抄録
In order to study the deformation-strength behaviour of soft sedimentary rock "Shirasu" derived from pyroclastic flows, drained triaxial compression tests were performed on undisturbed specimens prepared by cutting and trimming from block samples. The specimens were tested with the direction of applied major principal stress inclined at various angles to a bedding plane. An inherent anisotropy in the shearing behaviour of Shirasu was studied from the test results. The anisotropy was dependent on the dip of stratum and the confining pressure related to grain orientations and grain movements during consolidation and shearing. The effect of anisotropy on the shearing behaviour was remarkable under a low confining pressure and disappeared under a high confining pressure. That the shearing strength of sedimentary rocks depends on the direction of the major principal stress at failure and the stress level requires a special attention for the choice of the strength parameters in practical problems.
