Hollow-cylindrical torsional shear tests were conducted in order to examine in detail the mechanical properties of a saturated cohesive soil with shear stress history. The principal results of this study are summarized as follows:
1. The isotropically consolidated hollow-cylindrical specimen is almost isotropic with respect to deformation.
2. Shear history under constant p' has no effect on strength, and the strength is fixed uniquely by the effective confining stress p' and the intermediate principal stress coefficient b.
3. The non-coaxiality between stress and strain is generated by the shear history except when the directions of the shear history and the shear are coincident or are at right angles to each other. Although the shear direction during the shear history has a significant effect on the non-coaxiality, the effect of b is minimal.
4. The deformation characteristics are affected by the shear history because the elastic locus is changed by the shear history. The progress of the elastic locus is most marked when the shear directions during the shear history and the shear coincide, while the elastic locus changes little when the directions during the shear history and the shear are perpendicular.
5. The progress of the elastic locus is most marked when the intermediate principal stress coefficients during the shear history and the shear are coincident, while the progress is small when the difference in the intermediate principal stress coefficient between the shear history and the shear is large.
6. The boundary of the elastic and plastic loci due to the shear history can be expressed in the ry - α' - b' space, in which ry , α' and b' are regarded as predominant parameters.