Note: Descriptions are shown in the official language in which they were submitted.
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Method of the Shortest Inter-Hole Delay Blast and
the Blasting and Delaying Means
Field of the invention
The present invention relates to a method of blasting, and is particularly
concerned
with the initiation of the blastholes with the shortest inter-hole delay time.
The invention
further relates to the means for blasting and delaying.
Background of the Invention
In the conventional methods of the rock blasting the blastholes are drilled
into the
rock to be blasted. The blastholes are at least partially charged with the
explosives,
and one or more initiation means are associated with the each explosive
charge.
Initiation signals are transmitted to one or more initiation means in the
blastholes at the
blast site to cause the fragmentation.
Up to now various methods of the blasting has been developed, however, the
venting of the explosion gas and the production of excessive sound are
considered as
unavoidable companion of the blasting. Such phenomena clearly imply the loss
of the ,
energy of the explosive charged in each of the blastholes, applying much
horror and
shocks to the surroundings.
The efficiency of blasting can be measured by the degree of the rock
fragmentation.
The delay blasting method which is delayed at a certain intervals in blasting
at the
open bench pit have the several advantages of enhancing the fragmentation
quality of
the rock, producing less vibration destruction to the structures and improving
the
efficiency of the blasting.
The inter-row delay blasting method is widely used in the art, and the inter-
hole
delay blasting is still under study stage and many experiments and studies are
being
made to obtain reasonable inter-hole delay time.
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The most important factor is the decision of the reasonable inter-hole delay
along a
row in the open bench blasts, which will effect the combination of
stressfields
propagating from each of the blastholes.
It is important to define the inter-row and inter-hole detonation delay time
that
ensures the maximum quality of the fragmentation and to provide the delaying
device
as well as the blasting means that ensure the precise delay time.
Numerous blasting methods are known in the art that describe the arrangement
of
the explosive charges and the control of the detonation delay time which
attempts to
optimize the rock fragmentation without the need for excessive amount of the
explosive
material.
In one example, United States Patent US 3,903,79 issued Sep. 5, 1975,
discloses
a method of the blasting, wherein the fissure production occurs within 0 to 10
milliseconds of the blast initiation, the crack propagation proceeds from
approximately
10 to 60 milliseconds after the detonation, and the venting and subsequent
rock
removal starts after approximately 100 milliseconds following the detonation.
A plurality of the charges are arranged in spaced apart rows with the
detonations
within a row being detonated with the time delays of 10 milliseconds or more
and with
the detonations between the successive rows being detonated with time delays
of from
to 150 milliseconds.
20 The
Document WO 2005/124272 of the ORICA group published on Dec. 29, 2005
provided a blasting method, wherein the detonations between adjacent
blastholes
within a group of 2-7 holes were actuated with the time delay of below 5ms to
cause
the collision of the stressfields, as a result of which the fragmentation
quality of the rock
was improved with the attenuation of the blast vibration.
25
Blasting engineering hand book, kyorits-pub.co.jp, 2001.8.1.printed in Japan
also
suggests that the detonation time delay along the row that assures the
efficient quality
of the fragmentation can be decided by the following formula (1).
t=kxw (1)
k: Experiment Factor. ms/m , w: Minimum Burden
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k= 3-5(Langefors, 1967), 5-8(Gustafsson, 1981), 3.3-10(Stagg, 1987)
U. Langefors presented that the time delay is preferably 3-5ms per metre of
the
minimum burden, and when the time delay is calculated by the formula (1), if W
is
within the range of 3-12m, the delay time is within the range of 9ms-60ms.
The suitable detonation time delay is presented by R. Gustafsson as 5-8ms/m in
which if minimum burden is 3-12m, the delay time is 15ms-9ms.
M. S. Stagg and S. A. Rholl described that the suitable time delay is defined
as
3.3-10ms per metre of the minimum burden wherein if the minimum burden is 3-
12m,
the delay time is 9.9ms-120ms.
As the time delay along the rows is 9ms-120ms and the time delay between the
rows
is 25ms -120ms, the ranges of the above time delays are similar with each
other.
A surface connector disclosed in "Non-Electric Initiation System User's
Guide"(Austin, January 2014) provides the time delays of 9ms, 17ms, 25ms,
33ms,
42ms, 67ms, 100ms and 200ms.
Orica published on its online about their non-electric surface connector with
the -
time delays of 9ms, 17ms, 25ms, 42ms, 65ms, 100ms, 150ms and 200ms and
presented the open pit blasting method using the electronic detonator and
digital
blasting system that emits a large amount of the explosion gas.
