非水相有机液体作用下上海黏性土的结构演化及渗透性

Structural Evolution and Permeability of Shanghai Clay Subjected to Non-Aqueous Phase Liquid

摘要:

非水相有机液体（NAPL）具有较低的介电常数，因而会对黏土颗粒的双电层结构及其物理力学特性产生影响。我国沿海全新世海侵饱和黏性土地层中已经发现了大量NAPL类污染案例。为了了解NAPL作用下这类饱和黏性土的结构演化及其对污染物迁移的影响，采用原状上海饱和黏性土（以伊利石为主）开展了三种NAPL（煤油、煤油?乙醇、三氯乙烯）的长期浸泡试验（超过1.8年），并与膨润土（以蒙脱石为主）的结果进行对比。试验结果表明，上海饱和黏性土的结构演化体现为絮凝及收缩开裂，但比膨润土弱得多，结构演化剧烈程度为煤油煤油?乙醇三氯乙烯。除了NAPL的介电常数有关，自由相NAPL的入渗速度及含量也是影响结构演化现象与程度的重要因素。在收缩（孔隙率减小）与絮凝（比表面减小）的综合作用下，上海黏性土的渗透系数增大在两倍以内。

Abstract:

Non-aqueous phase liquids （NAPL） have very low dielectric constant. Therefore， they can affect the electric double layer， as well as the physical and mechanical characteristics of clay. NAPL contamination has been frequently discovered in the coastal saturated clays formed during the Holocene transgression. To investigate the impact of NAPLs on soil structure and the contaminant transport in these coastal saturated clays， long-term soaking tests （up to 1.8 years） were conducted on intact saturated Shanghai clays （primarily composed of illite） using three NAPLs： kerosene， trichloroethylene （TCE） and kerosene-ethanol mixture. The results were also compared with those obtained from bentonite （primarily composed of smectite）. Test results shown that under the long-term action of NAPLs， the Shanghai saturate clay exhibited shrinkage， cracking， and flocculation， but significantly less pronounced than in bentonite. The intensity of structural alteration follows the order of kerosenekerosene-ethanol mixtureTCE. Except for the dielectric constant of NAPL， the velocity and amount of the free-phase NAPL infiltrating in the soil are also important factors influencing the structural alteration. Under the coupled impacts of shrinkage （decreasing in void ratio） and flocculation （decreasing in specific surface）， the hydraulic conductivities of the Shanghai saturate clays are found to increase by up to two times.