Micro‐Macro Fracture Mechanism, Energy Evolution and Damage Constitutive Model of Rock‐Like Materials With Heterogeneous Parallel Double Flaws Under Triaxial Compression

ABSTRACT To investigate the effects of flaw geometric heterogeneity on the mechanical behavior of rock under triaxial compression, this study examines sandstone‐like specimens containing parallel double flaws, systematically evaluating the coupled effects of multiple parameters including flaw spacing and the apertures of primary/secondary flaws (considering non‐uniform configurations). Through triaxial compression tests and numerical modeling using the Particle Flow Code (PFC2D) for energy evolution analysis, a damage constitutive model incorporating microcrack event counts is developed, which accounts for the aperture ratio between primary and secondary flaws ( λ = a / c ) and flaw spacing ( b ). The results indicate that increasing flaw spacing significantly enhances both the strength and integrity of the specimen, whereas increasing the aperture of the primary flaw markedly reduces strength. Under non‐uniform flaw aperture conditions ( λ ≠ 1), a decrease in the aperture of the secondary flaw improves compressive strength but also induces a more complex crack network and more concentrated microcrack activity near the peak stress. Energy evolution is significantly governed by flaw geometry, with non‐uniform aperture conditions fundamentally altering energy accumulation efficiency and instability modes. The developed constitutive model accurately characterizes ( R ² ≥0.96) these complex mechanical responses, demonstrating that geometric heterogeneity in parallel double flaws is a key factor controlling rock mass stability, thereby providing important theoretical support for hazard prevention in underground engineering.