This study used silicate cement as the base material and nano-silica, fly ash, and bentonite as the composite modification components. Through laboratory tests, the engineering characteristics and impermeability and drying shrinkage properties of the modified slurry were systematically investigated. The results showed that the verification test mix proportion of the slurry was a water–binder ratio of 0.7, a nano-silica content of 2%, a fly ash content of 40%, and a bentonite content of 6%. This ratio of the slurry had the best comprehensive performance. Compared with pure cement slurry, the water loss rate decreased by 61.90%; the 3d, 7d, and 28d compressive strengths increased by 30.60%, 36.08%, and 20.08% respectively; the fluidity decreased by 6.38%; and the initial setting time decreased by 9.77%. The anti-seepage pressure of the verification test mix proportion slurry group reached 1.05 MPa, which was 43.84% higher than the pure cement reference group and was superior to each single addition group. Combined incorporation of nano-silica, fly ash, and bentonite remarkably improved the impermeability. The 56d drying shrinkage rate was 1257 × 10⁻⁶, which was 19.16% lower than that of the reference group. Based on X-ray diffraction (XRD) and scanning electron microscopy (SEM) tests, the microstructure was analyzed, and the hydration mechanism was discussed. The composite modification did not change the type of hydration products but significantly improved the microstructure. Nano-silica reacted with the hydration product Ca(OH)₂ in the early stage of hydration, accelerating the hydration process and promoting the interwoven coating of the hydration product on the calcium aluminosilicate crystals, thereby improving the compactness of the matrix. Fly ash participated in the pozzolanic reaction in the later stage of hydration, adhering to the secondary hydration products on the surface and gradually consuming them, further filling the pores and optimizing the interface structure. Combined with bentonite, nano-silica and fly ash jointly densified the matrix, refining the microstructure of modified samples and forming a continuous integrated hydration product network inside the grout.

Aiming at the challenges of lining cracking and water seepage in water conveyance tunnels under high internal water pressure, joint waterproofing is the key to improving the structural anti-seepage performance. This paper investigates the mechanical and anti-seepage properties of joint sealing materials, as well as the stress-deformation characteristics of the anti-seepage structure. Uniaxial tensile tests, bond tensile tests, and interfacial shear tests were conducted on three types of sealants—polysulfide, polyurethane, and polyurea—to systematically obtain the fundamental mechanical parameters. The results show that polyurea has the highest ductility, polysulfide exhibits the highest tensile strength (1.27 MPa), and polyurethane presents balanced performance. The interfacial shear strength between polysulfide and concrete reaches 0.5 MPa, demonstrating outstanding bonding performance. Based on the cohesive zone model, a numerical model of the joint sealing system was established to analyze the evolution of stress and deformation under two working conditions: inner-side water seepage and double-sided (inner and outer) water seepage. The results indicate that water pressure induces stress peaks at the contact interface between the sealing material and the segment. The stress peak under internal water pressure alone is significantly higher than that under combined internal and external water pressures. Comprehensive comparison shows that polysulfide sealant offers better stability in resisting internal water pressure and controlling deformation. The selection of sealant type in engineering should consider the stress characteristics, deformation requirements, and construction conditions of different structural locations.