Abstract
Triaxial compression tests on Ishikari sandstones, using a stiff servo-controlled machine, have revealed the following:
1. The peak strength criterion is expressed as a bent line in the (σ1-σ3)-space. The shear angles predicted based on the criterion coincide with the measured ones, and their values are constant for confining pressures higher than the pressure corresponding to the bending point.
2. When the difference between the maximum and minimum P-wave velocities is more than 4 %, the preferred orientation of the shear plane coincides with the direction of minimum velocity. On the contrary, when this difference is less than 4 %, the shear plane is randomly oriented. A yielding zone develops around the shear plane, whose width become narrower with the degree of brittleness. Inside this zone the material readily disintegrates when dipped into water, due to loss of cohesion.
3. Single shear-type fracturing is dominant for the specimen whose P-wave velocity transmitted perpendicular to the loading axis shows anisotropy; and cross-shear type for specimens whose velocity profiling reveals isotropic condition.
