Visualizing the failure surface of a laboratory vane shear in soft clay using transparent surrogate soil

The laboratory vane shear test is commonly used in offshore geotechnics to measure the undrained shear strength of very soft to medium clay samples. The assumed failure surface used to calculate the undrained shear strength resulting from rotation of the vane is a cylinder encompassing the outside edges of the blades. Laboratory vane shear tests were conducted in a transparent soft clay surrogate to visualize the resulting deformations and failure surface of the vane.A particle tracking algorithm was performed on images captured during testing to measure relative displacement and determine a failure surface. Results of the experimental study show rotational displacement within the volume enclosed by the vane. While no deformations occurred outside the enclosed volume in the vertical direction, relatively small deformations occurred outside the enclosed volume in the horizontal direction. These deformations show two distinct phases separated by the point where peak undrained shear strength was measured.