Abstract
Pyroclastic flow deposits distributed in southern Kyushu, Japan, are called Shirasu. In order to investigate the drained deformation-strength behaviour of Shirasu in disturbed state, hydrostatic compression tests and radial shear tests using triaxial testing apparatus with independent stress-control systems were performed on cubical specimens of loose Shirasu under three dimensional stresses. The thirteen radial shear stress paths on the deviatoric plane classified into five groups were given to the specimens. The test results indicated that Shirasu specimens prepared by pluviation through water had an inherent cross-anisotropy. In the hydrostatic compression tests, the anisotropic behaviour occurred in compressive strains less than 10-2. In the radial shear tests, deformation-strength behaviour was dependent on the relationship between the direction of the specimen-deposition and the directions of the major and minor principal stresses. The change of the shear behaviour was caused by the change of dilatancy, the strain increment ratio, with the radial shear stress path.
