海底堆積シラスの変形・強度特性

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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 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 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 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.
一般社団法人日本応用地質学会の論文
1979-03-30

著者

春山元寿
鹿児島大学

海底堆積シラスの変形・強度特性

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