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Advanced VibrationManagementQuarry production blasting in environmentally sensitive locations

By Brian Burke, blast-based services, Orica Mining Services (UK)

Stringent environmental regulatorycontrols are the accepted normfor many quarrying operations,and complying with these controls

while operating at an efficient productionlevel is a major challenge for theindustry.The prediction and control ofground vibration and airblast levels arekey factors for quarrying operations inmeeting this challenge.

As areas of extraction progresstowards vibration- and airblast-sensitivestructures, the challenge of operatingwithin environmental constraintsbecomes more difficult.Typically, thecharge weight per delay time must bereduced in order to comply withenvironmental restrictions, whichinevitably leads to an increase inproduction costs as blast performance isadversely affected.

The ability to predict ground vibrationand airblast levels directly influencessubsequent blast designs and, ultimately,the quarrys downstream productioncosts. Increasing the accuracy ofpredictions allows higher charge weightsto be utilized while maintainingenvironmental compliance.

Charge weightscalingTraditionally, charge weight scaling lawsare used as a basis for predicting blast-induced ground vibration.This involvesdeveloping an attenuation relationshipbetween ground vibration and distance.Usually a square root scaling relationshipis used, in the form:

v = a(SD)b

where: v = ground velocitySD = scaled distance =distance/(charge weight)a & b = site constants

For vibration-sensitive structures(points of interest) located at a constantdistance from a blast, scaled distancevalues increase as charge weights arereduced.As areas of extraction progresstoward vibration-sensitive structures, thechallenge for quarry operations is toreduce scaled distance values while

meeting environmental constraints, iemaintaining high charge weights (therebymaintaining production efficiency) atrelatively small distances.

Advanced vibrationmanagementOrica have the capacity, through theirAdvanced Vibration Management (AVM)service, to measure, analyse andpredict blast-induced ground vibrationsusing a proprietary model for themanagement and control of vibration atsensitive locations. Utilizing this service,predicted vibration levels can beincorporated to optimize blast designssubject, to maximum allowable groundvibration levels at specific points ofinterest1&2.

Typically, electronic initiation is used aspart of the vibration-managementservice, as the timing precision andprogramming flexibility affords resultswith the most effective vibration-controlmechanisms3.The need for this type ofservice is increasing as urbanizationencroaches on quarries, restricting theirability to operate.Vibration restrictionscan also limit the mineable assets ofquarries.An improvement in blastvibration prediction and control will

effectively increase those mineable assets a valuable outcome in an environmentof increasing urban encroachment andsensitivity to blasting operations.

Statistical vibrationprediction modelAdvanced vibration management is basedupon a statistical vibration-predictionmodel.This model uses a Monte Carlotechnique and has been successfullyutilized in the Australian mining industryto control vibration and airblast for over10 years4.The capability of the predictionmodel has been, and is still beingcontinuously improved on the basis ofcomprehensive field studies and researchwork5.

The application of the model theMonte Carlo engine requires thedefinition of a variety of inputparameters, as shown in the blockdiagram in figure 1.The input parametersinclude the vibration seed shapewaveforms from signature blastholes, thesingle blasthole scaling law, the groundvelocity, the delay scatter of the initiationsystem, the charge weights, the delaytime sequence and the geometric layoutof the blast pattern with respect to themonitoring site.The model also

Fig. 1. Block diagram of the vibration model (after Blair, 1999)

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considers the blasthole screening effect,ie the vibration reduction throughfractured rock caused by previously firedblastholes in the initiation sequence.

In simple terms, the model simulatesthe vibration and/or airblast at a point ofinterest for a given blast design by thesuperposition of a sequence of phase-delayed single-blasthole signatures.Theprediction output formats include:

Probability of exceeding aprescribed peak vibration level for aspecific compliance location.

Histogram for the expected peakvibration level for a specificcompliance location.

Predicted time-history envelope fora specific compliance location.

Mean amplitude spectrum for theexpected vibration at a specificcompliance location.

