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Leakage in liner system |
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University of Padua IMAGE Department |
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Leakage in liner system |
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• Leakage through a clay-only liner: |
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Qs = ks · i · A |
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Qs = leakage rate through the clay ks = hydraulic conductivity of the clay (m/s) i = gradient (dimensionless), expressed as the ratio of leachate head (m) to the liner thickness (m) A = area of liner considered (m2) |
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• Leakage through a single hole in a geomembrane-only liner: |
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QG = CB · a · (2gh)½ |
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QG = leakage rate through a hole in the geomembrane CB = dimensionless coefficient dependent on the shape of the orifice a = area of the hole (m2) g = acceleration due to gravity (m/s2) h = leachate head (m) |
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Assumptions: • Frequency of 10 holes per hectare, each having a diameter equal to the thickness of the geomembrane • Very high permeabilities of the media above and below the geomembrane |
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• Leakage through a geomembrane/clay composite: |
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QG = 0,21· a0,1 · h0,9 ks0,74 |
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Assuptions • Very large hydraulic conductivity of the materials above and below the liners • No lateral gradients |
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Leakage rates can be reduced by one or two orders of magnitude by the use of a composite liner. |
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Long-term performance and failure mechanisms |
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• A barrier system with lining materials performing perfect containment does not exist • Compacted clay liners may fail to function satisfactorily as cracking occurs due to adverse climatic conditions and deformation due to different settlement • Ageing of geomembranes may result in accelerated stress cracking phenomena with a possibility of ruptures and leakage • When designing a barrier system it is fundamental to take into account all possibilities of failure whilst bearing in mind, as data input, a certain percentage of material damage |