Computational modelling of the localized deformation associated with borehole breakout in quasi-brittle materials

The objective of this paper is to review the physical evidence for localized damage near boreholes that result in the borehole breakout phenomenon and to review computational modelling strategies that are able to represent the observed behaviour. A specific point emphasized is that the strength criterion must be augmented by an appropriate regularization strategy if the post-localization response is to be evaluated. Computational results are presented which illustrate that the incorporation of fracture energy concepts as a regularization strategy furnishes a constitutive model which exhibits mesh invariance of the energy dissipation and reproduces the observed size effect of the collapse pressure in thick-walled cylinder (TWC) tests.