Critical grain size and shear behavior of polycrystalline rocks under confining pressure: A moment tensor-based GBM approach

The stability and safety of geotechnical structures such as slopes and tunnels are critically dependent on the shear behavior of crystalline rocks. In this study, a shear model for crystalline rocks was developed by integrating grain‑based modeling with moment tensor, thereby enabling the quantitative characterization of source mechanisms. Employing this model, the shear response of crystalline rocks with varying grain sizes under different normal stress conditions was systematically investigated. The results indicate that, with increasing normal stress, the number of intragranular tensile cracks and intergranular shear cracks increases, although intergranular tensile cracks remain the dominant type. Elevated normal stress facilitates the propagation of intragranular cracks, while simultaneously suppressing the formation of horizontal secondary cracks and concentrating damage along the primary shear surface. The presence of normal stress alters the effect of grain size on shear strengt...