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.