Abstract
The fact that the permeability and microstructure properties of clay will be changed by NAPL (Nonaqueous Phase Liquids) pollution draws high attention in the study of the interaction between NAPL and contaminated soil. Through in-field contaminated clay soils from vinyl chloride and 1, 1, 2-trichloroethane-contaminated site in Shanghai, the variation of the content of vinyl chloride and 1, 1, 2-trichloroethane pollutants in clay with depth was obtained. The change of plasticity, permeability, and microstructure properties of the clay samples contaminated by vinyl chloride and 1, 1, 2-trichloroethane were investigated in detail. The measured test results were compared with the uncontaminated clay and indoor soaked contaminated clay samples by TCE (Trichloroethylene). The test results showed that the microstructure characteristics of clay were changed under the influence of the content of TCE, vinyl chloride, and 1, 1, 2-trichloroethane. The total porosity, accumulative pore volume, and the content of the macroporosity percentage of clay soils showed an increasing trend. The flocculation structure of contaminated clay samples was observed, but there were no overhead pores and connected cracks. Volatile organic pollutants were detected in both field and indoor contaminated clay samples. The plastic limit and liquid limit of each layer of contaminated samples decreased slightly, the plastic index did not change significantly, and the pore ratio and permeability coefficient increased gently. At the same time, the clay shrinkage was aggravated by TCE pollution, and cracks appeared on the surface of soil samples. However, no connected cracks were formed. Test results indicated that the self-developed improved permeability test device can be used to test the permeability coefficient of clay samples with shrinkage and to crack by NAPL pollution. The permeability coefficient showed an increasing trend, though the increase was not at the level of magnitude.
Highlights
NAPLs (Nonaqueous Phase Liquids) are one of the main factors that cause pollution incidents
It was found that the total mercury injection volume, average pore diameter, and total porosity of the clay samples in layer (4) under indoor TCE soaking contaminated were larger than those in layer (4) contaminated with vinyl chloride. is shows that in the same layer (4) clay sample, the microstructure damage of indoor TCE-soaked contaminated clay is more significant than that of field contaminated clay. is point is consistent with the discussion in the previous sections that k/10-7cm/s
Rough the pore size distribution test, it can be found that the mesoporosity and macroporosity in the field contaminated clay and indoor contaminated clay by TCE are increased, and the increase of indoor contaminated clay by trichloroethylene soaked is obvious. is showed that the long-term interaction between NAPL pollutants and clay samples would change the microstructural properties of the clay samples. is may be due to the fact that the intervention of pollutants has changed the structure of the electric double layer of the clay samples, the thickness of the electric double layer has become thinner, and the clay samples have flocculated
Summary
NAPLs (Nonaqueous Phase Liquids) are one of the main factors that cause pollution incidents. A rigid wall permeability test device is used to measure the permeability coefficient by injecting a certain organic solution or a mixture of several solutions into the uncontaminated soil samples, and the change of the permeability coefficient of the clay sample during the injection process was observed First of all, this injection test method has a prominent boundary effect problem, that is, the lateral shrinkage of the soil sample leads to leakage of the sidewall, resulting in an excessively large permeability coefficient [20,21,22,23,24]. Erefore, this paper studies the relationship between NAPL pollutants and saturated clay of the changes in microstructural properties and permeability properties under long-term interaction tests. In order to further understand and study the changes in the permeability characteristics of NAPL-contaminated saturated clay soils and indoor soaked contaminated clay samples under longterm interactions with pollutants, an improved rigid-wall permeability test was carried out in this paper, and the permeability coefficient of contamination samples after shrinkage and cracking was obtained. In order to further understand and study the changes in the permeability characteristics of NAPL-contaminated saturated clay soils and indoor soaked contaminated clay samples under longterm interactions with pollutants, an improved rigid-wall permeability test was carried out in this paper, and the permeability coefficient of contamination samples after shrinkage and cracking was obtained. e purpose of this paper was to investigate the changes of clay microstructure and permeability characteristics of NAPL and clay samples under the long-term interaction and interaction mechanisms
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