Life Source Pollutant Migration And Its Inducing Effects In Unsaturated Compacted Clay Layer

With the diffusion and migration of life source pollutants, the soils experience the variationof moisture state from unsaturation to saturation, and produce complicated physical, chemicaland biological reactions, thus transforming the properties and structure of the soil. Therefore, themigration patterns of pollutants in soils, as well as the induced property and structure variation ofunsaturated soils at different seepage depths, lay the premise and foundation of the evaluation ofenvironmental effects of pollutant migration and engineering geological properties of soils. Forthe purpose of building the theoretical model of life source pollutant migration based onsoil-water characteristic curve, such technologies as physical simulation, numerical simulationand mathematical theoretical model are adopted on account of the consideration of the migrationpatterns of life source pollutants as the main clue, and the induced influence on unsaturatedproperties of compacted clay at different seepage depths as the core issue. Meanwhile, theinfluencing patterns and mechanisms of pollutant seepage elements such as seepage pressure onunsaturated properties, permeability and structure of the soils compacted by different degrees arerevealed.With the breakthrough of soil-water characteristic curve test, the unpolluted southernXuzhou clay soil-water characteristic curve models with such parameters as initial dry density,initial moisture content, vertical stress, and pre-consolidation pressure, as well as the life sourcepolluted clay soil-water characteristic curve model with the parameter seepage depth are created.Meanwhile, a set of physical model is designed and established in order to simulate and study themigration patterns of life source pollutants in compacted clay layer under different seepagepressures and axial pressure, thus revealing the seepage features and permeability variationmechanisms of life source pollutants in clay layer at different depths under high seepagepressures and axial pressures. Subsequently, numerical simulation is adopted to clarify themigration patterns of five major ions of life source pollutants in the physical model and XuzhouYanqun landfill. Furthermore, the unsaturated properties response of compacted clay layer to lifesource pollutant migration is investigated. Finally, the theoretical model of life source pollutantmigration based on soil-water characteristic curve is created.The researches show that, the soil-water characteristic curves of life source polluted claycan be divided into boundary effect region, transition region and residual region; Soil-watercharacteristic curves of unpolluted southern Xuzhou clay with different initial dry densitiesintersect at the matric suction180kPa. The volume water content increases and deceases with theincreasing dry density before and after the intersection. The permeability coefficients of the clayat the same seepage depth gradually increase with increasing seepage pressure, but gradually decrease with increasing axial pressure. The first break seepage time gradient and the steadyseepage time gradient are defined and clarified. Under the same axial pressure and seepagepressure, the pore water pressure and seepage flow of the clay are negatively related to seepagedepth, while the first break seepage time gradient and steady seepage time gradient are positivelyrelated to seepage depth. Under the same migration time, with increasing leachate water head,the concentrations of five ions monitored in compacted clay layer increase with the concentrationincrease rates in descending order: Na+>Cu2+>Mg2+>Ca2+>CO32-. With increasing claycompaction degree, the concentrations of the ions decrease with the concentration decrease ratesin descending order: Na+>Cu2+>Mg2+>Ca2+>CO32-. The pore size distribution parameterscalculated by theory and taken in microstructure are basically the same, that is, the decrease oflife source polluted clay saturation and the pore size distribution uniform, as well as the increaseof pore size and porosity, is determined with increasing seepage depth. The theoretical model oflife source pollutant migration based on soil-water characteristic curve is created, which isconstructed of continuity equation, Darcy equation, flow equation, moisture migration equation,pollutant migration equation, the soil-water characteristic curve equation with the parameterinitial dry density, as well as the hydraulic conductivity equation of unsaturated clay. Theconsistency of physical and numerical simulation results is validated, which proves thetheoretical model of life source pollutant migration based on soil-water characteristic curve arereliable and reasonable.The innovation points of this paper contain:(1) the theoretical model of life source pollutantmigration based on soil-water characteristic curve is created;(2) The soil-water characteristiccurve models of unpolluted clay with such parameters as initial dry density, the initial moisturecontent, vertical stress, and pre-consolidation pressure, as well as the soil-water characteristiccurve model of the clay in pollution process with the parameter seepage depth are created;(3)The pressurized seepage simulation device is designed and established to simulate the solutemigration in compacted unsaturated clay. Meanwhile, the migration patterns of Na+, Cu2+, Mg2+,Ca2+, CO32-at different seepage depths are revealed;(4) The variation of microstructureinformation such as pore size distribution is tested and analyzed. Furemore, the effects andmicromechanisms of life source pollutant migration in compacted unsaturated clay layer arerevealed.