Under simple or combined stresses，homogeneous clay specimens exhibit localized deformation followed by strain localization. This phenomenon has been extensively studied under plane strain loading conditions. This paper studies the initiation and propagation of the strain localization that developed in rectangular block specimens of normally consolidated clay during undrained shear under plane strain loading conditions. Bifurcation behavior of specimens was simulated by applying bifurcation theory to the Finite Element Method（FEM），and axial strain and distribution characteristics of internal maximum shear strain at the initiation of bifurcation are presented．
Results of the FEM are then compared with the theoretical bifurcation soiution. The equivalent of the distribution characteristics at the onset of bifurcation is obtained，and shear band formation followed by the distribution characteristics is predicted by propagation of strain localization as an imperfection-sensitive problem. However，axial strain at the occurrence ofvariation of distribution charactenstics of internal maximum shear strain as computed by the FEM underestimates that calculated by the theoretical bifurcation solution．