Some measurements of strength anisotropy in soft clays using diamond-shaped shear vanes

Abstract

Soil strength anisotropy arises from two interacting anisotropies: geometrical anisotropy, i.e. preferred particle packing, and stress anisotropy. The authors explain that the in-situ diamond shaped vane was introduced for such measurements by Aas (1965) who carried out shear tests using a diamond vane making an angle of 45 degrees to the axis of rotation. By extending this concept and using diamond shaped vanes of different angles the variation of shear strength with direction may be measured. The diamond vanes used in the measurements presented in this note are described as being symmetrical and cruciform in cross section. They were used in conjunction with a Geonor H60 field inspection vane tester torque head, and were all designed to give the same torque as the conventional 2/1 rectangular head, assuming strength isotropy. The techniques adopted for carrying out the vane tests are described, and shear-stress relationships presented and discussed. Polar diagrams are used to illustrate typical results, and to compare these results with strength measurements obtained by the conventional rectangular shaped shear vane. /TRRL/