| Localization of deformation, or shear banding, is a common phenomenon associated with failure of soils subjected to external loads. The better understanding of localization phenomenon is important in the design and construction of soil structures (slopes, foundations). Guided by theoretical analysis, an extensive laboratory experimental program has been performed to study the localization and post-localization behavior in dry and water-saturated sand specimens in plane-strain conditions.;The formation of shear bands in dry sand is first studied within the framework of equilibrium bifurcation theory. The analysis focuses on the shear-banding state and shear-band orientation. Several elasto-plastic constitutive models are considered. Complementary biaxial tests are performed on two types of sand at different levels of confining pressure.;The comparison between analytical and experimental results shows that in fine sand the bifurcation theory adequately predicts shear banding. In coarse sand, however, only the deformation theory with a nonlinear yield function leads to satisfactory prediction.;Post-localization in dry sand is investigated with various experimental techniques (thin-section image analysis). A comparison of the test results with the prediction for non-local constitutive models shows satisfactory agreement in the initial shearing phase and disagreement at large shearing phase. A kinematic analysis of the deformation within the shear band shows that neither the material model nor the shock model alone can adequately describe the observed growth of shear bands; the tests seem to indicate subsequent appearance of parallel shear bands.;Localization in water-saturated sand in undrained conditions under displacement-controlled and force-controlled loading is studied experimentally. In displacement-controlled tests, an array of parallel shear bands appears in dense and medium dense specimens whereas no localization is observed in loose specimens. In contrast to dry sand, localization no longer occurs in the hardening regime of the material stress-strain curve. In force-controlled tests, an array of crisscrossing shear bands occurs in medium dense specimens whereas in dense specimens the deformation localizes in a manner similar to that in displacement-controlled tests. In both loading conditions, the shear bands dilate which, due to overall incompressibility, implies contraction of the material surrounding shear bands and internal water flow. This experimental finding should be incorporated in the bifurcation analysis. |
