Hydraulic Conductivity and Compressibility of Polyanionic Cellulose-Modified Sand-Calcium Bentonite Slurry Trench Cutoff Wall Materials

In some countries lacking sodium bentonite (NaB), polymer-modified calcium bentonite (CaB) has attracted attention for its application in sand-bentonite slurry trench cutoff walls to control groundwater contamination. Thus, this study used polyanionic cellulose (PAC), an environmentally friendly hydrophilic polymer, to modify CaB. The hydraulic and consolidation properties of cutoff-wall materials (including bentonite cake and backfill) containing CaB or modified CaB with 4% PAC (dry mass ratio, 4%PAC-CaB) under various stress conditions, CaCl 2 solution concentrations, and bentonite contents were investigated through a series of experiments, including modified fluid loss, slump, Atterberg limit, oedometer, and rigid-wall hydraulic conductivity tests. The results show that the 4%PAC-CaB cake had better salt resistance and impermeability than CaB and NaB cakes under different stress and salt concentration conditions, and sand-4%PAC-CaB backfill had a significantly higher liquid limit, ideal water content, and compression index, and a lower coefficient of consolidation and permeability than sand-CaB backfill with the same bentonite content. More importantly, the addition of 4% PAC had a more significant effect on decreasing the permeability of the sand-CaB backfill than increasing the CaB content. Overall, 4%PAC-CaB is a promising modified CaB that can replace NaB for the construction of cutoff walls with excellent impermeability.