Radiographic and microscopic observation of shear bands in granular materials Available to Purchase

Shear localisation in granular materials has been studied radiographically and microscopically. Thin columns and rows (lines) of lead silicate granules of distinct colour were embedded in a large hollow cylindrical specimen of granular materials, and a series of X-ray photographs were taken to capture the local micromechanical response during shear deformation, in both drained and undrained experiments. In drained tests, shear localisation, produced by monotonic deformation of the specimen, was directly observed. In undrained tests, the local deformation of the granular mass during liquefaction, induced by cyclic shearing, was examined. It was directly observed that shear localisation does occur in liquefied specimens. After shear bands were formed in drained tests, the specimen was frozen in situ. Later, samples were cut from the frozen large specimen, and their ice was replaced by a polymer resin, using a novel technique. The portion of the sample containing a shear band and a sheared section of a column of lead silicate granules was cut by a diamond saw along the column of lead granules, and the cut surface was polished in order to directly observe the arrangement of the particles within the shear band and measure the corresponding deformation. The lead silicate granules trace the localised zone, and provide details of the deformation pattern within and close to the localised zone. The shear strain at the middle of the shear band zone exceeds 500% although the overall nominal shear strain is only 10%. The localisation is accompanied by extensive necking. Based on these experiments, the deformation of the shear band zone is quantified.