An X-ray imaging facility to improve geosynthetic landfill liner materials

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The purpose of a landfill liner is to act as a hydraulic barrier between leachate produced in a landfill and our groundwater drinking water supply. A composite landfill liner typically consists of two barrier layers - the first a thin (e.g. 1.5 mm thick) high density polyethylene (HDPE) geomembrane (GM), and the second a 10 mm thick geosynthetic clay liner (GCL). This second layer is needed because the top GM layer will realistically always contain accidental punctures created during the construction process. A GCL consists of a layer of exceptionally low permeability clay (bentonite) that is bonded to one or more geosynthetics (e.g., sandwiched between two geotextiles using needle-punched fibres, or stitch bonding, or to a geomembrane using an adhesive). Because the GCL contains clay, it will shrink and swell with the loss and uptake of moisture. On the negative side, this means that if the GCL dries out, it will shrink and perhaps even crack. A cracked landfill liner is obviously not an effective barrier to either landfill gas (e.g. methane) or fluid. On the positive side, the potential for this clay to experience large amounts of swelling can create a situation where these cracks can be swollen shut resulting in the barrier self-healing and regaining its excellent hydraulic properties. However, this swelling is only possible in certain circumstances depending on the chemistry of the fluid that tries to resaturate the barrier (i.e. it will self-heal if permeated with water, but some components of landfill leachate or pore fluid from chemically complex foundation soils may supress this ability). Fundamental research is therefore needed to understand the complex mechanisms of cracking and self-healing in these materials. However, because the bentonite clay inside the GCL is fabric encased, these cracks are hidden from view and can only be seen using X-rays. The purpose of this grant is to seek funding for an X-ray imaging facility so that a team of 5 MSc. students and 4 Ph.D. students can to perform non-destructive testing (NDT) on GCL liner (and other) materials to quantify the risk of GCL damage under a wide range of field exposure conditions and aid in the on-going collaboration with a Canadian GCL manufacturer to develop new more damage-resistant GCL products.