Influence of fracture orientation and aperture on grouting reinforcement of fractured surrounding rock: Experimental and numerical study

Fractures in surrounding rock masses pose critical challenges to the integrity and containment performance of subsurface energy and environmental systems. Grouting is widely applied to mitigate rock fracture-induced weaknesses; however, the combined influence of fracture orientation, fracture aperture, and rock fabric on post-grouting mechanical response remains poorly understood. This study systematically quantifies how fracture geometry (orientation and aperture) governs the strength, stiffness, and damage evolution of fracture-grouted rocks using a nanomagnetic slurry across natural (limestone and dolostone) and 3D-printed (synthetic) rock specimens. Controlled experiments were performed on specimens containing co-planar or orthogonal fractures with varying apertures to obtain uniaxial compressive strength (UCS) and Young's modulus (E) before and after grouting. Complementary finite element (FE) simulations employing a damage-plasticity constitutive framework were conducted to investigate damage evolution and to validate experimental observations. Grouting resulted in substantial improvements in both strength and stiffness across all rock specimens, where dolostone exhibited the greatest enhancement (+285% UCS; +146% E), attributed to its higher porosity and pore connectivity. Orthogonally fractured specimens yielded greater relative grouting performance (+212% UCS; +129% E) compared to co-planar fractures (+196% UCS; +88% E), despite lower pre-grouting strength due to bi-planar weakness. Fracture aperture exerted a dominant control on rock grouting effectiveness, with larger apertures yielding strength gains up to + 203%, compared to + 52% for smaller apertures. Numerical simulations revealed that co-planar fractures promote localized single-plane damage, whereas orthogonal fractures generate diffuse bi-planar damage fields, consistent with experimentally observed lower pre-grouting strength. Further, grouted specimens exhibited suppressed and delayed damage progression, attributable to load redistribution through the grout-rock composite system. These findings demonstrate that fracture geometry and rock fabric collectively control grouting efficiency through their influence on failure-plane development and grout infilling. This study provides a validated framework for designing safer, more efficient stabilization methods in geotechnical and energy-related subsurface systems.