Dyno Nobel introduced surface connector providing time delays of 9 ms, 17 ms,
25
ms, 42 ms, 67ms in 2014.
The surface connectors for the blasting at the open pits and underground mines
which provide the delay time of 9ms, 17ms, 25ms, 33ms, 42ms, 50ms, 67ms, 72ms,
100ms, 150ms, 200ms and 250ms have been developed in US and many other
countries. However, as these connectors which belong to the NONEL non-electric
initiating system offer unidirectional initiation, the reliability of the
initiation is low. In
order to enhance the reliability of the connectors for the blast circuits,
documents such
as WO 2008/039484, Dyno Nobel, April 3, 2008 and WO 2010/046596, Davey
Bikford,
April 29, 2010, and so on, has been published for over 40 years. Yet, the
inventors of
the present invention clearly stated in their document WO 20008/,146954,
December 4,
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2008, that the reliability of those unidirectional systems could never reach
that, of
bidirectional system.
The US patent application US 7406918, Aug. 5, 2008 published a blasting method
including the arrangement of the blastholes and the precise control of the
time delay of
the electronic detonators, wherein rockpile displacement in a desired
direction is
increased by the use of inter-hole detonation delays along rows of blastholes,
the rows
being generally perpendicular to the desired direction of displacement, of up
to 4 ms
per meter of hole separation in such rows.
Specific blast geometries to enhance the rockpile displacement in a particular
direction include the use of an optimized blasthole pattern which is
preferably
staggered the pattern such that the ratio of the inter-hole spacing (a) along,
the rows of
the blastholes (where the rows are taken to be perpendicular to the direction
of the
required displacement) to the perpendicular distance (w) between the rows is
in the
range 1:2 to 3:2 and preferably in the range of 7:10 to 6:5. Most preferably
the ratio is
in the range7:10 to 1:1.
Increase and decrease of the required rockpile displacement is achieved by the
manipulation of the blast geometry and the delay between the blastholes.
Document WO 2011/127540 , ORICA, Nov. 20, 2011, disclosed a high energy
blast, wherein the nominal inter-row delay times of the bastholes are 150
milliseconds,
with an inter-hole delay along the rows of 10 ms in Row 1, 5 ms in Rows 2-6,
15 ms in
Row 7 and 25 ms in Row 8.
It demonstrates objectively that at the open bench pits the energy expended to
the
rock can be possibly controlled by the arrangement of the blastholes and
especially by
the regulation of the initiation time delay between the blastholes along the
row.
Although the significant advances have been made in the blasting methods over
recent years, there still remains the continued need to develop the improved
methods
of the blasting that provide the efficient rock fragmentation without the need
for
excessive quantities of the explosive materials.
Moreover, there remains the demand for the methods of blasting where the rock
fragmentation quality can be improved without the excessive impact upon the
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surrounding environment, for example, through a large quantity of the gushed
gas, the
loud explosion and the excessive ground vibrations.
Object of the Invention
The inventors of the present invention paid great attention to the prevention
of the
enormous economic loss due to the use of the millisecond delay detonators for
providing the inter-hole delay times of the detonation and the environmental
impact by
the venting of the explosion gas and the production of excessive sound, and
disclosed
the present invention.
It is an object of the present invention to provide a method of blasting the
rock that
prevents the explosive energy released to the venting of explosion gas and the
production of excessive sound.
It is another object of the present invention to provide a method of blasting
the rock
that results in the improved rock fragmentation by firing the explosive
charges with the
inter-hole delay time with which the maximum energy is exerted on the rock and
the
fatigue breakdown is formed.
It is also another object of the present invention to provide a blasting and
delaying
mean which ensures the precise inter-hole delay time at a lowest cost.
Description of the Invention.
- 1) A method of the shortest inter-hole delay blast at the open bench
pits
The present invention relates to a method of blasting the rock offering
considerably
improved rock fragmentation with little explosion gas and sound, which is
based on the
practical experiences of more than 50 years and already manifested its
efficiency for
over 20 years at the open bench pits, the method comprising of;
- drilling 2 or more rows of the blastholes in the rock, wherein a row
consists of
from 2 to 25 or more blastholes, each of the blastholes along and between the
rows is adjacent to another blasthole;
' - loading each of the blastholes with an explosive charge;
- connecting each of the explosive charges with blast initiation means;
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- firing the explosive charges via the connected blast initiation means in
such a
way that each explosive charge detonates with the shortest inter-hole delay,
thereby detonating a blasthole within the stressfield pre-propagated from the
preceding adjacent blasthole.
