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Design of Liner Systems Under Vertical Expansions. An Alternative to <br /> Geogrids <br /> 4 <br /> D.-J. Tang <br /> Golder Associates Inc., USA <br /> C. Montero T <br /> Golder Associates Inc:; USA <br /> ABSTRACT _ <br /> Acquiring and permitting new landfill sites is often a difTieult task. An attractive <br /> alternative to present landfill owners is to permit expansions to existing landfills. This option <br /> often involves the design and permitting of vertical expansions over old landfill-areas that were <br /> constructed before liners and leachate collection systems were required: At present, the <br /> literature on vertical expansions suggests that liners and collection systems overlaying old landfill <br /> areas require some type of reinforcement. The purpose of the reinforcement is to minimize the <br /> tensile strains in overlaying liner and leachate co 'on systems assuniing a void, created <br /> progressive degradation and sudden collapse of large objects buried in the old landfill areas, <br /> occurs. <br /> This paper presents the results of a model study .aimed to analyze and define the <br /> expression of a void occurring at depth, on the surface of a liner and leachate collection system. <br /> The purpose of the model is to define the shape of the deformed surface, and to predict the <br /> actual tensile strains on the liner surface. The model in this paper suggests that given a finite <br /> void size, excessive tensile strains will not occur; unless the object collapsing and creating a void <br /> is assumed to be in very close proximity to the liner. The model presented in this paper shows <br /> that if large objects likely to decay and create a void, are not present within 1.8 to 3 m (6 to 10 <br /> feet) (depending on the void size and the material properties used in the analysis) underneath the <br /> liner system, excessive tensile strains are not created and reinforcement of the liner is not <br /> necessary. <br /> Four analytical -models, which may be used to evaluate void-induced settlement, are <br /> briefly discussed in this paper. This paper illustrates how one of these models, which is based <br /> on an elastic solution, may be applied to the evaluation :and design of a liner and leachate <br /> collection system over an existing landfill that is proposed to be expanded vertically. <br /> Geosynthetic s'93-Vancouver,Chnsda-1497 <br />