Associate professor of soil science, University of Massachusetts, Amherst, MA
Professor of civil and environmental engineering, University of Wisconsin, Madison, WI
Pages: 9 Published: Jan 1988
Micromorphological studies of the mode of failure using thin sections of soil obtained during laboratory vane shear testing indicate that the actual failure surface is not a sharply defined cylindrical surface, but rather a shear zone. The diameter of the failure surface at large angles of vane rotation in a soft and a very soft silty clay appeared to be equal to the diameter of the vane device. The shear structures that develop as the vane rotates may or may not fully develop to a continuous circular surface when the maximum torque is reached depending on the consistency of the soil. The results indicate that undrained shear strength calculations based on the assumption of a fully developed cylindrical surface may somewhat underestimate the actual soil strength, but that the magnitude of this deviation is soil type dependent.
undrained strength, soil failure, laboratory vane shear, micromorphology
Paper ID: STP10329S