Study on Influence of Grouting on Mechanical Characteristics and Stress Concentration in Hole-Containing Rock

Grouting technology is a pivotal methodology for enhancing the mechanical properties of defective surrounding rock masses in tunnel engineering. Through uniaxial compression tests on intact, hole-containing, and grouted marble specimens, the influence of cement grout filling on the mechanical behavior of marble containing holes was investigated. Based on the experimental results, discrete element method (DEM) models were established for the three types of specimens, revealing the mesoscopic crack propagation mechanisms and stress distribution in potential stress concentration zones during failure. The experimental results demonstrated that the implementation of cement grouting enhanced the strength properties of the specimens by 22.38%. In terms of failure modes, the failure mode of the grouted specimens was similar to that of the intact specimens, and the filling material transformed the failure mode from tensile to shear failure. Numerical simulations revealed differences in microcrack evolution: cracks in the hole-containing specimens initiated near the upper and lower ends of the holes, while cracks in the grouted specimens originated around the filling material, with both types propagating axially. Microcracks in the grouted specimens initiated earlier, but the majority of microcracks in both types developed after peak stress and were predominantly tensile. The stress concentration coefficients for the intact, grouted, and hole-containing specimens were approximately 0.84, 2.25, and 2.96, respectively. The grouted specimens shortened the duration and alleviated the degree of stress concentration in the defect zones. This study elucidates the grouting reinforcement mechanisms in defective tunnel surrounding rock through a multiscale approach, providing theoretical underpinnings for optimizing tunnel support systems and preventing engineering hazards including collapse and rockburst.