Anatomy of Critical State Constitutive Models: Simulating Undrained Failure of K0-Consolidated Soils

Different features, such as rotational hardening and nonassociated flow, have been added to the classic modified cam-clay (MCC) model. However, there is little knowledge about their role and importance in simulating in situ soils. This study examined the effects of rotational hardening and associated/nonassociated flow on modeling the undrained shear strength of K0-consolidated clays. For this purpose, three types of rate-independent models were chosen: MCC, MCC with rotational hardening and associated flow (RAMCC), and MCC with rotational hardening and nonassociated flow (RNMCC). The capabilities of the three models in reproducing the K0 state were first discussed. Then, by proposing a dummy yield surface to account for the effect of rotational hardening, an analytical solution to predict soil undrained shear strength su directly from the K0 state was established. The predicted su values were examined against available T-bar data. Results showed that only RNMCC is able to produce a reasonable match no matter the over stress ratio (OCR) profile, while both MCC and RAMCC show overestimation, which increases with increasing OCR.