Citation: Karaoulis, M.; Kruiver, P.P.;
Hopman, V.; Beuving, B.
Geo-Electrical Detection of
Impermeable Membranes in the
Subsurface. Appl. Sci. 2022, 12, 1555.
https://doi.org/10.3390/
app12031555
Academic Editors: Yangquan Chen,
Simone Morais, Subhas
Mukhopadhyay, Junseop Lee, M.
Jamal Deen and Nunzio Cennamo
Received: 3 January 2022
Accepted: 28 January 2022
Published: 31 January 2022
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Article
Geo-Electrical Detection of Impermeable Membranes in
the Subsurface
Marios Karaoulis
1,
*, Pauline P. Kruiver
2
, Victor Hopman
1
and Bob Beuving
3
1
Deltares, Subsurface & Groundwater Systems, 3508 AL Utrecht, The Netherlands; victor.Hopman@deltares.nl
2
Royal Netherlands Meteorological Institute, 3730 AE De Bilt, The Netherlands; pauline.kruiver@knmi.nl
3
Beuving Civiel Advies & Management, 1213 AG Hilversum, The Netherlands; bob@beuvingciviel.nl
* Correspondence: marios.karaoulis@deltares.nl
Featured Application: Looking ahead capabilities of electrical resistivity tomography (ERT) for a
soil penetrating tool.
Abstract:
In this paper, we have investigate looking ahead capabilities of electrical resistivity to-
mography (ERT) for a soil penetrating tool with electrodes. In our case study, the desired detection
resolution (10 to 20 cm at a depth of at least 6 m) was much higher than what can be achieved from
classical surface ERT measurements. Therefore, we designed a logging-type tool, that can be pushed
into the ground. Our target was a buried PVC membrane which acts as an electrical insulator.
In this
phase, we performed numerical simulations and laboratory measurements.
The methodology
is
based on a two-step approach. First, we calculate the background resistivity of the tool’s path is
determined by inversion of near-looking electrode configurations. Next, the theoretical response (ker-
nel) of the far-looking configurations is calculated for different membrane positions. The root mean
square (RMS) error between the kernel and the measurements is minimized to detect the membrane.
If the membrane is within sensing reach, the RMS has a minimum for the kernel corresponding to the
true membrane position. If no minimum in RMS is found, the membrane is not within sensing reach
and the tool can be pushed closer to the membrane.
The laboratory
tests comprised measurements
in a tank filled with either water or saturated sand or saturated sand with clay slabs and chunks.
The laboratory
results were successful in pinpointing the position of the membrane with an accuracy
of 10 to 20 cm, depending on the dimension of the tool and the distance from the membrane.
Keywords:
look-ahead; detection of impermeable membranes; electrical resistivity tomography; geophysics
1. Introduction
Infrastructure works in low-lying countries with high water tables occasionally re-
quire measures to prevent groundwater from flooding the structure. An example is the
construction of a road below the groundwater table. In the case at hand, the road has been
constructed in a large trench which is lined with an impermeable membrane in the 1980
0
s.
Due to the increased traffic load, a lane needs to be added to the road inside the trench. The
road is of vital importance for the region and cannot be closed during the reconstruction
and excavation works. For safety and to avoid flooding during excavation and construction,
it is important to know the exact position of the membrane. The goal was to locate the
membrane with an accuracy of 10 to 20 cm at a depth of 6 to 10 m.
The approximate
location of the membrane is available from archive design drawings.
The actual
location
needs to be established through measurements. Geophysical methods that operate from
the surface do not have sufficient accuracy. Therefore, the measurement tool needs to
be inserted into the soil enabling measurements to be taken from a closer distance to the
membrane. The difficulty is that the PVC membrane has a thickness of less than 1 mm.
In addition, the tool needs to be kept at a “safe” distance of approximately 1 m from the
Appl. Sci. 2022, 12, 1555. https://doi.org/10.3390/app12031555 https://www.mdpi.com/journal/applsci
