Use of Stereophotogrammetry to Analyze the Development of Shear Bands in Sand

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Courtesy of ASTM International

Experimental results are presented from plane-strain compression of a fine-grained, water-saturated loose sand. Together with local measurements of boundary stresses and deformations, systematic analysis of photographs of the deforming specimen allowed for measuring deformations and computing strain fields inside and outside the shear band. The principles, details, and accuracy of the procedure are described. The capabilities of stereophotogrammetry are illustrated through typical results obtained from undrained and drained tests. A gradual transition from homogeneous deformation to temporary modes of localized strain to a highly localized strain field is systematically observed. Prior to strain 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 remains at constant volume or dilates. The nonuniformity of volumetric response throughout the specimen in globally undrained conditions implies there is water flow within the specimen.

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