Shear bands in biaxial tests on dry coarse sand

A series of plane-strain biaxial compression tests on dry coarse sand is described in which the state of shear-band formation, shear-band orientation, and shear-band growth are investigated. The results show that both the shear strain at shear banding and the shear-band orientation depend on the confining pressure. The experimental results are compared with the theoretical predictions of equilibrium bifurcation theory for a number of local and non-local incremental constitutive equations. Significant deviation between the experimental results and theoretical predictions for local constitutive equations involving the Mohr-Coulomb yield condition is observed at higher confining pressures. Much better agreement is obtained if a yield function possessing a corner is introduced. The analysis of the shear-band growth beyond the onset of localization reveals that simple purely kinematic models cannot describe adequately the observed evolution in the shear-band thickness.