USE OF STEREOPHOTOGRAMMETRY TO ANALYZE THE DEVELOPMENT OF SHEAR BANDSIN SAND

Experimental results are presented from plane-strain compression of a fine-grained, water-saturated loose sand. Together with local measurem ents of boundary stresses and deformations, systematic analysis of pho tographs of the deforming specimen allowed for measuring deformations and computing strain fields inside and outside the shear band. The pri nciples, details, and accuracy of the procedure are described. The cap abilities of stereophotogrammetry are illustrated through typical resu lts obtained from undrained and drained tests. A gradual transition fr om homogeneous deformation to temporary modes of localized strain to a highly localized strain field is systematically observed. Prior to st rain localization in the region where the final shear band eventually forms, the soil contracts more than the rest of the specimen. As soon as the final band is fully formed, the soil inside the band either rem ains at constant volume or dilates. The nonuniformity of volumetric re sponse throughout the specimen in globally undrained conditions implie s there is water flow within the specimen.