Environmental designs for vertical cutoff walls in coastal landfill sites

In the coastal landfill sites, the evaluation methods, construction technologies and long-term maintenance which ensure environmental feasibility of vertical cutoff wall using steel pipe sheet piles with the jointed sections (SPSP cutoff wall) are complicated both experimentally and analytically. In this study, the effect of SPSP cutoff wall in coastal landfill site on the containment of toxic substance was evaluated by seepage and advection/dispersion analysis, and the relevance examined with respect to performance and installation condition of SPSP cutoff walls and environmental soundness. The following conclusions were drawn from this study: (i) Hydraulic conductivity of the SPSP which have not conducted the penetrating lower clay layer does not demonstrate large effect for leakage control of toxic substance, (ii) Leakage control effect of the toxic substance which is accompanied by the order unit, while hydraulic conductivity change from 5×10^-7 to 1×10^-8 cm/s of the SPSP which have conducted the penetrating lower clay layer can be demonstrated, and (iii) for the use of steel pipe sheet piles as a vertical cutoff hydraulic wall, it is desirable that the hydraulic conductivity of 1 × 10^-8 cm/s order be ensured under the condition that it must penetrate to the lower clay layer.