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CONTRACT no 13RE2-CT92-0127

BLASTING CONTROL FOR UNDERGROUND MININGWITH SPECIAL REFERENCE TO IN-SITU

M E A S U R E M E N T S AND TESTS.. .

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FROM 01.11.1992 TO 31.07.1995,. . .‘., . . . .. ,’,.,.

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PROJECT REPORT No 8

ARMINES/CGES CoordinatorPOLITECNICO DI TOIUNO PartnerBAUXITES PARNASSE PartnerNITROBICKFORD . PartnerMONTANUNIVERSITY LEOBEN PaitnerVOEST ALPINE ERZBERG Major Subcontractor

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i1. OBJECTIVES OF THE PROJECT

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The improvement of an existing blast supposes two different cycling steps : first thediagnosys of the problem, then the application of a therapy in order to solve the problem.

If the therapy (or blasting planning) uses more or less the same principles sinceLangefors deveIoped his theorj, the diagnosys is still a highl y time-consuming process whichdoes not always provide all the necessary inforniation for a correct therapy.

The current project, under the name of Blasting Control, clearly addresses the firststep of the kycle : the diagnosys. Its industrial objectives are to :

more precisely control the bksting operation, by the use of an updated methodology,using the recent improvement in terms, of acquisition devices and explosivemanufacture,

indirectly, make available control tools for the main entities invoIved in b~astin~(fracturation, explosive energy, fragmentation, vibrations, and side effects). -

As a result, the application to any ‘underground mine of the Blasting Controlmethodology developed in the project should provide blasting experts (mining engineers,academic professors or technical services) with the relevant data for the improvement ofbiasting in this mine, in a time compatible with production constraints.

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2. CWMN’IZAT~(3N. OJ?:i’EEE PROJECT. ,,. .

In order to reach the objectives of the research, the project has been organized inthree main phases (figure 1) :

Analysis of the blasting practicai experience (without any specific control) in amine in production (Biiuxites Parnasse).

The idea was to show that it was not possible to propose a correct therapy to the minesimply with a manual observation, that is to say that there was a real need for thecurrent project !

Development of the Blasting Control methodology

This second phase was based upon measurement of M possible information before,during, and after blasting. It concerned the rock to be bIasted, the explosives used,the blasting process itself as well as the results of the blast Wd its environmentalimpact. The phase more precisely proceeded through the three foIlowing steps.:

Development of control devices, in a fully dedicated test mine (Erzberg testsite).

Contract 13RE2.CT92.0127 Pro.iect te~ort n“ 8Blasting Control 1 “ 01.11 .lj92 - 3~.07.1995

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This step included the choice and adaptation of the control devices, thematerial preparation of the test site and the organization of the tests, thedefinition of a “working blast”, and [he control devices tests, calibration andvalidation.

It provided the instrumentation, as well as the acquisition methodology, usab[ejn any underground mine.

ExpIcisives and detonators properties measurement, in a dedicated chemicallaboratory (Nitro-13ickford pkmt)

. .~ The different explosives and detonatorsfor future comparison and calibration.

Interpretation of the measurements

used in the project have been amdyzed

In order to provide the experts in charge of the therapy work with a-usable--information, it has been necessary to an~yze the measurements o~tputtti fromthe devices. ‘The geometrical data have thus been processed, and severalanalysis and correlation have been made on the other measurements, in orderto extract significant parameters on the controkd blast behavior.

This second phase answered the key questions of how can the blast be ccmtrokd,and what type of information can be extracted from the measurements.

. .- Validation ok the blasting control methodology in a mine in prod~ction (Bauxites

Parnasse) “’.

This last phase first concentrated on the validation of the acquisition with the workingconditions of a mine in production. This also has provided data, used by an expertgroup in order to propose a new blasting scheme (therapy). Finally, the new blastingscheme has been tested and validated in the mine in production.

This third phase of the research showed the feasibility of fuI1y controlled b[asts ina mine in production (diagnosys), as well as the efficiency of the measurements zfor a real improvement of the blast (therapy).

In order to realize such a research program, the project consortium was constitutedof a mine in production as an end-user (Bauxites Parnasse), of a partner able to provide afully dedicated test site (Leoben), of an industrial company specialized in explosives anddetonators manufacturing (Nitro-Bickford), and of three complementary academic parmers(.4rmines, Politecnico Torino and Leoben). For the performance of the mining, work i! thetest site, Voest Alpine Erzberg GesmbH was gained as a major subcontractor.

