I

SYNTHESIS REPORTFOR PUBLICATION

;ONTILACT NO: BRE.CT92.0315

ROJECT NO: BE-5887

rITLE: IMPROVEMENT OF PRODUCTIVITY IN QUARRYING DIMENSION

STONE USING NEW BLASTING AND DRILLING TECHNIQUES

>ROJECT

COORDINATOR: UNION ESPJ@OLA DE EXPLOSIVES (SPAIN)

‘ARTNERS : NATIONAL TECHNICAL UNIVERSITY OF ATHENS

(GREECE)

ARMINES - CENTRE DE GEOLOGIE DE L’INGENIEUR

(FRANCE)

DIONYSSOS MARBLE CO. (GREECE)

‘ROJECT STARTING DATE: 01.03.93 DURATION: 39 MONTHS.

E

PROJECT FUNDED BY THE EUROPEAN* * **

** * UNION UNDER THE 13RITE/EURAM*

* * * * PROGRAMME

DATE: 25.09.96

IMPROVEMENT OF PRODUCTIVITY IN QUARRYING DIMENSION

STONE USING NEW DRILLING AND BLASTING TECHNIQUES

J.A. Sanchidri4n, P. Garcia-Bermtidez (UEE, Madrid, Spain)

C. Tsoutrelis, G. Exadaktylos (NTUA, Athens, Greece)

t?. Cojean, J.A. Fleurisson (ARMINES, Paris, France)

d. Tsimidakis, C. Rogakis (D]ONYSSOS MARBLE, Athens, Greece)

ABSTRACT

Ornamental stone quarrying by drill and blast methods is surveyed. Although a traditional technique,significant improvements are identified along the course of the investigation.

A method for analysis of rock masses, with particular attention to systems of discontinuities, has beencast, so that planning of quarrying works is made in a sound and systematic way.

Numerical modeling has been used to get an insight of the action of explosive on the rock in the typicallyuncoupled blasting; both dynamic and quasi-static simulations were carried out in a variety of blasthole

● geometries (cylindrical and notched) and explosive charges. Preliminary critical (maximum) borehole spacingswere obtained by modeling.Laboratory and small scale tests in marbie and granite have been carried out to investigate the effect of

explosive charge, coupling ratio, notches and fill material on the quality of the cut and allowable blasttrolespacing. Some innovative methods, such as blastho[e lining with slotted tubes have also been tested inmarble. The positive effect of decked charges of b[ack powder has also been observed in granite cutting.

Some case studies have been analyzed in detail, and better use of drill and blast has been put intopractice: decking of black powder in granite primary and secondary blasting, notched holes in granite squaringand in marble secondary blasting. An evaluation of the benefits of these techniques is presented.

Practical considerations are given for blast cutting in granite and marb!e. Suitable drilling equipment isfound of great importance for good quaiity blasting, mostly for using notched drillholes efficiently. A preliminarydesign of a drill-and-notch machine is shown.

A computer program for the design of quany operations is presented.

INTRODUCTION

Ornamental stone quarrying is a relevant sector in

e the mining field of activity, particularly in SouthernEurope countries. Two methods are, basically, usedin ornamental stone quarries: mechanical, such asdiamond wire and saw, and controlled blasting. Othermethods are used, though in a minor and most oftencomplementary way, such as the jet flame.

Diamond wire and saws are commonly used inquarrying of soft rocks, such as marble, whilecontrolled blasting is generally used for harder rocks,such as granites. Nevertheless, most exploitationsmake use of both techniques, one of them beingdominant depending on the hardness of the rock.Economic reasons may well lead to the preference ofone method or the other, as investments needed formechanical cutting are higher than for drilling andblasting.

In most of the quarries, large blocks (dimensionsmay vary as much as 5 to 20 m long, 5 to 12 m highand 4 to 30 m in depth) are first extracted (see Fig.1). For it, vertical planes normal to the bench face arecut using diamond saw machines or diamond wire.

The remaining two planes are commonly cut bydrilling and blasting. Boreholes are almost universally28-34 mm in diameter, charged with detonating cordand very often with black powder as bottom charge.Detonating cords of 6 to 12 glm weight are the morefrequently used. Stemming is done by filling theboreholes with water, so that a certain couplingbetween the explosive and the rock is enabled. hsome cases, as in marble cutting, the explosive mustbe fully uncoupled to the rock for the shock pressureto be reduced, and no stemming is used at all.Blasthole spacing ranges from 20-25 cm in marbie,without stemming, to 30-45 cm in granite, with waterstemming. Holes are, sometimes, alternatively leftuncharged between charged holes. Lifters (horizontalblastholes) may, when weakness plane is horizontalin granite quarries, be reduced to a large diameterblasthole alone.

The secondary cutting (subdivision of the largeprimary blocks) is done in hard rock, again, by drillingand blasting along successive rows of blastholes.Further subdivision into commercial blocks may bedone by either drilling and blasting or by usingwedges. In softer rocks, such as marble, diamond sawand disk cutters are most often used for this phases.

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Improvement of productivity in quarryk?g dimension stone using new ciri[{ing and blasting techniques 2

- Special drilling, such as notched holes, is aknown technique that allows for a wider holesspacing. Nevertheless, it is not of general usein the quarries; improvements on drillingequipment could significantly enhance its use.

Optimum parameters for a cutting blast are highlydependent on the properties of the rock and thedirection of the cut. General solutions are hard tostate as the variety of geologic situations is rathervast. Hence, efforts were concentrated in obtaining,at least, as general as possible methodologies anddirections to follow.

Figure f. Typicai dimension stone quarrying sequence.

DESCRIPTION OF ROCK MASSES

The improvement of the cutting process by

● blasting means:- To reduce the drilling and blasting cost, byincreasing the boreholes spacing, or b;implementing better drilling devices.

- To reduce the waste of valuable rock.

These two goals involve a number of variablesand aspects, namely:

131asthole spacing, which is always a balancebetween drilling cost and quality of the cut.

Amount and distribution of the charge.Different detonating cords and black powderare customary. Filling of the boreholes can beeither water, sand or none. Some boreholesmay be left uncharged at alternate positions inthe borehole line. Use of explosives can besignificantly improved if loading operation ismade easier.

Directionality of the blasting. Cut blasting ismost often done along weakness planes of therock. There is not much chance to influenceon this in practice, as weakness planes aretaken into account when planning works atevery quarry.

This work is focused on granite and marb[e, thefirst being a typical hard rock and the latter a softone. Mechanical properties of those are summarizedin Table 1.

A detailed sumey was carried out in certaingranite and marble quarries in Spain and Greece, inorder to collect data on the controlled blastingtechniques used in the various phases of theextraction process. A specific methodology wasimplemented to obtain a good description of the setsof discontinuities and structure of the rock masses;3D geometrical models and serial sections wereobtained using SIMBLOC and VISIBLOC programs,making cutting planes apparent. Fig. 2 shows asample output of SlMt3LOC code, where sets ofdiscontinuities and preference directions of cut areshown.

An evaluation of the damaged zone aroundblastholes was performed using brazilian, bendingand ultrasonic tests. Elastic properties of the rockwere obtained as a function of the distance to theblasthote wall. As an example, Table 2 shows thevariation of the tensile strength of a marble frombrazilian and bending tests.

