Synergistic effects of crystal habit and confining pressure on the compressive mechanical behavior of crystalline rock: a grain-based modeling analysis.

This study investigates the synergistic effects of crystal habit and confining pressure on the compressive mechanical behavior of crystalline rocks using a grain-based model implemented in the Universal Distinct Element Code. Synthetic granite samples with euhedral, subhedral, and anhedral microstructures were simulated by adjusting grain boundary irregularity, quantified by fractal dimension (D), which increased from euhedral to anhedral. Deformation and failure were depicted using a compression-hardening contact model and a cohesion-weakening-friction-strengthening material model. Results show that Young's modulus and Poisson's ratio nonlinearly increased with confining pressure, insensitive to crystal habit. Under low confining pressure, compressive stress-strain curves exhibited significant dispersion during crack damage due to crystal habit variations. However, pre-peak curves increasingly overlapped at higher pressures, while post-peak curves remained dispersed. Peak compressive strength initially decreased and then increased with D under low pressure, but this trend diminished as pressure rose. Strength followed the Hoek-Brown criterion, with envelopes dispersing at low pressure but converging under higher pressure. Hoek-Brown parameters first increased and then decreased with D. Tensile stress magnitude and the number of concentration zones increased with increasing D but were suppressed by higher pressure, reducing their influence. As confining pressure increased, tensile stress concentration effects were inhibited, while grain contact shear strength increased, eventually matching grain material strength, diminishing the role of crystal habit and making confining pressure dominant. Additionally, with increasing D and confining pressure, intergranular cracks decreased in number and length, while intragranular damage zones became denser, highlighting the interplay between microstructure heterogeneity and stress state in controlling failure mechanisms.