Microstructure of shear bands and its relation to the mechanisms of dilatancy and failure of dense granular soils

作者：Masatoshi ODA, Hidehiko Kazama · 发表于：Géotechnique · 年份：1998 · DOI：10.1680/geot.1998.48.4.465 · 被引用次数：551 · 研究领域：Landslides and related hazards、Geotechnical Engineering and Soil Mechanics、Rock Mechanics and Modeling

Microstructural changes taking place in two shear bands of Toyoura and Ticino sands were examined by means of an X-ray method and optical measurements using a microscope and thin sections. The following must be taken into account in order to produce a realistic micro-structural deformation model for granular soils: (1) shear band boundaries are not straight, but are gently curved with different inclination angles to the major principal stress from section to section; (2) extremely large voids are produced in shear bands, and the resulting local void ratio can be larger than the maximum void ratio determined by standard methods; (3) the particle orientation changes sharply at shear band boundaries, so that a high gradient of particle rotation can be developed within a relatively narrow zone during the shear banding process; (4) particle rotation, on average, takes place in parallel with the corresponding geotoscopic rotation in the continuum sense; (5) the thickness of shear bands is about 7 to 8 times the mean particle size. In addition to these observations, photoelastic pictures taken from a biaxial test on a two-dimensional assembly of oval rods were analysed and used in proposing a microstructural deformation mode. In the model, the main microstructural change during the strain hardening process is the setting up of columns extending parallel to the major principal stress direction. The columns start buckling at the peak stress, and the buckling columns tend to concentrat...