use of dynamites water-gels and emulsion explosives in sri lanka

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  • 8/17/2019 Use of Dynamites Water-Gels and Emulsion Explosives in Sri Lanka

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    Use of Dynamites, Water-Gels and Emulsion Explosivesin Sri Lankan Quarrying/Mining Practice

    P. V. A. Hemalal, P. G. R. Dharmaratne and P. I. Kumarage

    Abstract:  In the Sri Lankan mining and quarrying industry, gelatine dynamite has been the widelyused explosive for rock blasting purposes. In the recent past, it has been phased out and replaced bylocally manufactured Water-gels(WG). So far, there had been only a very few tests conducted to assessthe suitability and to evaluate the performance of this explosive with other available explosives.Complaints made by the users of Water-gels have been a cause of concern and prompted research to beconducted with the aim of evaluating the performance of Dynamites, Water-gels and Emulsion explosiveswith the measurement of major performance indicators in local mining and quarrying practice.

    In this research, performance comparison of WG, Dynamite and Emulsion explosives with regard to rockbreakage in underground tunnelling and in metal quarrying has been carried out. Comparison offragmentation with the evaluation of particle size distribution in concrete block blasting using the threetypes of explosives has been one of the main tests. Gap sensitivity, density and the determination of

    velocity of detonation (VOD) has also been carried out.

    Keywords:  D’Autriche’s Method, Gap Sensitivity, VOD, Explosives

    1. Introduction

    Water-gel(WG) was introduced to Sri Lanka in2011 as a substitute for dynamite. So far therehad been only a very few tests conducted toassess the suitability and to evaluate theperformance of this explosive in contrast toother available explosives.

    Water-gel currently produced in Sri Lanka hasbeen introduced to the industry by thegovernment. The complaints made by theusers with regard to the performance of water-gels have been a cause of concern.

    In this research, performance of water-gelexplosives currently in use has been evaluatedwith that of emulsions and dynamite, with aview to identifying their deficiencies andpropose measures to overcome them with aview to optimize its usage in Sri Lankanmining practice.

    Fragmentation ability of explosives has beencompared using blasting in concrete blocks.Fragments were analysed using SPLITsoftware. Concrete blocks were used to obtaina homogenous material to obtain a betterreproducibility of tests.

    Underground tunnelling has been carried outboth with WG and dynamite and tunneladvances has been compared with identical cutole configurations.

    Density measurements and gap sensitivity hasbeen conducted to cross check themanufacturers’ specifications on WG.

    Measurement of VOD using D’Autriche’s method was carried out for the first time in Sri

    Lanka for Dynamite, Water-gel and Emulsionexplosives.

    2. Methodology

    2.1 Test Blasting on Concrete Blocks

    Concrete blocks of 0.5mx0.5mx0.5m in sizehaving a 32mm diameter centre hole of 30cmdeep were made to facilitate explosivecharging(Figure 1). Blocks were cured undersame conditions for 28 days. Average

    compressive strength of concrete measured bysample blocks was 40.6 N/mm2.

     Eng. P.V.A. Hemalal, M.Sc.(Hons)(Min.Eng)(Moscow), MIE(Sri Lanka),FIMMM(UK), CEng(UK & SL) Senior Lecturer,Department of Earth Resources Engineering, University of Moratuwa.

     Prof. P.G.R. Dharmarathne B.Sc. (Hons) (S.L.), M.Sc. (New Castle), Ph.D. (Leeds),C.Eng. (U.K.), FIE(Sri Lanka), F.G.A (U.K), F.G.G (Ger.),Senior Professor, Department of Earth ResourcesEngineering, University of Moratuwa.

     Eng. P. I. KumarageB.Sc. (Hons) Eng, AMIE(Sri Lanka) , Mining Engineer

    ENGINEER - Vol. XLVIII, No. 01, pp. [31-37], 2015

    © The Institution of Engineers, Sri Lanka

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    Figure 1 - Concrete block dimensions

    Three explosive types namely, Water-gel(WG), Dynamite and Emulsion were charged

    in quantities of 25g and 30g to study thefragmentation level by each explosive. Quarrydust was used as stemming material and noANFO was used.

    After the blast, all fragments were collected,weighed, photographed, and digitallyanalysed using SPLIT software.

    Figure 2 - Collected concrete fragments afterthe blast

    Figure 3 - Delineated image by the SPLITsoftware

    Figure 4 - Scaling with a reference object

    Boundaries of collected fragments wereidentified by the software by delineating. Thedelineated lines have to be manually edited toeliminate minor errors using the facilitiesgiven in the software package itself. Scaling isthe identification of the actual size of thefragments with the help of a given referenceobject in the image. (Figure 4).

    After completing the image analysis, particlesize distribution curve can be produced(Figure 5). These data have been exported to

    MSExcel for further analysis.

