Abstract: Cutoff walls are essential engineering structures that mitigate environmental risks at contaminated sites by restricting pollutant migration alongside groundwater flow. This study developed bentonite-geopolymer cutoff wall materials utilizing calcium bentonite (CaB) and modified calcium bentonite (mCaB). A series of macro- and micro-level experiments were conducted to evaluate their fundamental engineering properties and durability under dry-wet cycles. The mechanism by which CaB improves durability was clarified, and performance differences between CaB and mCaB were explained. Results indicated that increasing the bentonite content elevated hydraulic conductivity while reducing unconfined compressive strength in both CaB- and mCaB-based systems; however, all met the design requirements. The incorporation of 3% bentonite significantly enhanced durability during dry-wet cycles. After 10 cycles, the mCaB-geopolymer exceeded the hydraulic conductivity limit (1×10^⁻8 m/s), whereas the CaB-geopolymer still satisfied the design requirements. Bentonite addition increased water demand and altered the geopolymerization process, affecting material behavior. During dry-wet cycles, drying induced shrinkage and cracking near bentonite particles, while rehydration promoted swelling that hindered crack propagation. Compared to mCaB, CaB caused less debonding from the matrix due to its lower swelling capacity, thereby maintaining structural integrity and offering superior durability under dry-wet cycles.

Key words: cutoff wall, geopolymer, calcium bentonite, hydraulic conductivity, dry-wet cycle