Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
CA 02468576 2004-05-27
A BLAST MOVEMENT MONITOR AND METHOD FOR DETERMINING THE
MOVEMENT OF A BLAST MOVEMENT MONITOR AND ASSOCIATED ROCK AS
A RESULT OF BLASTING OPERATIONS
FIELD OF THE INVENTION
This invention relates to a method for determining the movement of a blast
movement
monitor placed within a rock body as a result of blasting of the rock. This
invention
also extends to a blast movement monitor and apparatus for use in performing
the
method. This invention also extends to a method of determining the movement in
a
boundary between two different rock or ore positions in a heterogeneous rock
body.
This invention relates particularly but not exclusively to a method of
determining the
movement of an ore boundary. Typically the boundary might be between high
grade
ore, e.g. a vein of gold ore, and a low grade ore, in a heterogeneous ore body
of an
open cast mine that practises open cut selective mining. It will therefore be
convenient to hereinafter describe this invention with reference to this
example
application. However it is to be clearly understood that the invention is
capable of
broader application. For example the invention may be used to determine the
movement in boundaries between ore and waste for many ores. It may also be
used
to measure the boundary movement between sulphide ore and oxide ore in
fractional
deposits. These ores require different concentration processes and therefore
need to
be recovered separately. It may also be used to measure the movement of the
edge
of a coal seam when the overburden is blasted.
BACKGROUND TO THE INVENTION
Open cast mining operations are well known and are conducted in a number of
countries around the world. Typically they comprise progressively mining
domains of
an ore body in a staged batch-like process. Each so called batch comprises
CA 02468576 2004-05-27
2
selectively placing explosives in the rock of the batch. Thereafter the rock
is blasted
to break and loosen the rock and form a muck pile. Typically the deposits in
these
mines are heterogeneous in the sense that the ore is disseminated in complex
shaped volumes of varying grade within a host rock which is waste. The shape
of
each ore zone on a horizontal plane is represented by a polygon when viewed in
plan.
The rock body for example might comprise one or more ore polygons that are
economic to recover and waste rock that is to be discarded. The ore is
selectively
removed from the muck pile and sent to a concentrator where the valuable
mineral is
extracted by an appropriate technique. Similarly the waste rock is removed and
sent
to a discard rock dump. Clearly an important part of this process is the
accurate
delineation of and identification of the boundaries between high grade ore and
low
grade ore and between ore and waste. A mixture of scientific know how,
geology,
computer modelling, and experience is used to determine the boundaries in the
body
of rock prior to blasting being conducted. This art has developed to the point
where
mining engineers and geologists have a good three dimensional picture of the
boundaries between the different ores in the virgin rock prior to blasting.
However it is quite clear that the rock moves when it is subjected to
blasting. The
blasting causes some expansion of the rock and in addition there may be some
differences in the amount of movement of the different parts of the rock. This
is
illustrated schematically in Fig 1. Currently there are no satisfactory
techniques for
measuring or modelling this movement in the rock and thereby also the ore
boundaries as a result of the blasting operations. Mining engineers and
geologists
sometimes work on the assumption that the ore boundaries of the blasted rock
are the
same as that for the unblasted rock and direct the broken rock to respectively
the
concentrator and the dump on this basis.
The problem is that it is clear that the rock and therefore also the ore
boundaries do
move. Accordingly if this movement is not accounted for by the mining
engineers in
CA 02468576 2006-10-10
3
the mining operation some of the ore is directed to the dump. This leads to a
loss of
product which is intended to be recovered. Similarly some of the waste is
recovered
in the ore stream and is sent to the concentrator. This can lead to a
significant loss of
efficiency in the concentrators as it processes more waste and less product.
This can
lead to a drop oft in the volume of concentrate produced per unit time.
It is universally recognised that this approach is unsatisfactory. It would
therefore be
highly desirable if a way could be devised of measuring the movement of the
rock and
thereby the ore boundaries. It would enable a three dimensional picture of the
ore
boundaries in the pre-blast rock body to be adjusted to account for the
measured rock
movement. This in turn would improve the correct reporting of the ore to the
concentrator and the waste to the dump,
SUMMARY OF THE INVENTION
According to one aspect of this invention there is provided a method for
determining
the movement of a blast movement monitor placed within a body of rock as a
result of
blasting of the rock, the method comprising:
placing at least one movement monitor in the rock body and noting its
position;
blasting the rock body to break up the rock body into a plurality of rock
pieces;
and
locating the position of at least one placed movement monitor by analysing a
signal passed between the monitor and an external communication device to
determine the post blast position of the monitor at least in a plane parallel
to the
ground;
whereby to measure the movement of the monitor/s by comparison of pre and
CA 02468576 2006-10-10
4
post blast positions as a result of the blasting.
The step of locating the position of at least one movement monitor may
comprise
locating the position of the monitor in three dimensional space. That is
locating its
position in three dimensions instead of two.
The signal may be an electro-magnetic signal having a specific frequency, e.g.
a low
frequency signal. The signal that is measured may be a magnetic field
component of
an electro-magnetic field and the frequency of the signal may be in the range
of 1-300
kHz. Preferably the signal is 10-200kHz, more preferably 20-150kHz, even more
preferably 30-80kHz, and most preferably about 66kHz.
A low frequency signal is preferred because it is attenuated to a lesser
extent by the
surrounding rock than a high frequency signal.
The monitor may include a transmitter for transmitting the signal and the
external
communication device may include a detector or receiver for detecting the
signal from
the transmitter.
Thus the signal is transmitted from the monitor to the detector.
The detector may sense the magnetic component of the electromagnetic field
generated by the transmitter and also the strength of the magnetic field at
that
particular point.
The transmitter may be received within a casing which in turn is received
within a
housing with the casing being movable relative to the housing within the
housing.
Each blast movement monitor may have means for enabling the transmitter to
orientate in a certain direction after the blast so that all monitors are
consistent in the
CA 02468576 2004-05-27
direction in which they emit their signal.
The orientating means may comprise self righting means wherein the transmitter
in
each monitor is able to return itself to an upright position after the blast
so as to
5 transmit its signal in a substantially vertically upward direction.
