井内混合效应对弥散尺度依赖性影响的实验研究

Experiment investigation on the influence of mixing effect on dispersion scale dependence

弥散度是刻画孔隙介质中溶质运移和扩散的重要参数,对于污染物的预测和修复至关重要,但野外示踪试验往往会选择忽略真实存在的井内混合效应。通过室内砂槽实验方法,模拟具有水平分层结构的含水层,该含水层主要由3种介质充填而成。采用埋藏传感器和井中布设传感器2种监测方式,对比在有/无混合效应情况下,穿透曲线的形态差异,进而探究井内混合效应对弥散尺度依赖性的影响情况。实验结果表明,井内混合效应会使穿透曲线呈现阶梯式增长,并伴有显著的拖尾现象;当使用对流弥散方程进行计算时,混合效应会导致弥散度被高估;观测到的弥散度与真实弥散度的差异会随着注入井和观测井间距离的增加而增大;此外,2种观测方式(埋藏/井内)均能发现弥散的尺度依赖性,且井内混合效应显著增强了弥散尺度效应,该实验结果可为污染物运移的评价和预测提供参考。

Dispersivity,a property parameter defined to characterize the degree of dispersion and mixing,is crucial for the prediction and remediation of groundwater contamination.However,in field tracer tests,the real mixing effect has often been ignored.In this paper,an aquifer with horizontal layered structure was simulated by laboratory experiments.Three kinds of media were chosen to reconstructed experimental aquifer.Two monitoring methods,buried sensor and sensor in the well,were adopted to compare the difference of breakthrough curves,so as to investigate the influence of mixing effect in the well on the dispersion scale dependence.The results showed that mixing effect made breakthrough curve increase in a gradient manner with significant trailing phenomenon.The results also showed that mixing effect led to an overestimation of the dispersivity,when the advection-dispersion equation was used.The difference between the measured dispersivity and the actual dispersivity increases with the solute transport distance.Moreover,scale-dependency of dispersivity was observed in both sensor buried in the media and sensor in the well,and mixing effect amplified the scale effect of dispersivity significantly,which can provide references for evaluation and prediction of contaminant transport.