Fracture mechanisms of rock-like specimens containing double resin-infilled fissures under three-point bending loading: Sand-based 3D printing experiments and discrete element numerical simulations

Fissures in natural rock masses severely weaken bearing capacity and threaten deep engineering stability. Grouting reinforcement is an effective method for restoring integrity and inhibiting crack propagation. In this study, the mechanical properties and fracture mechanisms of 3D-printed rock-like specimens with resin-filled dual flaws under three-point bending are investigated. Digital Image Correlation (DIC) and two-dimensional Particle Flow Code (PFC2D) numerical simulations were integrated to analyze crack evolution under varying inclination angles ( α ). Resin filling fundamentally reconfigures the failure mechanism, shifting crack propagation from low-energy shear slip to high-energy matrix tension. Unlike unfilled specimens where increasing inclination ( α ) degrades strength and stress blocking effects as α increased, resin filling restored stress transmission continuity. To quantitatively elucidate this reinforcement, we analyze the mechanism of stress transfer restoration and evaluate the energy evolution using a normalized energy dissipation ratio ( K d ). Analysis of the K d ratio reveals that resin filling stabilizes the energy conversion rate between 70% and 74%, effectively overcoming the brittle collapse observed in unfilled samples. Crucially, at the critical 60° angle, the resin optimizes the energy evolution process by enforcing a transition from interface slip to matrix fracture, providing a theoretical basis for stability assessment in deep engineering projects.