Table 1. Mechanical properties of granite and marble.

GRANITES MARBLES

Blanco Castilia Blanco Berroca[ Dionyssos Volakas Naxos

Uniaxial Compressive strength (MPa) 145 196 70-79 121-126 40-49

Tensile strength (MPa) 9.75 13.18 5,9-11.5 6.1-11.5 3.3-5.2

Bending strength @lPa) 15.1 15.9 9.3-25.6 8.2-10.2 12.8-17.7

Young:s Modulus (GPa) 55.1 67.3 42.5-47.1 56-62 36.8-41.0

Poisson’s Ratio 0.27 0.28 0,25-0.32 0.28-0.38 0.17-0.26

Density (g/cm3) 2.69 2.59 2,69 2,82 2.69

.-– —— —————

improvement of productivity in quarrying dimension stone using new dri#ing and blasfing techniques 3

Figure 2. SIMBLOC section of a quarry bench.

NUMERICAL MODELING

A mathematical model able to predict a priori the

●blasting variables (i,e., blasthole spacing andcharge), is probably out of reach, considering thelarge number of uncertainties that are always presentwhen describing a rock mass. Nevertheless,numerical modeling has been used as a means toobtain a deep understanding of the interaction ofexplosive and rock, and of the cutting process itself.This, in turn, allows a reasonable evaluation of theexperimental results.

Both rock and explosive materials must bemodeled. The use of explosives strongly calls fordynamic simulation, due to the highly transientphenomena induced upon the rock mass. However,it is possible, specially at blasting in ornamentalquarries, to study the dynamic fracture process apartfrom the gas pressure process. As a matter of fact,the shock wave is intentionally reduced by usingexplosives with low detonation pressure or lowcoupling ratios. The dynamic effects are considerably

*reduced and the gas pressure action can beconsidered as the main physical phenomenoninvolved in blasting. In any case, the possibiepresence of microcracks around the biasthoie has tobe taken into account.

Speciai geometries (notched holes} and influenceof anisotropy were also topics under study from themodeiing point of view.

a) Dynamic simulation with DYNA2D

The simulation of explosivelair interaction was afirst objective of the modeiing task. Then, the

simulation of the rock fracturing process waspursued, so that blasting patterns could be analyzedto determine optimum parameters (blastholespacing).

T h e explosivelair interaction has beendynamically modeled using a JWL-type equation ofstate (Lee et ai., 1968) for the explosive. JWLparameters for detonating cord of different PETNweights were calculated. A DYNA2D-standardmateriai model (pseudo tensor geological) was usedfor the simulation of the rock (Hallquist, 1988).

The expiosive/air interaction cannot be simuiatedin a direct way using a iagrangian code as DYFL42D,due to the large deformation suffered by the aireiements and the invoived numerical problems. inorder to soive this situation, the expiosive and airwere simulated as a whoie. For that purpose, a JWL-type equation of state was used for a “mock”expiosive fiiiing the borehole, reproducing thepressure histories computed in a real explosive~airinteraction over the borehole wall. The detonationand JWL parameters for this “mock” explosive wereobtained considering three different PETN detonatingcords of 3, 6 and 12 g/m within a 32 mm borehole.

When water is filling the borehoie, standard JWLparameters were used for PETN (Dobratz, 1985).Shock equation of state parameters for water weretaken from Mader (1 989),

Simulations were carried out to determine thecritical distance between blastholes to produce therock cutthg for different 2D blasthole patterns. Thedetonation action on the borehole wail was summedup by the pressure history obtained in this waii froma 3D -2D axisymmetric- simulation (see Fig. 3).Blastholes deiays were set in the modei, derived fromthe veiocity of detonation of the detonating cord andthe spacing (1.5 ps per centimeter spacing). A strain-based criterion was chosen to determine the criticaldistances, so that rock cutting is assumed if ail thematerial elements in the borehole iine have at anytime a transversal strain greater than a threshold,that is computed f r o m t h e geomechaniccharacteristics of each rock.

Figs. 4 and 5 show two samples of straincontours normal to the blasthole line; cut is obtainedin the first (6 g/m detonating cord, 38 cm spacing)and no cut in the latter (6 g/m detonating cord, 44 cmspacing). Criticai spacings (minimum at which cut isproduced) obtained are summarized in Table 3. Theyagree quite weii with available experimental data.

Table 2. Tensile strength of damaged marble.

Distance from blasthole wall (cm) o 2,9 5.3 5.8 8.7 10.6 11.6 f4,.5 15.9 ?7,4 21.2

Tensi{e strength, brazi{ian test (MPa} 5.3 6.2 7,0 6.3 7,4 7.7 7.0

Tensile strength, bending test (MPa) 7.6 13.1 16.3 96.2 164

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Improvement of productivity in quarrying dimension stone using new dri{ling and blasting techniques 4

Prm@ure *.,) *. (’mr]

Figure 3. Pressure in the borehole wall at a point 400 cmdown from the initiation point (collar); 6 g/mdetonating cord. Left: water filling the borehole;right: air in the borehole.

,.

Figure 4. Fringes of z strain (normal to the boreholeline) in granite in the vicinity of two 32 mmdiameter boreholes, 38 cm apart. 6 glmdetonating cord used; water in borehole.Time is 110 IJS after detonation of theborehole in the left. Cut is obtained.

ii-.d.f

Figure 5. Same as figure 4, but boreholes 44 cmapart; time is 120 ps. No cut is obtained.

Table 3. Critical spacings (cm) in granite obtainedwith numerical modeling.

ICylindrical hoies Notched holes

J

I Coupling I Coupling IWater Air Water Air

3 30 31Detonatingcord weight 6 40 20 41 30

(g/m) ,250 36 44

The importance of the use of notches, or thepresence of flaws in the material is apparent foruncoupled holes (“air coupling”), but it is notnumerically justified for blastholes filled with watercritical distance has a negligible increase in notchedholes when water is in the holes, while it increasessignificantly when fully uncoupled blasting is used.

b) Quasi-static simulation with FLAC

A parallel analysis to the one just described hasbeen undertaken using FLAC code (Itasca, 1993),the analysis based on the quasi-static action of thedetonation products. The fracture process itself, theinfluence of rock anisotropy and the geornetty of thenotched borehole were analyzed.

First of all, a parametric study concerning thequasi-static expansion of cylindrical cavities with orwithout cracks and notches has been carried out inorder to analyze the role of mechanical behavior andanisotropy of rock material, boundary conditions andnotches geometry, According to the fracture processtheory, the induced fracture propagates by openingthe material in tension, and therefore, the mainmechanical parameter is the tensile strength of rockmaterial. Concerning the notch geometty, the lengthplays a major role by increasing the tensile stressesat its tip, which promotes the fracture expansion. Itappears that the width of the notch has no significantinf[uence, and that the U-shaped notch is the mostappropriate. Moreover, the presence of notchesleads to decrease the tangential stress at the tip ofpossible micro-cracks located around the hole. Thisphenomenon will reduce the possibility of fracturepropagation at the tip of micro-cracks, and on thecontrary will make easier the fracture propagation atthe tip of the notch.

