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Geotechnical News • June 2014
www.geotechnicalnews.com
THESIS ABSTRACTS
Longevity of HDPE Geomembranes in
Geoenvironmental Applications
A. M. R. Ewais
A. M. R. Ewais, Postdoctoral Fellow, GeoEngineering Centre at
Queen’s-RMC, Queen’s University, Kingston ON, Canada, K7L
3N6, Tel: (613) 533-6000, ext. 77142. Fax: (613) 533-2128.
email: amr.ewais@ce.queensu.ca
With sufficient time, a high density polyethylene geo-
membrane will degrade and lose its engineering properties
until ruptures signal the end of its service-life. This thesis
examines the longevity of nine different geomembranes;
five of them were of different thickness manufactured from
the same resin. The degradation of properties and times to
failure are investigated for geomembranes: in immersion
tests; as a part of a landfill composite liner; and, exposed
to the elements. The different thermal and stress histories
associated with manufacturing geomembranes of different
thickness are shown to affect their morphological structure;
consequently, their stress crack resistance.
When immersed in synthetic leachate, it was found that: (a)
thicker geomembranes have a longer antioxidants depletion
time but the effect of thickness decreases with temperature;
(b) inferences of geomembrane’s longevity based on its ini-
tial properties may be misleading because a geomembrane
may chemically degrade despite the presence of a signifi-
cant amount of antioxidants/stabilizers (as manifested by
the measured high pressure oxidative induction time); and,
(c) stress crack resistance may change before antioxidant
depletion or chemical degradation takes place, likely, due to
changes in geomembrane morphological structure with the
maximum decrease being observed at 55
o
C. Reductions also
were measured for geomembrane immersed in air and water
at 55
o
C.
The geomembrane aged in a simulated landfill liner at
85
o
C is shown to have service-life as little as three years
with 30,000 to >2.0 million ruptures/hectare at failure. The
investigated degradation in the index properties of exposed
geomembranes to the elements at different climatological
conditions showed that geomembranes may lose portion of
its stress crack resistance due to changes in the morphologi-
cal structure of the geomembrane despite the presence of
significant antioxidants/stabilizers and/or no evidence of
chemical ageing. Nevertheless, exposed geomembranes may
not crack although its stress crack resistance had dropped to
70 hours.
Supervisor:
R. Kerry Rowe, Queen’s University, 58 University
Avenue, Ellis Hall, Rm 229b, Kingston, ON, Canada, K7L 3N6,
email: kerry@civil.queensu.ca
Interpretation of Pumping Tests in Confined
Aquifers in the Case of Interferences
(Original title in French:
Interprétation des essais
de pompage dans les aquifères à nappe cap-
tive en cas d’interférences
)
Simon Weber
Simon Weber
,
Department of Civil, Geological and Mining
Engineering, Ecole Polytechnique, P.O. Box 6079, Stn CV,
Montreal, Quebec, Canada, H3C 3A7, Tel: (514) 340 4711 ext.
4938, Fax: (514) 340 4477, email: simon.weber@polymtl.ca
The influence of an active well located in the neighborhood
of the tested well is often mistakenly neglected when inter-
preting pumping test data. This thesis presents analytical
methods to determine the hydraulic parameters of a porous
confined aquifer from data monitored during a pumping test
influenced by the interferences of one or several neighbor-
ing wells. These methods are easy to use, since they are
similar to the most commonly used methods in absence of
interference.
The interpretation of pumping test data influenced by a
neighboring well has first been studied in the simple case of
a homogeneous and isotropic aquifer of infinite extension,
before combining the proposed methods to existing methods
developed for the cases without interference to take into
account recovery, anisotropy or a partial boundary divid-
ing two areas of different hydraulic parameters but with a
similar diffusivity. Despite the simple proposed methods, it
is still difficult to take into account the interfering wells if
the pumping test is conducted in the vicinity of the aquifer
boundaries.
The drawdown resulting from the interfering well being
dependent on many parameters, it has not been possible to
establish an easy criterion to determine a priori whether an
interfering well influence will be negligible. Nevertheless,
equations have been proposed for this purpose, but further
studies on phenomena influencing the early times will have
to be conducted for these equations to be used.
Other useful results, not related to the well interference
problem but still relevant, have also been obtained: those
relative to the influence of the position of the three monitor-
ing wells that are used to interpret the pumping test data in
an anisotropic aquifer; and those relative to the influence of
the deviation from the diffusivity equality hypothesis in an
aquifer divided in two areas of different hydraulic param-
eters by a partial boundary.
Sponsoring Professor: Robert P. Chapuis, Department of Civ-
il, Geological and Mining Engineering, Ecole Polytechnique,
P.O. Box 6079, Stn CV, Montreal, Quebec, Canada, H3C 3A7,
Tel: (514) 340 4427 ext. 4938, Fax: (514) 340 4477, email: robert.
chapuis@polymtl.ca