抄録
Vertical cutoff walls using low-permeable materials are often constructed at contaminated sites to contain the contaminants and to prevent their migration in the aquifer. Although soil-bentonite cutoff walls can be expected not to lead shear failure even against ground motion due to its softness, cutoff walls are possible to be hydraulically damaged with slip failure or crack. 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 with hydraulic defects. In order to simulate cutoff walls with defects, 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 regardless of CaCl2 concentration of base soil. After 4-day permeation, the average hydraulic conductivity of specimens with hydraulic defects was up to 2.2 times that without the defects, while leakage along the cracks were relatively higher with higher initial CaCl2 concentration of base soil. It can be assumed that the self-recovery of soil-bentonite in hydraulic conductivity can be attributed to both the re-swelling of bentonite to non-cations permeant and to shrinkage of crack face and hole due to the softness of soil-bentonite. Thus, even when hydraulic defects occur in cutoff walls, soil-bentonite can recover its hydraulic barrier performance within several times of original hydraulic conductivity with time.