Case Study HowickQuarry vibration-management projectHowick Quarry is located inNorthumberland, to the north ofNewcastle, and is owned and operatedby Tarmac Ltd.All drilling and blastingoperations at the site are carried out byRitchies, the drilling and blastingcontractors.The geology of the siteconsists of a layer of basalt(approximately 15m) sitting on a layer oflimestone.A thin, discontinuous depositof limestone intermittently caps thebasalt and is intersected periodically asextraction progresses.The quarry isworked as a single bench in order toextract the basalt (fig. 2).

As the quarry progressed, the area ofextraction in the north-west region ofthe site approached two residences.Theenvironmental planning limit for blast-induced ground vibration at the quarry is6.0mm/s for 95% of blasts (measured atany residential property).Throughout2005 the area of extraction progressed

closer to residences A and B (as shownin figure 3).The planned extraction ofavailable mineable assets would progressto within 80m of residence B.As thearea of extraction approached theresidences, the charge weights used werereduced, bringing an associated increasein production costs. In close proximity tothe residences, the quarry conservativelylimited their blast designs to scaleddistance values greater than 40m/kg, inorder to ensure compliance with thevibration limit of 6.0mm/s. Chargeweights as low as 3kg were used in 2005.The least squares regression best-fit linefor the peak particle velocities measuredat the quarry in 2005 is shown in figure8.The best-fit line is derived from26 production blasts carried out in thenorth-west section of the quarry during2005.

Due to the increased production costsassociated with adhering to theenvironmental vibration limits, the quarrymanagement decided to implement anadvanced vibration-management project.The scope of the project was to allowblasting at lower scaled distance valueswhile complying with the vibration limits,and to extract all of the mineable assetsin the north-west section of the quarry.

The site exploration study for theproject was implemented in 20056 andthe projects production blasting phasebegan in January 2006.

Site investigationstudyThe initial step in an AVM program mustalways be a comprehensive siteinvestigation study, as the vibrationmodelling capability is entirely dependenton the quality of the input parametersfor the ground model.The siteparameter study has three mainobjectives:

to record the single-blasthole seedwaveforms, which represent theunique geological site signaturebetween the quarry blasting areaand the monitoring locations thepoints of interest (POIs)

to establish the site-specific scalinglaw for single decks of charge, whichdescribes the expected vibrationlevel as a function of charge weightand distance

to determine the wave propagationvelocity through the ground for theprimary wave.

All three objectives can be achievedthrough the firing of single blastholes. Inthis case 12 single blastholes were firedfor the site parameter study6.Afterrealization of the site investigation andsubsequent processing of the recordeddata, the site-specific model could beestablished for each point of interest.With the site-specific model in place, avibration-control and blast-optimizationprogramme could start.

Production blastingAVM production blasting involvesoptimizing the design for a productionblast based on simulations of thevibration prediction model.The site-specific parameters, along with the blastdesign data, are input and a predictionfor the vibration levels at each POI isderived from the model.

Fig. 2. Quarry geology

Fig. 3. Location of points of interest and area of extraction

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An example of the blast-optimizationprocess is outlined in figures 46.Allblast design and vibration modelling isperformed using SHOTPlus-i Prosoftware, Oricas proprietary blast-designsoftware incorporating the vibrationprediction model.The geometriclocations of the blastholes, togetherwith the charging details, are shown infigure 4.

These design parameters and the site-specific data are then run through thevibration prediction model.The variabilityof the input factors according toprobability distributions is modelledthrough Monte Carlo simulation, alongwith the superposition of seedwaveforms, and a predicted output isgiven for the vibration levels at the POI.Vibration prediction outputs are shownin figures 5 and 6.

Project outcomesAVM production blasting was carried outat the quarry throughout 2006 and 2007.The improved accuracy of vibrationprediction afforded by the vibration-management service allowed blasting tobe carried out at lower scaled distancevalues while complying with the quarrysenvironmental limits.The resultingfragmentation from a typical productionblast is shown in figure 7. It should benoted that the technical capability toimplement the optimized blast designs insitu as provided at Howick by Ritchiesdrilling and blasting service is afundamental component of the vibration-management service.

