Shear banding and strain softening in plane strain extension: physical modelling

Localization of deformation in systems of shear bands or normal faults, respectively, as a consequence of extensional loading can be observed on a wide range of spatial scales in soil and rock formations. A series of plane strain model experiments was achieved in natural (1 g) and increased (ng) gravity field (geotechnical centrifuge) with dry and moist sand as well as with dry and moist sand-clay mixtures. In these experiments, the geometry of the shear bands (inclination, width, spacing, sharpness) was detected by means of the digital image correlation (DIC) technique. Comparison with existing analytical approaches for the determination of the spacing of shear bands is presented briefly. The stress-strain behaviour of the materials was determined in a new biaxial test device, which allows for the performance of biaxial compression and extension tests. The evaluation focuses on the strain softening gradient, which is seen as a key parameter in the explanation of shear band spacing.