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11 <br />Design of Liner Systems Under Vertical Expansions: An Alternative to <br />Geogrids <br />D. J. Jang <br />Golder Associates Inc., USA <br />C. Montero <br />Golder Associates Inc.-,, USA <br />ABSTRACT <br />Acquiring and permitting new landfill sites is often a diffi- 6ult 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 />arm require some type of reinforcement. The purpose of the reinforcement is to minimize the <br />tensile strains in overlaying liner and leachate collection systems assuming a void, created by <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 finer. 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 />0 <br />Gcosynfttircs 93 - Vancouver, Canada —1497 <br />