The self righting means may comprise forming the casing with an asymmetric
weight
distribution with its centre of weight positioned directly beneath the
geometric centre
of the casing. This is achieved by having a preponderance of mass in a lower
half of
the casing so as to cause the monitor to tend to revert to its upright
position if it is
moved out of its upright position. The preponderance of mass in the lower half
may
be assisted by having the transmitter housed more in the upper half than the
lower
half with more solid casing material in the lower half than the upper half. It
may also
be assisted by designing the transmitter to have its centre of mass as low as
possible.
The detector may be used to locate the XY position of the monitor on an
imaginary XY
plane extending broadly parallel to the surface by locating the point on the
surface of
the muck pile where the magnetic field signal is at its greatest. This really
amounts to
locating the position on the surface beneath which the monitor is located. The
situation of the monitor on an imaginary XY plane or top plan view of the site
can be
established to an accuracy of less than one metre.
The vertical depth of the monitor within the muck pile can be gauged by
measuring
the strength of the magnetic field at the point on the surface where the
magnetic field
signal is at its greatest. The strength of the magnetic field on the surface
is a function
of the depth of the monitor. As a general rule the intensity of the magnetic
field
decays as a function of the cube of the distance from the source.
In preferred forms of the invention a said monitor can be detected up to a
depth of 15
meters on an imaginary Z axis.
CA 02468576 2006-10-10
6
Instead or in addition the vertical depth of the monitor within the muck pile
can be
gauged by measuring the angle of the magnetic field sensed by the detector.
The general principle behind this is that the angle at which magnetic field
lines cut the
surface of the rock can be used to locate the source of the magnetic field.
Generally
the angle of the magnetic field lines relative to an imaginary horizontal line
on the
surface is measured.
Thus the method can be used to measure the movement of the monitor in the muck
pile in three dimensions. That is its movement on an imaginary XY plane and
also
movement in its depth that is in a mutually orthogonal Z axis.
A plurality of said movement monitors may be placed within the rock body
spaced
apart from each other within the rock body. The monitors may be positioned 0
to 15
m beneath the surface of the rock body. Preferably each monitor may be
positioned I
to 10 m beneath the surface of the rock body. More preferably the monitors may
be
positioned at approximately half the depth of a bench of the rock body.
Conveniently each monitor may be placed within a hole, eg a drill hole, within
the
rock. Further each drill hole may be filled up with drill cuttings once the
monitor has
been placed in the hole.
According to another aspect of this invention there is provided a blast
movement
monitor for measuring the movement of rock within a rock body as a result of a
blasting operation, the monitor comprising:
a monitor body defining an interior space;
an internal communicating device that is received within the interior space of
CA 02468576 2006-10-10
7
the monitor body for either transmitting a signal outwardly to an external
communication device or being able to detect a signal transmitted inwardly by
the
external communication device; and
a housing having an inner surface defining an interior chamber within which
the
monitor body is received, the monitor body being capable of movement relative
to the
housing within the housing.
The internal communicating device may transmit a signal outwardly rather than
receiving a signal inwardly. In this configuration the internal communicating
device
includes a transmitter for transmitting said signal,
The transmitter may generate an electro-magnetic field that transmits a signal
at a
particular frequency. Conveniently the transmitter may comprise an electric
coil
coupled to an electrical supply through which electrical current can be passed
to
generate an electro-magnetic field.
Instead the signal may be a microwave signal.
The monitor body may comprise a casing made of a non conductive material. The
casing may be configured such that it can be moved in all directions across
the
internal surface of the housing. The internal surface of the housing may be
complementary to the casing such that the casing can slide over the internal
surface
of the housing. Preferably the surface of the casing is curved.
In one preferred form the casing is spherical. However it is not limited to a
spherical
configuration.
It is obviously desirable that the casing be reasonably robust as it has to
withstand
blasting of the rock. At the same time it needs to be reasonably light so that
it can be
CA 02468576 2004-05-27
8
moved around and preferably carried around. Nylon, polyethylene and
polystyrene
have been found to have these properties.
Thus the surface of the casing is deliberately chosen so that it can slide
over the
internal surface of the housing in all directions. That is it is capable of
universal
movement like a ball and a socket joint. It is not limited to movement in a
single plane
like a hinge joint.
The housing may contain a liquid intermediate the casing and the internal
surface of
the housing to lubricate movement of the casing relative to the housing. The
casing
floats in the liquid and this assists its movement relative to the housing.
The liquid
may be water or oil. The arrangement may be analogous to that of a floating
gimbal.
The casing and transmitter assembly is designed to have a density that is very
close
to that of the liquid within which it is immersed. Ideally it has a density
that is the same
as the liquid within which it is immersed. When this occurs it has zero weight
in the
liquid and a neutral buoyancy and the casing floats in the liquid. This
assists in
reducing friction between the casing and the internal wall. This is important
to enable
the casing and transmitter to self right after each blast.
In addition the liquid may serve to damp energy from the blast and thereby
reduce the
risk of damage to the transmitter.
The casing in turn may comprise two casing halves in the form of hemispheres
that
are releasably attached to each other. The casing may further include
fastening
elements for securely attaching the two halves to each other. The fastening
elements
may be in the form of bolts with screws, for securely attaching the two halves
to each
other. The casing may be opened up to provide access to the transmitter for
checking, maintenance or replacement of components of the transmitter.
CA 02468576 2006-10-10
9
In turn the housing may comprise two parts releasably attached to each other
to
enable the housing to be opened up when required to get access to the casing.
The
housing may further include fastening elements for securely attaching the two
housing
parts together. The housing may have a cylindrical configuration and be made
from a
plastics or nylon material.
The monitor may further include a cover within which the housing is received.
The
cover may be spaced outwardly away from the external surface of the housing
and a
padding material may be placed between the cover and the housing. The purpose
of
the padding is to help damp and for absorb the energy of the blast before it
reaches
the transmitter. The padding material may be a foam material, e.g. a low
density
foam.
Conveniently the cover may be made of plastics material and may have a
circular
cylindrical configuration.
