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Unformatted text preview: Journal of Scientific & Industrial Research
Vol. 63, November 2004, pp 927-930 Multielectrode resistivity imaging technique for the study of coal seam
K K K Singh*, K B Singh, R D Lokhande and A Prakash
Central Mining Research Institute, Dhanbad 826 001
Received 06 April 2004; accepted 05 July 2004
The multielectrode resistivity imaging method has been used to study the coal seam located in the northern part of
Jharia Coalfield of Dhanbad district. This method has been applied on experimental basis to know the efficacy of this
technique. The improvement of resistivity methods using multi-electrode arrays led to an important development of
electrical imaging for subsurface surveys. Such surveys are usually carried out using a large number of electrodes, i.e., 48 or
more, connected to a multi-core cable. Apparent resistivity measurements are recorded sequentially sweeping any
quadripole (current and potential electrodes) within the multielectrode array. As a result, high-definition pseudosections with
dense sampling of apparent resistivity variation at depths are obtained in a short time. It allows the detailed interpretation of
2-D resistivity distribution in the ground. In this experimental study, Syscal Junior Switch-48 electrode resistivity meter is
used for the exploration of the coal seam at east Basuria colliery of Jharia coal field, Dhanbad. Pole-dipole configuration of
the multielectrode resistivity survey has been carried out along two traverses R1 and R2, which were selected over
developed workings of coal seam II at an incline mine of the east Basuria colliery. These traverses lie in dip-rise direction
with station interval of 2.5 m. Coal seam is delineated having high resistivity values ranging more than 989 to 1632 ohm.m
at depths varying 10 to 31 m from the surface.
Keywords: Multielectrode resistivity, Imaging technique, Coal seam
IPC Code: Int.Cl.7: G 01 N 3/38 Introduction
Inundation is the main causative factor for coal
mines disaster in India. Generally, it occurs due to
puncturing of thinned coal barrier under water
pressure which is not shown accurately on the plan. In
most of the cases, one side of the barrier is old
waterlogged unapproachable workings, whereas other
side is current workings. The position of the coal
barrier in the active mine (current workings) can be
surveyed accurately whereas other side with
unapproachable old waterlogged workings can not be
surveyed physically. Therefore, it was felt necessary
to locate the position of coal seam either from the
surface or from the old waterlogged unapproachable
side for the safe mining and to check disaster in coal
Electrical resistivity methods have been widely
used for shallow and deep investigations. Several
researchers have proved the suitability and
*Author for correspondence
e-mail: [email protected] effectiveness of these methods by studying the
response of diverse structures, such as faults1-3,
dykes4-6, contact7-9, in the laboratory and in the field.
So far the problem of detecting coal seams has not yet
been studied adequately, even though it has
immediate application in coal mining. Verma and
Bhuin10 have carried out a study of this problem in
Jharia Coalfield. They found that the coal seams are
having high resistivity with respect to the surrounding
formation and its values vary from few hundred
ohm.m to a few thousand ohm.m. Their results
suggest that this method can be applied to detect coal
seams. However, there is a need for studying the
applicability of resistivity methods under different
geological conditions, because the natural and
physical environment of coal seams vary considerably
from area to area.
Multi-electrode resistivity system, which is
advance version of the old four electrode resistivty
system, is used here on experimental basis to know
the efficacy of this system over the surface for the
delineation of known coal seam in an incline mine of
East Basuria colliery of Jharia Coalfield. 928 J SCI IND RES VOL 63 NOVEMBER 2004 Fig. 1—Location map of resistivity traverses over workings of
seam II at East Basuria colliery Study Site
An incline coal mine of East Basuria colliery was
selected for the delineation of known coal seam at
known depth. This colliery is located about 11 km
west of Dhanbad district of Jharkhand state. The area
has an undulating topography with maximum and
minimum elevation ranges between 188-219 m.
However the natural features have been marred to a
great extent due to mining activities resulting in
subsidence and dumping of overburden in the area.
Two traverses R1 and R2 were selected over
developed workings of coal seam II, as shown in
Fig. 1. These traverses lie in dip-rise direction with
station interval of 2.5 m.
