Undrained shear band deformation in granular media

Shear banding, the localization of deformation into thin zones of intense shearing, is a phenomenon commonly observed in soils, yet it is still poorly understood. Stereophotogrammetry was used to study the deformation in a shear band as observed in plane strain compression tests of loose, moist-tamped specimens of saturated sand. A new analysis of shear band behavior is presented to evaluate the behavior inside a shear band. The analysis consists of determining displacement functions by applying a least-squares linear regression to discrete sets of grain displacements with the shear band. Deformation gradients are then determined from a finite strain formulation. Estimates of accuracy of the method follow directly from the statistically based regression analysis The mechanism of shear band deformation was found to be one of simple shear; that is, the band is inextensible along its length. During globally undrained plane strain compression of loose sands, the shear band deformed at constant volume, within the accuracy of the method, despite achieving magnitudes of shear strain of 50%-70%.