Field trial of constructing vertical barriers using small-scale TRD method at an organic compounds-contaminated site

This study presented field trial evaluation of using a novel vertical cutting equipment, namely small-scale TRD, to construct containment vertical barriers at an organic compounds-contaminated site. The small-scale TRD had merits of easy-construction at sites with relatively narrow space and superior uniformity of in-situ mixing as well. Vertical barrier with conventional method, namely, cutting-backfilling-mixing method, was also constructed for comparison purpose. The lengths and depths of barrier were 35.0 m and 7.0 m and 28.0 m and 5.0 m for the small-scale TRD, whereas those were 7.0 m and 5.0 m for the conventional method. The primary functional materials in the vertical barrier consisted of sodium hexametaphosphate-amended soil bentonite (SHMP-SB) for the small-scale TRD method, and organoclay-amended soil-bentonite (OC-SB) and activated carbon-amended soil-bentonite (AC-SB) for the conventional construction method. The workability of bentonite slurry used to construct the barrier via the small-scale TRD method was evaluated by Marshall viscosity, specific gravity, and slurry fluidity. The results showed that fluidity of sodium hexametaphosphate-amended bentonite slurry, prepared with a liquid-solid ratio of 4:1, could meet the construction requirement. 14 days post construction, the barriers were sampled and the coring samples were subjected to a series of particle size distribution, water content, liquid limit, pH, characteristic element (sodium) content, and flexible-wall hydraulic conductivity tests. The test results were used to assess the uniformity of geotechnical parameters along the barrier depths. Hydraulic conductivity test results revealed that the vertical barrier constructed by the small-scale TRD method exhibited lower hydraulic conductivity (1.3×10-10-2.4×10-10m/s) as compared to at constructed by the conventional construction method (7.5×10-10-9.3×10-10 m/s), indicating that SHMP-SB possessed superior impermeability. The barrier material constructed with small-scale TRD method had superior uniformity in terms of lower coefficient of variation values of moisture content, liquid limit, sodium content and pH along the depths.