Then, computer simulations were performed inorder to compare the numerical results with the onesfrom laboratory testings (described in the nextsection).

Numerous parameters that affect the studiedproblem were investigated. Coupling ratios rangingfrom 8 to 32 % and notch lengths of 1 and 3 mm longwere used. In each case, c o m p u t e d a n dexperimental maximum induced fracture lengthswere compared, as show in Fig. 6.

lmpmvement of pmduciivity in quarrying dimension stone using new ciriiling and blasting techniques 5

160 ~ mm ~o~c ~,1401.. ------.--1--.---!-----------+-1

@,20J----_-. ---_ -T_--- _--].. T- _ - _ < _ _ _ –––––.

-1~80 _ - . - - - - . - - - - - - / - ’ - - - - - - - - - - - - - - - -5g #T---------: A - ’ – - - - - - . – - - – - - - - - - - - ].~ ‘t------< --------------i-----d

2oL___:_ -A__–.---.._-* & - - - - - - - - - - - - - 101 1

5 io 15 20 25 30 35coupling ratio (%)

— nogascnnfinement. best iit . numericalmsulfs

-.. gas mnfmentmt. best fit . =57qAmentalresuks nogaswn fin

200 II 3 mm notches I

I~ 50-

>*+-=+

0 0 1 10 5 10 Is 20 2s 30 35coupling rdtio (Y.)

. best fit for experimental results _ numerical redts~ experimental resu[ts

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Figure6. Comparison between numerical andexperimental results on Plexiglas testings.

Asthe numerical model used does nottake intoaccountthegas penetration inthe propagating crack,the numerical results areve~ consistent with thenogas confinement ones, provided that the couplingratio is greater than 15Y0. Under this value, the gaspressure is lower than the plexiglas tensile strength,and consequently fracture does not open becausethe model assumes a perfectly homogeneous andisotropic material. The small experimentally observedcracks could come from local heterogeneities or fromextension of microcracks due to drilling.

Taking into account an elastic plastic law (Nlohr-Coulomb criterion) with a tensile strength, it ispossible to initiate the fracture process between twoboreholes by using the computer code FI-AC. Theobjective is to define a critical distance betweenboreholes as the greatest spacing required to opena continuous fracture between the two boreholes.

A parametric analysis was performed concerningthe role of the two main parameters involved in thefracture process: the tensile strength of rock materialand the opposite notches length. The boreholediameter is 34 mm and the gas pressure is 25 MPawhich are both usual values in ornamental quarries.The whole results underline particularly the positivecontribution of notches on the fractures process.Even short notches (15 mm) could increase thecritical distance by more than 50 ‘A in the consideredrange of tensile strength between 7.5 and 17.5 MPa,which corresponds to common values for ornamentalrocks (see Figs. 7 and 8).

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fmptvvement of productivity in quarrying dimension sfone using new drilling and btasfing techniques 6

The choice of an isotropic medium to representthe rock mass is obviously an idealization of thereality. The following simulations were implementedto analyze the efficiency of notched boreholes inrelation with the anisotropy of the rock.

First of all, local heterogeneities as weak zones(with very low tensile strength) were included in therock material model at the edge of the notchedborehoie. The presence of local flaws as well as theirlocation does not effect the initiation of the fractureprocess which starts in the direction of the notch. Onthe contrary, when the length of the heterogeneity isincreased (vein or discontinuity connected with theborehole), the fracture expands mainly in itsdirection. This phenomenon was expected becausetheory predicts that the longest crack alwayspropagates first.

In a second stage, full anisotropic model wassimulafed using the FLAC ubiquitous joint model.This is an anisotropic plasticity model which assumesa series of weak planes embedded in a Mohr-Coulomb solid. Yield may occur in either the solid orin the weak plane by overcoming tensile strength orMohr-Coulomb yie ld cr i ter ion. Results aresummarized in Fig. 9.

Provided the tensile strength ratio (joint to rock) isnot too small, the presence of two opposite notchescounterbalances the effect of the anisotropy and thefractures propagate mainly in the direction of thenotches. However, parasitic cracks are liable to growin the direction of the anisotropy, and the more thenotches deviate from the direction of the anisotropy,the greater they are.

Moreover, in these favorable cases, the spacingbetween boreho!es has to be adapted to therespective tensile strength of rock material and weakplanes regarding the angle between both directionsof anisotropy and notches. The other mechanicalparameters such as cohesion and friction angle donot play a significant role.

Anyway, these semi-quantitative results underlinethe importance of an accurate in-situ identification ofthe anisotropy and a good determination of theanisotropic mechanical properties, in particular thetensile strength.

15 ‘~~

o 20 40 60 80 100alpha ~)

Figure 9. Influence of the direction of anisotropy on thecritical distance (ubiquitous joint model).

LABORATORY TESTS IN PLEXIGLAS ANDMARBLE

A number of non-conventional techniques appliedto dimension stone cutting have been described inthe literature, namely:

A dummy hole between two live holes

- Lines of dummy holes

- Prenotched boreholes

- Charge holders with slits

- Charge holders with wedges

- Charge holders with a concentrated force

- Charge holders with two stages of detonation.

Laboratory experiments were split in two series:The first one with plexiglas which, being isotropic,homogeneous, brittle and transparent offers manyadvantages as reference material. The secondinvolved three different types of marble; tests in thisseries were based on the plexiglas results. Theparameters investigated were:

- Coupling ratio- Gas action- Geometry of notches- Introduction of water and other fill material

between the decoupled explosive and theblasthole wall.

The flow chart of Fig. ! 0 presents the series oftests and parameters investigated in the laboratoryscale using plexiglas as the testing material. As it canbe seen from this chart two main lines of testing werefollowed:

(1) plexiglas models with a single blasthole; and

(2) plexiglas models with three blastholes in arow.

Similar conditions were applied to tests on marble.A number of conclusions were drawn from thisexperimental work:

- Single hole blasting experiments have showedthat coupling ratio DJD is critical for thedevelopment of undesired fracturing aroundthe blastholes (see Fig. 11).

- The use of water as a filling substance in theregion between the hole wall and the explosiveincreases appreciably the relative parhcipationof the shockwave in the fracturing process, ascan be seen from Fig. 12.

- The gas pressure which succeeds the shockwave action is mostly responsible for the finalcrack lengths due to blasting. The shockwaveonly creates a dense network of micro-cracksaround the blasthole which are furtherextended in much greater lengths by thepressure of the gaseous products. This meansthat stemming of the blastholes is of major

improvement of productivity in quanying dimension stone using new drilling and blasting techniques 7

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LABORATORY BLASTING TESTS IN PLEXIGLASFLOW CHART

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I I1 BLKTHOLE

3 BL46TW7.ESI

-----LNO GAs CONTL%ME.W

IBLAS+HOLES

1i40TC.WD BL4STHOKS SLOTTW TIJ2:S

NO G4S CONFINEMENT G4S CONFINEMENT

““’~%=+—%-’ !

