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geogrid deflects into the depression as tensile stresses develop in.the geogrid. The other method, stabilizing existing refuse areas, includes surcharging, deep dynani compaction, and lime/fly ash slurry injection, among others (2). Time and/or field constrain- often onstrainoften render these methods impractical for the development of vertical expansions. All the methods currently in use are based on the assumption that "void-induced settlement will impair the liner. Since none of these methods require the calculation of th settlement, it is unknown whether "void-induced" settlement is a real or perceived problem And, whether other alternatives such as providing a thick buffer, or a strain-transition zon offers as effective a solution as those.methods currently in use. The calculation of 'void °induced" settlement, and the evaluation of an alternative design methodology are the subjects c a this paper.-- REVIEW OF METHODS FOR ESTIMATING DEUERENTIAIL SE NT To date, the authors are not aware of a specific methodology used to quantify tht settlement resulting from the presence of a void within a landfill. However, similar situation: I are often encountered in mining and classical geotechnical fields. Several methods to analyzt "void-induced" settlement have been developed and are documented in mining and geotechnici journals and conference proceedings. The following four methods of analysis are briefl} discussed in this paper: • Mining Subsidence Empirical Methods (3,4), which include influence and profile functions; • Numerical Methods (5,18), which include finite element (FE) and finite difference (FD) methods; • Displacement Method (11); • Two-dimensional and Three-dimensional Elastic Solutions (15, 16). Mining Subsidence Empirical Methods. A mechanism similar to the collapse of a large object within an existing landfill and the resulting differential settlement at the surface of a liner system exists in mining (3,4). Mining subsidence occurs in a bowl-shaped pattern. Empirical methods have been developed to analyze the subsidence of "long-wall" mines, an underground mining technique mainly used in rock formations. The method applied in a specific geographical region is unique, based on the geological characteristics of the region. Because there is no generic solution available for all geographical regions, this method is not suitable for the analysis of differential settlements for a landfill vertical expansion configuration. Numerical Methods. Finite element analyses of a void within a soil layer have been conducted in several research fields other than landfill engineering. Wang, M. C., et. al. used a finite JL element analysis and a physical 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 of Y` Geosynthetics 93-vancouver.Canada- 1499