    2.2 Underground Test blast of Water-gelvs. Gelatin dynamite.

    There are no complete or successfulcomparisons on the use of different types ofexplosives in underground situations in localcontext. Therefore several test blasts werecarried out in a tunnel at Bogala mines withidentical cut-hole configurations, to evaluatethe performance of explosives in undergroundrock blasting.

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    Cross-cut tunnel advance (as at June, 2012) ofBogala Graphite Mine, AruggammanaGraphit-Kropfmuhl (Lanka) Ltd Sri Lanka, in191m level was used for this study. Gelatinedynamite and locally-manufactured Water-gels by Kelani Fireworks Company were usedas explosives. Swedish-made millisecond andhalf second, number 08 detonators were usedin every blast as initiators.

    Adopted drill pattern consisted of 37 drillholes

    and is shown in Figure 6.Figure 6 Reamer hole at the centre (hole No.1)having a diameter of 45mm and charged drillholes of 35 mm diameter were drilled.

    In Figure 6 , hole Nos.1 to 9 make up cut-holeround of burn cut configuration. Centre hole(hole No.1) was left un-charged to facilitate asa free space for the rock to be blasted into.Hole No. 2 to 9, the remaining holes of theburn cut hole, were charged with 0.5kg ofWater-gel explosives each with no ANFO

    used.

    Burn cut requires high explosives as the freespace available is too small. All the remainingholes of the blasting round were charged with0.375 kg of water-gel and 0.4kg of ANFO foreach hole. Since the cut hole is already blasted,it provides sufficient free space for thesurrounding holes to blast into, and thereforeless strength of explosives is sufficient.

    Whole Burn Cut made up of hole No. 2 to 9and other stopping holes (hole No. 10 to 21)

    were initiated with millisecond delays whileperimeter holes (hole No.22 to 37) werecharged with half second delays.

    Tunnel face was charged with one explosivetype and the advance was measured. Test wasrepeated for other explosive types as well.

    Figure 5 - Particle size distribution curve produced by the software

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    Figure 6 - Drilling pattern

    Figure 7 - Measuring the tunnel advance afterthe blast using a reference mark on tunnelwall.

    2.3 Density measurement.Density measurements were carried out byweighing and measuring the volume by waterdisplacement. A graph was produced withweight over volume with different observedvalues.

    2.4 Air Gap sensitivity.Placing two half cartridges with varying gapbetween them, one half inserted with anelectric detonator of No.6 strength anddirected towards the other half was blasted.The initial gap in air was taken as 2 cm as thespecified gap of the locally made Water-gelexplosive is 2cm. For Water-gel, this test was across check of the given specification.

    The test determines the ability of an explosiveto transmit detonation through air from onecharge to another some distance away.

    Figure 8 - Gap sensitivity arrangement onfield

    2.5 VOD Measurement.Velocity of Detonation is to be measured usingthe D’Autriche’s method.

    Figure 9 - Schematic arrangement forDautriche method VOD measurement.

    As shown in Figure 9 above, two blasting capswere inserted to the explosive column of thecartridge and the separation was measured(m). A loop was made with a detonating codewith a known VOD. The middle part (centre)of the code was passed over a lead plate andtaped in place. Once the explosive column wasdetonated, the two ends of the cord ignitedsuccessively and the two waves meet head-onon the lead plate, a distance off centred of thegeometric centre of the code.

    After blasting, VOD of the explosive canbecalculated from equation 1, knowing theDetonating cord separation (m), off-centredistance (a) and VOD of the Detonating cord,D(M/s),

    VOD=Dm/2a (i) (1)

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    3. Results & Discussion

    3.1 Results of Concrete Block BlastingFollowing Figure 12 shows the particle sizedistribution after blasting with 25g of eachtype of explosives.

    Figure 10 - Particle Size Distribution graphfor 25g charge of explosives in the block.

    Figure 11 shows the particle size distributionfor 30g of explosive charge.

    From these graphs, it is clear that in both 30gand 25g charge tests, all D10, D30, D50 andD60 values have increased from dynamite towater-gel. This clearly shows thatfragmentation is best in dynamite second inemulsion and water-gels is the third.

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    Size [cm] WG 25g

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    Size [cm] WG 30g

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    Figure 11 - Particle Size Distribution graphfor 30g charge of explosives in the block

    Figure 14 shows the mass and the respectivevolumes for water-gel. Hence the gradient ofthe regression line is mass/volume which isthe density.

    3.2 Results of underground tunnel blasting.

    Figure 12 illustrates the drilling depths andtunnel advances after the blast. It is clear thatdynamite is capable of advances even beyondthe drilling length. With Water-gel it alwaysremains a part of the drilling length. Averageadvance with Dynamite is 113.7% of thedrilling length, whereas it is 92.9% with Water-gel.

    Number of mucking wagons, which indicatesthe amount of rock blasted is also higher indynamites than of water-gels (Figure 13).

