The Nuremberg GCL conference sessions finished on April 17 with a summary of the sessions by the five session chairmen. It was clearly apparent that to get the optimum service from a GCL, it is necessary to use a specifically designed product, as, for example, when a GCL is to be laid underwater in a canal, with ballast dropped on top of it (Heibaum). The lack of damage to such a GCL compares to the significant damage reported by Peggs when smaller stones (though still relatively large) were placed on top of a "standard" commodity GCL. Thus, as there are differences between and within geomembrane materials, there are differences in GCLs.
There was some emphasis on composite GCLs containing PE films (Reither/Eichenauer, Lucas) not thick enough to be considered "geomembranes," but sufficient to improve permeability characteristics.
Melchior described his controversial work starting in 1994 on GCL desiccation and cracking, but under a thin cover layer of 300 mm. Other presentations on exhumed GCLs under thicker, more typical cover layers, and using lysimeters, showed desiccation cracking not to be a significant problem. Heerten indicated that desiccation cracking is not a problem if there is sufficient confining pressure on the GCL. Controversial though it was, Melchior’s work has generated many additional studies on this durability topic. Typically it was reported that about 0.5% of precipitation seeps through a GCL (Sporer/Gartung, Henken-Mellies/Zanzinger/Gartung).
In line with Koerner’s presentation of a draft standard for a GCL, Sjoholm indicated Finland’s generation of draft standards for a GCL to protect ditches at the sides of highways. They found no problems with salt and freeze/thaw on GCLs, but there was some root penetration which will be resolved by the addition of a 0.3 to 0.5 mm geomembrane.
Rather than review the papers in his session (ranging from XRD of Montmorillonite to broken needles puncturing geomembranes), Peggs suggested where we should go next, as summarized in the attached slides. There is a possibility that we might "out-science" ourselves with the result that engineers new to lining systems will be afraid to use GCLs, viewing them as too complex to get right. While research is unquestionably needed and is making good progress, we must not forget that what we are learning must be put in very simple language for potential users. Thus, Koerner’s requirement for a GCL standard is most appropriate but must be taken further. There should perhaps be a number of standards for Types I, II, III, etc. GCLs to be used in different, but commodity, applications. These standards should include the associated geotextiles and the adjacent soils.
Other applications will require specifically designed GCLs. With such standards, as with NSF 54 and GRI GM13/17/20 for geomembranes, GCLs will become more widely used, the differences between commodity and specialty applications/products will be more apparent, and manufacturers can make more money and support more research and development. In this way only a half of the industry will be commoditized rather than all of it as is the present trend.
This GCL, or CGB (clay geosynthetic barrier, as now defined by CEN/ISO), conference was the second in the series – the first was in 1994. However, with the demise of the geosynthetics group at LGA, the location of the third conference is unknown. But, there must be a third, somewhere!
Conference proceedings can be obtained from Balkema
Dr. Ian D. Peggs
