Bedrock weakening is of wide interest because it influences landscape evolution, chemical weathering, and subsurface hydrology. A longstanding hypothesis states that bedrock weakening is driven by chemical weathering of minerals like biotite, which expand as they weather and create stresses sufficient to fracture rock. We build on recent advances in rock damage mechanics to develop a model for the influence of multimineral chemical weathering on bedrock damage, which is defined as the reduction in bedrock stiffness. We use biotite chemical weathering as an example application of this model to explore how the abundance, aspect ratio, and orientation affect the time‐dependent evolution of bedrock damage during biotite chemical weathering. Our simulations suggest that biotite abundance and aspect ratio have a profound effect on the evolution of bedrock damage during biotite chemical weathering. These characteristics exert particularly strong influences on the timing of the onset of damage, which occurs earlier under higher biotite abundances and smaller biotite aspect ratios. Biotite orientation, by contrast, exerts a relatively weak influence on damage. Our simulations further show that damage development is strongly influenced by the boundary conditions, with damage initiating earlier under laterally confined boundaries than under unconfined boundaries. These simulations suggest that relatively minor differences in biotite populations can drive significant differences in the progression of rock weakening. This highlights the need for observations of biotite abundance, aspect ratio, and orientation at the mineral and field scales and motivates efforts to upscale this microscale model to investigate the evolution of the macroscale fracture network.

Rock deforms by a variety of microprocesses, including brittle processes of fracturing and frictional sliding that are strongly pressure-dependent, as well as viscoplastic processes of intracrystalline plasticity and diffusive mass transfer that are largely pressure-independent, but strongly temperature-and rate-de

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Salt rock is a polycrystalline material of interest for geostorage because of its low permeability and because of its potential to self-heal by pressure solution at favorable stress and temperature conditions. It is often assumed that micro-crack propagation and healing lead to isotropic stiffness changes. The goal of this study is to check this assumption and to gain a fundamental understanding of the mechanisms that control the accumulation of damage and irreversible deformation. Cyclic axial loading tests are performed under a confining pressure of 1 MPa on synthetic salt rock generated by thermal consolidation. The stress-strain curves and the microstructure images taken at key stages of the cycles reveal the formation of a complex system of sliding and wing micro-cracks, the orientation of which is loading dependent. We interpret the mechanisms that control the coupled evolution of crack families by a discrete wing crack elastoplastic damage (DWCPD) model. Crack propagation is controlled by Mode I and Mode II fracture mechanics criteria. Sliding "main" cracks grow if a cohesive frictional criterion is met, while the wing cracks propagate in tension. Displacement jumps at crack faces are related to the deformation of the rock Representative Elementary Volume (REV). The DWCPD model can capture the nonlinear stress-strain relationship and the degradation of stiffness during the loading cycles. Simulations show that micro-cracks occur following two stages: (i) Wing cracks initiate and main cracks do not propagate; (ii) Wing cracks and main cracks then propagate simultaneously. Higher friction at the crack faces leads to higher