Geosynthetics June/July 2020 - 44

GSI NEWS

The pressure on the
system is gradually
built up until the
targeted value is
reached. In this test,
the targeted value was
7 kPa for saturation.
Subsequent to this,
the normal pressure is
built up incrementally
throughout the
experiment.

flange filled with soil and water, and finally
the upper domed lid with a rubber bladder between the central flange and lid for
applying normal pressure.
Attached to the pressure vessel is a
permeability control panel, shown in
Figure 2 on page 43, which controls and
monitors the normal pressure on the
system as well as the flow through the
liner system. The system is capable of
maintaining constant hydraulic pressures
to within ±5% and includes means to
measure the hydraulic pressures to within
a prescribed tolerance. In addition, the
head loss across the test specimen can
be held constant to within ±5% and can
be measured with the same accuracy or
better. Pressures are measured using electronic pressure transducers connected to
a digital readout, and flow is measured
with the burette panel.
Water is the liquid used to both permeate and pressurize the test specimen.
The flux through the system will be substantially influenced by the permeating
fluid. Deionized water is being used in
standardized testing and also for these
tests. However, any other liquid, e.g.,
leachate, may be used going forward.

Test procedure
The pressure vessel, materials and control panel are configured as shown in
the series of photographs in Figures
3a-3j. Figure captions describe the various stages in the setup. It is important
to mention that the soil under GM is
back saturated by introducing water into
the space under the GM until it is full,
assuring that no air pockets exist in the
flange or lid of the apparatus. The pressure on the system is gradually built up
until the targeted value is reached. In
this test, the targeted value was 7 kPa for
saturation. Subsequent to this, the normal pressure is built up incrementally
throughout the experiment.
44

It should also be noted that the following termination criteria was used for
each reading of the test: three flow values over 8 hours where inflow=outflow;
no up or down trends in results; and
three values of 0.2% on average. With
this in mind, 30 average results were
collected at five normal pressures and
six hydraulic heads.
The flux (q) was calculated, as follows:
q= Q/A t
where:
q = flux, (m3/m2-sec)
Q = quantity of flow, taken as the
average of inflow and outflow, m3
A = cross-sectional area
of apparatus, m2
t = interval of time, s, over which the
flow occurs
One calculates the hydraulic conductivity of the system knowing the thickness of the composite liner system, which
in this case is 0.35 inch (9 mm) (i.e.,
GM=0.04 inch [1 mm] and GCL=0.31
inch [8 mm]).

Results
Presented is a test that took four months
to complete due to very long saturation-equilibrium times (1.5 months),
in which we could only run one setup.
The experiment we chose to run was
with the 0.08-inch (2-mm) round hole in
the GM with a 1-inch (25-mm) wrinkle
that was underlain by a GCL. The two
geosynthetics forming a composite liner
system were a 0.04-inch (1-mm) thick
linear low-density polyethylene (LLDPE)
GM and an 0.31-inch (8-mm) thick GCL.
The setup had a wrinkle in the GM, and
the setup was saturated. The hole was
located at the 180° bend of the wrinkle.
The two variables during the test were
hydraulic head and normal pressure. The

Geosynthetics | June July 2020

0620GS_p38-cv4.indd 44

5/20/20 10:04 PM

Geosynthetics June/July 2020

Table of Contents for the Digital Edition of Geosynthetics June/July 2020