Under Cover

by Neno Duplancic, (M.ASCE), Vice President; Canonie Environmental Services Corp., Pleasanton, CA 94566,

Serial Information: Civil Engineering—ASCE, 1994, Vol. 64, Issue 12, Pg. 70-71

Document Type: Feature article


The impermeable properties of flexible membrane liners have made them hot properties for landfill closure-cover systems. But slip-resistant clay might still be the best cover material in areas where seismic stability is a major concern. For years, flexible membrane liners (FMLs) have proven to be successful components of landfill liner systems-so successful, in fact, that researchers and regulatory agencies are recommending FMLs more often for inclusion in closure-cover systems. They rightly argue that the impermeability of FMLs makes them desirable candidates for closure covers. What they fail to consider sufficiently is the issue of stability. If designers insist on installing FMLs as part of landfill cover systems, infiltration-potential and seismic-stability analyses must be performed before proceeding with installation of the final cover. The article discusses the results of tests conducted by the author for conditions prevalent in Solano, a typical county in California. If cover systems that consist only of clays and a vegetative soil layer provide sufficient impermeable barriers to percolation, then it makes no sense to risk stability problems by including and FMLs in a closure cover when the slope of the cover exceeds 10%. Thanks to the low hydraulic conductivity of a clay layer and the unsaturated conditions that exist in it, the small amount of water that might pass into it will not travel to the foundation layer until the clay is saturated.

Subject Headings: Clays | Landfills | Soil stabilization | Layered soils | Saturated soils | Linings | Membranes | Seismic tests | California | United States

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