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ScienceDirect Procedia Engineering 191 (2017) 1211 – 1217

Symposium of the International Society for Rock Mechanics

Explosive Energy Utilization Enhancement with Air-Decking and Stemming Plug, ‘SPARSH’ M.R. Saharana*, M. Sazidb, T.N. Singhc a

CSIR-CIMFR, Barwa Road, Dhanbad-826015. India b KA University, Zeddah. Kingdom of Saudi Arabia c IIT Bombay, Mumbai, India

Abstract Engineering blasting is considered the most economical means of rock fragmentation. The explosive energy utilization is limited to 7% to 22% for fracturing and fragmentation though. The rest of energy components manifests itself into deleterious effects of engineering blasting, namely – noise, air overpressure, ground vibrations, etc. It has been established that proper application of air-decking and stemming plugs may enhance explosive energy utilization to a good extent. This paper substantiates this fact wherein distinct explosive energy utilization enhancement has been achieved with the combination of air-decking and stemming plug. The stemming plug used has acronym as, SPARSH (Stemming Plug Augmenting Resistance to Stemming in Holes) and it is perhaps the only available device which can effectively be used with air-decking. Further, SPARSH doesn’t restrict the type of stemming material and stemming length. This is a significant advancement in the engineering blasting. © 2017Published The Authors. Published by Elsevier Ltd. © 2017 by Elsevier Ltd. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/). Peer-review under responsibility of the organizing committee of EUROCK 2017. Peer-review under responsibility of the organizing committee of EUROCK 2017 Keywords: Engineering Blasting; Explosive Energy; Rock Fracturing; Rock Fragmentation; Air-Decking; Stemming Plug; SPARSH

1. Introduction Engineering blasting has many notable advancements since Alfred Nobel had invented detonator and dynamite in 1865 and 1867, respectively. Since then this engineering application has grown with newer forms of blasting agents (they are not explosive by themselves) and electronic detonators. The notable technological advancement also covers application of air-decking as propounded by Mel’Nikov [1], de-coupling as illustrated by Worsey et al. [2] and

* Corresponding author. Tel.: ++91-326-229-6004. E-mail address: [email protected]

1877-7058 © 2017 Published by Elsevier Ltd. This is an open access article under the CC BY-NC-ND license

(http://creativecommons.org/licenses/by-nc-nd/4.0/). Peer-review under responsibility of the organizing committee of EUROCK 2017

doi:10.1016/j.proeng.2017.05.297

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M.R. Saharan et al. / Procedia Engineering 191 (2017) 1211 – 1217

various form of stemming plugs proposed by several researchers [3]. The explosive energy utilization for fracturing and fragmentation, however, accounts for only 7% to 22% despite of all these advancements [4]. Also, there is no change in different rules of thumbs or specifications those were recorded by John Burgoyane in 1849 [5]. The notable rule of thumb still in vogue dictates that blast hole shall be charged up to 2/3rd of its length and the remaining 1/3rd top column shall have stemming material. The specifications for stemming materials are also unchanged those enforces that inert light weight angularly shaped materials of about 1/6 th diameter with respect to blast hole diameter must be used for engineering blasting as stemming. These rules of thumbs and specifications creates practical problems for large diameter long hole blasting and yet the explosive energy ejects early from the borehole collar. This paper describes an interesting case study wherein the rule of thumb pertaining to the stemming column length was not followed. The stemming material specifications are generally not followed and the same was done in this case too. Yet the part blasting where the combination of air-decking and stemming plug was used demonstrated distinct explosive energy utilization enhancement. The results proved that explosive energy utilization can be greatly enhanced compared to conventional achievements by combining air-decking and stemming plug. The stemming plug used for the case study has acronym as SPARSH (Stemming Plug Augmenting Resistance to Stemming in Holes). This is perhaps the only available stemming plug which can amalgamates with air-decking and there is no need to follow the stemming material specifications. In fact, there is no other stemming material required with SPARSH application and stemming column above SPARSH can be greatly reduced. 2. Case Study Description Jhamar Kotra Mine of Rajasthan State Mines & Minerals Ltd. (RSMML) is situated near to the village of Jhamar Kotra in the Udaipur district of Rajasthan state (Figure 1). The latitude and longitude of the mine are positioned about 24º 28’ 23.76’’N and 73º 50’ 43.94’’E, respectively. Jhamar Kotra rock phosphate deposit formation comes under the Debari formation. Joint pattern for the experimental blast face are measured using Brunton Compass and the results are shown in Figure 2 which shows the joint pattern having E-W strike direction aligned with the face strike direction and the joint sets dip towards the face. This form a suitable condition for dislodging blasted muck with ease from the explosive energy [6]. The experiment blast face has two major joint sets with spacing more than 20cm (horizontal direction joint set) and 80 cm (vertical direction joint set) with aperture less than 2 mm.