Many attempts have been made to prevent the explosive energy released to the
venting of explosion gas and the production of excessive sound, which only
delayed
) the venting of explosion gas, but failed to prevent it completely.
Inventors, while performing the various blast trials, came to a conclusion
that even
the high resistant stemming materials (such as fast-setting concrete),
stemming closed
charges and deck loadings could not prevent explosion gas, and through the
long
terms of research, found out that the appropriate inter-hole delay time could
solve this
problem.
For this reason, the inventors believed that the venting of explosion gas is
concerned with the collision of stress waves propagating from each of the
blastholes.
For example, if the stress waves propagating from two neighbouring blastholes
collide
with each other at a line where two blastholes join and thereby causing stress
concentration, then fissure is produced within the said line prior to the
production of
fissures in the other parts. High pressure gas within the blastholes enlarges
the
fissures and finally escapes into the atmosphere prior to the displacement of
the rock to
be blasted.
Inventors took and analyzed the photographs of the open bench pit blasting
using
the detonating fuse as a blast mean, and confirmed that the venting of
explosion gas
occurred immediately following the detonation.
'
Considering characteristics of the detonating fuse and the rock, and factors
of the
blasting at open pits, successive creation of the stress waves from each of
the
blastholes results in successive combination (colliding).
At the open pit blast where the ratio of inter-hole Spacing along the rows of
the
blastholes to the perpendicular distance between the rows at first and second
rows are
1:2 and 1:1(m=a/w=0.5 and 1) respectively and the inter-hole spacings(a) are 5-
7m
(the diameter of the blastholes is 265mm), stress waves propagated from the
6
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blastholes are intensive and the blasting takes place with the successive
combination
(colliding) of the stress waves.
The arrangement of the blastholes increases the combination (collision) of the
stress waves, e.g., 2 stressfields propagating from the first and the second
blastholes
combine (collide) around the spot 0.5m near the wall of the second blasthole,
and 3
stressfields propagating from the second and the third blastholes around the
spot 0.5m,
lm, respectively, near the wall of the third blasthole._
Supposing that a row consists of the number of n holes, the successive
combination (collision) of the incident stresses numbering n - 1 and the
reflected
stresses numbering n - 5 will result in the localized stress concentration,
and at the
same time the fatigue breakdown will be accompanied.
Usually, the application of the fatigue breakdown to a material decreases the
strength of the material by 1/2 - 1/5. The concentration of the fatigue
breakdown and
the production of the fissures near the walls of the blastholes are more
severe than any
part, by which the explosion gas starts escaping from the blastholes
immediately
following the initiation of the detonating fuse, where the explosion gas is
vented to the
height of as high as 25m-35m.
For this reason, the collision of the stress waves should be prevented to
avoid the
venting of explosion gas.
Since the collision of the stress waves occurs while the stress waves from 2
blastholes meet with each other, the collision could be prevented by
detonating a
blasthole after the stress wave pre-propagated from the adjacent blasthole
passes
=
through.
In order to completely prevent the explosive energy released to the explosion
gas
and the excessive sound in blasts geometries where the ratio of inter-hole
spacing
along the rows of the blastholes to the perpendicular distance between the
rows is in
the range of 1:2 - 6:5 (m=a/w=0.5-1.2,) the shortest inter-hole delay should
be applied
to provide the optimized fragmentation.
The shortest inter-hole delay time chosen may depend Upon the factors such as
the rock type and the condition, and the blast geometry.
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In a preferred embodiment, for most rock types, the shortest inter-hole delay
time
per metre of the inter-hole spacing ranges from 0.182ms to 0.334ms, within
which
range it is possible to exert maximum energy to the fragmentation of the rock
and avoid
explosive energy released to the production of excessive explosion gas and
sound.
If the inter-hole spacing ranges from 0.5m to 7m, the shortest inter-hole
delay
times range from 0.1ms to 2.5ms.
The inter-hole delay time from Oms to 0.181ms - 0.333 ms per metre of the
inter- ,
hole spacing causes the environmental impact such as the venting of explosion
gas
and production of excessive sound, wherein even the use of the plugged-in, the
deck
loading and the stemming closed charges only provides the delays of a few or a
few
decades of milliseconds.
