The Effects of Inaccurate Drillingon D&B Costs and Blast Performance

Neal Lee, Jeremy Short₁Nelson Brothers, LLC

Drill Pattern Accuracy…

• Affects all aspects of mining

• The Most Effective Blast Design, ExplosiveProducts, and Initiation System in ExistenceWill Not Be Effective Until Drill PatternAccuracy is Achieved

• Transforming a Blast Design into an evenlydistributed muck-pile is nearly impossiblewithout accurate drilling…

Drill Accuracy Matters

Drilling Costs

• One of the easiest ways to improve a drilling andblasting program is to effect accurate drilling practices.

• Drilling costs have been increasing steadily to the pointwhere drilling costs alone can approach 30-50% of theDrilling and Blasting Costs for some mining operations,and up to 15% of overall mining costs¹

• Many operators do not have a good grasp of theiractual drilling costs per foot, most do not capture allcosts, and so do not consider pattern deviation to be amajor issue

Estimated Drilling Costs² per Linear Foot Drilled

• Depreciation $0.32?• Fuel $0.75?• Labor $0.50?• Steels, Subs, and Bits $0.25?• Repairs $0.15?• Lubricants $0.05?• Dust Collection $0.05?• Insurance ?• Interest ?• Supervision ?

$2.07+/ft???

Drill Pattern Deviation• Most drill pattern deviation measured is skewed

to the negative side (actual burdens and spacingare almost always LESS than designed)

• This is because ‘tighter’ patterns are oftenoverlooked, whereas patterns that are too widequickly manifest themselves as difficult toexcavate, or exhibit high vibrations when fired

• In order to document this, over 50 patterns wereselected at random and measured accuratelyafter drilling…

Results of Accurate Pattern Measurements ofPreviously Drilled Patterns Laid Out Manually

Results of Patterns Measured and Compared with Design Values

Drill Collaring Errors Found

• Borehole Deviation Within the Rock was notexamined

• Two Types of Collar Location Errors WereNoted

1. General Pattern Dimension Reduction-

2. Front Row Burdens Universally Less than Designed

Drill Pattern Deviation, at What Cost?

• The Average Blast Exhibited a Drill Pattern thatProduced 7.5% Less Rock than the DesignedPattern

• In order to Calculate the Economic and DrillProductivity Effects, Let us First Examine aHypothetical Blasting Situation

• We will utilize a fixed D&B Cost per Hole, anddetermine what impact various amounts of drillpattern collaring error have on costs and drillproductivity

Results of Various Amounts of Drill Error for Typical 50’ (15.24m) DeepShot

• Drilling and Blasting

Cost per Hole =

$392.04

* 3.6 cents per bcy at design pattern dimensions

(305m/shift)

(200mm)

(.762m)

(2.74m)

(6.09m)(6.09m)

(15.24m)

($6.23/m)

(566m³)

$392.04/740.7yd³=$0.53/yd³

($0.69/m³)

Economic Impact of Various Amounts of Drill Error for Typical 50’(15.24m) Deep Shot

-5%

-10%

-14%-19%-8% Average

Productivity Impact of Various Amounts of Drill Error for Typical 50’(15.24m) Deep Shot

The Effects of Reduced Front Row Burdens

• Many operations will reduce bydesign the front row burden in aneffort to improve cast % orgeneral breakage

• This is counter-productive frommany standpoints, and actuallycan reduce cast % andfragmentation, because the frontrow burden loses pressure toorapidly³, increasing the work-loadon successive rows*

* This problem is exacerbated when the blaster increases stemming on row #1,further overburdening Row #2

There Exists a Need to Accurately Lay Out theDrill Pattern

• Pattern Inaccuracy Increases Costs

• Insufficient burden is a primary cause offlyrock from a highwall face⁴.

Reduced Front Row Burdens Increaseoverall Costs by reducing average Burden

• Typical

Scenario:

Let us Examine what VariousDegrees of Front Row Burden

Deviation have on the OVERALLDrilling and Blasting Costs per

Million bcy blasted;

The Effects on D&B Cost of Moving Just the

Front Row Closer to the Face in 1’ Increments:

For this 78’ cut on 24x24, moving the front row burden to20ft will cost an additional $8,950 per million bcy

The Effects on Drill Productivity of Moving Justthe Front Row Closer to the Face in 1’

Increments:

For this 78’ cut on 24x24, moving the front row burden in to 20ftwill mean an additional 1.34 Drill Shifts per million bcy

Blasting Utilizing a Full Face Burden

Drilling Too Close To the Face

Utilizing Available Technology toAccurately Lay Out Drill Patterns, OrCheck Existing Patterns- 3-D Profiling

• 3-D Stereo Photogrammetric Face Profiling

• Quickly and Accurately Lay out Front Row ofHoles

• Requires only a digital camera, software, andde-limiters (rods used for scale)

• Generally only Two Photographs Needed

Typical Stereo Photogrammetry System

System in Use..