“THo”TNoT”” m ‘-A’;FWar?Juk Tcarq-,la,

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Ik.lal-dar notd-ms

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1~Vabb water 1 I- NOTCi+O water@L&STH~E,

%tchm~=mdwla

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1 , Kg&i. k@.3 mkqth=l mm

Notch Notc,b Nolch I

&@=). %m+irlr &@P&mNOTCHED BLWTHCLES

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Figure 10. Flow chart of laboratory blasting tests using plexiglas models.

mxm

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Figure 11. Comparison of producing crack area in singlehole plexiglas specimens:1: Blasthole filled with water2: Blastho[e filled with marble powder3. Bk%%.thole open to the air.

importance in fracturing of rocks by blasting.On the other hand there is not an effectiveway (material and process) up to now forstemming of the blastholes without a negativeeconomic and time impact on the process ofrock fracturing by blasting.

The presence of the notches at the blastholewall affects the final effective crack length (50-80 % increase of final crack length relative to -the un-notched holes), however, it does not

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No WS ,.”1,”-.$

.

Figure 12. Effect of coupling ratio and of fillingmaterial (air, marble powder, water) inthe crack surface area produced in theblasthole wall under gas confinementand unconfined conditions.

affect the degree of undesired damage aroundthe hole in comparison to un-notched holes.

Notches characterized by the same iength butwith different shapes (rectangular, triangular,semi-circuiar) produce approximateiy thesame finai effective crack iengths.

As it was found both numerically andexperimentally, the initiai notch size does notaffect the finai crack iengths due to biasting ofsingie hoies w i thou t stemming (gasconfinement); see Figs. 14 and 15.

in gas confinement conditions, both theeffective crack iength and peripheral damage

[mpmvement of productivity in quarrying dimension stone using new drilling and blasfing techniques 8

.Figure 13. Influence of couplin”g ratio ‘in the oriented and

parasitic crack propagation in plexiglasmodels; Notch length = 3 mm; No gasconfinement.

‘“rrl-rrrr’l

I : ‘2%%3%2?2,——-— . . ..—.

Figure 14. Influence of coupling ratio in the oriented andparasitic crack propagation in plexig[asmodels. Notch length = 1 mm; No gasconfinement.

increase as compared to unconfined holes(without notches or slotied tubes). In the caseof notched Mastholes, gas confinementincreases only the effective cracks whileperipheral damage is the same as in the un-notched blastholes with no gas confinement.

The employment of either piastic or metaiiicslotted tubes gives similar resuits to thoseproduced by notching. More specifically, theuse of metallic tubes may reduce theperipheral damage to zero or to increase itdramatically. This fact depends mainiy on theratio D/D~, where D= Blasthole diameter andD~ =tube diameter, for all the other parametersremaining the same.

- The contribution of the shock wave tofracturing in marble appears to be lesser ascompared to piexigias fracturing. in general, inunconfined conditions no visibie fracturing ofmarble was observed in specimens of 20 mmthickness. However, it is expected that theincrease of specimen thickness wiil iead to anincrease of marbie fracturing when aii theother conditions remain the same.

- The employment of bronze and piastic siottedtubes in marble was effective for the directedcrack propagation aiong the biasthoies plane.On the other hand, the notches were not foundto be as effective as siotted tubes, especiai[yin iow coupiing ratios (i.e. DJ’D = O. 15).

SMALL SCALE FIELD TESTS IN GRANITE

in order to obtain data on the influence of thebiasting parameters (blasthole spacing, coupiing ratioand type and characteristics of the explosivecharges), a good number of different tests in graniteat a mesoscaie were performed,

The holes were drilied at different orientations withrespect to the preferential fracture or weaknesspianes, Commercial blocks (about 7 m3) were used.Severai rows of holes were drilled, with differentspacings.

The variabies studied were: explosive charge perunit length of blasthole and per unit area of newsurface, spacing between b!astholes, couplingmaterial and geometric placing of the charges. Thefollowing types of expiosive were tested:

- Detonating cord 3 g/m.- Detonating cord 6 g/m.- Detonating cord 12 g/m.- ANFO deck charges- Low energy explosive. A newly formulated

NG-based, low energy, iow brisance expiosive~EPN”) was manufactured for this work. EPNcharges were 11 mm diameter, 1 m iengthrigid tubes filied with explosive. They wereprimed using electric caps.

Explosive to rock coupiing was either air (i.e.,uncoupled) or water. When ANFO charges wereused, an air deck was piaced between the expiosiveand the stemming. In some of the blasts, when waterwas used to coupie the charges, a coloring agentwas added in order to identify the direction ofpropagation of the fractures.

Ail the tests consisted in progressiveiy varyingeach of the parameters, evacuating the resultsobtained in each shot in order to determine theoptimum combination of the design parameters.

Resuits are summarized in Figs. 15 and 16. Thefoiiowing conclusions can be derived:

The use of water as filling substance allowslarger blasthole spacings to obtain a specificquaiity of cut. By the same token, srnailercharges (e.g. 6 g/m instead of 12 g/mdetonating cord) can be used when water ispresent.

When air is used as “coupling” material (i.e.,no fiiiing is present inside the borehoie), ahigher charge of explosive is required toproduce the cutting. This leads to a higherdegree of fracturing around the biasthoies, notoniy in the direction of the boreholes’ line, butin other radiai directions. As a result, a higheramount of materiai is lost. In granites, it isadvisabie to use iow charges (e.g. 6 glmdetonating cord), with water inside theborehole, than high charges (e.g. 12 g/mdetonating cord) without fiiiing.

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ltnproven?enf of productivity in quarrying dimension stone using new dri~ling and blasfing techniques 9

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Figure t 5. Relationship between damage to the rock andspacing.

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Figure 16. Relationship between damage and specificcharge per unit surface.

- cutt ing along preferential (weakness)directions enables wider blasthole spacings -for a given charge- or smaller charges -for agiven blasthole spacing-. The increase inspacing allowed when blasting along theweakness directions is of the same order asthe reduction in compressive strength of thegranite along those directions with respect toperpendicular ones. The same is truewhenrefering to cutting in granites of difFerentstrength.

- The effect of dummy (uncharged] holesbetween charged holes has also been studied:more uniform cuts are normally obsewed withdummy holes.

[n what regards EPN$ tests with this explosiveproved the following:

- Shock energy transmission to the rock was byfar very high, resulting in an excessivefracturing of the rock. This was particularlyapparent when water was used as fillingmaterial. While brisance of the explosive wasbrought to a minimum (V.0. D. below 2000 mlsvs. more than 7000 m/s for PETN), couplingratio was higher (7Y0 for 6 g/m detonating cordvs. 32% for EPN tubes), this resulting insevere damage to the rock.

- Priming of the explosive tubes, either with adetonator or with detonating cord wasarduous. Further development should beneeded to improve this feature.

- For charges of great length, a male-femaleplugging system would help.

- EPN is highly trygroscopic, this propertyresulting in a certain probability of malfunctionafter lengthy storages. A certain degree ofwater resistance of the explosive pipes provednecessa~.

- Larger borehole diameters (probably above 50mm) sho,uld be used, so that the couplingratio, which adversely affects the smoothb~asting, is reduced.

The use of black powder in ornamental stonequarries is complementary -as bottom charge-to thedetonating cord. The main effect of black powder isto open the rock joints to fracture; it has also animportant heaving action, to separate the block fromthe rest of the rock mass or from the primary block.

