stemming material and inter-row delay timing effect on
TRANSCRIPT
Stemming material and Inter-row delay timing effect on blast resultsin limestone mines
BHANWAR SINGH CHOUDHARY, ANURAG AGRAWAL* and RAJESH ARORA
Department of Mining Engineering, Indian Institute of Technology (Indian School of Mines), Dhanbad 826004,
India
e-mail: [email protected]; [email protected]; [email protected]
MS received 7 August 2019; revised 28 August 2020; accepted 11 December 2020
Abstract. Safe and efficient blasting is the prime objective of any blasting engineer. The safe and efficient is
generally called when there are no fly rocks, less ground vibration and optimum fragmentation with loose
muckpile. This study describes the use of stemming material and inter-row delay timing effect to improve the
efficiency of the blast and its results. From the study, it was found that the use of aggregates or screened drill
cuttings having a size of 3-7 mm helps in reducing the collar generated boulders as well as increasing the
looseness of the muckpile. Change in delay timing between rows also determined that the mean fragment sizes
are fair and uniform, muckpile parameters were improved when the delay between first and second row was 8-14
ms/m of burden and the delay gap between last two rows was 5 ms/m of the burden.
Keywords. Blast; quarry; stemming material; delay timing; muckpile shape parameters.
1. Introduction
The Stemming of blasthole collars in surface mines with
an inert material redirects blasting energy to the rock
more efficiently. The stemming length is a function of
many variables, such as stemming material, plug,
explosive, etc. Excessive stemming causes increase in
stiffness accompanied by excessive confinement and
resulting in the excessive boulders in the blasted muck-
pile, in the collar zone [1] and [2]. Zhu et al [3] found
that the robust confinement of stemming material can
intensify the extent of rock damage and enhance blast
efficiency. Jimeno et al [4] and Konya [5] found that the
use of coarse angular material for stemming in compar-
ison to the fine powdered drill cuttings offer increased
resistance to the premature ejection of blast hole pressure
due to the interlocking properties. According to Dobri-
lovi’c et al [6], stemming material consisting of broken
limestone that the ?16–32 mm fraction is the best-suited
material. Choudhary and Arora [7] found that the use of
aggregates (10-12 mm size) and screened drill cuttings
(3-7 mm sizes) as stemming material reduced the frag-
mentation sizes in collar region compared to the drill
cuttings. Chung and Mustoe [8] and Cevizci [2] advo-
cated the use of plaster stemming for better
fragmentation.
Besides stemming material, the proper delay time is also
an essential parameter for improved fragmentation results.
It exerts a significant control on ground vibration, air blasts,
fly rocks, back break, end break related problems [9–13].
Selection of delay between rows is essential for the effec-
tive blast results in the large-scale blast [14]. According to
Chiapetta and Postupack [15], a proper burden is very
crucial to maintain the momentum for inter-row displace-
ment. Yang and Rai [16] advocated that the instances of
short inter-row delay timing, the burden from front row
remains in place before the charges from the second row
are fired resulting in improper relief and excessive con-
finement to the consecutive rows. This causes upward
cratering (vertical uplift) that results in poor fragmentation
(with little heave) and tight muck piles close to the face. On
the contrary, if the delay time between the rows is too large,
the material of the first row fails to act as a screen and thus
does not confine the remainder of the blasts, which results
in unwarranted lateral scattering, poor fragmentation, fly
rocks, etc.
