Undrained shear behaviors of high plastic normally K0-consolidated marine clays

Isotropic normally consolidated-undrained and K-0-consolidated-undrained triaxial compression tests were carried out in order to investigate the effects of K-0-consolidation and secondary consolidation on the undrained shear behavior of undisturbed marine clay with varying plasticity index in this study. The deviator stress ratio M* mobilized at the maximum deviator stress q(max) of normally K-0-consolidated young clays at the end of primary consolidation became smaller than the critical stress ratio M due to stress induced anisotropy caused by the K-0-consolidation, this ratio M/M* was 0.85 regardless of plasticity index. On the other hands, the effective stress path for normally K-0-consolidated young clays was parabolic curves with plastic softening beyond the maximum deviator stress, which became more marked as the plasticity index increased. It was clearly showed that the shape of the curve will strongly depend on the plasticity index. Furthermore, it was found that experimental effective stress path of high plastic normally K-0-consolidated young clays showed remarkable plastic softening beyond the maximum deviator stress, and this phenomenon could be modeled using a quadratic equation and the parameters AP and initial deviator stress ratio after K-0 consolidation, eta(0), modified by an anisotropic kinematical hardening rule. The normalized maximum deviator stress increased linearly with the log of the normalized consolidation time and high plasticity K-0 consolidated aged clays subjected to secondary consolidation showed more brittle behavior. The effective stress paths for high plasticity K-0 consolidated aged clays initially maintained a constant mean normal stress p' until they reached a deviator stress ratio eta(1) which itself increased with consolidation time. It was found that the experimental effective stress path in the region with a deviator stress ratio eta greater than eta(1) could be modeled using M* and an extended quadratic equation in which the anisotropic hardening rule modified eta(1) instead of eta(0). This model was applicable across the wide range of consolidation time histories from young clay to aged clay subjected to secondary consolidation.