STRAIN LOCALIZATION AND UNDRAINED STEADY-STATE OF SAND

Experimental results are presented that characterize the behavior of a loose, fine-grained, water-saturated sand tested under globally undra ined conditions is a plane strain apparatus. Together with local measu rements of boundary forces and deformations, stereophotogrammetry is u sed to track the progressive localization of strain. The constitutive behaviors in the tests prior to localization can be characterized as e ither undrained local softening or undrained load softening and subseq uent rehardening. In both cases, a consistent pattern of onset of the formation of the persistent shear band, mobilization of the maximum ef fective friction, and the complete formation of the band was observed. Conditions approximating steady state only were observed in the shear bands. The effect of strain localization on the conventionally derive d steady state line was found to be minimal when undrained load soften ing behavior was observed, but significantly different steady-state li nes were found from results of plane strain and axisymmetric tests. Th e differences between tests conducted under these two stress condition s assessed to evaluate the practical implications of the observed diff erences.