Adaptive anisotropic constitutive modeling of natural clays

Abstract

In this paper, an adaptive anisotropic constitutive model, namely AA1‐CLAY, is developed for clays based on the critical state framework. The model has a non‐associated flow rule, and it can also reduce to basic critical state constitutive models. A versatile yield surface (YS) is implemented in the model which can generate a broad range of shapes to improve the possibility of capturing experimental yield points of different clay types with high accuracy. In addition to the isotropic hardening rule, an innovative rotational hardening (RH) rule is also incorporated into the model to control the YS rotation rate. The proposed RH rule uses a transitional function to govern the effect of plastic strains at different constant stress ratios more realistically. Furthermore, the equilibrium state of anisotropy, which the YS tends to reach during plastic straining, is defined uniquely based on the experimental findings. The detailed model formulation is presented, and important features of the model are elaborately discussed. The capabilities of the model are also demonstrated by comparing the simulation results of several element tests on a number of different clays against the available experimental data.

Double image stress point bounding surface model for monotonic and cyclic loading on anisotropic clays

“…Using a novel double-image stress point (DISP) method, a robust elastoplastic constitutive model is proposed in this paper to capture the realistic behaviour of a wide range of normally consolidated to highly overconsolidated clays under the application of cyclic and monotonic loadings. The new model which is the second member of the adaptive anisotropic [15] family of models is named AA2-DIS-P. This method enhances the model to tackle the difficulties associated with finding a suitable set of projection centre and mapping rule to simulate the highly overconsolidated behaviour more accurately.…”

“…Extensive experimental studies on finding the stress points associated with the initiation of plastic flow indicate that a flexible non-elliptical YS best represents the yield loci for different soil types [14,16]. The flexibility of the YS should be considered an inseparable feature of an accurate soil constitutive model since frequent studies prove that not only YS shapes are different from one soil to another, but also, even for a specific soil, they are highly dependent on the consolidation condition of the soil [15]. To this end, a flexible anisotropic YS is developed in the proposed model which can produce different shapes using two modelspecific shape parameters (n y and r y ) in comparison with a typical anisotropic MCC model (e.g., [13,28,29,61]).…”

Evolution of anisotropy with saturation and its implications for the elastoplastic responses of clay rocks

“…In particular, unsaturated soft clays exhibit an evolving anisotropy induced by plastic strain, in which plastic deformation erases or enhances the degree of plastic anisotropy 64,75 . Hence, many of these models adopt a rotational hardening law to capture the evolution of the inclination of the yield surface with plastic strain 63,64,72,73,76,77 . To incorporate the effects of partial saturation, the evolution of the hardening variables, including the rate of rotation of the yield surface, was made to depend on the suction stress and DOS.…”

“…64,75 Hence, many of these models adopt a rotational hardening law to capture the evolution of the inclination of the yield surface with plastic strain. 63,64,72,73,76,77 To incorporate the effects of partial saturation, the evolution of the hardening variables, including the rate of rotation of the yield surface, was made to depend on the suction stress and DOS. However, experimental evidence suggests that clay-rich shales exhibit inherent plastic anisotropy.…”

Anisotropic subloading surface Cam‐clay plasticity model with rotational hardening: Deformation gradient‐based formulation for finite strain

“…Constitutive modeling with anisotropic plasticity for geomaterials has been and is still a very active research area. We refer to several recent research works: anisotropic viscoplastic Cam-clay model for shale by Borja et al, 62 adaptive constitutive modeling with rotational hardening by Dejaloud and Rezania, 63 anisotropic model considering fabric evolution with the aid of DEM numerical tests by Wang et al, 64 and anisotropic model applicable to change in principal stresses and their axes rotation by Xue et al 65 These studies are; however, limited to the small strain framework.…”