The use of black powder shows two mainproblems: loss of time in preparation, and risk ofbreakage due to stresses during loading, resulting ina leakage of powder, which consequently becomeswet (as water is customary used as coupling materialbetween the detonating cord and the borehole wall)and losing efficiency.

Hence, charges of black powder were designedand prepared to obtain a safer and more efficient usewith detonating cord, avoiding the inconveniencesmentioned. Black powder is placed inside rigid plasticpipes, 41 mm diameter, 50 cm long, each onecontaining 130 g of black powder approximately; thetubes are sealed in both ends, so that they arewaterproo~ detonating cord (usually 6 g/m) is fixedalong the pipe by means of adhesive tape,

Charges of black powder prepared this way weretested for feasibility of use. Conclusions from thetests were the following:

- Cartridging provides some water resistance toblack powder, preventing it from wetting.

- Decking of the charge allows placing it at thedesired depths, avoiding underisable chargeconcentrations.

- Gas pressure is uniformly distributed along theblasthole, instead of being concentrated at thebottom.

- Flexible powder factor is enabled: it may beeasily varied from hole to hole, depending onthe local need of explosive strength.

LARGE SCALE TESTS

The more promising techniques pointed out in thepreceding sections were tested in actual large scaleblasts at different quarry sites.

a) Black powder decking in granite

[n the stage of subdivision of primary blocks into

Improvement of pmtfuctiWy in quarrying dimension stone using new drilling and biasting techniques 10

slices, drilling and blasting is extensively used inquarries of granite.. The cutting procedure consists ofdrilling 32 mm nominal diameter holes, 30 cm apart,with lengths alternatively one and three meter lessthan the height of the block (usually in the vicinity of10 m); the holes are, alternatively, about 6 and 8meter long. Each of the boreholes is loaded with acharge of about ~ 00 g of black powder, primed with6 g/m detonating cord; drill cuttings are used to stemthe black powder in the bottom of the hole; thisstemming prevents the water filling of the hole fromfully wetting the black powder.

Good enough cuts are obtained with thistechnique, but improvements were seen necessaryand possible, as:

Charging is time consuming

When attempts have been made to increaseborehole spacing, and larger charges of blackpowder are used, energy concentration in thebottom of the hole is also increased, therebyincreasing the undesired craking

Cuts are of good quality, but the displacementat the splitting line is small (generally below 4cm). This brings about the need of additionaldrilling and blasting of short length boreholes,in order to widen that separation (to aminimum of 11 cm), so that the edge of thepusher arm can be inserted, to overthrow theslice. This slows a great deal the process,and, at the same time, reduces the amount ofvaluable rock.

[n order to overcome this difficulty, an increase inthe charge was apparently needed, whereasadditional tincturing was to be avoided (that would bethe case if the charge remained concentrated). Inorder to provide a more uniform application of thepressure, a decking of the charge along the boreholewas used. This was done using the cartridges ofblack powder.

Decked charges of two cartridges of black powderper hole were tested. The cartridges were tied to thedownhoJe line of detonating cord (6 g/m) usingadhesive tape.

Six blastings were conducted in cutting slicesranging from 6,50 to 10,80 m long (face), 7 to 9,25 mhigh and 3,20 m thick.

Horizontal detachment of the primary block isdone by means of a large diameter borehole (90 mm)loaded with black powder in the bottom. This isenough to make the horizontal cut, as the weaknessplane is horizontal. As a consequence of using forthis blast a high charge concentration in the bottom,detachment in this area is more apparent, whichresults in easier secondaty cuts: [n the primary blockshown in Fig. 1, secondary cut W is easier than W.

Fig. 18 shows the influence of the amount of blackpowder per unit surface on the separation of theblock. Conclusions listed in the preceding section

1- -1(e..n,, m

Figure 17. Cutting of slices using decked charges ofb[ack Dowder.

,CO 1 I I I I I,,, . ,,, ,,,,

Figure 18.

SEPARATION {cm)

Separation of the block at the cutting line asa function of the charge of black powderand the position of the cut.

were confirmed. Besides, the following should beremarked:

- Time saving: Loading and priming is done fast,as no on-site cardridging operation is needed.

- Cuts of better quality are obtained, probablydue to the absence of charge concentration inthe bottom, resulting in a more uniformpressure along the borehole.

- Individualized loading pattern of the boreholes,depending on their position in the blasting line,is allowed.

- Favorable acceptance of the quarrimen.

b} Blasting optimization in granite using notchedholes

Several tests were carried out in granite quarriesin Bustatviejo (Madrid) to study which would be theoptimum design for cut blasting with notchedboreholes. The parameters used in the study werethe spacing between blastholes and the chargeconcentration, in order to find the most appropriatecombination.

Lines of blastholes were drilled in granite blocks,

Mprovernent of fxod.mtivity in quarrying dimension stone using new drii[ing and btasting techniques $1

of size ranging from 4 to 5 m3; uniaxial compressivestrength of the granite was 120 MPa. Notches 3 mmlong were made with a drill steel driven by a drillhammer whose rotary device had been disabled.Rows of 28-30 mm diameter holes were loaded witha bottom charge of black powder and detonatingcord. Boreholes spacing varied from 0.4 to 0.7 m;powder charge and cord weight were varied in thetests. Borehole filling was water in all cases.

The spacing between borehoies was varying inthe different tests from 0,4 m to 0,7 m. Four testswere made, with several rows blasted in each test.

Fig. 19 shows the maximum allowable spacingsas a function of detonating cord weight; results forcylindrical holes have been included for comparison.Spacing when using water coupling may beincreased, for a given cord weight, to more thandouble as cmmpared to that for an uncoupled charge.The use of notches, in turn, further increases the

espacing by some f 5 cm.

Decoupled borehole pressure required to get anefficient cut, for a given borehoie spacing, is shownin Fig. 20, for both cylindrical and notched holes. Thispressures are computed from the expresion (Calderand Bauer, 1983]:

S= D(PB. +T)/T

S being the maximum blasthole spacing for cut, !3diameter, PBe decoupled borehole pressure and Ttensile strength. It is apparent that borehole pressurerequired using notches is about 30V0 lower than thatrequired with cylindrical holes. There is, naturally, aminimum pressure required to produce the cut, thispressure being the critical pressure to initiate cracks.

Conclusions regarding tests with notched

● blastholes in granite can be summarized as follows:Hole spacing can be increased by 25 to 40percent.

Reduction in borehole pressure needed for thecut. This reduction in borehole pressure canbe achieved by reducing the column charge to1/3 of what is used with cylindrical holes.Hence, smaller charge concentrations couldbe used to propagate the fracture.

Excellent hole-to-hole fracturing was obtainedand very little parasitic fracturing in otherdirections was observed. Consequently, rockwaste is reduced.

Notched drilling increases by 20 to 30 percentthe unit drilling cost as compared to cylindricaldrilling.

Notches bring their full efficiency when theyare all drilled in one plane. Deviations from thissituation (customary, when made by hand)result in a drastic reduction of their benefit.Improvements of notches drilling equipment

en —...—....—..-...——.-—-———1

7 0 . — — — ,

m. / a.

-E50~p m.

~30-. . * . .

m 2D...4,

?0 ,-++-..