Contract BRE2. CT92.0127 Project report n“ 8Blasting Control 2 01.11.1992-31.07.1995

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ANALYSIS OF BLASTING PRACTICAL EXPERIENCE .--. > Limit of control

without devices

DEVELOPMENT OF BLASTING CONTROL NIETKOI)OLOGY

II. 1

11.2

H.3

Control devices development

. ,clevices adaptation

. test organization .---> How to control

. working blast with devices

. device tests

Explosives and detonators measurements

Interpretation of measurements

. geometrical data processing ---- > Wh,at to expect

. analysis and correlations from the control

VALIDA,TION OF BLASTING

111.1 Acquisition validation

111.2 Exarnple of therapy

.CONTROL mTHbDOLOGY

----> Feas ib i l i ty ofcontrol in workingconditions

----> Example o f

ImprovementImproved b l a s t i n g s c h e m e following the mntrol

. tests of the new scheme

Figure 1 : Organization of the projdct

Contract J3RE2.CT92.0127 Project report n“ 8Blasting Control 3 01.11.1992-31.07.1995

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PHASE 1: ANALYSiS OF BLASTING PRACTICAL EXPERIENCE

The first phase of the project has been dedicated to the analysis of the practicalexperience of blasting in the Bauxites Pamasse mine.

The work logically started with thedefinition ofa blastingagencfa, supposed to befilkdby mine foremen for each observed bIast, including the followingitems :

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of the

bIasts,

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GeneraI data (date, time, working area, drift, blast)Shape of the drift before blasting (actual profile, face situation, distances to referencepoint)Geological situation (rock type, disconthmities)Blasting geometry (actuaI cut, drilling pattern, charging, delay)BIasting results (pile profile, grain size distribution, advance profile after bksting)Scaling (length, volumes)Shape of the drift after blasting (profile, face situation)

The next step addressed. the observation itself which runned during the first 6 mcmthsproject on 43 blasts referring to 6 different drifts in limestone and in bauxite.

Finally, a detailed analysis (statistical and qualitative) concentrated on the 43 observedThe statistical analysis of the resuIts showed that, : .’ .”

\Simple correlations between obsemed parameters was not possible.’” ,

There were many deviations between actual and planned rounds, both in bauxite andin limestone. They mainly concern the cut pattern and the charging.

The results, in terms of advance and profile shape, were fm from the expectations.

The qualitative analysis of the results showed that :

The key point of the blasting success is the cut. The best results (regarding overbreaking and advance) are ob~ined when the actually drilled cut is different from theplanned one.

The drilling side seemed to be only indirectly affected by explosives, which raised theproblem of drilling accuracy and of explosives behavior.

The resuIt of these anaIysis, somehow quite poor and uncertain, was a goodillustration of the limit of classical diagnosys. It showed that not enough information wasavailable to propose quickIythere was a cIear need for

a correct and precise therapy to the mine. it lead to the fact thata better control of the bIasting process.

Con&act BRE2.CT92.0127 Project report n“ SBlasting Control 4 01.11.1992- 3i.07.199S

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l“” ‘PHASE 11: DEVELOPMENT OF BLASTING CONTROL METHODOLOGY

The main global entities involved in the Blasting process can be expressed in thefollowing list :

the rock to be blasted (hardness, microfissuration, natural fracturation, behaviorduring drilling, holes position and deviation, profiles),’the explosives and detonators used,the blasting itself (energy used, ignition efficiency),the blasting results (grain size distribution, profiles, advance, side walls weakening),the environmental constraints (vibrations, noise and air, gas).

For each element of the previous list, some fundamental parameters can bemeasured in order to provide u~ful information for the control of blasting. This is the preciseobjective of the blasting control methodology “developed in the project.

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e In order to reach such an objective, the idea has been to adapt arid test control devicesable to provide the searched parameters in a realistic time (compatible with productionconstraints) and at a reasonable cost (only existing low cost equipments have been used).

The phase has been organized around the control devices development (II. 1) realiz~in the Erzberg test site, the explosives and detonators rn&surements (X1.2) made in theNitroBickford plant, and the interpretation of measurem~nts (H.3).

Ill .CONTROL DEVICiiS D E V E L O P W E N T ,, ~~~ . ,

This part of ‘the work supposed to choose and adapt the devices, to prepare the testsite, to organize the tests, to find a working reference blast, and finally to validate thedevices. Main results are presented in the following.

