直压式电导法测定厚包气带土壤岩性的应用研究

Direct-push Electrical Conductivity Profiling for Soil Lithology in a Thick Vadose Zone

探索将厚包气带直压式测量土壤电导率(EC)用于绘制土壤岩性剖面的方法。研究区位于太行山山前平原,由于浅层地下水大幅度下降,该区已经形成了厚包气带。我们利用Geoprobe(r)直压式钻机和温纳排列(W enner Array)电极组测得EC剖面并钻取相应的土样。土样分析结果显示,深层土壤水分含量受岩性控制。由于研究区土壤为非盐渍土,因此土壤岩性是EC变化的主要控制因素,而土壤EC的空间变化也能表达岩性的分布。比较土样颗粒组成和EC值发现,EC值与土壤砂粒含量成负相关,与土壤粘粒含量成正相关。当土壤中砂粒含量由12%增加到100%时,EC由100 mS m-1减少到20 mS m-1;而粘粒含量由3%增加到26%时,EC由30 mS m-1增加到100 mS m-1。研究结果表明,厚包气带直压式测量EC资料可以推断土壤岩性。

In this paper, we explored the direct -push electrical conductivity measurement for mapping the distribution of soil lithology in a thick vadose zone. The study area is located in the piedmont of the Taihang mountains. The rapid decline of the water table in the piedmont of the Taihang mountains over past several decades has resulted in a thick vadose zone. We employ Geoprobe direct - push technology and a Wenner Array EC probe to collect a series of EC logs and corresponding soil core samples. The core sample analyses indicate that soil moisture ot the deep lager is controlled by the corresponding soil lithology. The study site is not saline so that soil lithology is the dominant control on the soil EC. The spatial variation of soil EC measurements reflect the change of soil lithology over space. By performing grain size analyses on the core samples and comparing with the EC logs, we found that EC signals decreased from 100 mS m^-1 to 30 mS m^-1 when the sand content of the core samples increased from 12% to 100 %. On the other hand,corresponding to an increase of clay content from 3% to 20%, the corresponcling EC could increase from 30 mS m^-1 to 100 mS m^-1. The soil EC and sand content are negatively correlated while the soil EC and clay content are positively correlated to each other. This suggests that the direct - push EC logging can be used to infer the soil lithology of a thick vadose zone in this area.