Revisiting the Paradigm of Critical State Soil Mechanics: Fabric Effects

Abstract

In a recent paper Li and Dafalias [1] proposed an Anisotropic Critical State Theory (ACST) as an enhancement of the classical Critical State Theory (CST) for soils, by introducing the requirement that a fabric and loading direction related scalar-valued quantity must reach a critical state value concurrently to the classical requirement of critical state values for the stress ratio η and the void ratio \(e = \hat{e}_c (p)\) . In this process a necessary ingredient is the introduction of a measure of fabric in the form of an evolving fabric tensor, motivated by DEM simulations based on the void vectors concept presented in Li and Li [2]. The so defined fabric tensor was shown theoretically to have a critical state value norm independent of the pressure p or the specific volume ν, and dependent only on the mode of shearing via a Lode angle expression. A thermodynamic consideration of the critical state in conjunction with Gibbs’ condition of equilibrium can provide proof of uniqueness of the critical state line in the e-p space in regards to various mode of shearing. The enhanced fabricrelated critical state condition can be used in a simple, if not unique, way to provide a corresponding constitutive framework for soil plasticity. The objective of this plenary presentation is to briefly outline the premises of the ACST, elaborate more on the motivation and thinking process behind the proposed theory rather than repeat several details that can be found in Li and Dafalias [1], and address several issues associated with current and future research objectives of the ACST.