To investigate the anchoring performance of self-drilling anchors in gravel-cobble strata, this study conducted indoor orthogonal tests based on soil grouting experiments to simulate actual construction conditions. The influence of fine particle content, grouting pressure, and water-cement ratio on anchoring parameters was analyzed. Additionally, a grouting simulation model was developed using PFC2D 5.0 numerical software to examine the effects of grouting pressure, drilling speed, and grout viscosity on the grout diffusion radius through orthogonal and single-factor experimental schemes. The results demonstrate that: fine particle content exerts the most significant impact on anchoring performance, with higher content reducing peak pullout resistance; the grout diffusion radius exhibits a positive correlation with grouting pressure but a negative correlation with drilling speed and grout viscosity, with viscosity having the strongest influence, followed by pressure and speed; the diffusion pattern follows a gradually decreasing trend along the drilling direction, while the radius increases at a diminishing rate with elevated pressure; when viscosity ranges from 83.3 to 833.3 mPa·s, the diffusion radius decreases by 72%; and multivariate regression analysis indicates a power function relationship between the diffusion radius and these three parameters.