UNDRAINED SHEAR-BAND DEFORMATION IN GRANULAR MEDIA

Shear banding, the localization of deformation into thin zones of inte nse shearing, is a phenomenon commonly observed in soils, yet it is st ill poorly understood. Stereophotogrammetry was used to study the defo rmation 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 she ar band. The analysis consists of determining displacement functions b y applying a least-squares linear regression to discrete sets of grain displacements with the shear band. Deformation gradients are then det ermined from a finite strain formulation. Estimates of accuracy of the method follow directly from the statistically based regression analys is. The mechanism of shear band deformation was found to be one of sim ple 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, d espite achieving magnitudes of shear strain of 50%-70%.