Traditional delay timing design principles in blasting
suggest that the fragmentation size decreases as the delay
time between holes decreases and it increases as the delay
time between rows increases up to a certain limit
[13, 17–24]. Hettinger [25] found that the short hole-to hole
delay times do not improve rock fragmentation. Inadequate
delay interval across the burden in multi-row blasts causes
the crowding of drill holes, and the broken rock does not
get enough space to heave, which becomes the cause for
more inferior fragmentation results. The success of an*For correspondence
Sådhanå (2021) 46:23 � Indian Academy of Sciences
https://doi.org/10.1007/s12046-020-01552-6Sadhana(0123456789().,-volV)FT3](0123456789().,-volV)
entire multi-row blast depends appreciably upon the ability
of front row charges to heave their burden forward. If front
row charges fail to displace their burden and the back row
burden also starts moving, then the progressive relief is not
attained and the blast never fully recovers. The longer delay
interval is generally recommended in such cases, which
provides greater progressive relief of the burden. To this
end, Hagan [26] stated that if the number of firing rows is
large, blast holes at or towards the rear may give entirely
unacceptable fragmentation, and may be incapable of dis-
placing the rock which results into tight muckpile and poor
collar breakages. Cox and Cotton [27] reported from their
studies in the Mt. Coot-Tha quarry that because of too short
delays, the rock body moves as a single unit resulting in
poor fragmentation.
The results of mean fragment size and the fragment size
distribution reveal that these parameters are significantly
affected by the delay interval between the rows. Katsa-
banis and Liu [18] reported that inter-row delay is
dependent on the size of the burden and the nature of the
rock. The high-speed observations made by Brinkmann
[28] and Stagg and Rholl [29] suggested that the optimum
delay interval in dolomite was close to 37 ms/m of
effective burden. Floyd [30] stated that the typical timing
ranges for optimum fragmentation depend on rock mass
type such as an inter-hole delay of less than 1 ms/m of
spacing for blocky and massive rock with an inter-row
delay of at least 2 to 3 times the inter-hole delay and an
inter-row delay of 2 to 5 ms/m of burden for highly
jointed or highly bedded rock.
Konya and Walter [31] mentioned that long stemming
depths on stiff benches promote backbreak. Additionally,
improper delay timing from row-to-row may cause back-
break. If the timing is too short, excessive confinement of
the gases occurs in the last row of the shot. Gate et al [32]found that when the number of rows of blast hole increases;
the chances of backbreak also increases and concluded that
short delay timing is the main reason of backbreak. Blast
pattern parameters such as burden, stemming, delay timing
and stiffness ratio (bench height/burden) are the most
effective factors in generating backbreak [31, 33, 34].
The study aims to investigate the effect of stemming
material and Inter-row delay timing on the blast results
such as better fragmentation and minimum or no back
break.
2. Field study and research methodology
From the literature review, it is evident that the blast design
parameters grossly influence the blasting results, at the
same time it is also evident that blasting results are sensi-
tive to complex interactions amongst various design
parameters, rock parameters and explosive parameters. In
order to minimize the complexity in result, blasts are
conducted in the quarries by varying crucial blast design
parameters under similar strata and explosive conditions.
However, despite this effort it can be very well appreciated
that in the field settings one to one congruity of blast design
parameters is almost impossible as such, given these limi-
tations the researchers have been trying to interpret and
rationalize the blasting results [2, 38]. According to these
limitations, the present study also addresses to evaluate the
impact of changes in stemming material and delay timing in
the field blast on fragmentation, muckpile shape and back
break results.
Based on the objectives, experiments were carried out in
three steps. The initial step was the field investigation,
where many blast parameters and results were taken for the
analysis. After statistical analysis, the two main parameters
(stemming material and delay timing) has selected as a
sensitive parameter. With this, the few modifications have
applied in selected parameters and number of output
results (muckpile shape and fragmentation) has been
accessed. These parameters are controllable and play a
very primary role in the disintegration of rock during
blasting. After that, fragmentation using image analysis for
mean particle size calculation and muckpile shape were
measured in the field. With this, correlation of mean par-
ticle size and muckpile shape was compared with the delay
timing and stemming from obtaining an optimum operat-
ing range. The scheme of experiments is depicted in
Figure 1.
To meet the stated objective number of blasts were
conducted in the two limestone mines. Both are mecha-
nized mines and producing limestone for their captive
cement plant. Mine-A is of M/s Shree Cement, Rajasthan
and Mine-B of M/S Wonder Cement, Rajasthan. The height
of benches is varied between 10 and13 m, and width of
benches varies from 30 to 50 m.
