Permeability Characteristics of Model Clay-Based Cutoff Wall Backfills

Abstract

Clay-based cutoff walls have been widely applied in the landfills or site remediations. The factors that affect the hydraulic conductivity of cutoff walls formed by mixing formation with clays are still unclear. Aiming at the issue, the Fujian standard sand was used to simulate the formation and three kinds of clays were taken as the additive and slurry material for mixing and pouring. Then the hydraulic conductivity and pore size distributions were measured. The results indicated when the Clay C formed the cutoff walls with the model formation, there was a critical clay additive amount Ccr corresponding to the minimum porosity, and there would be great change in the descent velocity of the hydraulic conductivity k before and after critical clay additive amount Ccr. In regard to Clay A and Clay B, the critical clay additive amount Ccr of sand-clay specimens didn’t appear as the additive amount of Clay A and Clay B reached 25%. For Clay A and Clay B, the pore size distributions of sand-clay specimens were relatively identical, and their hydraulic conductivity k declined with decreasing porosity n. However, the pore size distributions of the mixture corresponding to Clay C gradually widened with the increasing additive amount, and they would develop towards the smaller pore size. Meanwhile, P50 also declined correspondingly, and there was poor correlation between porosity n and hydraulic conductivity k. Comparatively speaking, the microscopic pore structure of the model formation improved by Clay C was the most obvious, and Clay C raising the sealing effectiveness of model formation was also best.