3-D Model of Face, Color Coding Pre-Programmed Burden Values

• +/- 1 Centimeter Accurate Global NavigationSatellite System (GNSS)

• Quickly Lay out Patterns, or Check ExistingPatterns

Base StationReceiver

Merge the Two Technologies…

3-D Face Profiling

Typical 3-D Image

Shot “A”

Typical 3-D Image

Shot “A” From Behind Face

Case Examples• Two “Pairs” of Shots Were Compared at the Same Mine

Site(s) in Appalachia• Each Pair of shots shared the same seam, hole

diameter, loading plan, etc, and were contiguous toeach other.

• Shot “A” and “C” were laid out our team using modernsurvey equipment (GNSS system) and 3-D Profiling

• The Second Patterns (Shot “B” and “D”) of each pairwere the “control” patterns, laid out by the drillersusing a tape measure as per existing (at the time) minepolicy

• After Each Pattern was Drilled, the GNSS System wasEmployed to check drill collaring error in each case

Case Examples

• The Patterns designed using this system weregeo-referenced twice, once in the process ofestablishing the pattern (marking for the drills)then again after drilling in order to check forcollar error relative to the pattern as markedout.

Shot “A”

9.0

73.0

78.0

($0.037/bcy)

($1.90/LF Drilled)

9”229mm

9.0

73.0

78.0

Shot “B”, $7,694 AdditionalCost per Shot ($0.041/bcy)

0.76 Additional drill shifts required

Shot “A”- Pattern Laid Out With GNSS,6/1/2012

• No Areas Where Pattern Deviation is >1ft fromdesign

Design Pattern is 24x24…..

Shot “B”- Pattern Laid Out Manually by Drillers,5/11/12

• Laying out the Pattern with a Tape Measure Has itsLimitations…

Areas with >1ft Negative DeviationAreas with >1ft Positive Deviation

Shot “B”- Pattern Laid Out Manually by Drillers

Shot “A”- Pattern Laid Out With Survey-Grade GNSS

Comparative Burden Relief, Pattern Laid out Manually vs Geo-Referenced

Burden Relief, ms per foot of burden

Comparison of Burden Relief Between ManualLayout (Shot “B”) and GNSS w/3-D Profile Layout

(Shot “A”)

• Inaccurate patterns reduced explosivesefficiency for shot “B”

• Pattern deviations affected burden relief andtherefore rock movement and fragmentation

• Accurate Pattern Layout in Pattern “A” yieldedmore uniform burden relief.

• This consistency removes some of theobstacles to reproducible improvements tothe drilling and blasting program

($0.037/bcy)

($1.95/LF Drilled)10.0

72.0

80.0

10.625”270mm

($0.037/bcy)

($1.95/LF Drilled)

10.625”270mm

10.0

72.0

80.0

Shot “D” Cost $28,668 AdditionalCost per Shot ($0.065/bcy)

2.33 Additional Drill Shiftsrequired

Comparative Burden Relief, Pattern Laid out Manually vs Geo-Referenced

Shot “D”- Pattern Laid Out Manually by Drillers

Shot “C”- Pattern Laid Out With Survey-Grade GNSS

Face

Face

Solid (pre-shear zone behind shot)

Solid (pre-shear zone behind shot)

Pre-line fromPrev. shot

Comparison of Burden Relief Between ManualLayout (Shot “B”) and GNSS w/3-D Profile Layout

(Shot “A”)

• Inaccurate patterns reduced explosivesefficiency for shot “D”

• Pattern deviations affected burden relief andtherefore rock movement and fragmentation

• Accurate Pattern Layout in Pattern “C” yieldedmore uniform burden relief.

Conclusions• Drill error is skewed almost exclusively to the

negative. This has a deleterious effect on safetywith regards to front row burdens and overallincreased Expls. Lbs/bcy.

• Drill Error is a Major economic drain on theindustry. For the applications we examined, theadditional expense ranged from $0.047/bcy to$0.065/bcy

• Drill productivity suffers from this driller error,the two shots not established with surveyinstruments required a total of 3.2 additional drillshifts to produce the same qty. of rock as thepatterns established with these instruments

Conclusions (continued)

• Drillers were very accurate at hitting the marksestablished, the error noted (design vs actual) forthe geo-referenced shots was less than 0.50%

• Burden Relief Values where much closer to designvalues when accurate hole layout occurs, yieldingmore uniform fragmentation.

• Technological advancements in pattern layoutmean that we do not have to accept drill collarerror

• With drill collar accuracy (and accurate electronicdetonators), complex changes in the blast designbecome reproducible..

References

¹ Cost Analysis of Rotary Blasthole Drilling, Bhalchandra V. Gokhal, 2010 CRC Press

Chapter 14

² A to Z of Down-the-Hole Drilling, HALCO Rock Tools Limited, 1989, pg. 8,Adjusted for Inflation and Current Exchange Rates by the authors

³ Cast Blasting in Light of the Electronic Option, Winfried Rosenstock, 29th ISEEproceedings 2003 by pg. 310

⁴ Flyrock Issues in Blasting, T. R. Rehak, T. S. Bajpayee, G. L. Mowrey, and D. K.Ingram, CDC 1998, pg 6