According to yet another aspect of this invention there is provided an
apparatus for
determining the movement of boundaries between different portions of a
heterogeneous rock body as a result of a blast, the apparatus comprising:
at least one blast movement monitor as described above according to the
preceding aspect of the invention; and
an external communication device for communicating with the blast movement
monitor.
The blast movement monitor may include any one or more of the optional
features
described above for the second aspect of the invention. Specifically each
monitor
may include a transmitter for transmitting signals outwardly.
CA 02468576 2006-10-10
The external communication device may be a detector or receiver for detecting
signals from a transmitter in the blast movement monitor. The detector or
receiver
may include an antenna.
5 The detector may be capable of detecting the magnetic component of an
electromagnetic field. The detector may be a magnetic coil tuned to the same
frequency as the transmitter thereby to receive a signal from the monitor.
The detector may further include an amplifier operatively coupled to the
magnetic coil
10 to increase the sensitivity of the detector.
Conveniently the detector may be hand held and in use it will be carried by an
operator moving across the surface of the blasted rock body.
According to yet another aspect of this invention there is provided a method
of
determining the movement of boundaries between different portions of a
heterogeneous rock body as a result of a blast, the method comprising the
following
steps:
placing at least one blast movement monitor as described in the second aspect
of the invention above in the rock body prior to blasting and noting the
position of the
or each blast movement monitor;
blasting the rock body to break up the rock body into a plurality of rock
pieces;
locating the position of at least one blast movement monitor as a result of
the
blast;
determining the movement of the rock in the region of the at least one blast
movement monitor due to the blast; and
CA 02468576 2006-10-10
11
adjusting the position of the boundaries between different rock portions in
response to the determined movement of rock to compensate for movement caused
by the blast.
The method may further include the step of providing a map of the boundaries
of the
different rock portions within the rock body prior to said step of adjusting
the position
of the boundaries,
The step of placing may comprise placing a plurality of said blast movement
monitors
in holes in the rock body spaced apart from each other. The step of locating
may
include locating the position of at least 50% of the placed monitors,
preferably at least
75% of the placed monitors after the blast. The blast movement monitors may be
placed in holes that are drilled in the rock body. The holes may be filled
with drill
cuttings once the monitor has been placed in the hole.
The holes may be spaced apart from explosives holes that are drilled in the
rock
body. Generally the position of the monitors will be selected by the mining
engineers
or geologists and will not follow a repeating pattern like the blast holes. At
least some
of the blast movement monitors may be placed in positions in the rock body
that are
on or are proximate to a boundary between different rock portions within the
rock
body.
The boundaries of the rock body may delineate rock portions that are a
recoverable
ore polygon and waste. For example the rock body may comprise a rock portion
that
is a polygon of high grade gold ore received within a large body of host waste
rock.
The boundaries of the rock body may delineate rock portions that are high
grade ore,
low grade ore and waste. The high grade ore may comprise polygons of gold ore
having a grade of about 5-7 g/t and the low grade ore may comprise polygons of
gold
ore of about 1-3 g/t that need to be recovered separately from the high grade
ore.
CA 02468576 2010-09-13
-12-
The boundaries of the rock body may delineate rock portions that are sulphide
ores,
oxide ores and/or supergene ores.
The step of adjusting the position of the boundaries between the rock portions
may
include adjusting each said boundary based on movement of one or more monitors
as a result of the blast. Preferably the step of adjusting the position of the
boundaries
is based on a distance weighted average of movement of a plurality of monitors
located on the boundary or in proximity to the blast monitor.
Finally the method may further include building up an adjusted three
dimensional map
of the boundaries of the different rock portions based on the measured
movement of
the blast movement monitors as a result of the blast.
Once the adjusted boundaries have been calculated then the broken ore can be
removed and transferred to the concentrator and the waste or low grade ore can
be
removed and sent to a dump or low grade ore treatment plant.
According to an aspect of the invention, there is provided a method for
determining
the movement of a blast movement monitor placed within a body of rock as a
result of
blasting of the rock, the method comprising: placing at least one movement
monitor in
the rock body and noting its position; blasting the rock body to break up the
rock body
into a plurality of rock pieces; and locating the position of at least one
placed
movement monitor by analysing a signal passed between the monitor and an
external
communication device to determine the post blast position of the monitor at
least in a
plane parallel to the ground; whereby to measure the movement of the monitor/s
by
comparison of pre and post blast positions as a result of the blasting,
wherein the
signal that is measured is a magnetic field component of an electro-magnetic
field
and the frequency of the signal is in the range of 10-200 kHz.
CA 02468576 2010-09-13
- 12a-
According to a further aspect of the invention, there is provided a method for
determining the movement of a blast movement monitor placed within a body of
rock
as a result of blasting the rock, the method comprising: placing at least one
movement monitor in the rock body and noting its position; blasting the rock
body to
break up the rock body into a plurality of rock pieces; and locating the
position of at
least one placed movement monitor by analysing a signal passed between the
monitor and an external communication device to determine the post blast
position of
the monitor at least in a plane parallel to the ground; whereby to measure the
movement of the monitor/s by comparison of pre and post blast positions as a
result
of the blasting, wherein the signal is a low frequency signal in the range of
20-100
kHz.
According to another aspect of the invention, there is provided a method for
determining the movement of a blast movement monitor placed within a body of
rock
as a result of blasting of the rock, the method comprising: placing at least
one
movement monitor in the rock body and noting its position; blasting the rock
body to
break up the rock body into a plurality of rock pieces; and locating the
position of at
least one placed movement monitor by analysing a signal passed between the
monitor and an external communication device to determine the post blast
position of
the monitor at least in a plane parallel to the ground; whereby to measure the
movement of the monitor/s by comparison of pre and post blast positions as a
result
of the blasting, wherein the movement monitor includes a transmitter for
transmitting
the signal and wherein the external communication device includes a detector
for
detecting the signal from the transmitter, wherein the detector senses a
magnetic
component of an electro-magnetic field generated by the transmitter and the
strength
of the magnetic field.