030 5 10 15 20 2s

Charge (@n)

I ----- QWl&Z4 lwks; em . . . . . . Qftidrba[ bks: w ater — M!chedhcA8s: W@ter I

Figure 19. Charge vs. maximum spadng for the differenttests.

(1)

Figure 20. Spacings vs. decoupled borehole pressure. (1)This point may not correspond to a maximumblasthole spadng tests at wider spacings werenot performed. Hence, pressure may be lowerthan as defined by this point.

would certainly widen the use of notchedholes, so far relatively restricted.

Improved splitting technique for secondaryblasting in marble

As the primary large marble blocks, which usuallyexceed 120 m3 in size, are quarried at the benchusing the diamond saw technique and that of drill andblast with black powder primed with detonating cord,fall down they break into smaller irregular boulders(blocks) due to the presence of fractures, joints andfaults. Such irregular boulders or blocks must then besquared in blocks of appropriate marketable sizes.Squaring under the given structural features of theDionyssos marble deposit yields an averagerecovery of about 12% of marketable blocks.

This secondary operation takes places in generalby using three different techniques in order to squarethe irregular blocks:

- By applying the traditional and well knowntechnique of drill and blast using decoupledlinear charges of standard type detonatingcord of 12 g/m charge in nominal 32 mmdiameter blastholes. Drilling of such blastholes

I

improvement of productivity in quarrying dimension stone using new drilling and blasting techniques 12

costs 1.1 to 1.7 ECU per meter and 8-9blasthoies are needed to produce one squaremeter of finished marble surface.

- By very dense drilling of holes with spacings aslittle as 3-10 cm followed by wedging (Fig. 21 ).

- In certain quarries the diamond saw techniqueis used which, however, for squaring smallsize blocks turns to be very costly and long.

Considering the high costs involved in squaringirregular blocks in order to produce a marketableproduct and the fact that squaring using the diamondsaw technique is a very costly operation, an attemptwas made to reduce this cost item. H is estimatedthat a reduction in drilling by 30% will reduce the costper mz of the cutting surface by 5-8 ECU.

Extensive experimental field tests were carriedout in Dionyssos, Naxos and Volakas quarries inorder to develop an improved detonating cordtechnique during the processes of marble extractionfrom the bench site and squaring during thesecondary stage. A detachable notching tool and adrill rod (with side-on flushing holes) were designedand constructed. Five different versions of thenotching tool were tried; Fig. 22 shows these. Thesenotching tools were effective for drilling diametricaltriangle notches of 3-4 mm in length.

Field tests were carried out first in Dionyssosquany. Blasthoies were drilled perpendicular to thebedding plane, in directions F-F [ZOX) and T-T (zoy)(see Fig.21 ). Only a single test was carried out withthe blastholes drilled parallel to bedding. Fivedifferent methods were tried in order to cut themarble blocks along the desired plane:

c}

a d)e)

All

Use of standard detonating cord of 12 g/m.

Use of a combination of slotted plastic (PVC)tubes and detonating cord.

Use of notches only.

Use of a combination of notches and standarddetonating cord.

Use of black powder combined with detonatingcord of 12 ghm.

blasting tests in which detonating cord wasused were ca~ried out with constant coupling ratio of9%. The blasthole diameter was in all cases between34-35 mm and the detonating cord used was of thestandard type of 12 glm having an effective explosive(PETN) diameter of 3 mm. The main conclusionsdrawn from these tests are:

- The use of detonating cord creates a damagezone (as measured with the projected crackiength in the perpendicular to the cutting planedirection), with crack lengths varying from 3 to7.5 cm depending on projected plane (thisreduces the marketable size of the block andshould be as small as possible}. Maximumspacing for achieving clean splitting along theF-plane is 14 cm while in the T-piane is 8.5cm.

(a)

Figure 21.

(h)

(a) Splitting of a primary block into smallerblocks. (b) Squaring of an irregular boulderinto a block. (Weak bedding and weakschistosity are only present in Dionyssosmarble),

. .. ——— .*..

~Q @~F.— *.— ---,—— --.--.--.—-— . ..—

— %.— ., . —-— —-- ._ L...+-..”—, ,’

Figure 22. Notching tools.

The use of slotted plastic tubes combined withdetonating cord is effective for cutting in thedesired plane, but causes wall damage to thesplitting plane.

Using only notched drillholes along the F-Fplane (zoy), clean splitting was achieved withspacing up to 17 cm with the assistance of aone mechanical wedge pushed in onedrillhoie. No damage effect was recorded.

The use of notched blastho[es combined withdetonating cord is effective for cutting themarble block along both the T-plane (zoy) andF-plane (ZOX). For cutting along the F-plane(minor schistosity plane), an increase ofspacing from 14 cm to 25 cm was observedwhile the damage effect remained the same.For cutting along the T-plane (the mostdifficult), spacing was increased from 8.5 cm

Improvement of productivity in quarrying dimension stone using new dfflling and blasting techniques 13

I

to 13 cm, while the damage effect was aboutthe same (6.5 -7 cm).

The use of combination of black powder anddetonat ing cord causes wall damageperpendicular to the splitting plane {5.5 cm].

- The notch in a drillhole causes c rackpropagation in the desired direction with lengthof 6 cm.

- When cutting along the T-plane using notcheddrillholes with spacing 9 cm the irregularity ofthe cutting surface obtained is commerciallyacceptable.

Field tests were also carried out in large marbleblocks ranging in volume from 1 to 4 m3 in Votakasquarry. Due to the high metamorphism of the Volakasmarble (dolomitic marble), no bedding or anyschistosity are visible. It is assumed, therefore, thatno anisotropy effects should be considered. Takinginto consideration the experience gained from fieldtests in Dionyssos quarry, methods a), c) and d)were used in order to cut the marble block along thedesired plane.

The main conclusions drawn from these tests are:

●

The maximum spacing between btastholes(edge to edge) for achieving clean splitting ofthe block using a single line of standard typedetonating cord was 15,5 cm and 14 cm forthe T-T plane and the F-F plane respectively.No damage zone due to blasting wasrecorded. The absence of recording anydamage zone even when using penetrantscan be attributed to the stress-strain diagramof the Volakas marble which exhibits highelastic strains at low stresses and a highmodulus of elasticity.

The use of notched drillhoies in combinationwith 3 mechanical wedges pushed into 3drillholes is etiective for cutting the marbleblock with spacings up to 33 cm between thedrillholes.

The use of a combination of detonating cordand notched blastholes is effective for cuttingthe marble block with maximum spacing of 20cm, while no damage effect was observedafter the examination using penetrants.

The notch in a driilhoie causes a crackpropagation in the desired direction with lengthof 5.5 cm.

A relationship between spacing of thedril!holes and the roughness profile of thesplitting plane seems to exist. As the spacingincreases, the surface roughness of thesplitting plane increases also.

Field tests were also carried out in blocks rangingin volume from 1 to 3 m3 in Naxos quarry. Nobedding or any schistosity are visible in this marble.Methods a), c) and d] were also used in order to cutthe marble block along the desired plane.

The main conclusions drawn from these tests are:

The use of detonating cord creates a damagezone (projected crack length in a directionperpendicular to the cutting plane), with cracklengths between 5 to 8 cm. This damage effectdoes not depend on the orientation ofrecording them.