The devices or measurement methods, chosen for test, are the following :

@ Hardness : Point Load Testing, Schmidts Rebound HammerMicrofissuration : Seismic wave velocity and R & D measurementsNatural fracturation : In-hole EndoscopeBehavior during drilling : Instrumented Drilling Jumbo

~ Holes !30 sition and deviation : TheodoliteProfiles : TheodoliteEnersw used : Moved to vibra[io~s measurement

Vibratioris : SeismographsGrain size distribution : Image Analysis c/o CCD-cameraNoise and airblast : Dedicated devices@ : Large scak measuring device

Contract BRE2.CT92.0127 Project report n“ 8Blasting Control 5 ‘ OL1l 1992 -31 07 1995

A fully equipped underground laboratory has then been realized in the Erzberg testsite, incIuding computer office, access galleries, wire and cable connections, ventilation,etc . . . The efficiency of this laboratory has been tested through 4 monitored blasts. Fromthese tests, it has been possible to define precisely how to organize the future work inErzberg.

Concerning the data acquisition, a biasting agenda, simikr to the one made forBauxites Parnasse, but including the devices, has been developed for Erzberg.

The following test period, aimed at finding a working blast, allowing control devicesmonitoring -without secondary blasting to correct its failure. This step of the work has beencarried out during 11 blasts made in two drifts. The objective of the 7 first blasts was to keepevery blasting parameter as constant as possible in order to evaluate the standard deviationsof the measured parameters. This helped to choose the range of planned variations for thefurther tests as well as to judge about the significance of different blasting results. Once thestandard working blast has been found, 4 more blasts have been made to standardize thedecomposed blasts process.

The last set of tests in Erzberg has been devoted to the blasting control itself. Theobjective was to have the control devices working and providing as many useful data aspossible. Nearly 30 blasts (full,, decomposed, and single shot) were made in two drifts. Fullblasts aimed at the full rnoni~oring testing. Decomposed blasts, made in three steps, tried toisolate seismic information from the cut, the production zone, and the contour zone. Singleshots controkd the drilling precision, the burden distances and the vibration records. Themain results of the tests are given in the following.

.’.’Rock’ hardness devices : Tests carried out on rock “samples showed a quite goodcorrelation between uniaxial compressive strength and the point load index determinedradially for the limestone area. Moreover, it was shown that [he various rockparameters measured correlate quite well on a global scale (10 m) and may vary verymuch on a blast per blast scale.

●Endoscope (natural fracturation) : The endoscope was used to detect big faults (andparticularly to see if they connect bordering holes). The results were satisfactory andthe image strip could be recons[ructesi from the recordings. F$evertheless, themeasur~ment was quite long and it was clear that a stronger equipment is needed toachieve the complete objectives.

DrilIin~ iumbo (behavior during drillin~ : The close monitoring of drillingparameters for purpose of the prediction of rock and rock mass parameters gave thefollowing results :

From monitoring of the drill speed the localization of major faults and opencracks in the ground is possible.

The presence of inhomogeneities in the rock (schist pkmes, etc... ) which areclosed cannot be localized on the spot. Heavy jointing results in a usualiy

Contract BRE2. CT92.0127 Project report no 8Blasting Control 6“ 01.11.1992-31.07.1995

increased drill speed.

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The prediction of changing rock properties from monitoring of drillingparameters is possible on a global point of view.

Theodolite (holes ~osition and deviation, ~rofiles) : The device worked as pkmned,but was very time consuming.

Seismo~raphs (vibrations} : The positioning of the devices is of a great importance.It will have to be tested in any new mine to be controlled. Moreuver, a filteringprocess of the signals is necessary before interpretation. ‘

Image analysis (grain size distribution) : With the adaptation for fines elimination onthe image, the system worked correctly.

Other devices (for noise and airblast measurements, for gas detection) have been

●tested for proper environmental controL Nevertheless, it is not pianned to bring them inGreece.

At the end of this control devices development part of the project, the initial keyquestion (how to control the blasting process with devices) is considered to be answered.

IL2 EXPLOSIVES AND DETONATORS MEASUREMENTS

The energy and the detonation speed of each type of explosives had to be measuredifi order to evaluate their actual efficiency, and to move from E~berg blasts (Austrianexplosives) to Bauxites Parnasie blasts (Greek explosives).

The measurements have been realized in the Saint-Martin de Crau plant of Nitro-Bickford, with standardized procedures. Their principle is to blast under water and tomeasure the maximum pressure of the chock wave (providing the chock energy Ec), and thelength of the bubble pulse first “pseudo-period” (providing the gas energy Eg). The totaI

@ energy Et available for the blast is given by the chock and gas energies sum.

