Abstract: Weathering cracks, structural cracks, and diagenetic cracks have a significant impact on the physical and mechanical properties of engineering rock masses. Conducting systematic research on the multi-scale development laws of rock mass cracks and accurately constructing heterogeneous fractured rock mass calculation models is an important method to deeply reveal the bearing capacity, deformation, permeability, and grouting reinforcement performance of rock masses. Considers the randomness and irregularity characteristics of rock fractures, and based on fractal theory, constructs a fractal model of the fracture network. Using the assumption of parallel plates and the cubic law of fractures, the fractal analytical expressions for the grouting amount and hydraulic conductivity of rock masses are derived. On this basis, the relationship between the ash consumption of fractured rock mass and fractal dimension and crack length was analyzed. It was found that the ash consumption of fractured rock mass increased with the increase of fractal dimension D_f and crack length t_max, and the influence of crack length t_max on ash consumption was more significant than that of fractal dimension D_f. Then, the variation law of ash consumption of fractured rock mass with hydraulic conductivity was explored, and the Chongqing Metro was selected for engineering measurement verification. The results show that the on-site measured data is basically consistent with theoretical speculation, indicating that the derived relationship between ash consumption and hydraulic conductivity is scientifically accurate and can be used as a reference for grouting design.