Use of a highly precise delay system, such as the non-electric PULKKOT firing
system or an electronic initiation system, allows these delays to be
controlled to within
a tolerance of less than 0.1 millisecond.
A further aspect of the invention for the regions where the fragmentation of
the
rock is to be enhanced is to use 1-3 or above high precision detonators within
each
blasthole with a delay of 1.5ms or less, preferably zero, between them.
According to the invention, upper part of a column of the explosive charges
may
have the booster or the detonators, which, too, allows little explosive energy
released
to the venting of explosion gas and sound.
Preferably one of these initiators is located close to the bottom or upper
column of
the blasthole and the others are located further up the explosive column at
the regular
intervals.
Additionally, it has been found that the fragmentation and the rockpile
displacement is enhanced by the use of the selected ratio of the inter-row
delay to the
inter-hole delay. Typically, the ratio will be in excess of 6:1 and
preferably, in excess of
-30:1.
Depending on the rock type and the blasthole geometry, the inter-row delay
time
trow is;
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LA, =25ms-65ms, when considering the maximum improvement of the
fragmentation of the rock and the displacement of the rockpile, but
trow =65ms-300ms, when considering the minimum displacement of the rockpile.
The inter-hole delay is usually constant along each row, however, it may be
varied.
The inter -row delay per metre of the rockpile burden may be kept constant or
varied from row to row depending on the quality of the fragmentation.
The position of the initiation detonators within the blastholes and ,the delay
between the in-hole boosters within the blastholes may also vary throughout
the blast,
according to the fragmentation required.
If the inter-hole delay time is (0.182-0.334)ms/m x a m, it is possible to
avoid the.
collision of stressfields propagating from each blastholes and provide the
propagation
of new stressfield within pre-propagated stressfield. For example, the
stressfield
propagated after the detonation of the first blasthole passes through the
second
blasthole,. after which the second blasthole is initiated, thereby propagating
the
stressfield from the second blasthole within the stressfield from the first
blasthole.
The stressfield propagated from the second blasthole passes through the third
blasthole, after:which the third blasthole is initiated, thereby propagating
the incident
stressfield from the third blasthole within the stressfields from the first
and the second
blastholes.
Likewise, the incident stressfield from the n-th blasthole will be propagated
within
the number of n-1 incident and reflected stressfields.
By avoiding the collision of the stressfields as described above, the venting
of the
explosion gas and the production of the excessive sound and also the
concentration of
the stress could be prevented, through which the explosive energy could be
distributed
more evenly on the rock to improve the fragmentation.
In addition, the production of new stressfield within a pre-propagated
stressfield
has influence upon the hardness of the rock.
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Mechanically, if a material carries the load or the repeated load which
changes
with the time, the strength of the material decreases rapidly (about 2-5 times
lower) to
be destroyed severely.
The successive propagation of the stressfield within the ,pre-propagated
stressfields of various dimensions results in the rapid decrease of the
hardness of the
rock, thereby improving the fragmentation with the application of the same
explosive
energy.
The propagation of a stressfield within the pre-propagated stressfields
provides the
advantages of:
= preventing the collision of the stress waves, thereby avoiding the venting
of
the explosion gas and the production of excessive sound
= preventing the concentration of the stresses, thereby providing even
distribution of explosive energy throughout the rock to be blasted,
= decreasing hardness of the rock by successively exerting the variable
dynamic
loads, thereby improving the fragmentation,
= maximizing the effect of tensile stress, the breaking force of which is
more
powerful than that of the pressure stress, thereby improving the
fragmentation.
=
=
Inventors confirmed through the blasting practice of over 20 years at the open
bench pits that the shortest delay time 0.182-0.334ms/m described above
provides the
blasting with little venting of explosion gas and sound.
As described above the inter-hole delay blast provides the improved
fragmentation
of the rock.
A point 0 within the minimum burden of the open pit is influenced by the
successively overlapping stresses propagating from the neighbouring
blastholes.
Subject to the constancy of the blast condition (such as the charge weight,
the
height of the column of the explosive, the blasthole pattern, the blasthole
geometry, the
burden, the inter-hole spacing, the height of the stemming), better
fragmentation of the
rock could be provided as the number of the stressfields which influence on
the point 0
increases.
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g
The intensity of the relative stress ( 80 ) of the second blasthole along a
row is
67% and that of the 9th blasthole along the row is 3.1%. Above percentages
show that
the remoter the blasthole is positioned from the point 0, ,the weaker the
intensity of
stress which influences the point 0 becomes.
