A strain space soil model with evolving stiffness anisotropy

Abstract

A complete formulation of the BRICK soil model in general strain space is presented herein for the first time. Like all elasto-plastic constitutive models, BRICK exhibits some anisotropic behaviour, owing to the development of plastic strains once its yield surfaces are engaged. However, an abundance of laboratory and field evidence demonstrates that stiffness anisotropy is also significant within the elastic domain. Because of the inseparable nature of strength and stiffness in BRICK, the simple use of an anisotropic elastic stiffness matrix would result in an unrealistically high degree of strength anisotropy. Therefore, in addition to the established BRICK formulation, this paper also presents a novel framework to introduce stiffness anisotropy by transforming the coordinate system in which the model is based. The transformed coordinate system evolves to enable a constant-volume condition during shearing at critical state, reflecting the reorganisation of the soil fabric. The superior performance of the enhanced BRICK model over the classic model is demonstrated by a variety of conventional and non-conventional laboratory tests on London Clay.