ABSTRACT
In recent years there have been considerable efforts towards developing a unified approach for the analysis of pre-and post-failure response of geo-structures. In the pre-failure regime, with the increased understanding of the essential mechanisms contributing to the overall soil behavior, a plethora of constitutive models are now available to simulate the key aspects of the stress-strain behavior of granular soils such as nonlinear elasticity as well as density and pressure dependence, an evolving shear-induced dilatancy, inelastic behavior upon reverse loading, and critical state. However, as the soil within a geostructural system approaches the failure state the non-homogenous distribution of void ratio, strains, and stresses within the soil mass as well as the boundary conditions of the system may lead to the emergence of highly localized shear zones which are usually an important precursor to instability and collapse of the geo-structure. The soil within these localized zones gradually approaches a critical state condition while the soil outside these zones may undergo an entirely different mode of deformation. Thickness of the localized zone normally depends on the average grain size of the soil and may change during the shearing process. It has been observed that within the shear band soil grains may undergo significant rotations and exhibit dilative behavior. The plastic dissipation due to grain rotations cannot be included in constitutive models that are formulated in the framework of classical Cauchy continuum. Various alternatives
such as nonlocal theories (Jirasek & Rolshoven, 2003), higher-order gradient theories (Pamin 1994), micropolar method (e.g., deBorst 1991; Forest 2001; Huang & Bauer 2003; Tejchman 2008; Manzari 2004), and viscosity approach (Loret & Prevost 1991), among others have been proposed to alleviate the shortcomings of classical continuum-based models.
