Abstract: Grouting in water-rich fracture networks with fillings is influenced by three factors:fracture distribution,filling medium properties,and groundwater action.In this work,to investigate pre-grouting behavior in filled fractures,a novel numerical simulation method is proposed,which enables a comprehensive computation of slurry transport and spatiotemporal viscosity variation.We numerically analyzed the effect of different slurry and filling properties on slurry transport and the results show that:(1) Quick-setting slurry only propagates through fractures near the tunnel surface,failing to seal deeper fractures,suggesting that flowability should be prioritized in slurry selection when targeting larger grouting ranges.(2) Compared to particle size,the compactness of the filling medium has more significant impact on slurry transport.As the porosity decreases,the cement slurry cannot penetrate into deep fractures and the uniformity of slurry transport is limited.Thus,under dense filling conditions,grouting ranges should be reduced to ensure even slurry distribution.(3) Under sparse-filling conditions,cement slurry achieves a uniform transport radius,but the interaction of slurry-water in deep fractures decreases slurry concentration,thereby affecting the quality of the grouting.The findings were successfully applied in the construction of an oil storage in Guangdong,effectively mitigating water inflow risks in the study area.