layer are calculated:
η=7.3×10⁴ (poise), τ₀=4.8×10⁴ (dyne/cm²).
The density, void ratio, water content, suction and texture of soils and rocks around the landslide and the mudflow were obtained by experiments.
On the basis of these experiments, it is concluded that the change from landslide soils into mudflow soils was a thixotropic phenomenon.

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In the Kuranami district, the layer of pyroclastic rock in the upper part of Kuranami has been slided by repeated madflows and landslides, to bury old valleys with talus deposits and to form a large-scale buried valley.
Aspects and transition of the sliding area have their delicate differences according to the landslides occurring adjacent to the upper or lower part of the buried valleys . These delicate differences of landslides seem to be ascribed to the flowing behavior of groundwater affected by border planes or discontinuous planes between the buried valleys and their surrounding rock formations . Based on the data obtained from the electrical surveying method, the elastic wave method and the boring survey, the structure of the buried valleys is discussed along with the relation between the buried valleys and the characteristics of landslides.

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