基于高密度电阻率成像法的低渗黏土中轻非水相液体运移规律探索

A study of light nonaqueous phase liquid transport in low-permeability clays based on high density electrical resistivity tomography

为了实时掌握轻非水相液体(LNAPL)泄漏后在黏土中的动态分布及入渗时的运移规律,进行了室内模型箱实验,由上至下设置均一含水土层及含毛细水土层,采用高密度电阻率成像法对土体的电阻率变化进行监测,获得了加注过程中及加注结束后LNAPL的运移规律。实验结果表明:LNAPL渗入黏土提高了黏土的电阻率,质量含水率为10%的黏土可提高50?·m左右,随黏土含水率的增加,该提高数值逐渐减小;0~9 h加注阶段,在质量含水率10%的土层中LNAPL水平扩散速度的峰值将近90 cm^(2)·h^(-1),运移至非饱和毛细带时,随土体含水率的增加,其水平扩散速度的峰值逐渐降低;停止加注后,LNAPL在黏土中的高浓度污染区位置逐渐下移,局部区域的污染羽锋面出现回缩,回缩速度可达0.15 cm^(2)·h^(-1)。该研究可为探索沿海、沿江等低渗黏土污染区中LNAPL的运移规律及分布特征提供参考。

In order to grasp the transportation law of light non-aqueous phase liquid(LNAPL) in clay after leakage,a modeling test was conducted.The soil layer was divided into two parts,with the upper clay having a uniform water content and the lower soil containing capillary water.The resistivity changes of the soil were monitored by electrical resistivity tomography,and the transportation law of LNAPL was obtained during the filling process as well as at the end of the filling process.The results showed that LNAPL infiltration into clay can improve the resistivity of the clay,and the resistivity of a clay with 10% water content can be increased by50 Ω·m.With the increase of water content,its effect on improving clay resistivity gradually decreased.During the filling phase of LNAPL from 0 to 9 h,the peak value of the horizontal diffusion velocity of LNAPL was nearly 90 cm^(2)·h^(-1) in the soil layer with 10% water content.When LNAPL transported to the unsaturated capillary zone,the peak value of its horizontal diffusion velocity gradually decreased with the increase of soil water content.The location of the contamination zone of high concentration of LNAPL in the clay gradually shifted downward after cessation of spiking.In regional area,the pollution plume front retracted with a speed of up to 0.15 cm^(2)·h^(-1).This study can provide a reference for exploring the migration and distribution characteristics of LNAPL in the low-permeability clay polluted areas along the coast and river.