- Maximum spacing for clear splitting using onlydetonating CQrd 12g/m is 15 cm, and it does notdepend on the cutting diredlon (XOZ or yoz)while for splitting in the S-plane was 20 cm.

- The use of notched drillholes is effective forsplitilng the marble block in the desired plane.Maximum spacing for splitting was 20 cm.Three wedges were used.

- The irregularity of the splitting surfaceincreases as the spacing between thedrillholes increases. This irregularity is criticalfor the commercial acceptance of the marbleblock.

- The use of notched blastholes does not affectthe spacing between the blastholes for un-confined blast conditions.

- The use of a drill-bit of 32 mm nominaldiameter, creates a drill hole of 35-36 mmdiameter in Naxos marble, while in the twoother quarries the diameter of the holes was33-34 mm by usirig the same drill-bits. This isdue to the bigger grain size of Naxos marble(3 mm) to the grain size of Volakas marble(0.4 mm) and Dionyssos marble (

improvement of productivity in quarrying dimension stone using new drilling and blasting techniques 14

one of the major disadvantages of this technique,despite its very good results.

In the best case, notched drilling may increase by20 to 30 percent the unit drilling cost, while the drillinglength may be reduced (as the spacing is increased)by

b}

25 to 40 percent.

Blasting parameters in granite with deckedcharges of black powder

Cutting of large slices from primaty blocks maybedone by drilling 32 mm nominal diameter holes insuccesive lines, with a spacing of 30 cm. Holes maybe drilled to a length, alternately, of approximately 1and 3 m less than the bench height, in order toprevent damage of the rock below the block. Theblock has been previously cut in the horizontal planeby a lifter blasthole. Short holes should be loaded

● with one cartridge in the bottom, and long ones withtwo cartridges, one in the bottom and a second oneabout 4 m from the collar (slightly above half depth ofthe borehole). In difficult cuts - front cuts, closer tothe face, where horizontal detachment is not so neat-it may be advisable to load two cartridges in everyhole.

Slices cut this way must be overturned by apushing arm mounted on a ioacter. [t is important, toimprove the operation, that the edge of the arm canbe inserted within the gap distance at the cutting line.Should this not be possible (the pushing arm edge is4 cm wide), auxiliary holes of short length must bedrilled and blasted, with a consequent slowing of theoperation. Blasting of decked charges allows a highercharge in the blastholes, with a better heaving actionand displacement, without bringing on an underisablecharge concentration.

● c) Drilling of notched holes

Manual drilling hammers are most often used tomake notches. This system makes it difficult to alignthem perfectly in acmrdance with the direction of thecut.

Attention has been paid to the improvement ofnotches-making by mechanical means. A prototypeof drill-and-notch borer (“block cuttet’) has beendeviced. Component features and suitable workingoutlines are described.

One or more drill hammers, working onpercussion only, are needed. Either if the rotationmechanism is a rifle bar or a ratchet wheel, it ispossible to disable the rotation movement by simplyremoving the pawls.

In what respects notching bits, it is possible tomake notches 3 mm long using Seriers 11 integraldrill rods for drilling and Series 12 for notching, as thedifference in bit diameter is 6 mm. This way, special

drilling accessories are not needed. Thedisadvantage of this notching is that the notch maynot be sharp enough, in order to direct the crack inthe desired direction.

An adaptation of a conventional twin-hammerdrilling system mounted on tracks is easily done: oneof the hammers works on rotopercussion and theother on percussion only. The air circuit must have apressure regulator, so that the power in thepercussion hammer is lower than that in therotopercussion one, in order to provide evenpenetration rates in both hammers: Notches, havinga much smaller transverse surface than theboreholes, need a lower power to be drilled. Sometests must be done in the beginning of the work, withdifferent air pressures (actuating on the pressureregulator) in order to determine the pressure thatgives the same penetration rate in both hammers.This position would be kept until variations in the rockadvise to change it.

Considering a block to be cut, and having theequipment on the working platform, and the trackslaid out, the working procedure would be asdescribed in Fig. 23. Hammer ~ in the figure isequipped with series 12 drill rods, while hammer 2with series 1‘1.

A limiting feature of the equipment is themaximum distance of the hammers in the frame, asthis is the maximum spacing allowed for theboreholes. A frame with four hammers can also beused, two of those working on percussion and theother two on rotopercussion. This needs a ratherlarge supporting frame, at least three times theborehole spacing. Fig. 24 shows a sketch of suchdevice (a two-hammer device would look similar, withtwo hammers in the frame}.

Another variant of the “block cuttei” is one withtwo independent frames, one of them conventional,with the desired number of hammers, and the otherone with percussive hammers. Both frames would

@dn1-tz

!—-_ .

❑ m-m:+ Standing (air reguiator Iocknd)~ A!fwwdy.n (high level)

Figure 23. Combined work cycle with two hammers. OPercussion (notching); @ Rotopercussion(drilling).

improvement of pmducf[vity in quarrying dimerrsion stone using new dtiiting and bkwfirrg techniques 15

.

l!?Q

,1!

I& ITable 4. Optimum spacings for squaring marble

blocks using notched holes.

I BW3THOLE SPACING (cm)

l--SPLllTING PLANE DIONYSSOS(Fig. 21)S-plane 17 VOLAKAS N A X O SF-plane I 14 I 13 I 12T-plane 9 13 ?3

Notes on correct operating procedure:

Figure 24. Four hammer “block cutter?

move on the same tracks. The first group would drillconventional holes at the desired spacing. Thesecond group would follow, matching notches. As thepenetration rate of the second group is higher than -

the first, the number of hammers in it can be smallerthan that of the first group.

d ) M a r b l e b l o c k s q u a r i n g using n o t c h e ddri[lholes

The drillholes should be drilled at a singlestraightline row with no deviations if thenotching is to be successful.

The orientation of notches should be alignedwith the drillholes row if they are to workproperly.

When notching, the drill steel axis has tocoincide with the drillhole axis, otherwise thenotches are not created properly and it wouldbe difficult to bring the drill steel and thenotching tool out of the drillhole.

The notching operation should be continuous.

If the splitting plane is next to the free surfaceof the irregular marble block, the spacing mustbe reduced by 20Y0, in order to prevent anyfree surface effect during the blasting stage(crack deviation from the desired splittingplane).

Outimum s~acinq for squarinu marble blocksCOMPUTER PROGRAM FOR QUARRYING

using” notched &ill h&s in the” three-different marblesanalyzed are given in Table 4. A computer code for the design of blasting

The cost comparison between the improved operations, named “Blaster”, has been developed.squaring technique (notched drillholes) and the The program is meant to help the quarry man in thecurrent applied technique is given in Table 5. design of his operation and the evaluation of costs.

Table 5. Cost comparison between notched holes squaring technique in marble and current technique.

