Mechanical behavior and microscale mechanisms of grout-consolidated fractured coal rock: Integrated 3D In-Situ CT reconstruction modeling and multiscale experimental analysis

• The strength of the GCFCR increases with the fractal dimension, with a higher proportion of fine particles leading to greater strength; • SEM analysis reveals that the polymer-modified grout enhances the structural performance of the GCFCR by filling gaps and improving interfacial bonding; • Both the random aggregate model and the CT-based in-situ reconstruction model successfully reproduce the macroscopic mechanical behavior of the specimens; • The CT-based in-situ reconstruction model demonstrates superior agreement with experimental results compared to the random aggregate model, providing a more reliable numerical approach; The stability of surrounding rock in deep coal roadways is predominantly governed by fractured coal rock masses, with grouting reinforcement serving as a critical technology for ensuring safety. To systematically investigate the controlling mechanism of fractal dimension on the macro-mesoscopic mechanical properties of Grout-consolidated fractured coal rock (GCFCR), this study integrates multiple observational techniques, including static uniaxial compression tests, scanning electron microscopy (SEM), and industrial CT scanning, along with two numerical simulation methods—the random aggregate model and the CT-based in-situ reconstruction model—for multi-scale analysis. The results demonstrate that the uniaxial compressive strength and elastic modulus of the grout-consolidated body increase monotonically with the fractal dimension, reaching optimal mechanical performance at a fractal dimension of 2.6. Moreover, a significant positive correlation is observed between strength and the content of fine particles (0–5 mm). Energy evolution analysis further reveals that specimens with higher fractal dimensions can store more strain energy prior to failure (peak value of 0.10837 MJ/m³) and exhibit a more gradual energy dissipation process. Microstructural observations indicate that polymer-modified grout significantly enhances the interfacial bonding between grout and coal rock by effectively filling pores and forming bridging structures. CT grayscale analysis further confirms a positive correlation between fractal dimension and the compactness of the consolidated body from the perspective of material density. Numerical simulations show that both the random aggregate model and the CT-based in-situ reconstruction model can effectively reproduce the macroscopic mechanical behavior of the specimens. However, the CT-based in-situ reconstruction model, which incorporates realistic meso-structures, demonstrates higher predictive accuracy, with a deviation of only 1.86% in compressive strength compared to experimental results, outperforming the random aggregate model (2.04%). This study provides important theoretical support and technical pathways for parameter design and performance prediction in grouting reinforcement of deep roadway surrounding rock.