  A constitutive model is presented for brittle granular materials based on a
recent reformulation of the breakage mechanics theory. Compared with previous
breakage mechanics-based models, the proposed model is improved to capture
strain softening towards the critical state following the peak stress observed
in dense specimens under shearing, and simultaneous evolution of breakage and
dilation. Considering the competition between dilation and particle breakage
allows the model to capture breakage-induced reduction in dilatancy and peak
strength as confining pressure increases. The influence of the model parameters
on the overall material response is described through a detailed calibration
procedure based on a benchmark experimental dataset. Comparison of the results
of drained triaxial compression experiments on two sands with the predictions
of the model indicates that the enriched model successfully captures strain
softening in dilatant specimens, the shearing-driven evolution of stress-strain
behavior towards the critical state at different confinement levels, the
transition from dilatant to compactive volumetric response, and the evolution
of particle grading due to distributed breakage events. The proposed framework
is capable of qualitatively reproducing the experimentally observed
stress-dilatancy-breakage relationship in brittle granular materials in the low
pressure regime.
