Site-bond modelling of porous quasi-brittle media

Geological repositories' designs employ a multi- barrier approach. The materials, which include: backfill, host-rock and wastforms, are typically porous quasi-brittle. Mechanical damage, e.g. nucleation and growth of microcracks, can result in significant changes in permeability. A knowledge of how the permeability is affected is critical to accurate modelling of radionuclide transport. Particle Methods (PM) offer an advantageous route by which to study damage evolution. In PM, solid-phase grains are considered to reside at the sites of a lattice; interactions between grains are ascribed to bonds connecting neighbouring sites. Current PM for concrete and graphite are based on un-realistic, simple cubic lattices with six-fold site coordination. Despite some successes, such models are generally incapable of representing the linear elastic response of the solids studied. The present work proposes a PM version employing novel site-bond models based on non-cubic lattices that offer physically realistic grain shapes with coordination of 14. We demonstrate the major advantage of the models; they can be used to represent any required macroscopic elastic response. The porosity in these models is distributed on the grain boundaries according to any predefined pore size distribution. The size of a pore on a boundary dictates the failure strength of the corresponding bond. The ability of the models to predict the macroscopic stress-strain response with emergent non-linearity due to damage evolution is also demonstrated. The models can be used for deriving mechanism-based constitutive damage laws for finite element models. They can also be linked elegantly to pore system changes in dual site-bond models of the pore space for predicting permeability changes with damage evolution.