Due to the considerable variation in the range of rock content of the soil-rock mixture, when grouting experiments were conducted according to the existing grouting theory, it was found that a large number of pores not entirely filled by the slurry existed in the concretions of the medium to high rock content backfill area. Therefore, the existing slurry permeation grouting diffusion equation was optimized by adding the filling factor (gamma). Based on the Bingham fluid rheological equation and the Newtonian fluid rheological equation, the optimized calculation equations for Bingham fluid and Newtonian fluid permeation diffusion considering the filling factor (gamma) were derived. Furthermore, the indoor grouting experiment data are compared and analyzed with the calculation results of the original formula and the optimized formula. The results show that when ignoring the unfilled pores, the original formula calculating the diffusion radius will be small; the calculation results of the optimized formula considering the filling factor (gamma) are closer to the actual experiment results. Moreover, based on the calculation results of the optimized formula, the order of influencing factors of the permeation diffusion radius is rock content > void ratio > water-cement ratio > grouting pressure.
