A means of detecting sample disturbance and the anisotropy of undrained strength of clay soils by use of the standard vane is presented. If the sample is appreciably disturbed it is not possible to derive any values for the anisotropy of undrained shear strength from the analysis. The technique permits the determination of this anisotropy using only one vane by considering the elliptical distribution of strength in a plane perpendicular to bedding.
The standard vane, with a length/breadth ratio (k) of 3/2, theoretically permits the determination of an average strength within 18 per cent of the true value for real soils depending on the angle of insertion. A vane with k = 2/3 is theoretically the least sensitive to anisotropy of strength and would consequently be the best shape for determining an average value in preliminary investigations. For real soils the average strength recorded would be within 2 per cent of the true value no matter what the angle of insertion of this vane.