EXPERIMENTAL STUDY ON THE SELF-SEALING CAPABILITY OF SOIL-BENTONITE MIXTURE CUTOFF WALLS

摘要

Soil-bentonite mixture is a material used as containment barrier for contaminated soils due to its low hydraulic conductivity values, high deformability, and few surplus-soil discharges. In this study, laboratory-scale hydraulic conductivity tests were conducted with a flexible-wall permeameter, with emphasis on the self-sealing capability of soil-bentonite mixtures with hydraulic defects. In order to simulate cutoff walls with defects such as slip surface, specimens with a crack or hole were subjected to permeation. We found as a result that hydraulic conductivity values decreased with time due to the self-sealing capability of soil-bentonite mixture, regardless of the original hydraulic conductivity value of undamaged specimens. Since, after 4-day permeation, significant differences in the average hydraulic conductivity were not observed between samples with and without hydraulic defects, it was concluded that soil-bentonite mixtures can maintain a hydraulic barrier performance. It can be assumed that the self-recovery in hydraulic conductivity can be attributed to both the re-swelling of bentonite to permeant, and to the shrinkage of crack surface and holes due to the softness of soil-bentonite. Thus, the hydraulic conductivity of soil-bentonite cutoff walls can decrease with time even when hydraulic defects accidentally appear in the cutoff walls.