Use of DEM and elastic stability analysis to explain the influence of the intermediate principal stress on shear strength

In this study, a fundamental mechanism that explains the influence of the intermediate stress ratio (b) on soil shear strength is proposed. Prior experimental, numerical and analytical studies have indicated that soil failure occurs when the strong force chains that transmit stress through the material buckle. Discrete-element method (DEM) simulations of true triaxial tests show that as b is varied, so too is the relative support provided by the force chains orientated in the directions of the intermediate and minor principal stresses. The DEM dataset is complex, and so a conceptually simple model is used to assess the influence of lateral support on the buckling resistance of a single column of connected nodes, analogous to a single force chain. When the stiffnesses of these springs are selected to reflect the variation in axial stiffness with b observed in the DEM simulations, the reduction in axial buckling load with b is found to be similar to the reduction in major principal stress with b.