Steps for design of experiment
1. Field Inves�ga�ons
Sta�s�cal analysis of the blast parameter
Selec�on of two (stemming material and delay �ming) effec�ve parameter for the blast output taking other as
constant
Fragmenta�on and muckpile
shape assessment
Drill cu�ng assessment for
stemming
Row Delay Timing
2. Modified -Delay �ming
between rows
Screened drill cu�ng for stemming
Correla�on between Fragmenta�on, Muckpile shape with delay �ming and stemming material
3. Developing the standard screened size drill cu�ngs and delay
�ming
Figure 1. Scheme of experimental design.
23 Page 2 of 12 Sådhanå (2021) 46:23
2.1 Drilling and blasting practices
Down the hole hammer (DTH) drills of 165 mm are
being used to drill blast holes. The holes are made
close to vertical. The drilling pattern was staggered.
Blasting has been carried out using EMULSION
BOOST, KELVEX-600 and Ammonium nitrate fuel
oil (ANFO) explosives. The explosive was deto-
nated using shock tube-based detonator and the dif-
ferent firing pattern used in mine are shown in
Figures 2a–c.
250ms in hole delay
Stemming column10.5m (3-3.5m)
Explosive columnPrime cartridge
(a)
Initiation point
17ms 34ms 51ms 68ms 85ms 110ms
42ms
84ms
59ms
Free Face
II = 25msI = 17ms
= 42ms
101ms
76ms
118ms
93ms
135ms
84 109 134 159 184 209 234 259 284 309 334 359 384 409 434
42 67 92 117 142 167 192 217 242 267 292 317 342 367 392
0 25 50 75 100 125 150 175 200 225 250 275 300 325 350
Free FaceInitiation point
II = 25ms = 42ms
8
Initiation point
I = 17ms II = 25ms = 42ms
(b)
(c)
(d)
Figure 2. (a) Blast hole section, (b) Staggered drilling with diagonal firing pattern, (c) Rectangular drilling with Line firing pattern,
(d) Staggered drilling with V-type firing pattern.
Sådhanå (2021) 46:23 Page 3 of 12 23
2.2 Stemming material
Different sizes of aggregates/ drill cuttings of minus (-)
10 mm size (3–7 mm) and plus (?) 10 mm size (10–12
mm) were used to investigate the influence of blast
results. The variation of stemming material is shown in
Figure 3.
2.3 Delay timing in back rows
Different delay detonators having a delay of 42 ms,
67 ms, 92 ms, 100 ms, 117 ms and 125 ms were imple-
mented between rows to assess their effect on blast
results.
2.4 Fragmentation assessment
Digital image analysis technique was used in the present
study by the capturing of scaled digital images of the
blasted muck pile to quantify the mean size and its uni-
formity. In order to cover the entire muck pile, the images
were captured at a period interval of 1-hour throughout
the excavation history of the muck pile, giving due cog-
nizance to the recommendations made by several
researchers [35, 39]. The captured images were analyzed
by Fragalyst�, a commercial, state-of-art image analysis
software. The image processing sequences are shown in
Figures 4a–c.
Digital image analysis software was developed
through the 1990s, and at present, these are worldwide
accepted tool in the mining and mineral processing
industries. Its main advantage is that it can be used on a
continuous basis without affecting the production cycle,
which makes it the only practical tool for evaluating
fragmentation of the run of mine, despite its inherent
limitations; a thorough discussion of such systems was
published by Maerz and Zhou [40]. Some of the errors of
image analysis systems can be overcome to some extent
using an on-site calibration from sieving data, as Latham
et al [41] suggest for industrial applications.
+10mm size -10mm size
Figure 3. Use of aggregates for stemming the blast holes.
