Long-term durability of soil-bentonite cutoff walls used for containment of ground contamination

摘要

Cutoff walls used for prevention of the migration of mobile contaminants in the aquifer must maintain its high barrier performance for a long period. Soil-bentonite (SB), which is a mixture of in situ soil and bentonite, has many advantages as a barrier material such as high softness, high homogeneity, and high material stability because the SB consists only of inorganic soils. To ensure long-term durability of the SB cutoff walls, we have studied factors affecting hydraulic conductivity of SB, self-recovery in the hydraulic conductivity against occurrence of hydraulic fractures, and the role of chemical diffusion in transport of mobile substances. These approaches confirmed that the hydraulic conductivity of the SB is strongly affected by chemicals in pore water and the content of bentonite powder. The effect of chemical diffusion on transport of mobile substances is not negligible because the relative concentration of a chemical substance attained 0.26 after 50 years only by the chemical diffusion when not considering the adsorption onto soil particles.