Investigation Of Coupled Behavior Of Large-strain Consolidation And Solute Transport In Layered Soils

China is currently facing numerous environmental pollution problems,such as black smelly water bodies,improper disposal of wastes,soil pollution and hazardous waste disposal.To solve these environmental pollution problems,many methods have been developed and used,among which the confined disposal of contaminated geomaterials,landfill disposal of municipal solid wastes and in-situ capping of contaminated sediments are commonly used.How to design and operate these applications to provide better containment of contaminant is worth exploring.Revealing the mechanisms of coupled large-strain consolidation and solute transport in these applications can help us make a better design.This dissertation presents a numerical investigation of the effect of soil consolidation on the transport of contaminant in a multi-layered soil media,including(a)transport for the confined disposal of contaminated sediments,(b)transport through the GMB/GCL/CCL composite liner system and(c)transport through the subaqueous in-situ capping system.The numerical simulations were performed using the model CST3,which is a piecewise linear numerical model for coupled large-strain consolidation and solute transport in multi-layered soil media and has been extensively validated using analytical solutions,numerical solutions and experimental results..The main work of this dissertation is as follows:(1)Based on the consolidation equation and advection-dispersion transport equation,this dissertation derives a solution for coupled self-weight consolidation and contaminant transport in confined disposal of contaminated sediments.Using the proposed solution,the CST3 model is verified and used to simulate the contaminant transport in confined disposal of contaminated sediments.Using the CST3 model,a series of parametric studies is conducted to investigate the effect of several important parameters(i.e.,consolidation effect,initial thickness of sediment,sediment compressibility,sorption effect and effective diffusion coefficient)on the contaminant transport process for confined disposal of dredged contaminated sediment.The results indicate that the self-weight consolidation of sediment can significantly accelerate contaminant transport rate.In general,the effects of consolidation of the sediment on contaminant transport increase with increasing initial thickness of sediment,compression index and effective diffusion coefficient.The higher contaminant distribution coefficient of sediment produces a greater effect of sediment consolidation on contaminant transport in the early stages but smaller effect of sediment consolidation on contaminant transport soon afterward.(2)The analytical solutions are derived for predicting one-dimensional diffusion of contaminant through a triple-layer composite liner system comprising a geomembrane(GM),a geosynthetic clay liner(GCL),and a compacted clay liner(CCL),and are verified against the CST3 model.CST3 model is then used to investigate the effect of liner consolidation on the transport of contaminant through the GML/GCL/CCL composite liner system.The simulation results indicate that,depending on conditions,consolidation of the GCL and CCL can have significant impact on the transport results of contaminant(i.e.,contaminant mass flux,cumulative mass outflow,and distribution of contaminant concentration within the GCL and CCL),both during the consolidation process and long after the completion of consolidation.In general,the effects of consolidation of the GCL and the CCL on contaminant transport increase with decreasing loading period,increasing linear nonequilibrium sorption rate constant for CCL and increasing first-order degradation constant of contaminant.The compressibility of both GCL and CCL and the permeability of CCL can affect the effects of consolidation of the GCL and the CCL on contaminant transport significantly,whereas the permeability of GCL can hardly affect the effects of consolidation of the GCL and the CCL on contaminant transport.(3)Analytical solutions are derived for predicting one-dimensional diffusion of contaminant through a four-layer in-situ capping system,which is comprised of,from top to bottom,clean capping material,an RCM layer,contaminated sediment and uncontaminated sediment.The proposed analytical solutions are verified against the CST3 model.CST3 model is then used to investigate the effect of sediment consolidation on the transport of contaminant through the subaqueous in-situ capping system.The simulation results indicate that the consolidation of sediment can significantly accelerate the transport of contaminant.The traditional approach for the assessment of cap performance neglects consolidation of the sediment and can significantly underestimate the contaminant outflow.These differences for with and without the consolidation effects can range over several orders of magnitude,especially in the process of consolidation.In general,the effects of sediment consolidation on contaminant transport increase with increasing cap thickness,increasing contaminated sediment thickness,increasing uncontaminated sediment thickness and decreasing distribution coefficient of RCM.RCM can significantly decrease the contaminant outflow and decrease the effect of sediment consolidation on contaminant transport.The sorbing clay cap yields better contaminant containment than the sand cap.