Figure 4. (a) Fragmented material after blasting. (b) Processedimages (edge detections). (c) Fragmentation distribution (Rosin
Rammler) curve.
23 Page 4 of 12 Sådhanå (2021) 46:23
In the assessment of blasting results, rapid analysis of
muckpile fragmentation is important for meaningful con-
clusions and equipment productivity can be related to
muckpile properties. Once the reliability of the method had
been established, then the blasting trials can be meaning-
fully compared. The industry requires optimal blast design
by more accurate and rapid fragmentation assessment.
Cunningham [37] provides an excellent overview of auto-
mated measuring systems. The errors associated with image
processing systems are commonly due to the following
factors:
• Image analysis can only process appeared on the
image, which represents only the surface of the
objects.
• Particle sizes that can be analyzed usually fall into a
certain range.
• Fine sizes are often underestimated.
The use of a digital image analysis system in a lime-
stone quarry, Sanchidrian et al [36] reported that twenty
photographs per blast must be manually edited for get-
ting good results of a blast. Manual editing of the pho-
tographs had proved to be required in order to obtain
acceptable result.
2.5 Muckpile shape parameters
Throw, drop and lateral spreading of the muckpile are
essential parameters for the excavation operation. Greater
throw, drop and spreading may be considered to be
favourable for digging of the muck by the payloaders while
loose muck with less spreading is favourable for shovel and
backhoe. During the fieldwork, throw, drop, spread and
muckpile angle for each blast were measured (Figure 5)
immediately after the blast using tape measurements on
blasted muckpile.
3. Result and discussions
Total of 24 trial blasts was conducted in both the mines to
investigate the stemming material and inter-row delay
timing effect on blast results. Field observations and the
blast results are tabulated in Tables 1 and 2 for further
analysis.
It is evident from Table 1 that the fragment sizes are
influenced by delay interval. The delay interval between the
successive rows of these blasts varied from 5 ms/m to 23.4
ms/m of the geologic burden. This gap plays a crucial role
in inter collision of rock and congestion of blasted muck.
Figure 6a, b exhibit the congested Muckpile and boulders
due to improper delay gap (less than 5 ms/m) and loose
muck having uniform fragmentation when the delay gap is
more than 5 ms/m.
The results shown in Table 2 are suggestive of the sig-
nificant influence of the screened drill cuttings in stemming
column on the fragment sizes, muckpile parameters and high
wall stability. Five blasts (WB-1 to WB-5) were monitored
when only drill cuttings were used for stemming while nine
blasts (WB-6 to WB-14) were monitored with 3-7 mm size
aggregates as the stemming materials. The use of screened
drill cuttings made less effort to stem the hole. The boulder
generation was less, therefore; the secondary breakage was
almost 1% of the total broken material. There was increased
throw, drop and spread of material that resulted in loose
Muckpile. No dust, fly rock was observed during blasting as
there was almost negligible gas ejection from the stemming
part. It was found that the use of angular aggregates appears
to assist in the proper utilization of explosive energy and in
providing adequate progressive relief for good fragment size,
boulder count and throw results. Figure 7 shows boulder
generation due to the escape of gases from the stemming part
when drill cuttings are the stemming material while Figure 8
exhibit good fragmentation and muckpile shape parameters
where no stemming ejection occurred due to use of screened
drill cuttings.
Figure 5. Muckpile shape parameters and actual measurement at the field.
Sådhanå (2021) 46:23 Page 5 of 12 23
Table
1.
Field
observationsandblastsresultsforthedelay
betweenrowsforquarry-A
.
Blast
No.
