ABSTRACT: A series of true triaxial tests on tall prismatic specimens of sand at three different void ratios form the basis for analyses, prediction and verification of the influence of shear banding on the three-dimensional failure conditions in granular material. The results of the true triaxial tests are reviewed and discussed in view of the shear banding that is observed in these tests. Theoretical conditions for shear banding, which are based on the behavior of the material near the observed shear banding phenomenon, are reviewed. The detailed procedure for shear banding analysis is explained in general and calculations are performed for a single hardening elasto-plastic constitutive model. The predicted shear banding events are compared with those observed in the experiments. It is shown that the predicted stress conditions for shear banding match those observed in the true triaxial tests, and it is concluded that shear banding plays an important role in the three-dimensional strength of granular materials. Thus, peak failure is caused by shear banding in the hardening regime in the approximate range of b=(s₂-s₃)/(s₁-s₃) from 0.18 to 0.85, while it occurs in the softening regime outside this range of b-values. A smooth, continuous 3D failure surface is therefore not generally obtained for granular materials.

Key words: bifurcation, constitutive model, failure criterion, granular materials, hardening plasticity, sand, shear banding, strain localization, three-dimensional strength, true triaxial tests (IGC: D6)