The internal friction angle of soils mobilized during the motion of landslides is the most important factor for the prediction of landslide motion. However, this will be not the same with the internal friction angle obtained from the conventional (almost static) shear tests, because the speed and displacement of shearing used in the conventional shear tests are quite different from those in moving landslides.
Using a new high speed ring shear apparatus, the internal friction angle of granular materials was measured by changing normal stress through the continual shearing at a constant shear speed of 0.01-100cm/sec, under the dry or the drained condition. The friction angle in the tested materials did not change so much, but varied from -3.2° to + 3.7°at different shear speed of 0.01cm/sec-100cm/sec, and the sense of difference of friction angle was not the same in materials. Possible mechanisms to interpret the variation of the internal friction angle during motion were discussed.

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The propagation processes of the failure plane in clay specimens, kaolin HA, bentonite, and the Yonaihata landslide clay, were detected using a new technique with constant volume direct shear tests. Before the shearing experiments, several pieces of “sohmen” coated with electro-conductive paints were inserted perpendicularly to the specimen in a line, and direct electric currents of 5V were applied to the electrodes. The electrodes were softened by absorbing soil moisture, and then can be deformed in the same manner with the clay specimen.
The electrode's voltage sudddenly reduced to about OV with increasing the displacement of the specimen during the shear process. Soft X-ray photography revealed that this sudden voltage drop can be attributed to the shear zone formation at the electrode position in the specimen.
The failure plane appeared in the stage of post-peek strength, and propagated into the inside from the margin of the specimen. The relationship between the failure propagation rate and the consolidation pressure of clay specimens varied with the clay types (clay minerals, physical properties of soil etc.). The results suggest that this method can provide an experimental background for landslide prediction.

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Three-dimensional stability analysis was done to evaluate the safety factor and slip surface of a modeled cut slope which is assumed from a practical case. The methods of calculation used here are Fellenius method and the elasto-plastic FEM. The safety factor calculated from the elasto-plastic FEM in the case of the associated flow rule (ψ=φ) coincides with the result from Fellenius method. However, it should be noted that the deformation of sliding mass is impractical because of excessive dilatancy on the slip surface developed by the assumption of ψ=φ.
The results predicted from FEM in which the soil parameters of the slope and slip surface coincide, are different from the failure mechanism assumed in Fellenius method and the observed failure surface. In order to investigate the actual phenomena of the slope failure it may be effective to make use of FEM in addition to the conventional method.

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In order to investigate the influence of preparation methods on shear characteristics of cohesive soils, direct shear tests have been performed on undisturbed and remoulded cohesive soils from Tokyo Bay.
The test result that the shearing strength of undisturbed samples turned out to be larger than that of remoulded samples. This difference may be attributed to the fact that the undisturbed samples have a natural soil structure of the soil remained unchanged. Engineering implication of the test results was turned out in making stability analysis of ground.

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The movements of many survey points that had been arranged about in a lattice at intervals of 2-4m in a small-scale landslide were repeatedly surveyed by an electro-optical distance-meter. From the results of survey, the distribution and the changes of horizontal strain of the ground surface were obtained by the theory of two-dimensional finite homogeneous strain. Consequently, this method was proved very effective for the detection of local movements in a landslide and further for the acquirement of data on a forecast of a landslide and measures against it.

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Slope hazard by earthquake shows a couple of types. Strong seismic intensity brings fall or failure to rock slope, type A, and seismic energy of large magnitude leads earth slope deformation, type B. As to this difference, the writer deals with nature of slope materials and earthquake factors on types A and B making a comparison.
Type A: 1) Slope material is elastic.
2) Stiffness depends on a peak strength.
3) Strong stress or acceleration brings disasters.
4) Short epicentral distance becomes a major impact while large magnitude is a minor one to disasters.
Type B: 1) Slope material is plastic.
2) Stiffness depends on large work or energy consumption.
3) Either large seismic energy in unit time or its long continuation brings disasters.
4) Large magnitude is a major impact while short epicentral distance is a minor one . In other words, an earthquake of large magnitude spreads slope hazard very widely.
According to the items 3) and 4), the writer shows two earthquake hazard maps, types A and B. He finds out a regional character between them. Notable difference is seen in Northeast Japan and Kyushu.
Earth slope hazard is due to seismic work, which depends on either total energy or shape of wave . The difference between source energy and work, energy consumption, is dealt with in this paper, too.

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