Contaminant Mobility and Compressibility of Dredged Sediment using Seepage Induced Consolidation Tests

Christopher Baxter

In the proceedings of: GeoVancouver 2016: 69th Canadian Geotechnical Conference

Session: PROBLEMATIC SOILS - II Soft, Collapsible, Residual Soils

ABSTRACT: A laboratory testing program was developed to determine the behavior of soft dredged sediments placed in Confined Aquatic Disposal (CAD) Cells. These sediments are sometimes contaminated with various concentrations of contaminants, such as non-aqueous phase liquids (NAPL), polycyclic aromatic hydrocarbon (PAH), polychlorinated biphenyl (PCB), and there is concern regarding the transport of these contaminants during placement, capping, and consolidation. The objective of this study was to develop a combined Seepage Induced Consolidation (SIC) and Incremental Load apparatus capable of measuring both the advective transport of contaminants as well as the compressibility and hydraulic conductivity behavior of the sediment. A modified triaxial cell was used, and both SIC and IL consolidation tests were performed on the same samples. The SIC tests were performed using flow pumps to collect expelled pore fluid for further contaminant testing. IL and permeability tests were then performed to determine values of compressibility and hydraulic conductivity over a wide range of effective stresses. An extended power law relationship was applied to the results to extrapolate the compressibility to very low effective stresses (<0.1 kPa). Results are presented from three different marine soils (CH from Gulf of Mexico, CL from Boston, and a CH from Maine) and a kaolinite clay mixed with mineral oil to simulate a Non-Aqueous Phase Liquid (NAPL). The results show the ranges of compressibility and hydraulic conductivity among the samples with different initial void ratios. The results also show that the synthetic NAPL reduced the compressibility of the kaolinite sample. No mobility of the synthetic NAPL was observed during either SIC or IL consolidation. Further tests are planned for contaminated sediments from dredging projects to improve our understanding of the mobility of contaminants in these very soft sediments.

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