SD-1
SD-2
SD-3
SD-4
SD-5
SD-6
SD-7
SD-8
SD-9
SD-10
Burden
(B),m
55
54.5
4.5
54.5
4.5
4.5
4.5
Spacing,m
66
66.5
66
66
5.5
5.5
Depth
ofholes,m
12.27
10.48
12.11
10.94
11.3
12.08
11.01
11.98
10.96
11.36
No.ofholes
50
60
100
77
83
73
82
50
80
64
No.rows
54
45
55
55
55
Stemminglength
3.25
33.5
3.5
3.25
3.25
3.5
34.25
3.5
Explosiveper
hole,kg
144.2
124.3
144.1
130.4
121.6
145.5
122.1
112.5
110.5
117.2
TotalExplosive,
kg
7209
7494
14413
10040
10090
10620
10015
5623
8840
7500
PF,kg/t
0.157
0.159
0.159
0.163
0.159
0.161
0.164
0.139
0.163
0.167
TotalBroken
rock,t
46013
47175
90844
61571
63332
66131
60953
40433
54249
44999
Firingpattern
Diag.
Diag.
Diag.
Diag.
Diag.
Diag.
Diag.
Diag.
Diag.
Diag.
Frontrow
burden
32.5
3.25
22.5
3.5
2.25
1.75
32.5
Row
torow
delay
42,67,92,
117
67,92,
117
67,92,
117
42,67, 100,100
67,92,
100,125
25,42,67,
100,117
25,42,67,
100,100
42,67,117,117
42,42,75,75
67,67,100,100
Delay
ofB,ms
8.4/13.4/
18.4/23.4
13.4/18.4
/23.4
13.4/18.4
/23.4
9.3/14.8/22.4/22.414.8/20.4/22.2/27.75/8.4/13.4/20/23.4
5.5/9.3/
14.8/22.4
9.3/14.8/20.4/20.49.3/9.3/16.6/16.614.8/14.8/22.2/22.2
Throw,m
16
16
14
15
4.5
14
14.5
43
2.5
Drop,m
5.5
2.6
5.5
30.75
5.5
3.5
1.75
0.75
1.3
Spread,m
50.2
40
53
17.5
45.5
57
40.5
45
35.5
38
Endbreak
length,m
1.0
0.5
0.5
1.0
0.3
1.5
1.5
2.0
2.5
2.0
K20,m
0.18
0.13
0.13
0.09
0.15
0.35
0.25
0.25
0.15
0.2
K50,m
0.25
0.17
0.18
0.15
0.25
0.5
0.45
0.45
0.3
0.4
K80,m
0.35
0.23
0.25
0.25
0.35
0.67
0.7
0.65
0.5
0.6
K95,m
0.55
0.33
0.37
0.45
0.65
1.0
1.3
1.2
1.1
1.2
23 Page 6 of 12 Sådhanå (2021) 46:23
3.1 Results of effect of delay timing between rowsat mine-A
3.1a Results of the fragmentation size distribution: The
results of the effect of delay timing between rows have
been deduced from Tables 1. Curves for fragment size vs
cumulative passing for each blast round is obtained after
processing of field captured photographs using the Fraga-
lystTM software. From the distribution curve, a fragment
size of K20, K50, K80 and K95 are taken for analysis. These
curves were manually plotted on one sheet (Figure 9) in
order to compare the fragment size distribution results.
A perusal of Figure 9 appraises the improvement of blast
performance. The relative improvement of blast perfor-
mance SD-1 to SD-10 to this end it is observed that blast
no. SD-1 to SD-5 are steep while blasting no. SD-6 to SD-
10 are flatter. Flatness and spread of the curve indicate non-
uniformity of fragmentation, whereas steep and less spread
curves reveal uniformity in fragment size distribution.
3.1b Analysis of row delay timing effect on mean frag-ment size (MFS): Figure 10 shows the relationship between
the delay timing between rows and mean fragment size.
It is evident from the Figure 10 that the mean fragment
sizes are lower and uniform when the delay between first
and second row is 8–14 ms/m of burden and the delay gap
between last two rows is 5 ms/m of the burden. When the
delay gap between the first row and the second row is less
(5 ms/m) and the delay between last two rows are zero
(same for both rows although the delay is 22.4 ms/m or
different) than the fragment sizes are bigger and non-
uniform.
