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%.