    Hence Tunnel advance using water-gels is lessthan that of dynamite for the same charge andsame cut hole configurations.

    3.3 Results of density measurements.

    Figure 12 - Drilling depth and Advance aftereach blast

    Figure 13 - Number of mucking wagons after

    the blast

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    Figure 14 - Mass vs. Volume for WG

    Average density of WG was 1.19g/cc. In thesame manner densities of Emulsion andDynamite were 1.21g/cc and 1.29g/ccrespectively.

    Table 1- Average densities of explosivesExplosive Type Average Density (g/cc)

    Water-gel 1.19

    Emulsion 1.21

    Dynamite 1.29

    From the Table 1, it is clear that dynamite hasthe highest density equal to 1.29g/cc.

    Density of water-gel and emulsion lies close bywith a gap of 0.02g/cc, although emulsion hasslightly a high density of 1.21g/cc.

    3.4 Results of gap sensitivity for water-gel.

    After the blast, the immediate environmentwhere the donor was placed was observed.The discolouration due to burning of thelocation of the receptor was a clear indicationof the detonation of the receptor. Hence, itcould be concluded that the receptor has got

    the detonation through air from the donor and,the test result was positive for an air gap of2cm.

    Followed by successful results of the first test itwas decided to carry out one more trialincreasing the air gap to 3cm. The result withthis increased gap was also positive.

    3.5 Results of VOD measurements.Table 2 below presents the results of theD’Autriche’stest.

    Table 2 - Resultant VOD values fromD’Autriche’s method

    Explosive

    Type

    Gap

    between

    DC

    nodes

    (mm)

    Off set

    gap on

    lead

    plate

    (mm)

    VOD

    of DC

    (m/s)

    VOD

    (m/s)

    Water-gel 100 84 6,750 4,018

    Emulsion 100 68 6,750 4,963

    Dynamite 100 60 6,750 5,625

    It is clear from Table 2 that dynamite has thehighest VOD of 5,625 m/s and Water-gel hasthe lowest of 4,018 m/s. VOD of emulsion is inbetween with a value of 4963 m/s.

    4. Conclusions

    In underground blasting water-gel isenvironmentally friendlier than dynamite. Thisis due to the absence of odour ofNitroglycerine emanating from the cartridge inthe course of charging and post-blast toxicfumes causing headaches and dizziness inconfined underground mining environments.

    Gap sensitivity of Water-gel was found to bebetter than the expected value of 2cm. Theresults were positive even with a gap of 3cm.

    Water-gel is a low energy explosive thandynamite and emulsion. Fragmentation ofwater-gel was found to be less than that ofdynamite as demonstrated in surface concreteblock blasting and underground muck pileanalysis. The conclusion to be arrived is thatdetonation characterised by the low velocity ofdetonation creates a weak fracture systemaffecting the level of fragmentation of the rock.

    Tunnel Advance with dynamite was betterthan with that of Water-gels. Although theexplosive material cost per blasting round isless in Water-gel due to its low price, thisadvantage has been overrun due to the lowrate of tunnel advancements and consequentadditional blasting rounds required withwater-gels.

    It can be conjectured that Water-gel is deadpressed in underground shot hole tunnelblasting at Bogala mines due to the closeproximity blast holes in the order of few centi-meters in the cut hole configuration. Therefore,explosives residues were a frequentobservation.

    y = 1.189xR² = 0.999

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    Density of Water-gel lies within the range ofthe manufacturer, i.e. 1.16g/cc to 1.26g/cc.and, it is 1.29g/cc and 1.21g/cc with dynamiteand emulsion respectively. It is clear thatdensity of Water-gel is lower than that ofdynamite.

    VOD was successfully measured by theD’Autriche’s  method for the first time in SriLanka. By referring to Table 2 it is clear thatdynamite has the highest VOD and WG hasthe lowest.

    Acknowledgement

    Our gratitude goes to:Messers. KDA Weerasinghe quarry, Kalutara;BogalaMines, Aruggammana, Limestone

    Quarry, Holcim Lanka Ltd., Aruwakkalu;Explosive controller, Deputy Controller andAssistant Controllers of explosives - Kalutaraand all other organizations who assisted us inthe course of field work.

    Prof. Manoj Pradhan, Department of Mining,National Institute of Technology (NIT),Raipur, India is gratefully acknowledged foradvices given on VOD testing of explosives.

    References

    1. 

    Persson, P.-A., Holmberg, R., & Lee, J. “RockBlasting and Explosives Engineering”,  CRCPress (2001). 

    2.   Jimeno, C. L., Jimeno, E. L., & Carcedo, F. J. A.“Drilling and Blasting of Rocks”. Taylor &Francis. (1995). 

    3. 

    Meyer, R., Köhler, J., & Homburg, A.“Explosives”, Wiley-VCH. (2007). 

    4.  Cooper, P. W. “Explosives Engineering”, Wiley-VCH (1997 ).