According to yet another aspect of the invention, there is provided a method
for
determining the movement of a blast movement monitor placed within a body of
rock
CA 02468576 2010-09-13
- 12b -
as a result of blasting of the rock, the method comprising: placing at least
one
movement monitor in the rock body and noting its position; blasting the rock
body to
break up the rock body into a plurality of rock pieces; and locating the
position of at
least one placed movement monitor by analysing a signal passed between the
monitor and an external communication device to determine the post blast
position of
the monitor at least in a plane parallel to the ground; whereby to measure the
movement of the monitorls by comparison of pre and post blast positions as a
result
of the blasting, wherein the movement monitor includes a transmitter for
transmitting
the signal and wherein the external communication device includes a detector
for
detecting the signal from the transmitter, wherein each movement monitor has
means
for enabling the transmitter to orientate in a certain direction after the
blast so that all
monitors are consistent in the direction in which they emit their signal.
According to another aspect of the invention, there is provided a method for
determining the movement of a blast movement monitor placed within a body of
rock
as a result of blasting of the rock, the method comprising: placing at least
one
movement monitor in the rock body and noting its position; blasting the rock
body to
break up the rock body into a plurality of rock pieces; and locating the
position of at
least one placed movement monitor by analysing a signal passed between the
monitor and an external communication device to determine the post blast
position of
the monitor at least in a plane parallel to the ground; whereby to measure the
movement of the monitor/s by comparison of pre and post blast positions as a
result
of the blasting, wherein the external communication device is used to locate
the XY
position of the monitor relative to the surface of the broken rock by locating
a point on
the surface of the broken rock where a magnetic field signal associated with
the
monitor is at its greatest.
According to another aspect of the invention, there is provided a method of
determining the movement of boundaries between different portions of a
CA 02468576 2010-09-13
- 12c-
heterogeneous rock body as a result of a blast, the method comprising the
following
steps: placing at least one blast movement monitor including a monitor body
defining
an interior space, an internal communicating device that is received within
the interior
space of said monitor body for either transmitting a signal outwardly to an
external
communication device or being able to detect a signal transmitted inwardly by
an
external communication device, and a housing having an inner surface defining
an
interior chamber within which the monitor body is received, the monitor body
being
capable of movement relative to said housing within said housing, in the rock
body
prior to blasting and noting the position of the or each blast movement
monitor;
blasting the rock body to break up the rock body into a plurality of rock
pieces;
locating the position of at least one blast movement monitor as a result of
the blast;
determining the movement of the rock in the region of the at least one blast
movement monitor due to the blast; and adjusting the position of the
boundaries
between different rock portions in response to the determined movement of rock
to
compensate for movement caused by the blast.
According to a further aspect of the invention, there is provided a blast
movement
monitor for measuring the movement of rock within a rock body as a result of a
blasting operation, the monitor comprising: a monitor body defining an
interior space;
an internal communicating device that is received within the interior space of
the
monitor body and is able to communicate with an external communication device;
and
a housing having an inner surface defining an interior chamber within which
the
monitor body is contained, the monitor body being capable of movement within
said
interior chamber relative to the housing.
According to a yet further aspect of the invention, there is provided an
apparatus for
determining the movement of boundaries between different portions of a
heterogeneous rock body as a result of a blast, the apparatus comprising: at
least
one blast movement monitor as described above; and an external communication
device for communicating with the blast movement monitor.
CA 02468576 2010-09-13
- 12d-
BRIEF DESCRIPTION OF THE DRAWINGS
A method for determining the movement of a set of blast movement monitors in a
blasting operation at a mine and an apparatus including blast movement
monitors for
use in the method may manifest themselves in a number of forms. It will be
convenient to hereinafter provide a detailed description of several
embodiments of
the invention with reference to the accompanying drawings. The purpose of
providing
this detailed description is to instruct persons having an interest in the
subject matter
of the invention how to put the invention into practice. It is to be clearly
understood
however that the specific nature of this detailed description does not
supersede the
generality of the preceding statements. In the drawings:
CA 02468576 2004-05-27
13
Fig 1 indicates schematically in plan view a likely movement of a rock body as
a result of blasting;
Fig 2 is a schematic sectional view of a blast movement monitor in accordance
with a first aspect of the invention;
Fig 3 is an exploded sectional front view of a casing for the monitor shown in
Fig 2;
Fig 4 is a schematic front view of the movement monitor of Fig 2 received
within a cover which is in turn received within a drill hole within a rock
body
about to be blasted;
Fig 5 is a schematic front view of a magnetic field generated by a movement
monitor within the rock body showing the magnetic field lines generated by the
monitor;
Figs 6 to 8 show the strength of the signal measured along respectively north-
south and east-west axes centred on a drilled hole in which a monitor was
located, the different figures showing the signal when the monitor was at
different depths;
Fig 9 is a depth calibration graph for the monitor showing the strength of the
magnetic signal measured by a detector on the surface as a function of the
depth of the monitor within the rock body;
Fig 10 is a schematic cross sectional front view of a monitor in accordance
with
a second embodiment of the invention;
Fig 11 is an exploded view of a casing for the monitor of Fig 10;
CA 02468576 2004-05-27
14
Fig 12 is a front view of a transmitter for the monitor of Fig 10;
Fig 13 is a three dimensional map of the strength of the magnetic field sensed
by the receiver across the area proximate to the location of two movement
monitors;
Fig 14 is an exploded view of a movement monitor in accordance with a third
embodiment of the invention;
Fig 15 is a schematic plan view of a blasting site indicating the position of
blast
holes and also indicating the position of movement monitors amongst the blast
holes and also the movement of the monitors as a result of the blasting of the
rock body;
Fig 16 is a graph showing the correlation of horizontal movement of monitors
as a function of the initial depth of the monitors in one of the field trials
carried
out by the applicant; and
Fig 17 is a graph showing the most likely movement of monitors in each of top
and bottom flitches of a blasted rock body.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
In Figs 2 to 4 the blast movement monitor is indicated generally by the
reference
numeral 1.
The monitor 1 comprises broadly a communication device that is a transmitting
device
or transmitter 2 received within a monitor body that is in the form of a split
casing 3.
The casing 3 comprises two hemispherical halves 4, 5 and may conveniently be
made
CA 02468576 2004-05-27
of a material such as nylon, polyethelene, polystyrene or other engineering
plastics
although clearly other materials may also be used.
