Geosynthetics April/May 2020 - 57

Annealing is a general method to
reduce residual stress. In theory, annealing temperature has to be higher than
each plastic's glass transition temperature
so that stress relaxation might be rapidly
achieved. However, this temperature level
can also cause bending and warpage, so
annealing must be done quickly within
the maximum limit of dimensional
change caused by stress relaxation.
There are many methods for measuring residual stress. Methods were once
destructive, but preference is growing for
nondestructive methods. Neutron diffraction, X-ray diffraction and a photoelastic measurement of birefringence
methods are available as nondestructive
methods. However, the destructive methods of determining residual stresses by
the hole-drilling strain gages or solution
soaking component in different solutions
at varying method temperature are still
very relevant and the norm in the polymer industry. Please note that all the previous methods measure residual stress on
a micro scale. By contrast, we are interested in residual stress on a macro scale
post material fabrication.
The residual stress behavior of geosynthetics is a measure of load changes
in a specimen as it is exposed to the
temperature changes over a given time
period. The force generated by this
modulation of temperature can be compared to the ultimate tensile strength of a
material. All of this becomes much more
interesting when we deal with composite materials, of which the geosynthetic
industry has many.
That said, the Geosynthetic Institute
(GSI) is working hard on several projects to better understand how different geosynthetics react to changes in
temperature. It was surprising to find

that all geosynthetics do not expand
when heated (even those made with
olefin polymers). The equipment used
for these projects are shown in Figures
1 and 2. As these projects progress, we
will finalize GRI test methods, which
hopefully will aid the industry to better
understand the fundamental behavior
of polymeric products used to solve civil
engineering opportunities.
References
Giroud, J. P., and Morel, N. (1992). "Analysis of
geomembrane wrinkles," Jour. Geotextiles and
Geomembranes, 11(3), 255-276.
Koerner, G. R., and Koerner, R. M. (1995). "Temperature
behavior of field deployed HDPE geomembranes." Proc.,
Geosynthetics '95, IFAI, St. Paul, Minn., 921-937.
Koerner, G. R., and Koerner, R. M. (2006). "Long-term
temperature monitoring of geomembranes at dry and
wet landfills." Jour. Geotextiles and Geomembranes,
24(1), 72-77.
Lord, A. E., Jr., Soong, T.-Y., and Koerner, R. M. (1995).
"Relaxation behavior of thermally-induced stress in
HDPE geomembranes." Geosynthetics Int., 2(3), 626-634.

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Tsuboi, M., Imaizumi, S., and Miyaji, H. (1998). "Effect of
the temperature on tensile behavior of geomembranes."
Proc., 6th ICG, IFAI, St. Paul, Minn., 201-204. G

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Geosynthetics April/May 2020

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