Evaluation of the Stiffness and Volumetric Behaviors of Medium Dense Sand under Principal Stress Rotations

Abstract

Effects of principal stress rotations are important features of granular materials. Experimental data obtained in directional shear cell experiments for dense sand are re-analyzed and re-evaluated in terms of distortional (shear+deviatoric responses) and volumetric behaviors. Principal stress rotations in loading cause greater initial contraction but greater dilation in further shear deformation. In particular, principal stress rotations in unloading cause relatively greater contraction. The mechanisms of principal stress rotation effects on sand behavior are illustrated and interpreted. Rotations of principal stresses can mobilize more sand particles in various orientations facilitating particle rearrangement. Therefore, principal stress rotations cause greater contraction if sand tends to contract under shear but greater dilation if sand tends to dilate under shear. Loading and unloading with significant principal stress rotations are common stress states for underground soils during non-proportional foundation loading, excavation, and tunneling. The effects of principal stress rotations on the volumetric behavior of sands are important phenomena when analyzing settlements in the field involving these geotechnical problems.