Geology of the Area
East Basuria colliery is located in the northern part
of Jharia Coalfield of Dhanbad district. All the
working coal seams lie in Barakar formation of Lower
Gondwana. Barakar formation consists predominantly
of sandstone of varying grain size, intercalation of
shale and sandstone, grey and carbonaceous-shale and
coal seams. The general strike of the formation is EW and dip of the coal seam varies from 10-15o
The purpose of electrical surveys is to determine
the subsurface resistivity distribution by making measurements on the ground surface. The resistivity
measurements are normally made by injecting current
into the ground through two current electrodes, and
measuring the resulting voltage difference at two
potential electrodes. From these measurements the
true resistivity of the subsurface can be estimated. The
ground resistivity is related to various geological
parameters such as the mineral and fluid content,
porosity, degree of fracturing, the percentage of the
fractures filled with ground water and degree of water
saturation in the rock. Electrical resistivity surveys
have been used for many decades in hydrological,
mining and geotechnical investigations.
The improvement of resistivity methods, using multielectrode arrays has led to an important development of
electrical imaging for subsurface surveys. Resistivity
multi-electrode imaging system (an advanced version of
DC resistivity four elect-rodes) has been used in this
experimental study. Such surveys are usually carried out
using a large number of electrodes, i.e., 48 or more,
connected to a multi-core cable. A laptop
microcomputer together with an electrode-switching unit
is used to automatically select the relevant four
electrodes for each measurement. Apparent resistivity
measurements are recorded sequentially sweeping any
quadripole (current and potential electrodes) within the
multi-electrode array. As a result, high-definition
pseudosections with dense sampling of apparent
resistivity variation at shallow depth are obtained in a
short time. It allows the detailed interpretation of 2 D
resistivity distribution in the ground. It is also being used
for the delineation of underground in-homogeneities
such as cavities11,12, fractures13 and caves14 . A resistivity
meter Syscal Junior Switch is used in the present study
with 48 electrodes connected to the meter through a
multi-core cable. Pole-dipole array of this system is used
in this study.
Results and Discussion
The pole-dipole configuration inverted resistivity
section along traverse R1, lying over solid coal pillars
and level galleries (Fig. 1), is shown in Fig. 2. A high
resistive zone of over 989 ohm.m shows an incline
coal seam in black color, which is located at surface
position from 30-80 m. The depth of coal seam at this
surface position varies from 10-31 m. In this section,
level galleries or voids are not delineated due to poor
resolution although coal seam is developed i.e., there
is alternet voids/galleries of size 2.5 m after 18 m
solid coal pillar in the incline mine of the east Basuria
colliery. SINGH et al.: MULTIELECTRODE RESISTIVITY IMAGING TECHNIQUE FOR THE STUDY OF COAL SEAM Fig. 2—Resistivity section using pole-dipole configuration along traverse R1 at East Basuria colliery Fig. 3— Resistivity section using pole-dipole configuration along traverse R2 at East Basuria colliery 929 J SCI IND RES VOL 63 NOVEMBER 2004 930 The pole-dipole configuration inverted resistivity
section along traverse R2 lying along dip-rise
direction over solid coal pillars and level galleries
(Fig. 1) is shown in Fig. 3. It appears that a high
resistive zone of over 1632 ohm.m (marked by black
color) exists at surface positions 32.5–82.5 m at the
depth of 10-31 m. This may be due to the presence of
coal seam II. But, voids and coal pillars of lengths 2.5
and 18 m, respectively, are not distinguished in this
section due to poor resolution of this method.
However, both the traverses (R1 and R2) lie on the
same seam II, but the resistivity value obtained along
the traverse R2 is greater than the value along traverse
R1, which is due to some air filled fractures present
along the traverse R2 and air filled fractures have high
resistivity values because of high resistivity value of
Resistivity imaging conducted at East Basuria
colliery of Jharia leads to the following conclusions:
• • Coal seam II has been delineated with this
system, which depth varies from 10- 31 m
and resistivity values vary from more than
Size of coal pillars and voids could not be
delineated very clearly using Resistivity
Imaging surveys due to some constraints like
The authors are thankful to Director(Technical),
Koyala Bhawan, Dhanbad for providing financial
support to undertake this experimental study for the
evaluation of barrier thickness at the East Basuria
colliery of Kusunda Area. Thanks are also due to Mr R N Singh, Mr S N Rajak and Mr B Pashwan of
Central Mining Research Institute, Dhanbad for their
kind co-operation during field investigations.
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