Experimental and numerical simulation assessment of fracture evolution and tensile strength recovery in Grout-reinforced fractured surrounding rocks.

The surrounding rock around deep underground excavations generally contains fractures and joints that significantly reduce mechanical integrity, particularly in zones where excavation-induced unloading, stress rotation, and anisotropic deformation generate tensile stress concentrations. These tensile regimes govern crack initiation, fracture propagation, spalling, and progressive instability around tunnels, caverns, mines, and wellbores. Although rock grouting is widely used as a reinforcement strategy, its effectiveness in restoring the inherent strength of tension-dominated surrounding rock is often assumed, and the tensile fracture behavior of fracture-grouted rock remains insufficiently understood. This study investigated the evolution of tensile strength (TS) and tensile-induced fracture behavior in fractured surrounding rock before and after fracture grouting, providing mechanistic evidence for assessing strength recovery. In addition to TS, failure modes and total fracture length (TFL) were quantified to assess fracture propagation and grout-reinforcement performance in tension-prone surrounding rock zones. Brazilian disc tests (BDT) were conducted on natural (limestone and dolomite) and synthetic (3D-printed) rock samples, allowing direct comparison of the same samples in ungrouted and fracture-grouted states. To mechanistically interpret and validate the experimental findings, a finite element model employing the cohesive zone method (FEM-CZM) implemented in ABAQUS was developed to simulate the evolution of tensile strength and the initiation and propagation of micro-fracture in the specimens before and after grouting. Results revealed that while fracture grouting does not fully restore the inherent tensile strength of fractured rocks, it significantly altered the tensile failure process. Grout-rock interfaces in the fracture-grouted rocks constrained and redirected crack propagation, reduced total fracture length, and shifted failure modes toward more localized and controlled fracture patterns. A positively correlated TS-TFL relationship observed in ungrouted samples reversed in fracture-grouted samples, indicating that higher tensile resistance in grouted rock mass corresponds to more limited fracture development. The FEM-CZM simulation confirmed the experimentally observed post-grouting delay in rock damage onset with reduced fracture path and an increase in Mode-II energy dissipation, and provided direct visualization of stress concentration, damage evolution, and fracture-path control. These findings demonstrate that surrounding rock control in tensile regimes depends not only on tensile strength recovery but also on the ability of grouting to suppress fracture propagation and damage evolution. The results provide new mechanistic insight into fracture-grouting performance in tension-prone underground environments and demonstrate that TFL, when used alongside tensile strength and other mechanical parameters, is a valuable metric for assessing reinforcement effectiveness. This work advances the understanding of grouting as a surrounding rock control strategy and informs the design of reinforcement systems aimed at stabilizing underground excavations subjected to tensile stress concentrations.