Vane shear mechanism in soil by particle image velocimetry and discrete-element simulation

The vane shear test (VST) is a crucial technique for estimating the in situ undrained shear strength of clay. However, traditional approaches for estimating strength employ simplified assumptions, particularly regarding the geometry of the shear plane and uniform shear stress distribution. Therefore, this paper conducts the VST by combining particle image velocimetry (PIV) technology and complements simulations based on the discrete element method (DEM), focusing on the evolution of shear failure, shear plane geometry and shear stress distribution. A distinct progression of soil failure is shown across the area with increasing vane rotation angles. The observed and simulated shear planes of the soil display an arc-shaped area that narrows toward the centre along the direction of rotation, deviating from the cylindrical shear plane predicted by classical theory. The horizontal shear stress at the vane’s top and bottom surfaces decreases and increases from the centre toward the edges, whereas the vertical shear stress is most pronounced at the top and bottom, with a near-linear distribution observed in the middle. By considering the revised shear plane geometry and non-uniform shear stress distribution, the estimated vane undrained shear strength can be as much as 1.7 times greater than that obtained from classical solutions.