Abstract
The effect of density on the drained deformation properties of pyroclastic flow deposits, so called Shirasu, distributed in the Southern Kyushu, Japan, was investigated by using a triaxial testing apparatus with independent stress-control systems. Hydrostatic compression tests and radial shear tests maintaining a constant mean principal stress were performed on Shirasu specimens prepared by pluviation through water. The test results indicate that the reconstituted specimens of Shirasu were characterized by an inherent cross-anisotropy and a density-dependence of their deformation properties. In general, the specimens had a low compressibility and a high expansibility in the direction of specimen-deposition compared with the direction along the bedding plane. The maximum shear strength in the identical stress state having different stress-path occurred when the major principal stress was applied to the direction of the specimen-deposition. The change of the deformation-strength properties was caused by the change of strain increment ratio which depends on the dilatancy occurring under the different stress path.
