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The <br /> maxim.; m tensile strain-generated by the differential settlements was exam <br /> evaluate the integ 'ty of a composite liner, which included aeomem <br /> g brand and a clay lay( <br /> The geomembranc can sustain tensile strains higher than those that the clay component of <br /> composite liner casustain behDre tensile failure or tension cracks develop within -the cl <br /> component. Ther fore, the tensile strain limit of the clay component can be used as <br /> acceptable design criterion to evaluate the integrity of composite liners. <br /> From the m2ximum tensile strains versus soil/waste thickness t <br /> a soil layer thickness � characteristic eury <br /> y (T) equals to 2.7 in (9 feet), the maximum tensile strain caused by the 0 <br /> m (3 foot) wide by 0.9 m (3 foot) deep by 1.9 m (6 foot) long void is.0.2 percent. This stra <br /> is within acceptable lirnits for a clay layer as illustrated on Figure 5 from Gil-ert and Murpl <br /> On the basis f the.above example analysis, a 2.7 m (9 foot) thick-soiUwastc Iaycr c <br /> serve as a strain trg 'tion zone to prevent grade reversal, excessive tensile strains and stresst <br /> developed in a liner .stem. Therefore, a 2.7 in (9 foot) thick Iaycr of soil or_"select" wasp <br /> can be placed, in this example, before constructing the vertical Iandfill containment Iiner. <br /> Suummary For slope angles other than the 7 percent used in the example analysis, the tensil <br /> strains and potential for grade reversal on a liner surface can be evaluated according to th <br /> thickness versus maxim um tensile strain and thickness versus liner grade characteristic curve, <br /> settlement contours and containment liner design criteria. From this evaluation, the <br /> backfill thicknesses in different liner grades and liner systems can be determined and des <br /> dw - <br /> collection system. <br /> to prevent grade .ever al and excessive tensile strains on a vertical expansion liner and leachat <br /> Y_ <br /> CONCLUSIONS <br /> The Elastic Met iod-provides a conservative and efficient method to evaluate the potentia <br /> differential settlement ause-d by a void within an existing landfill when a-vertical expansion o <br /> the landfill is planned. The results from this method closely agree with the results from Brit:ist <br /> NCB's field mining su sidence surveys. The method provides a conservative estimate of the <br /> potential differential se tlement, and therefore can be used to design a vertical expansion liner <br /> system. <br /> Characteristic cu rves of thickness over the void (T) versus maximum .tensile strain, and <br /> of thickness (T) versus maximum differential settlement slope can be developed for specific void <br /> size, as shown in the example presented in this paper_ These characteristic curves can then be <br /> used for the design of c ntainment liner systems in a landfill vertical expansion. <br /> As shown in the C haracteristic curves provided, the differential settlement diminishes as <br /> the soil/waste thickness over the void increases. Thus, it is possible to increase the distance <br /> between the .potential vo -d and the surface of the liner, to reduce the differential settlement t <br /> Gcosynd)cs'93-Vancouver.Canada- 1507 <br />