In this study, a test area is chosen in the region of the Ryoke granitic rocks, in Kawachinagano city, Osaka Pref., where rocks are weathered relatively uniformly and continuously to a considerable degree from the top to the depth. Core samples from there are examined by the various experiments. First of all, alternation of mineral particles is examined by X-Ray diffraction and ignition loss, and then, void ratio, specific surface area, and pore size distribution of core samples are determined. Moreover, the relationship between solid surface and water molecular are studied in detail. As a result, change in pore size distribution is not uniformly continuous, and there is a zone in which the uniformity coefficient of pore size distribution takes the maximum value. In conclusion, it is possible to classify the profile of weathered granite into three zones, which are named U-zone, M-zone, and L-zone respectively on basis of the properties of solid phase.
In order to clarify the stress-strain behaviour of the submarine deposit originated from pumice flow and fall deposits, that is to say, Shirasu and welded tuff, consolidated-undrained triaxial compression tests were performed on Shirasu specimens under the artificial conditions such as deposit in situ with the equally effective stress under various depth below the water surface and with the variously effective stress under equal depth. For example, the former is the inclined layer of equal depth below the surface of submerged slope, assuming the effective stress is equal in some plane of this layer, and the latter is the horizontal layer below the submerged slope, assuming that is various. Basing on the study, the following conclusions might reasonably be made: (1) The hydrostatic pressure corresponding to depth in situ is loaded as back pressure and this pressure is called initial pore-water pressure. The effective strength of submarine Shirasu is independent of this pressure. The development of excess pore-water pressure over a steady-state pressure increases with the water depth, but it approaches to a constant pressure in some depth. This excess pressure depends on the initial void ratio of specimens and on the effective-confined pressure at initiation of exerting shear. (2) Under the condition of a given depth, the higher the effective-confined pressure is, the larger the principal stress difference and the excess pore-water pressure are at same strain. The angle of shearing resistance has the tendency of decreasing with an increase in effective-confined pressure. Shirasu is characterized by this tendency under such low effective pressure as used in the tests. Stress ratio-axial strain curves have a point of maximum curvature in early stage of shearing, and this point corresponds to the minimum value of the sum of effective principal stress in axial and radial directions for looser state than critical state and to the minimum value of effective-confined pressure; namely the maximum of excess pore-water pressure, for denser state. The strain of specimen does not largely develop until the stress level of the point of maximum curvature is attained, and large strain is developed after this stress level. Therefore, physically speaking this point is similar to a yielding point. (3) The looser specimen than critical state always has a “line of phase transformation” in the diagram of effective stress-path, the denser one, however, has no such line.
The main shock (M=7.0), occurred in near Izu-Oshima Island on January 14, 1978, caused the violent disaster in central part of Izu peninsula. Disasters were found out in roads, railways and buildings. Slope failures occurred remarkably in the area. A total number of slope failure was awfully counted as about six hundred and twenty, and the greater part of slope failure occurred on near mountain ridge, that is, near slope changing line. Half number of failures was 20-40 meter in height and 10-20 meter in width as shown in Fig. 1 and 2. Geology of failure site was mainly tertiary and andesitic lava, and a few failure occurred in scoria and volcanic mud flow as shown in Fig. 10. Failures taked place along the earthquake fault by the shock and coincided with after shocks as shown in Fig. 12. The ratio of failure area is about 6% near the earthquake fault and about 0.1% farther than 5 kilometer away from the fault.