  This paper discusses a continuum approach to track the evolution of
permeability in granular rocks by accounting for the combined effect of
porosity changes, grain breakage and cement bond damage. To account for such a
broad range of microscopic processes under general loading paths, the Breakage
Mechanics theory is used and the computed mechanical response is linked with
the Kozeny equation, i.e. a permeability model able to evaluate the reduction
of the hydraulic conductivity resulting from the simultaneous loss of porosity
and growth of surface area. In particular, the evolution of the internal
variables of the model has been linked to idealized geometric schemes at
particle scale, with the goal to distinguish the contribution of the fines
generated by the disaggregation of the cement matrix from that of the broken
fragments resulting from the crushing of the skeleton. Compression/flow
experiments available in the literature for different granular rocks are used
to validate the proposed methodology. The analyses illustrate that the drop of
the permeability of damaged rocks would be severely underestimated without an
accurate computation of the growth of surface area, as well as that the
distributed fragmentation of skeleton particles tends to have stronger
implications than the generation of cement fines. These findings, along with
the satisfactory agreement between model predictions and experiments, stress
the benefits of adopting microstructure-based constitutive laws for the
analysis of coupled hydro-mechanical problems.