The transmitter 2 comprises a cylindrical coil oscillating at a suitable
frequency for
5 example 50 to 90 kHz. In the illustrated embodiment a frequency of 66 kHz
was used
although clearly many other frequencies could equally have been used. An
advantage of using a low frequency is that it is attenuated to a lesser extent
in rock.
The coil is oriented vertically in the casing as shown in Fig 2. This has the
effect of
generating a dipole shaped magnetic field as shown in Fig 5 with magnetic
field lines
10 6.
Each hemispherical half 4, 5 is generally solid but has a profiled cut away
defined
therein. When the two halves 4, 5 are assembled to define the casing 3 as a
whole
then the cut aways define an approximately cylindrical interior space within
which the
15 transmitter 2 is received. The cut away is greater in half 4 than half 5 to
assist self-
righting of the casing. This will be described in more detail below.
Each of the hemispherical halves 4, 5 has channels 8 defined therein through
which
suitable fastening elements can be passed to secure the two halves 4, 5 to
each other
and form the assembled casing 3.
The illustrated embodiment shows four said channels 8 that are positioned
broadly
towards the corners and are suited to having screws passed there through. The
channels 8 pass fully through the half 5 and a short distance into the half 4.
At least
part of each channel within the half 4 defines an internal screw thread to
engage a
screw thread on the screw and thereby effect a positive attachment. In the
illustrated
embodiment 3 mm nylon screws (not shown) were used but this should be regarded
as merely one of many different possible screws that could be used. Figs 2 and
3
show how the spherical casing 3 is assembled.
CA 02468576 2004-05-27
16
The transmitter 2 is mounted in the casing 3 as follows. The two halves 4, 5
are
separated from each other and the transmitter 2 is placed into the lower half
4. The
upper half 5 is placed in position over the lower half 4 and the two halves 4,
5 are
attached together by the fastening elements.
The casing 3 is designed so that its centre of mass is lower than the centre
of the
sphere. In the illustrated embodiment this is accomplished by having a greater
mass
of the casing body in the lower half 4 and having this excess mass evenly
distributed
around the centre of the casing 3. This confers on the casing 3 an ability to
right itself
when it is displaced out of its upright position, e.g. due to a blast. The
casing 3 pivots
back until the centre of mass is directly below its centre and it is again
upright. The
signal is therefore transmitted directly upwardly.
The monitor 1 also includes a housing 10 (shown in Fig 2) within which the
casing 3 is
received. In the illustrated embodiment the housing 10 is cylindrical although
clearly
any other shape could also be used. The housing 10 may be solid and have an
internal surface defining an internal chamber of complementary shape to the
casing 3.
The casing 3 is received within the internal chamber in the housing 10 of
complementary shape with at least a small amount of clearance. This enables
the
casing 3 to move in the housing 10 by sliding over the internal surface of the
housing.
As such it can move or rotate within the housing 10. This is an important
feature of
the monitor 1 as will be described in more detail below.
The chamber of the housing 10 is filled with liquid, e.g. water or silicon
oil, that sits
between the casing 3 and the internal surface of the housing 10. The casing
assembly comprising the casing 3 and the enclosed transmitter 2 has a specific
gravity that approximates very closely that of the liquid so that it floats in
the liquid
with close to zero weight. This is important to ensure that movement of the
casing 3
within the housing 10 is not hindered by friction between the casing 3 and the
housing
CA 02468576 2004-05-27
17
10. The liquid assists in lubricating the sliding surfaces of the housing 10
and the
casing 3. In addition the liquid may assist in damping and absorbing energy
from the
blast before it reaches the transmitter 2.
The housing 10 comprises an upper part 11 and a lower part 12 each of which
define
hemispherical cut outs within which the assembled casing 3 is received. The
upper
part 11 of the housing defines four screw threaded passages 15. Similarly the
lower
part 12 of the housing has four screw threaded passages 16 that are aligned
with the
passages 15 on the upper part 11 when placed in position.
The two housing parts 11, 12 are attached to each other by mounting the upper
part
11 on the lower part 12 and then passing screws 18 through the passages or
screw
channels 15 in the upper part 11 and through into the passages or receiving
channels
16 in the lower part 12.
Optionally a cover 20 may be mounted over the housing 10 as shown in Fig 4.
The
cover 20 may conveniently comprise a section of PVC pipe having a diameter
somewhat greater than that of the housing 10. The space between the housing 10
and the cover 20 can be filled with a material 22 for damping the force of the
blast.
This material 22 might be low density foam.
The foam 22 in the cover 20 acts to reduce the force of the blast reaching the
transmitter 2 as follows. When a shock wave, e.g. from a blast, reaches an
interface
of different materials, the amount of energy that crosses the interface
decreases
proportionately to the difference in density of the two media. The foam 22 has
a
substantially lower density than rock and consequently when the shock wave
moves
into the foam a large amount of energy is dissipated and this energy does not
reach
the transmitter 2.
An apparatus for use with the monitors also includes a detector or receiver
(not
CA 02468576 2004-05-27
18
shown) for detecting the signal from the monitor. In essence the detector is a
hand
held device that has a wire coil for sensing a magnetic field and an amplifier
for
amplifying the detected signal to assist in measuring its strength. The
detector
enables a user to locate the point on the surface of the broken rock beneath
which the
monitor is located. The detector also enables the approximate depth of the
monitor
beneath the surface to be determined.
Figures 10 to 12 illustrate a monitor in accordance with a second embodiment
of the
invention.
The monitor 1 is structurally and functionally very similar to the monitor
illustrated in
Fig 2 to 4. Accordingly unless otherwise indicated the same reference numerals
will
be used to refer to the same components.
The following description will focus on the major differences between this
embodiment
and the earlier embodiment.
The transmitter 2 comprises a coil with a battery mounted within the coil.
This coil has
a more compact shape than the coil of the Fig I embodiment.
The transmitter 2 is snugly received within complementary cut outs in the
casing
halves 4, 5 and the casing 3 is then in turn received within a spherical
chamber
defined in the housing 10.
The casing 3 is received within the chamber with some clearance and the casing
floats in a pool of liquid which is oil 40 within the chamber. As described
above the oil
lubricates the casing relative to the housing and also damps the shock of the
blast.