The least-squares regression best-fitline for the peak particle velocitiesmeasured at the quarry in 2006 and2007 is shown in figure 8.The best-fitline is derived from 54 AVM productionblasts carried out in the north-westsection of the quarry during 2006 and

Fig. 4. Hole positions and charging details

2007. Scaled distance values of less than40m/kg were regularly used for theprojects production blasts withoutexceeding the vibration limit of 6.0mm/s.The lowest scaled distance value usedwas 24m/kg.

The maximum instantaneous chargeweights per blast utilized ranged from5kg to 35kg, with an average value of13.3kg during the projects productionblasts of 2006 and 2007.As shown infigure 9, extraction of the available assetsclosest to the residences in the north-west section of the quarry has beensuccessfully completed.

ConclusionsThe implementation of a vibration-management project at anenvironmentally constrained quarry hasbeen successful in improving theproduction efficiency of the blastingoperation as extraction progressedtowards vibration-sensitive structures.The

improved accuracy of vibration predictionhas allowed higher charge weights to beused, while production blasts haveremained compliant with stringentregulatory ground-vibration limits.Theproject has also allowed the extraction ofthe total available volume of mineableassets in close proximity to residentialproperties.The AVM service has provento be of benefit to the quarry operationin making optimum economic and designdecisions based on the predictedenvironmental impact at sensitivestructures.

During the course of the project,significant work was carried out todetermine the effect of various grounddisruption zones on transmitted vibration.This work covered a large number ofvariables including delay sequencing,spatial layout of holes and chargedistribution, with the aim of determiningthe best procedure to reduce groundvibration within a disruption zone7.

Fig. 5. Predicted vibration histogram for Residence B Fig. 6. Predicted vibration probability for Residence B

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AcknowledgementsThe support of the quarry managementand staff is gratefully acknowledged alongwith, in particular, Barry Smith (Ritchies),blast supervisor for the project, for hisefforts throughout the blastingprogramme.The drilling and blastingexperience and technical input of

Ritchies staff throughout the project wasvital in ensuring that complex blastdesigns could be successfullyimplemented.

The authors involvement in thisproject is restricted to the vibrationmodelling and design of the projectsproduction blasts since September 2007,

together with the regression analysis ofthe projects data measurements.All datameasurements prior to September 2007were obtained by Nathan Cotter. Peakparticle velocity results at HowickQuarry remain the property of TarmacLtd.

The significant work carried out atHowick since 2005 by the authorscolleagues at Orica Mike Noy, DirkGrothe, Dane Blair and Nathan Cotter ensured the success of the Howick AVMproject.

REFERENCES1. GROTHE,, D., and M. BREHM: Analyse und

Reduktion von Sprengerschtterungen,Hrsg. Deutscher Sprengverband, Band 28,2006, Heft 3, pp27-30.

2. GROTHE, D., and P. REINDERS: Advancedvibration in quarries using a predictive blastvibration model, EFEE Conferenceproceedings, 2007,Vienna.

3. BLAIR, D.P., and L.W.Armstrong: Thespectral control of ground vibration usingelectronic delay detonators, Fragblast -International Journal of Blasting andFragmentation 3, 1999, pp303-334.

4. BLAIR, D.P.: Statistical model for groundvibration and airblast, Fragblast International Journal of Blasting andFragmentation 3, 1999, pp335-364.

5. BLAIR, D.P.: Non-linear superpositionmodels of blast vibration, Int. J. Rock Mech.& Min. Sci., 45, 2008, pp235-247.

6. NOY, M.J., and D. GROTHE: Monte Carlovibration modelling at Howick Quarry, UK,Orica Internal Report 58743, 2005, pp71.

7. NOY, M.J., and D.P. BLAIR: Thedevelopment and implementation of a newground vibration-screening algorithm,Orica Internal Report (in preparation).

Fig. 7. Production blast result at Howick (November 2007)

Fig. 8. Peak particle velocity measurements20052007

Fig. 9. Area of extraction November 2007 (view towards north-west corner)