Abstract: Conventional bentonite-, cement- and geopolymer-based cutoff walls suffer sharp rises in hydraulic conductivity during dry-wet cycling, compromising long-term performance. To address this problem, carbide slag (CS), red mud (RM), ground-granulated blast-furnace slag (GGBS) and silica fume (SF) are combined to fabricate four full-solid-waste geopolymer materials (CG, CGS, RCG, RCGS). Their basic properties and dry-wet durability are tested, and MIP/SEM-EDS are used to track pore-structure evolution and reveal durability mechanisms. After 7 days of curing, all four materials meet the anti-seepage design requirement for cement-based cutoff walls for unconfined compressive strength and hydraulic conductivity; the CG mix still meets the design requirements after ten dry-wet cycles, far outperforming conventional walls. The fraction of medium-to-large pores (≥50 nm) governs hydraulic-conductivity evolution, and keeping it ≤ 5% effectively suppresses pore connectivity and the deterioration of anti-seepage performance. Mechanistic analysis shows that although the CS-RM co-activation system forms a denser early-age gel structure, the high water demand of SF increases shrinkage-swelling stress, and the inert RM particles cause stress concentration, jointly accelerating durability deterioration. In contrast, CS-only activation enables ongoing secondary hydration and crack self-sealing, refining the pore structure and minimizing durability degradation. The results guide rational design and engineering application of full-solid-waste geopolymer cutoff walls.