Study on service performance and design method of vertical cutoff wall under multi-time-varying point source...

Vertical cutoff wall is widely used as one of the in-situ remediation technologies for contaminated sites. In this paper, considering the unsaturated characteristics of porous media, a three-dimensional pollutant transport model of inner aquifer-vertical cutoff wall-outer aquifer is established. The main conclusions are as follows. The breakdown time t_b changes significantly when the finite pulse release point source release time t_f≤ 25 a and the decay release point source decay coefficient λ < 0.04 (1/a). When the distance between multi-point pollution sources d≤ 1.0 m, the point source coupling effect is stronger, and the pollutant concentration at the entrance is in a single peak distribution. The cutoff wall breakdown time t_b changes significantly in the range of 3 a < t_{1/2_cw} < 15 a when the degradation characteristics of pollutants in the inner and outer aquifers are not considered. When the degradation characteristics of pollutants in the inner and outer aquifers are considered, the sensitive range of t_{1/2_cw} increases. The breakdown time t_b of the cutoff wall increases approximately linearly with the increase of the distribution coefficient k_{p_cw}, and decreases approximately linearly with the increase of the cutoff wall permeability coefficient k_{s_cw}. In addition, the design drawings of the cutoff wall thickness T_cw and the position D_s are given, and the comprehensive design method of the vertical cutoff wall is summarized.