IEEE Geoscience and Remote Sensing Magazine - September 2019 - 96

structures, such as the water-bearing areas in the roof sandstone aquifers and the karst or fractured zones in the floor
of coal-mining faces; it is also used for the adjacent blind,
mined-out areas. The spatial locations of the objects, roadway support modes, and working environment of the roadways are the main factors that need to be considered in the
selection of an advance-detection method and in the design of a measurement strategy.
According to different measurement principles, there are
numerous advance-detection methods for coal-mining faces, including roof and floor electrical sounding, dc perspective, coal seam sounding, multidipole electrical profile, and
2D or 3D resistivity imaging methods.
After years of practice, operators often employ asymmetrical devices to make full use of the limited construction space
of the roadway and to improve anomaly resolution and detection distance as much as possible. Among these, the threepole Schlumberger array is often used in roof and floor electrical sounding, mainly for determining the thickness of each
layer of the coal roof and floor or for evaluating water content
as well as delineating the local water-bearing structures. The
three-pole sounding data of the A and B configurations are
usually mixed together to draw a unified pseudo-section of
apparent resistivity. Because the sounding data of A and B arrays are equal for horizontal strata, the unified pseudo-section
of apparent resistivity of A and B arrays can therefore highlight the anomalous response of 2D or 3D geoelectric bodADVANCE DETECTION FOR A COAL-MINING FACE
ies [32]-[34]. The dc perspective method is mainly used to
Advance detection for a coal-mining face explores hidden
detect electrical anomalies either in a coal mine face or in its
karst pillars, which are small geological anomalies in coal
roof and floor strata. Its power supply electrodes and measeams, specifically to delineate the hidden water-conducting
suring electrodes are deployed in two
roadways, working in either the proRoof
file mode, where all electrodes move
together, or the tomographic mode,
where the measurement electrodes
Roadway
Coal Seam
move symmetrically but the source
B∞
electrodes are fixed. On the basis of
V
the electrical characteristics of the coal
......
seam, its roof and floor, and the relaM3
N2
M2
N1
M1 A
N3
tive position of the detecting objects,
Move
Floor
one of the electrode configurations,
(a)
such as dipole-dipole, pole-dipole,
or pole-pole arrays, can be selected
Roof
and placed in the right azimuth. In
general, equatorial dipole arrays are
Coal Seam
Roadway
used for detecting conductive anomaB∞
lies, such that the coal seam sounding
N∞
V
method adopts the equatorial dipole
......
array to detect the conductive waterA
M6
M5
M4
M3
M2
M1
bearing structures in highly resistive
Floor
Move
coal seams; the source dipole AB and
(b)
the measurement dipole MN are deployed in the same roadway. During
FIGURE 1. The configurations of underground resistivity methods. (a) A is the position-fixed
the measurement, the source dipole
source supply pole, measurement poles M and N move point by point, and another source
is fixed while the measurement dipole B is at infinity. (b) A is the position-fixed source pole, measuring pole M moves point by
pole moves point by point [35], [36].
point, and source pole B and measurement pole N are located at infinity.
exploration mode is typically adopted for coal mines.
Ground-based geophysical methods, such as 3D seismic
and electrical prospecting methods, are used first to delineate geophysically anomalous areas. Second, a variety of
electrical prospecting methods and other mine-based geophysical methods is used ahead of the roadway, especially
in suspected anomalous areas. In this latter stage, vertical
and horizontal drilling techniques are used to check the
geophysical results [31].
The resistivity methods and transient electromagnetic
time-domain methods are mainly used in advance detection for the coal mine roadway. Advance-resistivity methods
often utilize pole-dipole and pole-pole arrays, as shown
in Figure 1. In terms of electrode deployment, underground
resistivity methods work in three ways: the middle axial line
of the roadway floor, the U-type midline of the roadway side,
and the central line of the borehole (see Figure 2).
Small multiturn coils are generally used as the transmitter
and receiver for the underground transient electromagnetic
method, with either coincident loops or separate loops (Figure 3). According to the measurement position and orientation of the loops, the advance transient electromagnetic
method for the heading face also works in three ways: as the
ring-type sounding along the roadway side, for azimuth scanning, and for advance in-borehole measurement (Figure 4).

IEEE GEOSCIENCE AND REMOTE SENSING MAGAZINE

SEPTEMBER 2019

IEEE Geoscience and Remote Sensing Magazine - September 2019

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