Soil Resistivity Measurements ( Ρ Position); Advantages/Disadvantages Of Wenner & Schlumberger - AEMC 6471 User Manual

5.6 Soil Resistivity Measurements ( ρ Position)
To measure the resistivity of the soil, two measurement methods are possible:
Wenner and Schlumberger
The difference between the two methods lies in the positioning of the electrodes.
By default, the device selects the Wenner method. The Schlumberger method,
which allows you to move only 2 measurement electrodes rather than 3, is better
suited for measuring soil resistivity at multiple depths.
The soil resistivity measurement with different distances d, and therefore in dif-
ferent layers (in depth) of the soil, can be used to establish resistivity profiles of
the soil in question, which can be useful for geological analysis, the exploration
of deposits, hydrological studies, etc., and to determine the location of an earth
electrode.
5.6.1 Advantages and Disadvantages of Wenner and Schlumberger
Schlumberger
Advantage
Need to move the two
potential electrodes ES
(Xv) and S (Y) only for
most readings. This can
significantly decrease the
time required to acquire
a sounding
Because the potential
electrodes remain in
fixed locations, the ef-
fects of the near surface
lateral variations in
resistivity are reduced.
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Disadvantage
Because the potential
electrode spacing is
small compared to
the current electrode
soakings, higher meter
sensitivity is required.
In general, interpretations
based on DC soundings
will be limited to simple,
horizontal; layered
structures
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Wenner
Advantage
Potential electrode
spacing increases
as current electrode
spacing increases. Less
sensitive meters may
be used.
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Disadvantage
All four electrodes, the two
current E (X) and H (Z) and
the two potential ES (Xv)
and S (Y) must be moved
equally to acquire each
reading.
Because all electrodes
are moved for each
reading, this method can
be more susceptible to
near-surface, lateral, and
variations in resistivity.
These near surface lateral
variations could potentially
be misinterpreted in terms
of depth variations in
resistivity.
In general, interpretations
based on DC soundings
will be limited to simple,
horizontal; layered
structures.
Source: DC Resistivity - T. Boyd
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