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

垃圾填埋场衬垫的目的是在垃圾填埋场产生的渗滤液和我们的地下水饮用水供应之间充当水力屏障。复合填埋场衬垫通常由两层屏障组成-第一层是薄的(例如1.5毫米厚)高密度聚乙烯(HDPE)土工膜(GM)，第二层是10毫米厚的土工合成粘土衬层(GCL)。这第二层是必需的，因为最上面的GM层实际上总是包含在施工过程中产生的意外穿孔。GCL由一层极低渗透性的粘土(膨润土)粘结到一种或多种土工合成材料上(例如，使用针刺纤维或缝合夹在两个土工布之间，或使用粘合剂粘合到土工膜上)。由于GCL含有粘土，随着水分的流失和吸收，它会收缩和膨胀。不利的一面是，这意味着如果GCL干涸，它将收缩，甚至可能破裂。破裂的垃圾填埋场衬垫显然不是垃圾填埋场气体(例如甲烷)或液体的有效屏障。从积极的方面来看，这种粘土经历大量膨胀的可能性可能会导致这些裂缝膨胀闭合，从而导致屏障自我愈合并恢复其优异的水力性能。然而，这种膨胀只有在某些情况下才可能发生，这取决于试图重新饱和屏障的流体的化学成分(即，如果渗入水，它将自我愈合，但垃圾渗滤液的某些成分或来自化学复杂地基土壤的孔隙液可能会抑制这种能力)。因此，需要进行基础研究，以了解这些材料中破裂和自我修复的复杂机制。然而，由于GCL内部的膨润土被布料包裹着，这些裂缝被隐藏在视野中，只能用X光才能看到。这笔赠款的目的是为一个X射线成像设施寻求资金，以便一个由5名理科硕士组成的团队。学生和4名博士生可以对GCL衬垫(和其他)材料进行无损检测(NDT)，以量化在广泛的现场暴露条件下GCL损坏的风险，并帮助正在与加拿大GCL制造商合作开发更抗损坏的新GCL产品。

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.