Fig 14 illustrates a monitor in accordance with a third embodiment of the
invention.
While this monitor is substantially more different from the first embodiment
than the
CA 02468576 2004-05-27
19
second embodiment, it does still have many structural and functional
similarities.
Accordingly the description below is to be read together with that for the Fig
2
embodiment.
Broadly the monitor 100 comprises a casing 111 with a transmitter 109 received
within the casing 111. The casing in turn is in turn housed within a housing
126.
We now discuss each of these components in more detail in turn.
The transmitter 109 comprises a battery pack 102 received within a coil former
and
associated coil 104. A gasket 106 is mounted over an end of the battery pack
102
and the coil 104. A printed circuit board 110 in turn is mounted over the
gasket 106
on the side remote from the coil 104.
In the illustrated embodiment, the gasket 106, printing circuit board 108 and
the coil
former and coil 104 are all assembled together as a separate sub-unit by means
of
fastening elements 107 which are passed through aligned apertures on each of
the
printed circuit boards 110, gasket 106 and coil 104.
The casing 111 has a substantially spherical configuration and is made up of
upper
and lower hemispherical halves 114, 112 that are attached to each other. The
hemispheres 114, 112 while being fairly solid define an interior space within
which the
transmitter subunit 109 is received with some small clearance. The cut-out in
the
upper half 114 is much greater than that in the lower half 112. As a result
more
weight remains in the lower half. This assists the self-righting property of
the casing
111.
The illustrated casing halves 114, 112 are made of polyethylene which is
reasonably
solid and robust and non-conductive without being too heavy. Nylon has also
been
found to be suitable for the casing but clearly many other materials could
also be
CA 02468576 2004-05-27
used.
The casing 111 further includes a sealing O-ring 122 between the upper and
lower
halves 114, 112. In the illustrated embodiment an O-ring of the type BS039
sits in a
5 45 degree chamfer 116 defined in the rim of the lower half 112. This O-ring
has been
found to be very efficacious in performing the function of sealing the two
halves 114,
112 when assembled. This prevents water from entering the casing 111. If this
occurs, the self-righting mechanism will fail. Protecting the electronics is a
secondary
function of the O-ring.
The two halves 114, 112 are connected together by four screws 118 passing
through
complementary passageways 120, 123 in each of the halves much like the Fig 2
embodiment.
The housing 126 comprises a circular cylindrical body having closed ends. As
with
the casing the housing 126 can be opened up into upper and lower halves 130,
128.
Each said half has an internal surface 131 defining a hemispherical chamber
that is
complementary to the casing 111 and within which the casing 111 is received
with a
small amount of clearance.
The housing 126 is solid apart from the hemispherical cut-outs and is of solid
construction. The halves are assembled by four bolts 136 that are passed
through
passageways 138 in the upper half 130 and down into passageways 142 in the
lower
half 128. Further another sealing O-ring 134 of the same general type as that
used
on the casing is positioned between the upper and lower halves 130, 128. The
illustrated housing is made of nylon but clearly other engineering plastics
materials
could be used.
The casing 3 floats in the liquid as described above for the Fig 2 embodiment.
This is
important to facilitate free movement of the casing within the housing. Thus
the space
CA 02468576 2004-05-27
21
between the casing and the internal surface of the housing is virtually
completely full
of water.
The short screw in the centre of the upper housing 130 is a filler plug. Once
everything is assembled 100, liquid which is water is injected through the
said hole
until the internal chamber is completely filled. The screw (un-numbered) is
then
inserted to seal the hole.
When fully assembled with the transmitter 101 within the casing 111 and the
casing
within the housing 126 the monitor 100 forms a neat compact body of solid
construction that is portable.
In use a plurality of monitors 1 are placed in holes in a rock body 30, spaced
apart
from each other and from the explosives.
As shown in Fig 4 each monitor 1 may be placed in a drill hole 32 in the rock
body 30
when the rock body is prepared for blasting. Typically the monitor 1 is packed
and
buried under drill cuttings 34. Optionally the monitor 1 includes a cover 20
of PVC
pipe covering the housing 10. The embodiment illustrated in Fig 4 shows such a
cover.
After the placement of the monitors a blasting operation is carried out which
breaks up
the rock body 30. The blast involves some expansion of the rock body and
inevitably
the rock 30 and the monitors 1 within the rock will be moved from their
original
position. After the blast the casing 3 within the monitor 1 self rights which
causes the
transmitter 2 to orientate its generated magnetic field in an upward
direction.
An operator with a detector (not shown) then moves over the broken rock and
senses
the signal from the transmitter. The location of the blast movement monitor 1
is
identified by finding the point on the surface of maximum magnetic field
strength.
CA 02468576 2004-05-27
22
Applicant has been able to detect the position of the monitor on an imaginary
XY
plane extending across the surface of broken rock with an accuracy of less
than 1
metre. This post blast position is compared with the original position of the
monitor
and thus gives a measure of the movement of the rock due to the blast.
The depth of the monitor 1 can be established by further analysis of the
magnetic field
signals detected by the detector. For example, the strength of the magnetic
field at a
point broadly above the monitor is a function of the depth of the monitor.
Thus by
depth calibration of the monitor using experimental data on the particular
rock an
operator can establish the approximate depth of the monitor in the broken
rock. From
this the amount of vertical or Z axis movement, if any, of the monitor can be
detected.
This is important to build up a three dimensional picture of movement of the
monitor
as a result of the blast. The measure of the depth of the monitor also assists
with
retrieval of the monitor if required. Applicant has been able to determine the
depths of
the monitor with a reasonable degree of accuracy.
The depth of the monitor can also be determined by measuring the angle of the
magnetic field lines sensed by the detector. This utilises the principle that
the angle at
which the magnetic field lines cut the surface of the rock, ie their angle to
the
horizontal, can be used to locate the source of the magnetic field.
In practice an operator locates position the where the detector or receiver
registered a
null signal. The receiver is then moved away from the null point and the field
angle
can be measured. This can then be repeated for other distances. The angles and
distances from the marker can then be used to determine the depth of the
monitor.
