The influence of constitutive models on localization conditions for porous rock

Alternative constitutive models are employed to examine localization conditions for high porosity sandstone. Two deformation types are considered: shear bands and compaction bands (planar zones of pure compressional deformation, perpendicular to maximum compression). The proposed two-yield surface model, motivated in part by observations of two microstructural damage mechanisms, consists of a shear yield surface (dilatant, frictional mechanism), combined with a cap (compactant mechanism). Results from this model are consistent with limited experimental observations: both band types are permitted for probable values of key material parameters. Conversely, the single-yield surface model, previously employed for sandstone, cannot predict the observed compaction bands.