This thesis is concerned with the current contentious issue of environmental containment. This work provides an assessment of contaminant migration through Geosynthetic Clay Liners (GCLs). GCLs are thin liners usually consisting of three layers, defined in section 2.2.4. These are factory manufactured materials, used extensively in the waterproofing and environmental containment markets. The predominant, if not the only "low flow" element in GCLs is bentonite, described in section 2.4.1. Bentonite has been found to be most advantageous as the waterproofing core of GCLs. During this research, emphasis was placed on an investigation as to the nature of the low flow core of the GCLs in terms of mineralogy and microstructure. GCL types can be divided into two generic categories; granulated/powdered and extruded (pre-hydrated). One of each of the generic types were selected for this study to provide a representative overview of the GCL product range. The main type of laboratory assessment was that of fluid migration through the liners. Due to the paucity of knowledge in relation to diffusion, emphasis was put on diffusion assessment. At an early stage in this research, it was found that suitable equipment for the assessment of diffusion was not available and, as a result the author developed two main types of diffusion test cells which were key to this work. These cells were the constant stress and constant volume diffusion cells. In the author's opinion, the constant stress cell, in particular, offers many advantages over current diffusion equipment. During the production of these cells, emphasis was placed on the following factors; sample size, control of effective stress, mixing of fluid, reduction in sample and fluid contamination, reservoir size, sample boundary, reduction of leaks and ease of sampling. Following the development of the diffusion cells, extensive testing was carried out. Using solutions of sodium, potassium and calcium chloride the assessment of contaminants was selectively limited. A concentration gradient was created across the GCL sample by placing a cation solution on one side and deionised water on the other. Following hydration of the GCL samples with deionised water, 1000ppm of prepared solution was placed in the source reservoir whilst fresh deionised water was placed in the receptor reservoir. Samples were taken at regular intervals, from both source and receptor reservoirs, and their concentrations assessed. Profiles of source and receptor concentrations were plotted versus time. A tabulated Microsoft Excel spread sheet was used in the determination of diffusion coefficient. This was achieved by incorporating equations from the concentration plots with Ficks' law. Extensive hydraulic conductivity tests carried out by the author on the GCLs were compared with the diffusion tests. Standard triaxial, Rowe & large column hydraulic conductivity tests were produced. A large part of the investigation was the assessment of the characteristics of the waterproofing core of the GCLs. A number of techniques were adopted for this assessment. These included the following; X-ray Diffraction (XRD), X-Ray Fluorescence (XRF) & Scanning Electron Microscope Analysis (SEM). These assessments provided an overview as to the characteristics of the bentonite core. The SEM, in particular, was used to assess the microstructure of the two types of GCL under investigation and was used to determine if there was any variance in the particle frequency, type, shape and orientation. The XRF and XRD equipment were used to make an assessment of the mineralogy of the bentonite core. These procedures were conducted on a number of available bentonite granules and assessed relative to that of the core product of the GCL under investigation. Tests were also conducted on samples used in the diffusion experiments. Sections of the samples were removed from the source, middle and receptor sides of the samples and taken for analysis. The discussion and concluding remarks of this thesis have highlighted a number of key findings. It was noted that there is a marked difference between the granulated and extruded (pre-hydrated) GCLs assessed. It was found that the extruded (pre-hydrated) GCL exhibits an orientated microstructure. The bentonite particles were predominantly orientated flat across the width of the GCL. The granulated bentonite, when hydrated, did not exhibit any preferential orientation of bentonite particles.
| Identifer | oai:union.ndltd.org:bl.uk/oai:ethos.bl.uk:487412 |
| Date | January 2004 |
| Creators | McLoughlin, Michael |
| Publisher | University of East London |
| Source Sets | Ethos UK |
| Detected Language | English |
| Type | Electronic Thesis or Dissertation |
| Source | http://roar.uel.ac.uk/1271/ |
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