The use of the monitors 100 described above on a mine to measure the movement
of
rock due to blasting and thereby compensate for movement in the ore boundaries
will
now be described below.
CA 02468576 2004-05-27
23
A region or batch of a domain of rock to be mined is demarcated. The region is
then
prepared for blasting by inserting explosives into holes in the rock in a
pattern and
with a spacing established by blasting experts. An example of such a pattern
is
illustrated in Fig 15.
In addition a plurality of blast movement monitors are also placed in holes in
the rock.
The monitors are spaced apart from each other and are also spaced apart from
the
blast holes 150. Generally a monitor 1 will be placed about midway between two
adjacent blast holes 150. The location of the monitors 1 is chosen by the
mining
engineer or geologist based on characteristics of the rock body. Generally it
is not
based on a uniform repeating pattern like the explosive holes. The initial
position of
the monitors on the region to be blasted is noted.
Thereafter the blasting is carried out and the rock body is broken up into
pieces of
rock. Overall there is some expansion of the rock body and also considerable
movement of the rock within the body.
The position of the monitors after the blast is then established using the
hand held
detector in the manner described above. The location of the monitors on an
imaginary XY plane is obtained by identifying the point of maximum magnetic
field
strength of the signal transmitted by the monitor. Fig 15 shows schematically
the
movement of monitors in one test result due to the blast.
The movement of monitors varied considerably from location to location. The
movement of any one monitor would depend on factors such as the strength of
the
surrounding rock, the proximity to the explosive, the direction of the blast,
and the
depth of the monitor. These results show that usually one cannot make a
reliable
assumption about the movement of the rock based on one monitor alone.
The depth of the monitor is also ascertained from the magnetic field signal
received
CA 02468576 2004-05-27
24
by the detector. In broad terms the depth of the monitor is a function of the
strength
of the magnetic field signal received by the detector. This depth can
therefore be
determined by depth calibration of the monitors in a particular body of rock.
The movement of the monitors that are seated in the rock is thus
representative of the
movement of the rock in that region of the rock body. It thus enables the
mining
engineers and/or geologists to quantify the extent of the rock movement
throughout
the three dimensional rock body. This information can then be used to adjust
the
three dimensional picture that the miners have of the boundaries between
different
ore grade and waste within the rock body to compensate for the rock movement.
The movement of the monitors for example as shown in Fig 15 is then used to
build
up an adjusted three dimensional map of the boundaries between the different
rock or
ore portions.
This result or picture can then be used to predict the adjustment of rock
movement to
make on similar batches of rock in the same domain. The extent of movement of
the
rock body can be assumed to be the same for other rock bodies particularly in
the
same domain and at the same site. Thus it is envisaged that the placement of
the
blast movement monitors need not be carried out each time a rock body is
blasted.
They will however be done on a regular basis and will provide a good way to
test
and/or validate the movement assumptions of the mining engineers.
However where a completely new body of rock is to be mined or the blasting
configuration is changed, then the method and apparatus described above can be
used to characterise the movement of the rock and to assist engineers to
quantify the
direction and extend of boundary movement that occurs. Similarly if the
performance
of the mining operation drops off then one or more movement tests could be
conducted to see if the movement assumptions of the rock that are being
utilised are
correct.
CA 02468576 2004-05-27
This will then lead to improved reporting of ore to the concentrator and waste
rock to
the dump.
5 Open cast coal mining comprises progressively mining a seam of coal
positioned
underneath a layer of overburden in sections or stages. The stages are mined
progressively from one end of the seam to the other. Consequently when a stage
is
mined one side of the coal is open forming a coal edge and the other is closed
off by
the contiguous section of coal which is as yet unmined.
Each stage is mined by blasting the overburden by means of a controlled blast
with
explosives. The blast blows or moves the overburden into the open pit adjacent
the
coal edge. The displacement of the overburden into the open pit adjacent the
coal
edge exposes the coal section and thereby enables it to be physically
recovered from
the mine and sent for beneficiation.
The blast also causes movement of the coal body towards the coal edge. This is
the
side that has the space to permit expansion as a result of the blast. The
movement of
the coal edge needs to be measured or quantified so that it can be removed
with the
rest of the coal. Otherwise it is at risk of being left in the pit adjacent
the coal seam.
This will lead to a loss of product and will thus be undesirable.
The blast movement monitor as described above with reference to Fig 14 can be
used
to measure or quantify the movement of the coal edge. The monitors would be
placed in holes in the coal proximate to the coal edge. After blasting the
post blast
position of the blast movement monitors will be measured using the detector as
described above and then the extent of movement of the coal edge into the pit
could
be ascertained. This provides mining engineers with the information to
substantially
recover all the coal from that section as coal product.
CA 02468576 2004-05-27
26
EXPERIMENTAL WORK
The movement monitors described above have been trialled on mining sites to
confirm their efficacy and also to measure their reliability.
FIRST FIELD TRIAL
A field trial was carried out using the monitor shown in Fig 2. The objective
was to
test the suitability of the transmitter and receiver for performing their
intended
function. All measurements were conducted prior to blasting. The transmitter
was
lowered into an empty blast hole to a depth of 2 m and the receiver or
detector
response was noted.
Specifically, the strength of the signal was measured by the detector along
two
perpendicular scan lines on the surface of the rock. That is the strength of
the field
was measured along two orthogonal lines in an imaginary XY horizontal plane.
The trial was repeated with the monitor at respectively 4 m and 6 m below the
surface.
These results are graphically depicted in Figs 6 to 8. The results show that
the
method is reasonably reliable in accurately locating the surface position of
the
markers. It also shows that the method is accurate up to a depth of up to at
least 6 m.
Fig 9 illustrates the field strength sensed by the detector or receiver as a
function of
the depth of the receiver below the surface of the rock. This graph shows that
there is
a significant drop off in field strength from 1 m to 4 m below the surface.
Thereafter
the rate of drop off with further depth decreases significantly. This result
shows that
the strength of the signal can be used to measure the depth of the monitor.
CA 02468576 2004-05-27
27
SECOND FIELD TRIAL
A second field trial was conducted to assess the ability of the monitor
illustrated in
Figs 10 to 12 to withstand field conditions. Specifically the Applicant wanted
to be
satisfied that the transmitter and its associated electronic circuitry would
be able to
withstand the forces generated by the blast.