Concerning the explosives used in the Erzberg test site, 25 kg samples of GelatineDonarit 1, Gelatine Donarit 2E, Lambrex 1 and Lambrex 2 have been required from Nobei-Vienna and imported in France.

Concerning the explosives used in the Bauxit& Parnasse mine, due to very strongimportation / exportation and transportation problems, chemical formulas of pulverdentdynamite NAD 1 and crashed D7, of gum dynamite Robex 1, and of gum dynamite Handmachine 3, have been required from Elviemek. 25kg of each explosives have then beenmanufactured from the formulas specifically for the tests.

Contract BRE2.CT92.0 127 Project report no 8Blasting ControI 7 01.11.1992-31.07.1995

Concerning the detonators, the Czech detonators used in Greece and the Schafflerdetonators used in Austria were nearly identical to the Nitro-Bickforcl ones (Davey), in termsof PETN loading and of energy. For that reason, tests have been performed with Daveystandard electrical detonators with 0,2 g of lead nitrite and 0,6 g of PETN under 400 barscompression.

11.3 INTERPRETATION

The first step of the

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OF MEASUREMENTS

interpretation has been the realization of a database in order tostore the results (from observation and measurements) and allow geometrical representationsand calculations. This database, realized with Access, ExceI, and Sumac softwares rxovidesthe main following outputs :

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calculation of the advancecalculation of dip and azimuth of each borehole

●extraction of the real drilled lengthshape of the facedrillhoIe position on the facedrillhole p o s i t i o n i n 3 Ddrilled volume of cut, production, and contour zonesposition and amount of explosives in each holeblasted volumeprofilesfor all data, comparison between actual and planned values ‘

Examples of vie;;ng capabilities are given on” figures 2 and 3.

The next step was to evaluate the significance of the data obtainedcontrol devices, that is to say to know if:

from the chosen

the measurements reflect the actual physical parameters (which supposes an individual ‘analysis of each device and of their links to real parameters involved in the blastingprocess),

the provided information is useful to the blasting improvement (which supposes aglolxd analysis of the devices capability to explain a g;ven biasting result). -”

The Erzberg tests and the following analysis period allowed to define more preciselythe potentialities and the limitations of some of the devices. Although this analysis workwould have needed much more time, the results are very promising. They were :

The complete geometrical survey of the blasting process allowed an efficient controlof the blasted volume related to each single hole.

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Contract BRE2.CT92.0127 Project report n“ 8Blasting Control 8 01.11.1992- 3i.07.1995

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The vibration analysis appeared to be a very useful tool for controlling single shotsin the delay sequence. MultipIe shots caused problems. They might be recognized bytaking more parameters (specially rock parameters) into account.

The correlation between the drilIing parameters, the main faults detected with theendoscope, and the missing peaks of the cut seismograms, provided promising resultson the blastability characterization during drilling, but were not sufficient to concludeon this point.

The grain size distribution measurement showed an homogen~us family of grain sizedistributions for the blasting pattern used in Erzberg. Nevertheless, some significantdifferences in some bIasts can be linked to a bad explosives ener~v distribution(confirmed by the explosives measurements), - ‘“

This last step of the phase dedicated to the development of the blasting controlmethodology fiswered the initial key question of what to expect from the control of the

9blasting process.

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Contract IHUZ2. CT92.0127 Project report n“ 8Blasting Control 9. 01.11.1992-31.07.1995

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Contract BRE2.CT92.0127Bki.sting Control

Project report n“ 810 01.11.1992-31.07.1995

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C(]ntrwct IIRE2.CT92.0127 Pro.jwt report no 8Bkisting Control 11 01.11.1992-31.07.1995

PIIASE 111: VALIDATION OF BLASTING CONTROL METHODOLOGY

I

The last phase of the project has been dedicated to the validation of the developedmethodology. This validation took place in a mine in production (Bauxites parnasse) underworking conditions.

The first step aimed at proving that the complete monitoring of blasts was realistic inworking conditions (acquisition validation). The following step aimed at showing that sucha control could provide the blasting expert with efficient information for the blastingimprovement (example

111.1 ACQUISITION

of therapy).

OF VALIDATION

The validation of the acquisition with control devices has been made in the Bauxites

eParnasse mine through nine blasts made in two drifts (5 in bauxite and 4 in limestone).

The first two weeks were used to prepare, install and calibrate the chosen devices, toprepare the measurement places, and to install the data recording system.’ Then the tests tookplace. Finally, a database, similar to the Erzberg’one, has been realized.

