Consolidation, Pre- and Post-Peak Shearing Responses from Internally Instrumented Biaxial Compression Device

An internally instrumented, servo-controlled biaxial compression device is described for evaluating shear band formation in soils. Internally measured vertical and lateral soil displacements as well as lateral deformations of a very low friction bottom sled allow one to observe the progressive development of shear bands in a specimen. Anisotropically consolidated specimens of relatively insensitive, soft Chicago glacial clay were sheared under undrained conditions. Differences in responses based on the internal and globally derived stress and strain quantities illustrate the uniformities which are attained during both consolidation and shear. Small, outward lateral displacements were observed during K0 consolidation, which was based on globally observed axial and volumetric strains; yet, observed Ko values were similar to those measured by other means. Observed lateral deformations during undrained shear and bottom sled movements showed the progressive development of a shear band in all tests. Nonuniformity of the deformations arose after attaining a peak shear stress. The globally observed strain-softening response was both constitutive and geometric in nature.