On certain critical material and testing characteristics affecting shear band development in sand

Laboratory tests on samples of sand typically show instabilities in response related to shear band nucleation and evolution. Influences of constitutive characteristics ( for instance, plastically driven elastic anisotropy), sensitivity to changes in constitutive parameters, and effects of testing conditions ( for instance, related to stress conditions or to membrane penetration or stretching) on different types of material instability occurring in the post-localisation behaviour of sand specimens are investigated. Comparison between model prediction and available experiments shows that certain constitutive and testing features, which do not much influence the global response of a sample, may nevertheless strongly affect the critical and post-critical behaviours. The results obtained show that the proposed approach is general enough to permit the investigation of effects of experimental features that have not previously been studied.