. .The testing period in Greece has been successful in terms of data acquisition. The

applied measuring system (on basis of the experience gained at Erzber~ test site) proved to,work properly. Some minor technical problems occurred, which should be easily eliminat~for further operations. Table 1” summarizes the main results :

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device technical time data furtherprobIerns constraint storage improvement

drilling no less good s e n s o r sl i f e t i m e

@ endoscope no big under work handling

grain size ‘ no less gooddistribution

vibration yes less good

surveying no big good handling

core drilling no big under work

deviation no m e d i u m under work

Table 1: Results of the acquisition validation tests

Contract BRE2.CT92.0127 kojc~t report n“ 8Blasting CcmtroI 12 01.11.1992-31.07.1995

This test phase reached its two objectives : the tools work and the feasibility of fullmonitoring in working conditions is proved.

The acquisition is then considered to be validated.

IH.2 EXAMPLE OF THERAPY

Measurements made during the acquisition validation have been used by blastingexperts in order to propose a new blasting scheme supposed to improve the geometricalresults of the blasts. For this, the blasting experts group choose to concentrate on thege6metncal problems in bauxite where the actual advance, the actual profiles and the grainsize distribution were ve~ far from the planned ones. In order to reach their conclusions, ~emain ideas developed where the following :

The obviously high drilling deviation is the main reason for the generally bad blastingresults. Other influencing parameters can be neglected regarding the deviation. Thenew blasting scheme must have an easier drivability.

- Some weakness of planned drilling pattern exist, in particular for the first helpersconsidered to

- The un~oadedoptimal. This

be too far from the cut. This point explains the bad granulometry.

borehole length is generally too ‘high and the energy distribution is notpoint also explains the bad granulometry.

In order. to solve the problin of fines (too numerous)” and. in addition to the two“previous points, the ex~losives have been changed for a combination .of gelatine andammonite. This change will also help a proper contouring, of the blasts.

As the center hole cannot be enhrged (no specific drilling equipment is available), aspecific delay pattern for the spiral cut has to be used in order to provide freevolumes.

From their analysis, new drilling, loading and ignition schemes have been proposedfor bauxite in order to increase the advance, ameliorate the profiles, ad produce less finematerial.

To validate these shemes, 4 blasts were done in one drift, monitored with a theodolite(for profile and advance), seismographs (for efficiency) and image analysis (for the finematerial).

All but the vibration data from the different devices (electronic based data orhandwritten) were stored immediately after the blast in the database Access, and transferredto Surpac for immediate calculations and visualizations.

The main geometrical results of the tests can be commented as follows :

Contriict BEZE2.CT92.0127 Project report n 08Blasting Control 13 01.’11.1992-31.07,1995

There is a quite satisfying correspondence between the planned and actual values ofthe drilled volumes for the cut, the production zone and the contour zone. Especially tin the cut zone the result has been considerably improved.

The comparison between the actual and planned total volume drilled and blasted againgives satisfying results.

Especially the advance achieved is excellent. Of the length drilled, actually in average94,5 % could be blasted.

The- immediate measurements calculations and visualizations ‘enabled to discuss theresults of the validation tests direetly in the mine at the end of the validation testp e r i o d .

The results of the tests were demonstrated in front of an audience of mining enginkersand foremen at the offices of the mine. The example of therapy, centred around the advanceand the fine materials, looks very promising and interests Bauxites I%rnasse a lot. Such a

O P .attem could be extended to account for mechanical properties of rock and desiredgranulometry of blasted material. This could turn out to be an extremely useful tool in thehands of the underground mining engineers and foremen of the mine.

It is thus considered that the objectives have been reached and that the key questionon the possibility to propose an efficient therapy from the controt measurements is

“positively answered.

4 . . . . CONCLUS1ONS

The generaI conclusionsThey are :

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of the project can be directly linked to its initial objectives.

aIt is considered that the blasting control methodology developed in the project provedto be realistic (in terms of working conditions in a mine in production) and efficient(in terms of blasting improvements].

The application of the results in our end-user mine (Bauxites Parnasse) is verypromising and opens the door to other types of improvements.

The adaptation of the methodology to any new underground mine should not be of agreat difficulty.

Several controI’devices, adapted to mining working conditions, are now available forfurther uses or developments. They can be directly used for production control (grainsize distribution) or envirorimental control (seismographs; noise and airbiastequipments). They can also be developed in other industrial research projects (drillingjumbo or endoscope).

Contract BRE2.CT92.0127 Project report n“ 8Blasting Control 14 01.11.1992-31.07.1995