ABSTRACT
A numerical analysis of the shear band type strain localization is presented for a series of undrained triaxial compression tests on normally to highly overconsolidated kaolin clay. The concept of instability due to the singularity of acoustic tensor with the loss of strong ellipticity is applied in the analysis using a non-associative elastoplastic model that predicts the stress-strain relationship and pore pressure response reasonably well for the experimental data.