Application of small-scale TRD method in constructing vertical barriers at an organic compounds-contaminated site

A vertical cutting equipment is used as the main equipment to construct vertical barriers at an organic compounds- contaminated site. The vertical barriers with a length of 70 m and depths of 7.0 m and 5 m are constructed by the small-scale TRD and the cutting-backfilling-mixing method. The workability of bentonite materials is studied through a combination of field and laboratory tests. The results show that the organo clay-enhanced bentonite material can not be effectively hydrated, and the viscosity and slurry fluidity of the activated carbon-enhanced bentonite does not meet the construction requirements of the small-scale TRD method with a liquid-solid ratio of 4:1. In contrast, the sodium hexametaphosphate-enhanced bentonite slurry prepared well meets the construction requirements of the small-scale TRD method. The barriers are sampled and the coring samples are subjected to a series of testing programs including grain-size distribution, water content, liquid limit, pH, characteristic element (sodium) content and flexible-wall hydraulic conductivity tests after construction of 14 days. The test results are used to assess the uniformity of geotechnical parameters along the barrier depths. The hydraulic conductivity test results reveal that the vertical barriers constructed by the small-scale TRD method exhibit lower hydraulic conductivity (1.3×10^-10~2.4×10^-10 m/s) as compared to that constructed by the conventional construction method (7.5×10^-10~9.3×10^-10 m/s), indicating that the SHMP-SB possesses superior hydraulic conductivity. The barrier materials constructed by the small-scale TRD method have superior uniformity in terms of lower coefficient of variation values of water content, liquid limit, sodium content and pH along the depths.