Geosynthetics February/March 2021 - 45

As mentioned earlier, we placed the
entire direct shear apparatus within an
insulated chamber. We had weathering
issues with the equipment; however, with
proper maintenance and a lot of grease,
we persevered. Type J thermocouples
were placed within the shear box to
monitor the actual interface temperature
during testing. Upon completion of the
test, the shear box was dismantled and
the interface observed.
Several databases have been compiled
comparing direct shear results. An example
can be found in GRI Report 30, which has
seen wide circulation (Koerner and Narejo
2005). We took the saturated response
from this reference and superimposed the
hot and cold responses in contrast.
Important in this regard is the interpretation of the shear stress versus strain
curves. For the hot tests, we saw little
difference in the shear strength versus
deflection response. However, for the cold
tests, the shear stresses fell sharply to their
residual values. Table 1 presents the comparison of the extreme conditions with the
baseline standard saturated conditions.

interfacial friction can be affected by
temperature extremes. However, we
were surprised that there was not significant reduction in shear strength at
the extreme temperatures for the samples
we tested. This was noted not only by the
small differences in results but also by
the minor changes in surface conditions
post-test. We were pleasantly surprised to
see so little change in the peak frictional
response for both the smooth and textured geomembranes.
In conclusion, the author feels that further investigation into geosynthetic shear
strength while under extreme conditions
warrants consideration. This adds a complexity to the test, however attainable, with
a slight modification to current equipment.
It is yet another way to extend the current
method into modeling actual in situ conditions. In addition, it provides confirmation
that our industry makes products that will
handle such extreme conditions.

Summary and conclusions

Koerner, M. R., Koerner, G. R., and Koerner, R. M. (2019).
" Veneer instability of a frozen geomembrane-togeotextile interface. " Proc., Geosynthetics Conf. 2019,
Houston, Texas, 212-226.

A somewhat unusual extension of the
standard direct shear test was presented.
Hot and cold conditions were presented herein. Clearly, the geosynthetic
SMOOTH

References
Giroud, J. P., Williams, N. D., Pelte, T., and Beech, J. F.
(1995). " Stability of geosynthetic-soil layered systems
on slopes. " Geosynthetics International, 2(6), 1115-1148.

2c
FIGURES 2a, 2b and 2c Photographs of
geosynthetics used for extreme direct shear
testing: 2a) smooth HDPE; 2b) textured HDPE
from cast line; 2c) NPNW geotextile

Koerner, G. R., and Narejo, D. (2005). Direct shear
database of geosynthetic-to-geosynthetic and
geosynthetic-to-soil interfaces, GSI Press, Folsom, Pa. G

Test Temperature

Peak Friction

Peak Adhesion

Residual Friction

Residual Adhesion

Saturated

21°C

Hot

85°C

0 kPa

Cold

0°C

0 kPa

Test Temperature

Peak Friction

Peak Adhesion

Residual Friction

Residual Adhesion

Saturated

21°C

8 kPa

0 kPa

Hot

85°C

7 kPa

2 kPa

Cold

0°C

12 kPa

3 kPa

Condition

TEXTURED
Condition

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Geosynthetics February/March 2021

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