Fig. 1. Google image of Jhamar Kotra Mine.

Fig. 2. Joint set Rosette plot of experiment blast face (Dips, 5.1). [7]

Jhamar Kotra Mine is an open pit operation and it has adopted large diameter vertical downward holes for drilling (165 mm and 215 mm) and Site Mixed Emulsion explosive with initiation from detonating fuse for blasting as a standard practice. The shovel (6 m3) – dumper (75 t) combination are deployed for rock loading and handling. The bench height is 10 m. The mine uses 5 m x 7 m burden and spacing pattern for large diameter holes (215 mm)


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and 6 m x 6 m, 3 m x 4 m and 4 m x 5 m pattern for small diameter holes (165 mm). The mine uses square and staggered blasting pattern. Experimental blast conducted in the upper most bench of the hangwall side, which is the boundary limit of the mine. The site has proximity with human populace and a critically important potable water conveying pipeline crossing near to the proposed blast site (Figures 3 & 4). The mine management has requirement to widen the transport roadway for ease in movement of heavy earth moving machinery. Pushback operation considered to widen the roadway which necessitated a careful blast without damaging the critical pipeline and to the habitat. Figure 3 & 4 shows the face details, which is approximately 300 m long and 153 holes of different depths in three row and diameters were drilled in this location for a single blast event (Figure 3). Total 22 tonne of explosive used in 153 holes. The strike of experiment blast was in E-W direction (Figure 3). The face having large spacing joints and compact strata as compare to the other benches of the mine. The bench height reduces from 8 m to 2 m towards the west to east side of the face. The blast face was divided into three sections (Figure 4). SPARSH was used in 8 m deep holes (total 40 number of holes) in the extreme west side as a change in blasting parameter and the remaining two sections were stemmed with drill cuttings stemming material as a general practice of the mine. SME was charged up to 3m in 8m deep holes (Figure 5). This charging was low considering the strength of the mining block and it was apprehended that it will result as an inappropriate blast in terms of the fragmentation. The management, however preferred for a safe blasting (proximity to the pipe line and human populate) over a production blasting (good fragmentation to handle with). In section-1, 2.5 m air gap was maintained above the 3m explosive column using SPARSH and then the remaining borehole column was filled with the stemming material up to borehole collar (Figure 6). The locking position of SPARSH was ensured and measured by the pushing rod. The locking arrangement could not be effectively achieved in couple of holes. This was probably due to oversized drill holes diameters (due to collapse of wall) at those particular locations and the same was reflected later in blasthole ejection.

Fig. 3. A view of trail blast face.

Fig. 4. Sketch diagram of all three section holes with details.

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Fig.5. Conventional charging pattern in Section-2

Fig. 6. Charging pattern with SPARSH in Section-1.

3. Experimental Blast Observations Motion analysis of the experimental blast was accomplished with FastCam camera (12.5 to 75 mm zoom lens) operating at 250 frames per second with high resolution of 512*480 pixels (Horizontal * Vertical) (normal video camera produces 25 frames per second). The camera records about 5.4 second of a blast event which shall be triggered after 5-6 second of the event to be recorded. The camera produces monchrome images. The position of the camera was chosen to record the stemming ejection and the ejection velocity from a safe distance. The data received from the high-speed camera are analysed and presented in the form of the stemming confinement time (stemming retention time) and stemming ejection velocity. The motion analysis of the high-speed video recording involves separating each frame of the motion into a still image and then mark the ejection time, retention time and ejection velocity with respect to the initiation of the blast as can be noticed through detonation of the detonating cord in the present case. A survey of the muck profile, muck displacement and a general fragmentation analysis was also done and digital images were recorded immediately after the blast. The back break was recorded from observations of stones placed behind the last row of holes at a determined interval and marked with different colouring scheme to demarcate different blasting zones. Figure 7 shows different views of blasted muck from the post blast observation of SPARSH section-1. The SPARSH block moved from in-situ rock mass with 3-4 m distance. Muck pile created was pliable, straight and neat face was observed in the post blast observation (Figure 7a). Back break of 1m was observed as the first colour marker stone was moved with the muck pile (Figure 7b). Beyond this SPARSH section, ground movement was observed from a location termed as transition zone 1 covering about 20m distance away from the last column of SPARSH charged holes. Beyond this transition zone 1, the face did not show any sign of blasting/fragmentation, holes were ejected as shown in video observation and left with intact rock mass to a length of about 120 m (Figure 8). In this zone conventional stemming was adopted with the blast holes. The holes were either completely blown out (Figure 8) or developed surface crater cracks (Figures 9). The first hole of section-2 ejected after 12 ms. The average retention time of 14.7 ms observed for the Section-2. Whereas, SPARSH provided enough retention time of 76ms. The calculated average initial ejection velocity of the conventional blastholes is nearly about 380 m/s (Figure 10). Whereas, calculated average initial ejection velocity of blastholes stemmed with SPARSH is nearly about 250 m/s (Figure 11). SPARSH provided higher retention time of about 5 times to the conventional stemming and reduced stemming ejection velocity of about 0.65 times to the conventional stemming. The ejection velocity will


