Abstract: Vertical cutoff wall is one of the most effective technologies to restrict the migration of contaminants and has been widely used for in-situ management and control of contaminated soil and groundwater. The traditional cutoff wall materials are highly susceptible to performance degradation under dry-wet cycles, leading to a significant reduction in service life. Through a series of macroscopic and microscopic experiments, the influences of sodium bentonite, magnesium oxide, and microcapsules on the evolution of permeability characteristics and microstructure of fly ash-based geopolymer cutoff wall materials under dry-wet cycles were investigated. The results showed that the unconfined compressive strength (UCS) and permeability coefficient of different geopolymer cutoff wall materials all met the anti-seepage design requirements for cement-based cutoff walls, achieving 6.62 MPa and 4.73×10−11 m/s, respectively, after being cured for 28 days. The permeability coefficient of samples without modified materials exceeded 1×10−8 m/s after the first dry-wet cycle, while that of samples with modified materials could still meet the design requirements after five cycles. The three modified materials can effectively influence the proportions of micropores (<0.05 μm), mesopores [0.05 μm, 0.10 μm], and macropores (>0.10 μm), thereby improving the anti-seepage performance of geopolymer cutoff wall materials under dry-wet cycles. This study has significant implications for the performance evaluation and scientific design of cutoff walls.

Key words: cutoff wall, dry-wet cycle, geopolymer, permeability, micro-mechanism