ELECTRICAL RESISTIVITY
IMAGING SURVEYS
GEOPHYSICS
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Electrical Resistivity Imaging Geophysical Surveys:-
Electrical resistivity imaging geophysical surveys (also known as resistivity tomography, ERI or ERT) measure
the resistivity properties of the sub-surface by assessing the potential drops
between electrodes in a variety of configurations, depending upon the
type of geophysical survey data required.
Electrical resistivity surveys can be completed
using a 4 electrode frame and the survey completed by walking the
grid lines. The resulting data will give apparent electrical resisitivty data from a fixed depth range
governed by the electrode spacing, usually 0.25 to 1m.
Requirements
for deeper resistivity surveys to provide engineering and environmental geophysics data can
often benefit from making use of the latest development in resistivity surveying. Electrical Resistivity Imaging or Tomography surveys use
an array of electrodes to measure apparent ground resistivity. The system uses a set of up to 256 electrodes under computer control to
develop a pseudo-section using combinations of electrode readings.
The photograph shows the
resistivity imaging system in the field. The control unit is located in the vehicle in the
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The electrical resistivity tomography survey data are split into
levels representing depth intervals and powerful modelling software
is used to convert the data into calculated apparent resistivity depth sections. Depths of
study up to 30m are not uncommon and on occasion 100m. This is a very powerful means by
which to image the sub-surface over large sites for engineering or environmental
projects.
Below is an electrical resistivity imaging survey
section collected to determine the internal situation within a closed landfill site. Note the low resistivity wastes (blue)
over higher resitivity (reds) bedrock. Internal structures such as cell bunds and areas of drier waste are also visible.
Applications :-
- Locate mineshafts, pipelines, foundations, voids.
- Landfill formation level surveys for voids, faults and solution cavities
- Soil electrical resistivity / earth testing for wind farm projects.
- Depth to rockhead, bedrock overburden, water table, peat thickness.
- Locate pollution plumes, buried waste.
- Identify solution features
- Locate historic or unmapped landfill / quarry site extents.
- Pipeline / road route surveys.
- Archaeology.
Benefits :-
- Output to client
as sections and/or plans
- Wide depth range
- Easily correlated
with borehole data
- Ideal for covering
large sites where a number of vertical profiles assist
interpretation.
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