Date of Award

Spring 2009

Project Type

Dissertation

Program or Major

Civil Engineering

Degree Name

Doctor of Philosophy

First Advisor

Jeffrey S Melton

Abstract

Reactive cap technology is a promising in-situ remediation solution for contaminated sediment, mainly because it has the potential to reduce costs and environmental impacts when compared to solutions that rely solely on dredging and disposal. Reactive capping mats have been recently used in demonstration projects as a passive remediation technology for contaminated sediment. The mats used in this research were comprised of two geosynthetic fabrics bound to a fibrous core filled with a reactive material. The type of geotextiles and reactive material are selected based on the characteristics of the contaminated material and the contaminants on site. The mat is deployed on top of the sediment to trap the contaminants as they migrate out of the sediment via diffusion or advection. The upper geosynthetic acts as a filter and prevents clean sediment migration into the cap, while the bottom geosynthetic provides strength to the mat during installation and recovery of the system. The reactive mat is deployed over the sediment and is typically protected by 0.3 m of clean permeable sand or silt.

Fine grained submerged sediment is a challenging geotechnical material because its soft nature has the potential for complex consolidation behavior, variable permeability, and transport of contaminants. The sediment experiences a self-weight consolidation process in addition to the consolidation induced by the weight of the reactive cap. The installation of the cap applies a load on top of the sediment and induces pore pressure build-up that is dissipated over time, and gradually changes the void ratio and permeability of the underlying sediment, which in turn causes a change in the ground water flow regime. This complex behavior modifies the transport of contaminants within the sediment over time, and it may also modify the efficiency of the reactive cap. Current engineering practice accounts for these aspects only in a very simplistic manner as part of the design process of in-situ caps, even though they define the long and short term performance of the reactive cap. This dissertation presents a detailed study on each of these subjects, and how the interactions affect the efficiency and performance of reactive cap technology.

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