Bifurcation behavior of soils with higher plasticity index occurs at smaller stress ratios compared to soils with lower plasticity index：it is，therefore，important to cany out bifurcation analysis on normally consolidated cohesive soils with high plasticity index（PI=100）．We studied bifurcation analysis using a non-coaxial Cam-clay model of normally consolidated cohesive soils during undrained shear under plane strain condition．
The results show that the bifurcation stress ratio of the antisymmetric first deformation mode decreases with increasing plasticity index．However，bifurcation stress ratios of other deformlation modes do not vary with plasticity index．In the case of soils with high plasticity index，maximum shear strain is clearly localized．