Moreover, the shorter the inter-hole delay times along the row are, the more
the
number of the stressfields which influence on the point 0 are, thereby
increasing the
intensity of the combined stressfields. For example, 1.5 ms of the inter-hole
delay will
have 7 stressfields stressing the point 0, 5 ms delay 3 stressfields, and 17
ms delay 1
stressfield, hence the efficiency of the explosive energy of 5 ms delay is
over 1.5 times
greater than that of 17 ms delay and the efficiency of the explosive energy of
1.5 ms
delay is over 2 times greater than that of 17 ms delay.
It is important to provide even distribution of the explosive energy
throughout the
rock to achieve better fragmentation using the same amount of the explosive
charge.
Generally it is easier to crack the rock with the tensile stress although the
intensity
of which is 1/10-1/15 of that of the pressure stress. Therefore, when the
ratio of the
inter-hole spacing along the rows of the blastholes to the perpendicular
distance
between the rows is 1:1 (m= a/w= 1), the range of the inter-hole delay per
meter of the
burden or the hole spacing is 0.43ms-0.8ms in most rock types.
The reflected stressfield formed by the reflection at a free face propagates
to and
reaches the second blasthole within (0.43-0.8) ms/m x a m, within which 100%
of the
fragmentation areas corresponding to the first and the second blastholes lie
inside the
incident and reflected stressfields propagating from the first blasthole.
Therefore, the intensity of the reflected stressfield, although it is weaker
than that
of the incident stressfield, exercises greater influence.
Efficiency of the reflected stressfield on the improvement of the
fragmentation
could also be proved through the wide hole-spacing blasts.
Inventors examined the propagating procedure of the stress waves in the wide
hole-spacing blasts, and concluded that when the ratio of the inter-hole
spacing along
the rows of the blastholes to the perpendicular distance between the rows
increases
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from 1:1 to 4:1, the propagating area of the incident and reflected stresses
increases
only within the fragmentation area per the blasthole, thereby improving the
fragmentation.
Trials carried out by U. Langefors proved better fragmentation in the wide
hole-
spacing blasts. This shows that the reflected stressfield allows the enhanced
fragmentation of the rock.
The maximum inter-hole delay may be limited to the time before the
displacement
of the rocks after the production of fissures.
If the size of the fissures within the cracked rock is more than 10mm, then
these
fissures can be considered as a free face, in which case, it is in fact
impossible to
propagate the stress waves within the rock.
Referring to the result of the high-speed shooting (quarry mangement 1992.3
25-27p) and other information which disclosed that at the open pits each of
17ms,
33ms, 50ms after the detonation of the first blasthole resulted in the
displacement of
45%, 70%, 90% of the rock, respectively, inventors limited the maximum delay
time to
17ms.
Hence, the inter-hole delay time which allows the best fragmentation for most
rock
types and provides little venting of explosion gas and sound is;
t=(0.182 -0.334), (0.43-0.80) ms/m x a m
2) The Blasting and Delaying Means
Many inventors proposed their opinions that the inter-hole delay blast may -
enhance the fragmentation .of the rock, but such blasting method has not been
widely
used mainly due to the absence of the practical and cost-effective blasting
and
delaying means that can provide the precise delay time and the highly reliable
blast
circuit.
Since the unidirectional non-electric initiation systems such as NONEL, EXEL,
SHOCK *STAR and SINB systems using the delay detonators with the inter-hole
delay
of 9n,is, 17ms, 25ms, 42ms and 67ms provide the lower reliability than the
bidirectional
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Detonating Fuse initiation system, the former is not widely used as the latter
at the
open pit blasts.
The inter-hole delay may be provided by the electronic initiation system,
wherein
the system is programmable so as to control the precise delay times. However,
the
production cost of such electronic system is more than 5 times expensive, and,
besides,
the system is liable to be effected by external interferences such as the
electric or
electro-magnetic field.
Inventors, on the basis of their practical experiences of over 50 years,
conceived a
simple idea that the above problems may be solved with the length of the shock
tubes
in the bidirectional initiation systems, more preferably in non-electric
Pulkkot parallel
initiation system, by which system the shock tubes are allowed to offer the
bidirectional
transmission of the initiation signals as the detonating fuses do.
The detonating fuses have the detonating velocity of 6000 - 6500m/s which is
1.2
- 2 times faster than the propagating velocity of the longitudinal stress
waves (3000 -
5500m/s) inside the rock, therefore, it is impossible to avoid the venting of
the
explosion gas produced by the collision of the stress waves propagating from
the
blastholes without the help of the delay detonators, and besides, the
production cost is
over 2 times expensive.
