Directional Variation in Undrained Shear Strength and Fabric of Winnipeg Upper Brown Clay
The undrained shear strength and the fabric of a lacustrine clay from Winnipeg, Manitoba, have been determined with respect to the orientation of the natural bedding plane. Unconfined compression tests show that both the undrained shear strength and the normalized secant modulus of 'undisturbed' clay were anisotropic. The fabric, determined by X-ray diffraction analysis, was also found to be anisotropic in the 'undisturbed' samples. The same material in the remolded condition was isotropic with respect to both undrained shear strength and fabric. Observations of the failure plane have been used to calculate the resolved shear stress on the failure plane, and the results agree qualitatively with prediction, according to Jaeger's weak plane hypothesis. The variation of undrained shear strength with orientation may be due to (1) the clay fabric and (2) stratification, although these two factors may be interdependent.