Quarry Dionyssos Volakas

Splitting plane (Fig. 22) s F T AH s

C: Current method i N: Notched holes C N CN CN CN C N

Drillholes spacing (cm) 10 17 7 14 4 9 4 13 8 13

Drilled m per mz of split surface 8 5 10 6 14 8 14 6 9 7

Cost of single hammer machine in a 88 55 11 66 154 88 154 66 88 -retro arm (ECU/m2)

Drilling time {min/m2) 107 67 134 8 487 1 0 6 187 8 - -

Cost of worker with drill hammer 136 85 17 102 238 136 2 3 8 102 153 119(ECU/m2)

Drilling time (min/m2) 254 16 318 19 445 255 445 19 254 223

Drilling reduction (%) 37 40 42 57 22

Cost reduction (%) 37 37 42 57 22

=HCNCN6 12 6 13

11 7 11 7

11 - 154 -

- - - .

187 119 187 119

.

“ fmproven?ent of productivity in quarrying cfimension stone using new drilling and blasting techniques 16

It became soon apparent that a program devotedexclusively to drilling and blasting in quarryingdimension stone would be of little use, as mostquarries combine several techniques during theextraction process. For this reason, besides drillingand blasting, other techniques used in dimensionstone quarrying are considered in Blaster: diamondwire, jet flame and wedges.

Software and hardware requirements areminimum, so that it can be used virtually in any typeof personal computer. Input data required for theprogram are the following:

~ Explosive: Name, VOD, density, price, weightper meter (detonating cord).

~ Rock: Name, density, compressive and tensilestregfhs.

Data files are provided with properties of someexplosives (black powder and detonating cords of

● several weights) and rocks (spanish granites andgreek marbles).“ Dimensions of the block. Blaster requires the

size of blocks in every cutting phase. At thefirst cutting, the initial dimension of the block tobe extracted is defined by its height (ALT),width (ANC) and depth (FON). The secondphase consists in subdividing the block intosmaller ones with the same depth and heightthan the initial block. The ‘width of these blocksmust be defined (EC). At the final phase, theuser must define the height (E.), depth(FOND) and width (ANCD} of the final block.Blaster gives the weight and number of totalfinal blocks, and the geometrical recovery rate.

Calculations proceed through three phases, whichcorrespond to the three stages of extraction andcutting process:

●- Phase 1: Separation of the block from the rock

mass.

- Phase 2: Cutting of slices from the primaryblock.

- Phase 3: Final cut to marketable blocks(typically of size around 5 to 10 m’).

Taking drilling and blasting technique as example-this being the main purpose of this work, and for thesake of concision-, calculations are summarized inTab}es 6 (drilling) and 7 (blasting). Formulae forcalculations are inciuded in Tables 6 and 7; fordetonating cord core diameter and blasthole spacing-notes (1) and (2) from Table 7-, the followingexpressions appiy (meaning of symbols is given inTable 6}:

(1) For detonating cord, core diameter d (mm}is calculated by:

d ’24m

where W is the cord weight (glm) and p, is

the PETN density; a typical value is 1,25g/cm3.

(2) Blasthole spacing is calculated as follows:

First, borehole pressure P13 (MPa) iscomputed:

PB =228 X10”6Pe. Vdz/(1 +0.8 P,)

For a decoupled shot, detonation gases willexpand within the borehole to a pressure PB@:

PB~=KPB. (& .d/D~’4

where K (coupling constant) accounts for anincrease in wall pressure when materials otherthan air are filling the borehole. Final!y,spacing E (cm) is calculated:

E= O.l” DO(PB, +KwTS)/(KWTS)

where TS is the tensile stregth (MPa] of therock & is a “weakness” factor that accountsfor preference directions along which cutting isfavored. & is 0.8 for cuts along suchdirections, and unity for others.

Variables in the tabies may be input (1) data,output (0), or read from data files [DB). In mostcases, when input variables are required, defaultvalues supplied by the code may be used, if noguessing exists from the user.

CONCLUSIONS

The following conclusions should be highlighted:

Driiling and blasting methods are efficient inevery cutting phases in medium and hardrock.

Decking of charges of black powder primedwith low-weight detonating cord increasespowder efficiency and produces better splitsurfaces. Charge concentrations are avoided.

Linear charges of high expiosive should havea coupling ratio beiow 25-30% to avoidexcessive parasitic cracking.

Water coupling allows low linear charges (e.g.6 g)m) to be used in granite, while no suchcoupiing is needed in marble.

Blasting of notched holes enables widerspacings (from 30 to over 100Y0, dependingon the tensile strength of the rock). Notch sizedoes not affect significantly the. notching effect.

Maximum allowable borehole spacings havebeen obtained for granite and marble spjitting.

Careful drilling is of extreme importance,particularly when notching.Borehole deviations and bad alignment of

●

✎ improvement ofproductivify in quarrying dimension stone using new driliing and biasfing techniques 17

Table 6. Calculations for drilling and blasting: drilling.

STAGE OF CUT: FIRST, SECONDARY, FINAL

SYSTEM: DRILLING AND BLASTING

PHASE: DRILLING

ITEM SYMBOL

MOP

D

UNIT

u

MAX. MIN.

f

26

)EFAULT FORMULA

Labor 3

51

2

Drilling diameter mm 36

Length of charge tolength of blastholes ratio

Core or charge diameter

1i

l/DB

1

mm

mts

d D Formula

v, DBV,O.DDensity of explosive DB gfcm3P,

For air K = l

For sand K = 2,5

For water K = 5

coupling K i Formula

Blastholes Spacing E o Formulacm -2PHASE 1:

Cuts A & C Nb=l+100F0N/E

Cut B Nb=l+100ANC/E

Lift up cut Nb=l +1 OOANf2/E

PHASE 2:

Single cut Nb=l+100.ANC/E

PHASE 3:

cut A Nb=l+100.FC)ND/E

Cut B Nb=l+100.ANCD/E

Number of blastholes Nb o

0

u

m

Formula

L,Length of holes Formula PHASE 1: ~ = ALT

PHASE 2: ~ = ALT-0,4

PHASE 3: ~ = ALT-0,4

Total length drilled o FormulamPenetration rate cm[min 200 10 100Penetration time

Availability

~xh yym

%0

Formula

75

$= (5.LJ / (3.VP)

~=~lp

100 50PFormulaDrilling time xxh yym

Fuel consumption c I I/h i 00 40 40

Table 7. Calculations for driiling and blasting: blasting.

[ STAGE OF CUT: FIRST, SECONDARY, FINAL

SYSTEM: DRILLING AND BLASTING

PHASE: BLASTING

ITEM SYMBOL 1/0 UNIT MAX MIN. DEFAULT FORMULALabor MOC [ u 3 1 2

Detonating cord length cd o m Formula C,= [(%X LJ + 0,015 E] X N b

Black powder mass Polv I kg 20 0 0 I

Caps Det I u 1

I Loading time L o xxh yy m - Formula ~ = 0,084. Nb

r improvement of productivity in quarrying dimension stone using new dti}ling and biasting techniques 18uI

notches lead to poor splitting surfaces,parasitic cracking and smaller boreholespacings to ensure the cut.

- Quality and productive notching may only bemade with drill-and-notch hammers (twin-hammer systems}. A preliminary design andworking procedure for such equipment hasbeen described.

ACKNOWLEDGEMENTS

This paper was prepared as an account for theDirectorate General X11 of the European Commission,under a research project funded by the EuropeanUnion within the Brite-Euram Program, Contract No.BRE.CT92.0315, Project No. BE-5887. EuropeanUnion support is gratefully acknowledged.

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