Hydraulic Performance of Soil-Bentonite Mixture Barrier

Flexible-wall hydraulic conductivity tests were conducted to assess the hydraulic barrier performance of the soil-bentonite mixture (SBM), that is employed as a barrier material in the vertical cut-off wall constructed with the TRD (Trench cutting and re-mixing deep wall) method. Although the vertical stresses in the SBM wall were reduced to magnitudes below overburden pressures due to the arching effect, hydraulic conductivities lower than l × 10⁻⁸ cm/s were obtained under the estimated stress state. Another main focus was placed on the chemical compatibility of SBM, since the bentonite swelling is very sensitive to chemicals that can lead to increases in hydraulic conductivity. SBM specimens were compatible against CaCl₂ solution, MgCl₂ solution and artificial seawater; hydraulic conductivities of SBM specimens permeated with these permeants were less than 5 times higher than those permeated with the distilled water. In addition, the self-recovery property of the SBM with regard to its hydraulic performance was evaluated when the SBM is subjected to the accidental defects. Testing results indicated that no significant leakage from the induced crack in the SBM occur under the vertical stress of larger than 30 kPa.