Geosynthetics June/July 2020 - 42

GSI NEWS

By George R. Koerner

Test method for determining leakage
through imperfections in GMs of a
composite liner system
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George R. Koerner is the
director of the Geosynthetic
Institute in Folsom, Pa.

0620GS_p38-cv4.indd 42

his article describes a large-scale test method intended to determine the leakage
through imperfections in a geomembrane (GM) under a given head. It can be used as
a performance test to simulate field conditions where the GM is physically breached. The
test method places a GM test specimen of 2 feet (0.6 m) in diameter on a subgrade within
a high-pressure test vessel. The GM can be underlain by a geosynthetic clay liner (GCL),
thus comprising a composite liner system. Upon adequate sealing of the GM around the
perimeter and closing of the upper portion of the vessel, hydrostatic plus normal pressure
can be applied to the specimen by a control panel system attached to a pressure vessel
cell. Note that the normal pressure is applied by an additional rubber bladder over the
top of the assembled cross section. The leakage through any imperfection in the GM can
be monitored at differential pressures by a flow measurement system attached to both the
influent and effluent lines, above and below the GM respectively.
This test method is used to evaluate the rate at which liquids leak through holes, slits
or cracks in a GM by itself or as a component of a composite liner system. In this regard,
the GM is underlain by a GCL, thus it becomes a GM/GCL composite liner. The relatively
large pressure vessel used for this experiment can accommodate a number of variables:
e.g., flaw size and shape, GM type and thickness, the influence of a geotextile (GT) in the
cross section, the permeability of the soil subgrade and overburden soils, the liquid head,
and the liquid characteristics.
Imperfections in GMs can be characterized into those resulting from either physical factors (Kays 1977) or chemical or biological factors (Haxo 1982). Physical failure
mechanisms include punctures that may result from equipment pressure or soil (subgrade
or overburden). These mechanisms may also include tears, creep, freeze-thaw cracking,
wet-dry cracking, differential settling, thermal stress, differential hydrostatic pressure,
abrasion and seam failures. Chemical failures are caused by deterioration that results from
factors such as ultraviolet light, oxidation, hydrolysis, extraction or solvent attack. Causes
of biological degradation include factors such as microbial attack, burrowing animal attack
or damage resulting from animals trying to escape from inside a containment facility.
At the present time, there exists a considerable amount of theoretical knowledge on
leakage rates through such flaws in liner systems. Therefore, it is important that leakage
rates be quantified and the principles governing leakage rates be understood so that better predictions of in situ performance can be made. This investigation will illustrate the
leakage through a composite GM/GCL liner system. The GCL is in intimate contact with
the underside of the GM except for the section of GM fold, which can be seen in Figure
3d of the setup on page 45.
To experience leakage through a liner system at a greater rate than diffusion, one needs
a physical perforation in the GM, i.e., a "hole." To compound this preventable defect, a
wrinkle with a crack may exist where the GM is not in intimate contact with the GCL.

5/20/20 10:04 PM

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Geosynthetics June/July 2020

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