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: v . The maxim in tensile strain-generated bar the differential settlements was exami evaluate the integ 'ty of a composite liner, which included a geomembrane and a clay�c. The geoinembrane -can sustain tensile strains higher than those that the clay component of composite Liner ca sustain before tensile failure or tension -thecracks develop within cl component. Ther fore, the tensile strain limit of the clay component can be used as acceptable design c 'tenon to evaluate the integrity of composite liners. From the m - 'mum tensile strains versus sdd' /waste thickness M characteristic cury a soil layer thieknes (T) equals to 2.7 in(9 feet), the maximum tensile strain caused by the 0 m (3 foot) wide by 0.9 m (3 foot) deep by 1.9 in (6 foot) Iong void is.0.2 percent. This s-tra is within acceptable limits for a clay layer as illustrated on Figure 5 from Gilbert and Murpl (6). . ; On the basis f the above a :`• le analysis, a 2.3 m.(9 foot) thick-soil/waste.layer ct serve as a strarn tri ition zone to prevent grade reversal, excessive tensile strains and stresst developed in a liner stem. Therefore, a 2.7 in (9 foot) thick *er of soil or_"select" wast can be placed, in thi example, bef®rc constructing the vertical landfill containment liner. Su�mmary For slope angles either than the 7 percent used in the example analysis, the tensil strains andential or p� grade reversal on a liner surface can be evaluated according to th thickness versus m i - um tensile strain and thickness versus liner grade characteristic curve.- settlement contours ai d containment liner design criteria. From this evaluation, the requim. backfill thicknesses in different liner grades and liner systems can be determined and des-i to prevent grade rever al and excessive tensile strains on a vertical expansion liner and lead collection system. CONCLUSIONS The Elastic Met iod provides a conservative and efficient method to evaluate the potentia differential settlement used by a void within an existing landfill when a vertical expansion o: the landfill is planned. The results from this method closely agree with the results from Bri-tisl NCB's field mining s- -sidence -surveys. The method provides a conservative estimate of the potential differential se tlement, and therefore can be used to design a vertical expansion liner system. Characteristic curves of thickness over the void (T) versus maximum-tensile strain, and of thickness (T) versus in laximum differential settlement slope can be developed for specific void size, as shown in the ex ImPle presented in this paper. These characteristic curves can then be used for the design of c ntai-nment liner systems in a landfill vertical expansion. As shown in the <h-aracteristic curves provided, the differential settlement diminishes as the soil/waste thickness : ver the void increases. Thus, it is possible -to increase the distance between the potential vo d and the surface of the liner, to reduce the differential settlement to Gcosyndn cs'93-Vancouver,Canada- 1507