Geosynthetics June/July 2022 - 41

resistance is recorded, then the material
is an insulator. For a material to be a good
conductor, the electricity passed through
it must be able to move the electrons.
The more free electrons in a material,
the greater its conductivity (Figure 1b).
Multimeters measure resistance by
injecting a small current into the circuit,
and then measuring the voltage
drop across those points in the circuit.
The known current and the resulting
voltage drop are then used to calculate
the resistance using Ohm's Law, which
states that the current through a conductor
between two points is directly
proportional to the voltage across the
two points. Introducing the constant of
proportionality to the resistance, one
arrives at the mathematical Equation
1, which describes this relationship.
Please note that the inverse of resistance
is conductance.
V=I^2*R
Where:
I=Current through the conductor
in units of amperes
V=Voltage measured across the
conductor in units of volts
R=Resistance of the conductor
in units of ohms
Like most things with electricity, we
had to tone down our enthusiasm with
this method from its inception in the
summer of 2020. At first, we thought
we would write a method for conductivity,
which is the reciprocal of resistivity.
As most of you remember from
your first physics class about electricity
and magnetism, resistivity is equal
to the product of the resistance times
the cross-sectional area divided by the
length of the conductor, as shown in
Equation 2.
ρ=RA/L
Where:
ρ=Resistivity
R=Resistance of the conductor
in ohms
A=Cross-sectional area of
the conductor
L=Length of the conductor
Unfortunately, our specimen had conductive
film of unknown thickness and a
multitude of competing circuits wherever
the multimeter is engaged with the circular
specimen. That is why we decided to
simply report resistance over 4-inch (100mm)
increments in multiple directions
to assure conductance of the specimen.
Conductive geosynthetics are increasingly
being used in critical applications.
For years, quality assurance/quality control
(QA/QC) professionals have been
asking for such a method to assure the
material is of proper quality prior to commissioning
an ELL survey, as discussed
by Thiel, Beck and Smith (2005). We
finally have a test that can be included in
future specifications when dealing with
conductive geosynthetics that will help
us on the way to achieving regulatory
required allowable/action leakage rates
(ALR) of less than 1 gallon per acre per
day (10 lphd).
References
Thiel, R., Beck, A., and Smith, M. E. (2005). " The value
of geoelectric leak detection services for the mining
industry. " Proc., GRI-18 Conf. on Geosynthetics R & D InProgress,
GeoFrontiers 2005, American Society of Civil
Engineers, Reston, Va. G
>> For more, search GSI at
GeosyntheticsMagazine.com.
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41
FIGURE 1a Performing the test on a conductive
geosynthetic with a multimeter. (We are
measuring resistance over 4-inch [100-mm]
increments as indicated on the specimen.)
FIGURE 1b Wiring schematic of the test
illustrating Ohm's Law
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