Tadahiro UNO

Effects of Anisotropic Consolidation on Undrained Shear Strength of Cohesive Soil

Hirofumi TOYOTA

Unconfined compressive strengths of undisturbed samples are generally used for design in Japan where widely distributed saturated alluvial clays. It has been well known that there is effect of strength anisotropy on slope failures because a shear direction is different at each sliding point. However, only limited experiments have been carried out to examine effects of anisotropic consolidation on undrained strength.
Therefore, torsional shear tests were performed for specimens consolidated in different directions to elucidate effects of anisotropy on undrained strength in this study. Anisotropic consolidations are conducted under constant K, ƒ¿ and b conditions, and undrained torsional shear tests were carried out under constant ƒ¿ and b conditions. The parameters, ƒ¿ and b, were set up optionally in each process. Furthermore, to treat two-dimensional problems, undreind torsional shear tests were also carried out under the plane strain conditions where the radial strain does not generate.
The main results are summarized as follows:
1.It became possible that effects of strength anisotropy were investigated using a torsional shear apparatus by which K-consolidation could be reproduced in various directions.
2.When the difference in direction between consolidation and shearing was larger, larger excess pore water pressure and smaller undrained strength generated during shearing. Similar tendency was also confirmed in the plane strain conditions.
3.When the difference in intermediate principal stress between consolidation and shearing was larger, larger excess pore water pressure and smaller undrained strength generated during shearing.
4.The relationships between undrained strength ratios, shear directions and intermediate principal stress coefficients were represented as a curved surface in those three-dimensional space. It was demonstrated that the results of plane strain conditions were also plotted on the curved surface.
5.Reductions of undrained strengths induced by shear directions and intermediate principal stresses could be estimated from the triaxial compression strengths by using proposed equations.