Research On Transport Rule Of Dredged Sludge Contaminant Through Clay Impermeable Layer

The research on the infiltration and transport of contaminant in clay impermeable layer and obstruction of contaminant to clay layer is very important to prevent secondary pollution. In this paper the transport model of contaminant is set up in deformed porous medium on the base of combing the consolidation theory with contaminant transport theory. Relying on the project of state 863 important special problem, the research on transport and obstruction of contaminant in clay layer in sludge site is conducted using the abundant clay layer in peripheral area. The main research result is shown in the following:1 Using the duplex triaxial permeability testing machine and the muddy and silty clay of Xuelang heap site in Wuxi, a great deal of indoor tests on infiltration and static adsorption and dynamic soil column have been done, the effect of consolidation deformation on infiltration and transport of contaminant in soil column in tests is considered. The permeability coefficient of ammonia nitrogen in soil sample is found through infiltration test, the adsorption coefficient of soil sample to ammonia nitrogen is measured by static adsorption test, and the diffusion coefficient of soil sample to ammonia nitrogen is also measured by dynamic soil column test. Through the infiltration test results it can be gained that the heap site soil layer and coffered soil layer have good obstruction effect, and the transport rule of contaminant is presented in deformed clay layer.2 On the base of combing the Biot consolidation theory with contaminant transport theory the one-dimensional mathematic model of contaminant in clay layer is put forward. The greatest feature of model is considering the effect of soil deformation on contaminant transport through introducing the contaminant chroma adsorbed the solid grain to the contaminant transport model.3 The analytic solutions of transport model are gained through rational predigestion, they include considering the decaying of pollutant source and without considering the decaying of pollutant source. The numerical calculation on transport of ammonia nitrogen in muddy and silty clay layer is done, and the space-time distributing of ammonia nitrogen chroma in soil layer is predicted. The impermeable ability of heap site is estimated according to the calculated result of model and test result and investigated data. The results have shown the cofferdam and ground soil layer has enough ability to obstruct the contaminant of dredged sludge and can't produce secondary pollution in the fixed number of year of heap site.4, The transport model of contaminant in layered elastic ground is found according to the consolidation model of multilayer ground. Using the transport model the change of ammonia nitrogen chroma with the time and depth is calculated in the double layer. Because the layered soil is abundant in actual impermeable layer, the transport model of contaminant in layered soil has important project value and realistic meaning.5 The expression of transport model of contaminant considering soil consolidation large deformation is put forward according to the approximate solution of large deformation consolidation equation in material coordinate.