Optimization of anti-dispersion grouting material parameters for leakage treatment of tunnels in water-rich sandy cobble stratum

To solve the problem that empirically prepared grouting materials often fail to meet the requirements for water blocking in operating tunnels crossing water-rich sandy cobble strata. The grouting material used in this study was based on sulphoaluminate cement (SAC), combined with hydroxyethyl methyl cellulose (HEMC) and high-performance polycarboxylate superplasticizer (PS). Response surface methodology (RSM) was employed to investigate the effects of component proportions on fundamental slurry properties and establish predictive models for these performance indicators. A sand gravel stratum grouting anti-washout experimental device was specifically designed to explore the combined influences of formation porosity, water flow velocity, and Slurry ratio on grouting retention rate ( GRR ), resulting in the derivation of a regression equation for retention prediction. The key findings include: (1) Sandy cobble formations significantly enhance the GRR , and the GRR exhibits an exponential decay pattern with scouring time, and the decay rate is primarily governed by velocity of dynamic water. (2) The flow velocity of dynamic water exerts the most pronounced effect on the GRR , followed by water-cement ratio, HEMC content, formation porosity, and PS content. (3) Based on these performance prediction models and the GRR regression equation, a multi-objective optimization framework was proposed for designing grouting parameters tailored to sandy cobble strata under dynamic water conditions. This methodology provides a scientific basis for material parameter selection in operating tunnel water-blocking grouting engineering.