Constitutive Model For Overconsolidated Clays Research Articles

Elastoplastic constitutive model for overconsolidated clays with an advanced dilatancy relation

AbstractThe dilatancy behavior of overconsolidated (OC) clays is a key factor in determining their strength and deformation characteristics. Recognizing the limitations of previous dilatancy relations for OC clays, a novel dilatancy relation is proposed that can effectively capture the changes in dilatancy point, volume dilatancy and contraction with the overconsolidation ratio (OCR). As OC clays revert to the normally consolidated (NC) state, the proposed dilatancy relation smoothly transitions to that of the modified Cam‐clay (MCC) model, ensuring a unified description of the dilatancy relation between OC and NC clays. The dilatancy relation can be easily incorporated into the constitutive model of different theoretical frameworks. Subsequently, this advanced dilatancy relation is integrated into a new elastoplastic constitutive model for OC clays within the framework of bounding surface and generalized plasticity theory. The validity of the proposed model is confirmed through drained triaxial compression and extension, undrained triaxial compression and extension, as well as complex stress path tests for clays with various OCRs, and the simulation results of the proposed model are compared with those of the SANICLAY model. The comparative analysis demonstrate that the model performs well in simulating the behavior of OC clays.

A fractional-order two-surface plasticity model for over-consolidated clays and its application to deep gallery excavation

This paper proposes a novel fractional-order two-surface constitutive model for over-consolidated clays within the framework of the fractional plasticity and bounding surface theories. It incorporates the stress-fractional operator of the loading surface into isotropic and progressive hardening rules, thus obtaining an incremental stress–strain relation without an explicit plastic flow rule. The proposed fractional-order model can replicate the main features of over-consolidated clays well, including stiffness non-linearity, the occurrence of plastic strains before high peak strength, non-associativity, weak/strong dilatancy, and cyclic behavior. In model simulations on a set of element tests along different loading paths on natural Boom clay and remolded Fujinomori clay, the proposed model reveals better agreement than the modified Cam-Clay model (MCC). Next, the fractional-order model, ACC-2 model and MCC model are implemented via a user-defined material subroutine in ABAQUS with an explicit integration scheme based on the forward modified Euler method with automatic sub-stepping and error control. The different models are then applied to the fully coupled two-dimensional hydromechanical modeling of the excavation of two deep underground galleries in natural Boom clay. The results ultimately verify the validity and applicability of the proposed model.