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be lower if the retention time is higher. The higher retention time provides the explosive energy enough time for positive effects of blasting (fragmentation) to a larger area and a lesser amount of the energy with smaller amount of ejection velocity is left for fractures meeting the daylight. The higher ejection velocity also means for larger chances of fly rock to a greater distance. It can be noticed from comparative evaluation of Figure 10 and 11 that the rate of decrease into the ejection velocity is higher with the application of SPARSH whereas the conventional stemming is not able to rapidly retard the ejection velocity. This has the possible explanation from the fact that SPARSH holds the explosive energy within the boreholes for a longer period thus able to generate higher borehole pressure which push into the rock mass for better fragmentation and once the borehole expands it partly releases it into the atmosphere. In contrast, the boreholes stemmed with conventional stemming uniformly allows escape of the borehole pressure as it keep on generating and thus poor utilization of explosive energy is resulted for fragmentation purposes. A contour diagram of total ejected blast holes of experiment blast, which includes Section2, a transition zone 1 and Section-1, is also drawn based on ejection height at 2000 ms time frame as depicted in Figure 12. It is apparent from Figure 12 that the total ejection height is more for Section-2 where conventional stemming was used in comparison with the section 1 where SPARSH was applied to retain the explosive energy for positive blasting work. The results of image analysis for fragmentation assessment are summarized in Figure 13. Optimum rock size fragmentation from all photographs are merged and analyzed in Fragalyst [8] using multiple image analysis technique. The average K50 value is 0.25 m obtained by the use of SPARSH, which is very favorable size for shovel (6 m3) and dumper (75 t) [9]. The average K98 values is 0.45 m, which is also shows the does not require secondary breaking or blasting.

Fig. 7. Muck pile and fragments out of SPARSH section.

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Fig. 8. Intact ground after blasting in section-2.

Fig. 9. Close up view of a 2.8m diameter surface cracks crater in Section-2.

700

500 400 300 200 100 0 0

500

1000 1500 time, ms

2000

2500

3000

Fig. 10. Ejection velocity with time for section-2.

E. Velocity, m/s

E.Velocity, m/s

600

500 450 400 350 300 250 200 150 100 50 0 0

500

1000 1500 time, ms

2000

Fig. 11. Ejection velocity with time for section-1.

2500


Fig. 12. Ejection height for without SPARSH and with SPARSH.

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Fig. 13. Cumulative size distribution curve using Fragalyst analysis.

4. Conclusions The application of SPARSH in amalgamation with air-decking proved to be a blessing in disguise. The experimental blast site was forced to reverse the rule of thumb pertaining to explosive height and stemming column length. The conventional blast section didn’t yield a single fragmentation due to this change while the blasting section with SPARSH could generate pliable muck pile. This marked distinction in the explosive energy utilization demonstrated the fact that the explosive energy utilization for rock fracturing and fragmentation can be greatly enhanced with the combination of stemming plug and air-decking. The conventional blasting practice could not generate the fractures and fragmentation in the trial blast despite the favourable geological conditions. The SPARSH can be a useful tool for special purpose blasting such as destress blasting and bottom deck blasting for clean mine floor.

References [1] N.V. Melnikov, Utilization of energy of explosives and fragment size of rock in blasting operations. Gorn Zh. 5 (1940) 565–572. [2] P.N Worsey, I.W. Farmer, G.D. Matheson, The mechanics of pre-split blasting to rock slopes, in: Proc 22nd US Symp Rock Mech, MIT, Boston, Massachusetts, 1981, pp. 205–210. [3] M. Sazid, M.R. Saharan, T.N. Singh. Effective Explosive Energy Utilization for Engineering Blasting - Initial Results of an Inventive Stemming plug, SPARSH. Harmonizing Rock Engineering and the Environment, 12th ISRM Congress, 2011, pp. 1265–1268. [4] M.R. Saharan, Dynamic numerical modeling of rock fracturing by distress blasting, Ph.D. thesis, McGill university, Montreal, 2004, 267 p. [5] J. S. Burgoyne, Rudimentary treatise on the blasting and quarrying of stone, London, 1849. [6] P. Lilly, An empirical method of assessing rock mass blastability, in: Large Open Pit Mining Conference, Newman (The AusIMM), 1986, pp 89–92. [7] Dips V 5.1 software, Rock Science. [8] CMRI, Fragalyst4.0 – A Digital Image Analysis Tool, 2000. [9] V.V. Rzhevsky, Opencast Mining Unit Operations, Mir, Moscow, 1995.