Experimental and Numerical Investigation on the Aging and Plugging Performance of a Modified Waterglass/Polyurethane for Underground Engineering

Water leakage in underground and geotechnical structures is a widespread issue that poses serious risks to construction safety and long-term service performance. Grouting reinforcement is a commonly adopted and effective mitigation approach. In this study, a novel organic–inorganic hybrid composite grouting material was developed using polyurethane, water glass, and a silane coupling agent as the primary components. The material exhibits high strength, good flexibility, and excellent durability. To evaluate its long-term performance, durability tests, including water immersion, thermal–oxidative aging, and hygrothermal aging, were conducted. Results show that the material demonstrates strong water resistance, with the strength retention rate remaining around 55% after prolonged immersion, and only minor changes in physical and mechanical properties. Under hygrothermal conditions (40°C and 93% relative humidity), combined experimental results and predictive modeling indicate a service life exceeding 20 years. Further, numerical simulations were carried out to investigate the diffusion and leakage-blocking processes of the grouting material under flowing water conditions. The analysis reveals the influence of flow velocity and grouting pressure on leakage control effectiveness and clarifies the underlying sealing mechanism. Overall, the proposed hybrid composite grouting material not only ensures reliable durability but also achieves efficient leakage remediation, providing technical references for the practical application of modified polyurethane/water glass in water-bearing engineering environments.