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geogrid deflects int the depression as tensile stresses develop in.the geogrid. The other m thud, stabilizing existing refuse areas, includes surcharging, deep dynam. compaction, and li e/fly ash slurry injection, among others (2). Time and/or field constrain- often render these ethods impractical for the development of vertical expansions. f All the meth s currently in use are based on the assumption that "void-induced settlement will imp the liner. Since none of these methods require the calculation of th settlement, it is u - own whether "void induc od" settlement is a real or perceived problem And, whether other ternatives such as providing a thick buffer, or a strain-transition zon :).offers as effective a solation as those..methods tly in use: The-calculation of "void ---induced! settlement, -d the evaluation of an altemative design methodology are the subjects o this paper.- OF =ODS FOR ESTRYUTING S£TTLE1M1UNT To date, the uthors are not aware of a specific methodology used to quantify the Isettlement resulting m the prince of a void within a landfill. However, similar situation are often encountered in mining and classical geotechnical fields. Several methods to analyze "voi-d-induced" settler ient have been developed and are documented in miwingand geotechnica journals and conference proceedings. The following four methods of analysis am briefl` discussed in this pape : • Mining ubsidence Empirical Methods (3,4), which include influence and profile functions- • Numeri - Methods (5,18), which include finite element(FE)and finite difference (FD) me ods; • Displace eat Method (11); • Two-d m nsional and Three-dimensional Elastic Solutions (15, 16). Minin Subsidence Errk irical Methods. A mesh-aniism similar to the collapse of a large object within an existing la rr fill and the resulting differential settlement at the surface of a liner system exists in mining (3,4). Miming subsidence occurs in a bowl-shaped pattern. Empirical methods have been dev -loped to analyze the subsidence of "long-wall" mines, an underground mining technique maim used in rock formations. The method applied in a specific geographical region is unique, bas on the geological characteristics of the region. Because there is no generic solution ava22 bl for all geographical regions, this method is not suitable for the analysis of differential setdemen for a landfill vertical expansion configuration. a Numerical Methods Fi 'te element analyses of a void within a soil layer have been conducted in several research &-- s other than landfill engineering. Wang, M. C., et. al. used a finite element analysis and a p ysical model to analyze the bearing capacity of a shallow footing above a void embedded in clay (18). The results of Wang's finite element analysis and the results Goosynthetics'93.Vancouver.Canada-1499