Two monitors were placed in drill holes during a normal blasting operation at
a
commercial mine. Blast movement monitors of the type shown in Fig 2 were
fitted with
a cover as shown in Fig 4. The monitors were positioned about midway between
their
two closest blast holes. The distance between each marker and its nearest
blast hole
was 5 metres. The markers were placed at a depth of 4 and 5 metres. This depth
approximated the depth of the top of the explosive in the nearest blast hole.
The rock body was then blasted in the usual way to break up the rock body into
pieces of rock in the usual way.
The location of the monitors was then determined in the following way. The
detector
was used to measure the strength of the magnetic field signal on a grid
centred on the
approximate location of the monitors. The detected signal was measured in 1
metre
increments on a 7 metre grid or matrix. Thus for each marker there were 49
readings.
The results of these field strength readings are graphically illustrated in
Fig 13. It
provides a representation of the field strength over the matrix and clearly
shows the
location of the two markers after the blast.
Further, the monitors were retrieved from the rock to see if they had been
damaged
by the blast. Generally the monitors had stood up to the blast conditions well
and
were still working satisfactorily.
CA 02468576 2004-05-27
28
THIRD FIELD TRIAL
A third field trial was conducted at the Placer (Granny Smith) Wallaby open
pit. This
measured the movement of blast movement monitors for a total of 12 blasts. The
rock mass for all blasts was very hard with widely spaced joints. The mine
environment on which the testing was done was that a 10 m high bench was being
mined in two 5 m high slices or flitches, namely a top flitch and bottom
flitch. Table 1
summarises each of the blasts.
The initiation timing was the same for all blasts. The monitors used in this
trial were
those illustrated in Fig 14. The monitors were placed directly into the drill
hole without
a cover.
By comparing the post blast position with the pre blast position the movement
of the
rock associated with each monitor could be measured. This very quickly showed
that
the blast caused very substantial movement in the rock.
Table I - Summary of all Blasts
Date Blast # Powder Description of Blast Initiation
Factor*
(kg/M3)
02-Jul-03 280-40 1.17 Edge blast, reverse echelon
02-Jul-03 280-41 1.17 "V" Initiated, partial free face at front
22-Aug-03 270-41 Removing Stage 1 ramp
25-Aug-03 265-05 1.50 Ramp, Drop cut
28-Aug-03 260-25 1.17 Centre lift, long narrow pattern
31-Au -03 260-27 1.17 Edge blast, reverse echelon
02-Sep-03 260-28 1.17 Edge blast, reverse echelon
06-Sep-03 260-30 1.17 'V' Initiated, choked
09-Sep-03 260-31 1.17 'V' Initiated, choked
11-Se -03 260-32 1.17 'V' Initiated, choked
15-Sep-03 260-33 1.17 Double initiated, 2 x reverse echelons
19-Sep-03 260-35 1.17 'V' Initiated, (partial choked
* mass of explosive per cubic metre of rock
CA 02468576 2004-05-27
29
The total number of Blast Movement Monitors (BMMs) installed in the 12 blasts
was
81. The location of 68 of these monitors was detected after the blast by
operators.
Table 2 summarises the ability of the blast movement monitors to survive the
blast
conditions. There was a greater loss of monitors from the bottom flitch. It is
suspected that most of the monitors that were lost ended up too deep to be
detected.
The maximum depth at which a monitor was detected was 9.5 m and it does appear
that some of the monitors may have ended up deeper than this.
Table 2 - Summary of BMM Detection
Bottom
Top Flitch Flitch Total
Number 51 30 81
Detected 46 22 68
Percent 90% 73% 84%
The average horizontal movement of monitors in the bottom flitch was 9.3 m
which
was approximately twice as great as movement of monitors in the top flitch
which was
about 4.7 m. The maximum distance by which a monitor was moved was 15.4 m.
This observation can be explained by the fact that most of the explosive
charge is
within the bottom flitch and the energy of the explosive reduces very rapidly
with
increasing distance from the explosive. Thus its influence on the surrounding
rock
mass also reduces very rapidly with distance.
Figure 16 is a histogram of horizontal movement from all tests separated by
top and
bottom flitch.
CA 02468576 2004-05-27
The multi-modal nature of the histograms is caused by different regions in the
blast -
e.g. front, back, edge and body - behaving slightly differently.
5 Figure 17 is a graph of horizontal movement plotted against the initial
depth of the
BMM. Although there is quite a lot of scatter in this data, there is clearly a
direct
relationship, with movement increasing with depth. The horizontal direction of
the
movement is typically perpendicular to the blast initiation timing contours.
10 In these tests the apparatus performed most satisfactorily. In general
Applicant found
that the monitors were able to withstand the blasting without suffering
damage.
Specifically the self aligning mechanism proved to be effective at directing
the signal
upwardly and the transmitters were generally not rendered inoperative by the
blast.
Further Applicant was often able to locate the position of the monitors with
an
15 accuracy of less than 1 metre.
An advantage of the method described above with reference to the drawings is
that it
can be used to accurately identify the movement of a monitor as a result of
blasting
and thereby the movement of rock around the monitor. The results can be
available
20 within 1-2 hours of the blast. The technique that it uses of transmitting a
magnetic
field signal from the monitor and then locating the monitor on the basis of
the strength
of magnetic field has been proved to give accurate and reliable results.
Further the
self righting feature of the monitor ensures that the transmitter will always
transmit its
signal vertically upwardly where it will be able to be detected.
A further advantage is that the components of the monitor are not unduly
complex.
The casing and the housing are fairly simple pieces of hardware. Similarly the
transmitter works on fairly simple principles and is assembled from off the
shelf
equipment. Further as a result of the simplicity of the monitors and the
components
they contain, the monitors are not unduly expensive to make and use.
CA 02468576 2004-05-27
31
It will of course be realised that the above has been given only by way of
illustrative
example of the invention and that all such modifications and variations
thereto as
would be apparent to persons skilled in the art are deemed to fall within the
broad
scope and ambit of the invention as is herein set forth.
