During this past year I have seen a disturbing trend towards increasing
numbers of failures and problems associated with geosynthetic lining
systems, few due to inadequate materials, but primarily due to lack of
knowledge of designers in the performance characteristics of polymeric
materials. Such problems are aften ignored, for the same reason, by those
performing on-site CQA. If you are entering the geosynthetics CQA field and
would be interested in some on-site practical education/training during
January and February 99 we may be able to help.
I have come across a geosynthetic clay liner (GCL) that was installed in
soils containing stones up to 150 mm and with a very low proportion of
fines. The GCL contained holes up to 40 mm diameter before it was even
subjected to a hydrostatic test, which, of course, it failed. The GCL
manufacturer informed the designer that the GCL would not work in that
environment. The engineer proceeded anyway! The installer had to install a
replacement liner at its own expense, before the problem was resolved. A
GCL will only work when significantly and uniformly confined.
A geomembrane liner was used because "it has worked successfully in other
installations" so the engineer had heard. He specified that "the
geomembrane be made from XYZ that is resistant to the process chemicals".
The two requirements were probably mutually exclusive! It turned out that
the "other installations" operated at temperature significantly less than
the subject one. When asked to provide a fix, the engineer shrugged his
shoulders and said "whatever the geomembrane manufacturer recommends".
This is not good engineering.
The weld of a geomembrane to an anchor strip in a concrete structure had
been successfully spark tested according to the installer's QC records.
When the seam failed and samples weretaken there was no wire behind the
weld - effective spark testing was not possible. When the weld was further
examined there was a spot where the weld bead had all been placed on the
geomembrane, none had made a seal to the anchor strip, but the weld had
still passed spark testing according to QC records!
Geomembranes should not be treated as commodity items. They are relatively
sophisticated engineered products that need proper attention at all stages
(design, specification, installation, CQA, testing, covering, and operation)
if their beneficial performance characteristics are to be optimally and
cost-effectively mobilized.
Let's all listen and learn more in '99. Happy New Year.
Ian D. Peggs
I-CORP INTERNATIONAL, Inc.
+1 561 369 0795(vox), 0895(fax), http://www.geosynthetic.com
Geosynthetic and engineering polymer materials performance
consulting/testing and workshops ---- internationally.
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