不飽和層中有機液體保持特性研究

Abstract

本研究的主要目的在於以壓力儀試驗方法，瞭解有機液體在不飽和層中的保持行為。 試驗係採用壓力儀，以控制壓力求取液體在低壓範圍(0~0.3bar)時與土壤間的互制關係， 藉以瞭解不飽和層中液體的行為。試驗採用的土壤為渥太華砂及四種不同細粒料含量的頭 前溪砂，代表現地中不同情形的土層狀況；所採用的有機液體則為汽油、柴油、庚烷、三 氯乙烯。 試驗的第一階段進行空氣-液體實驗，結果顯示細粒料含量越高者，在各個張力狀況 下，孔隙中所殘留的液體較多；而液體與空氣間的界面張力越高者，在同一張力下所殘留 的液體也較多。第二個階段進行水-有機液體實驗，此時有機液體視為非濕相液體侵入。 同樣地，細粒料含量越高，在各個張力狀況下，水的殘留量越高，代表了濕相液體佔據小 孔隙的能力。此外，回吸部份的結果顯示，液體在試體內回吸，多半不能回到初使飽和狀 態，但有機液體與空氣的界面張力較與水的界面張力小，因此回吸量較大。 實驗結果中發現，對於相同的土壤結構，不同流體對(空氣-液體或水-有機液體)的保 持曲線仍會有相近的趨勢，尤以水-有機液體試驗中，則因各有機液體與水之界面張力相 近，所得的保持曲線(MDC)則更具有其一致性。此研究結果對於不飽和層中，或者侵入地 層中的有機污染液體，土壤及流體性質對於流體在土壤中遷移及分佈的影響具有重要意義 ，或可作為工程界在設計清除方法及預估清除目標時的依據。 To understand retention behavior of non-aqueous phase liquids (NAPLs) in vadose zone, pressure cells were used to determine the relationship between the liquid potential and the amount of liquid remains in the soils for suction at low range(0~0.3 bar). The soils used in the study were Ottawa sand and Tochen sands with four different fractions of fines content. The liquids used were gasoline, diesel, heptane, and trichloroethylene. The first stage of the study was to perform the traditional retention tests with single liquid. The results show that the larger the fines content of soils, the higher the liquid content at a given suction. In addition, the liquids with higher surface tension seem to have a better ability to remain in the soils. The second stage of the study was performing retention tests with water and organic liquids. The organic liquids acted as nonwetting fluids invading the sample. The results show a similar trend whicsoils with higher fines content have higher water retention in pores. Furthermore, the test results show that end point of imbition curve may differ from the starting point of MDC curve. The magnitude of imbition increaseswith decreases interfacial tension between the pair of fluids in the soils. The test results also suggest that for any specific soil, the retention curves of different fluid pairs show a very similar trend. In particular, the MDC curves obtained from the water-organic liquids test give a better consistency, which may be the results of similar interfacial tension between organic liquids and water. The results of this study will help the engineers to better understand the migration and distribution of organic liquids in the vadose zone and near the ground water table. The engineers can estimate the amount of organic liquids retained in the subsurface more accurately from the characteristics of the soil such as those obtained in this study.