Behaviour of Geosynthetic Drainage Materials in Landfills

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Gratchev, Ivan
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Jeng, Dong Sheng
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As one of the most important aspects of urban development, waste management is gaining importance as a result of the dramatic increase in the total world population and consequently in the volume of generated waste during recent decades. Landfills have been most widely adapted as long-term containers for disposed waste worldwide, and the collection and effective removal of the leachate produced represents an important element in the efficient functioning of a landfill facility. For this purpose, leachate collection and removal systems are designed in landfills to remove and transport the generated leachate to leachate management facilities for treatment or another approved method of disposal. Geosynthetic drainage materials have been widely used in leachate collection systems for drainage purposes. To function efficiently in a leachate collection system, the in-plane flow capacity of a geosynthetic material should be investigated appropriately over its service lifetime. Inaccurate estimation of the long-term flow capacity of the geosynthetic drains will result in inefficient or inappropriate performance of the system. The traditional approach to determine the long-term flow capacity of geosynthetic drainage materials is to perform a short-term index transmissivity test and then apply the reduction factors to consider the effects of the factors that influence drainage capacity. Recent studies have shown that the real decrease in the flow capacity of geosynthetic drainage materials can be much higher than that considered when applying reduction factors to the results of an index transmissivity test, as some factor boundaries that could significantly affect the hydraulic behaviour are not appropriately considered in this approach. These factors include the magnitude of the compressive stress that the drainage material experiences during its lifetime in a landfill, which is mainly influenced by the landfill size; the physical and geometrical properties of geosynthetic drains; and the characteristics of the materials that are placed atop and underneath the drainage layer. These deficiencies can lead to misestimating the drainage capacity of leachate collection systems and cause serious safety complications in landfills. In this study, a new approach was developed to more easily and accurately determine the in-plane flow capacity of the geosynthetic drains used in waste containment facilities. In this innovative method, for the first time, the effect of both creep and intrusion are systematically considered, and the deficiencies of the traditional methods are resolved. This approach concentrates on the close relationship between thickness and in-plane flow capacity. For this purpose, new equipment was specifically designed and manufactured. In this study, the effect of the geometry and rib configuration of geosynthetic drains on the hydraulic behaviour was investigated by conducting transmissivity tests performed on different samples under the specified range of compressive stress and hydraulic gradients. In the next step, the theoretical relationships that quantify the effect of thickness reduction of drainage materials on the transmissivity reduction were derived based on the classical Kozeny–Carman equation for each type of drain, considering their geometrical characteristics. The equation was then modified to be used in various boundary conditions. Later, the accuracy of these modified equations was investigated by comparing the results of the two types of experiments, including transmissivity and intrusion tests. Finally, the effect of the non-rigid flow boundaries on the hydraulic capacity of the geosynthetic drains was quantified. For this purpose, a series of intrusion tests were performed and experimental equations were derived based on the results. The innovative approach proposed in this study can significantly contribute to enabling improved estimation of the long-term hydraulic behaviour of leachate collection and removal systems, which is an integral part of safely designing new waste disposal facilities and expanding the existing facilities.

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Thesis (PhD Doctorate)
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Doctor of Philosophy (PhD)
School of Eng & Built Env
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The author owns the copyright in this thesis, unless stated otherwise.
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Geosynthetic drainage materials
Leachate collection systems
Hydraulic behaviour
Creep and intrusion
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