3.1c Analysis of row delay timing effect on muckpileshape parameters: Figure 11 shows the relationship
between the row delay timing and the muckpile shape
parameters.
It is evident from the Figure 11a, b that the throw and
drop are higher when the delay between the first and second
row is 5-9 ms/m of burden and the delay gap between the
last two rows is 5 ms/m of the burden. While it is evident
from Figure 11c that the spread is not much affected by the
variation of the delay pattern between the rows. It is also
found that when the delay gap between the last two rows is
same then the throw and drop are very low.
3.1d Analysis of row delay timing effect on back break:Figure 12 shows the relationship between row delay timing
and back break.
It is evident from the Figure 12 that the back break is
lower when the delay between the first and second row is
8-14 ms/m of burden and the delay gap between the last
two rows is 5 ms/m of the burden. When the delay gap
between the first row and the second row is less (5 ms/m)
and the delay between last two rows is zero (same for both
row although the delay is 22.4 ms/m), then the substantial
back break was observed.
3.2 Results of use of screened drill cuttingsat mine-B
3.2a Analysis of fragmentation results: Figure 13 shows the
fragmentation size behaviour due to a change in the stem-
ming material.
Table 2. Field observations and blast data for stemming column adjustment (Aggregates) for Mine-B.
Parameters
WB-
1
WB-
2
WB-
3
WB-
4
WB-
5
WB-
6
WB-
7
WB-
8
WB-
9
WB-
10
WB-
11
WB-
12
WB-
13
WB-
14
Bench height (m) 10 9.5 10.25 11 10.5 10 9.75 10 10 9.5 10 10 9.75 10
Burden (m) 4.5 4.5 4.75 4.5 4 4.5 4.5 4.5 5 5 4.5 4.5 4.5 4
Spacing (m) 6.5 6.5 6.75 6.5 6 6.5 6.5 6.75 7 7 6.5 6.5 6.5 6
No. of holes 10 13 10 20 12 20 10 10 7 10 10 11 10 20
No. of rows 2 2 2 2 2 2 2 2 2 2 2 2 2 2
Explosive per hole (kg) 55.25 42.3 55.25 62.3 53.9 60.25 57.75 55.25 57.4 50.3 57.8 59.3 55.3 62.5
Total Explosive (kg) 552.5 742.3 552.5 872 1456 1205 577.5 552.5 401.8 502.5 577.5 652.8 552.5 1255.0
Throw (m) 8 7 8 5 5 10 15 10 12 10 15 10 12 15
Drop (m) 1 0.5 1 0.5 0 2.5 1.5 1.5 2.5 1.5 2.5 1 2 1.5
Spread (m) 15 15 10 12 19 30 20 20 25 20 30 20 20 25
End break length (m) 2 2 2 1.5 2 1 1.5 2 1 1 1 1.5 2 2
Total broken rock (t) 9393 10288 7309.5 9049 18782 15356 7312 8015 6125 8750 7496 8445 7312 12600
PF(kg/t) 0.059 0.072 0.076 0.096 0.078 0.078 0.079 0.069 0.066 0.057 0.077 0.077 0.076 0.100
Mean fragment sizes
(MFS), (m)
0.51 0.7 0.55 0.63 0.59 0.36 0.27 0.22 0.32 0.37 0.16 0.25 0.28 0.32
Fly rock distance Fly rocks generated due to
stemming ejection (30-50 m)
No stemming ejection, so no fly rock was generated (only 3-5 m
vertical lift)
Sådhanå (2021) 46:23 Page 7 of 12 23
Figure 6. (a) Boulder generated due to less delay. (b) Uniform fragmentation due to proper delay in the front row with the proper high
wall.
Figure 7. Boulder due to the escape of gases from the stemming part (drill cuttings).
23 Page 8 of 12 Sådhanå (2021) 46:23
From the above Figure 13, it is evident that the mean
fragment size is affected by the compaction of stemming
part. The mean fragment size (MFS) is lower in all the blast
in which the screened drill cuttings of 3-7 mm or 10-12 mm
size aggregates were used compared to only drill cuttings.