The shock tube, since its detonating velocity is 1600-2000m/s and the
deviation
rate is 1.09%, could be used as a means for both blast and delay that can
allow the
propagation of a stressfield within another stressfield in most rock types.
Depending on the detonating velocity (D) of the shock tubes, delay times ((t
per meter of the shock tube are;
D=1631 17.7m/s, t
.delay = 0.613 0.0063ms/m;
D =2000 21.7m/s, t
-delay = 0.50 0.0051ms/m.
In blasts at the tunnels and mines, the preferred range of the delay time per
0.5m
of the inter-hole spacing is from 0.1ms to 0.4ms.
The delay time provided by 0.5 meter of the shock tube is 0.25-0.30ms.
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Since the length of the shock tube ranges from 2m ¨ 7.5m when the inter-hole
spacing in blasts at the open pits ranges from 2m to 7.5m, the inter-hole
delay time
ranges from 1.0ms to 4.5ms.
As seen above, the shock tube, which transmits the initiation signals from
hole to
hole provides the most precise delay time with its length, the deviation of
which is not
exceeding 0.0063ms.
The deviation of the delay time of the electronic detonator is below 0.1ms.
In order to enhance the reliability of the blast circuit, 7 to 20 blastholes
along a row
may have a bidirectional inter-row delay connector (as illustrated in figures
below). The
said bidirectional inter-row delay connectors provide contra-directional and
instantaneous operations, thereby allowing the initiation signals be
transmitted from the
back row to the front row if, at the open pit blast, the front circuit is cut
off, wherein the
inter-row delay connectors are arranged in such a manner that the last
initiation signal
reaches the last blasthole of the front row within or not exceeding 100ms.
The Inventors, availing above principles, disclosed in their document WO
2008/146954 (Dec. 4, 2008) new, initiating system (non-electric Pulkkot
parallel
initiating system) with the multi-ringed circuit comprising the
parallel(bidirectional)
connector without a detonator and the shock tube, the system having been
utilized at
the open pits for the mass mining since 1995. The production cost of the
system is only
75% of that of the unidirectional NONEL or EXEL systems and the reliability of
the
open blast circuit is advantageous over that of the electronic system. The
shortest
inter-hole delay blast method which used the non-electric Pulkkot parallel
initiating
system has already been introduced to large-scale open blasts in many mines,
and
produced over 1.5 billion tons of ore and rock.
The present invention offers the effective use of the length of the shock tube
which
was given less importance in the conventional non-electric initiating systems
(such as
NONEL, EXEL, SHOCK*STAR, SINB) controlling the inter-hole delay with the delay
detonators. 0.1ms¨ 4.5ms, the shortest inter-hole delay time provided with the
length of
the shock tube produces 'little explosion gas and sound, thereby exerting 1.5
times
greater energy when compared with the method using the delay detonators with
the
inter-hole delays of 9ms, 17ms, 25ms, 42ms and 67ms to remarkably improve the
fragmentation.
14
CA 02962230 2017-03-22
WO 2016/047812
PCT/KP2015/000035
Description of the drawings
Fig.1 shows the shortest inter-hole delay blast circuit at the open pits with
the inter-
hole delay time 2.5ms and inter-row delay time 45ms.
Figs.Z shows the fragmenting procedure of the rock at the open-bench pit that
is
blasted with the shortest inter-hole delay time.
Fig. 3 shows the shortest inter-hole delay blast circuit underneath the
tunnels with
the inter-hole delay time 0.1ms and inter-row delay time 25ms.
Fig. 4 shows the-shortest inter-hole delay blast circuit at the open and
underground
mines with the inter-hole delay time 1ms and inter-row delay time 30ms.
Fig. 5 shows the shortest inter-hole delay blast circuit at the open pits with
the
inter-hole delay time 2ms and inter-row delay time 45ms.
Fig. 6 shows the shortest inter-hole delay blast circuit at the open pits with
the
inter-hole delay time 3ms and inter-row delay time 45ms.
Fig. 7 shows the shortest inter-hole delay blast circuit at the open pits with
the
inter-hole delay time 3.5ms and inter-row delay time 45ms.
List of the reference numerals:
1 the bidirectional shock tube
2 the bidirectional inter-row delay connector
3 the parallel connector
4 the delay time in milliseconds
=