Therefore, it can be inferred that the aggregate size of 3-7
mm/10-12 mm as stemming material helped in the proper
utilization of explosive energy.
Figure 8. Good fragmentation with improved Muckpile parameters (screened drill cuttings).
0102030405060708090
100110
0 0.2 0.4 0.6 0.8 1 1.2 1.4
Cu
mu
lati
ve
pas
sin
g %
Fragmentation size (m)
SD-1
SD-2
SD-3
SD-4
SD-5
SD-6
SD-7
SD-8
SD-9
SD-10
Fragmenta�on size Vs Cumula�ve passing
Figure 9. Composite fragment size distribution curve for blast
SD-1 to SD-10 in Mine-A.
0
0.5
MFS
, (m
)
Delay �ming (ms/m of Burden), ms
Delay timing between rows vs MFS
Figure 10. Row delay timing vs MFS for Mine-A.
(a)
(b)
(c)
05
101520
Thro
w, (
m)
Delay �ming (ms/m of Burden), ms
Delay timing between rows vs Throw
0123456
Drop
, (m
)
Delay �ming (ms/m of Burden), ms
Delay timing between rows vs Drop
0102030405060
Spre
ad, (
m)
Delay �ming (ms/m of Burden), ms
Delay timing between rows vs Spread
Figure 11. (a) Relation between delay timing and throw.
(b) Relation between delay timing and drop. (c) Relation between
delay timing and spread.
Sådhanå (2021) 46:23 Page 9 of 12 23
3.2b Analysis of muckpile shape parameters: Figure 14
shows the muckpile shape parameters behaviour due to a
change in the stemming material.
It is evident from the above Figure 14a–c that as the use
of screened drill cuttings having sizes of 3-7 mm/10-12 mm
were helpful in blocking the ejection of gases from stem-
ming column. These resulted in improving the muckpile
shape parameters such as throw, drop and spread.
4. Conclusions
During the study, various changes were made in stemming
material and delay sequencing and found the following
results.
(1) The aggregate size of 3-7 mm/10-12 mm generated
good fragmentation sizes in overall and especially in
collar region with improved muckpile shape
parameters.
(2) The delay of 8-14 ms/m of burden between the first and
second row and the delay gap of 5 ms/m of the burden
between last two rows generated good fragmentation
sizes in overall and especially in collar region with
improved muckpile shape parameters.
0
5
Back
bre
ak, (
m)
Delay �ming (ms/m of Burden), ms
Delay timing between rows vs Back break
Figure 12. Row delay vs back break for Mine-A.
0
0.5
1
1 2 3 4 5 6 7 8 9
)m( ,
SF
M
No. of blast
Mean fragment size for stemming column adjustment
without aggrgatesWith aggregates
Figure 13. Aggregates vs MFS for Mine-B.
0
10
20
1 2 3 4 5 6 7 8 9
)m( ,
wo rhT
No. of blast
Stemming column adjustment vs Throw
without aggrgatesWith aggregates
0
1
2
3
1 2 3 4 5 6 7 8 9
)m(,por
D
No. of blast
Stemming column adjustment vs Drop
without aggrgates With aggregates
(a) (b)
0
20
40
1 2 3 4 5 6 7 8 9
)m(,
daerpS
No. of blast
Stemming column adjustment vs Spread
without aggrgatesWith aggregates
(c)
Figure 14. (a) Relation between no. of blasts with aggregates and without aggregates and throw. (b) Relation between no. of blasts withaggregates and without aggregates and drop. (c) Relation between number of blasts with aggregates and without aggregates and spread.
23 Page 10 of 12 Sådhanå (2021) 46:23
(3) The delay gap between first and second row is less than
5 ms/m and the delay gap between the last two rows is
zero (same for both row) then the huge back break was
observed.
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