03 Timing Precision ASIEX Workshop-C Cunningham

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Blast Timing PrecisionWhen does it matter?

Claude Cunningham

Blasting Investigations and Consultancy

Explosive column

AQUARIUM



Claude Cunningham: Blasting Investigations and Consultancy 2

Road Map

Why the presentation?

Blasting mechanics

Timing Parameters

Delay Limitations Minimum requirements

Shock tube and ED characteristics

Wrap-up…

October 202



Claude Cunningham: Blasting Investigations and Consultancy !

"hy the presentation#

Involved with ED’s since 1993

Focussed on application, specs and expectations

General confusion over when and how timingprecision can help

Guidelines to help anticipate likely benefit ofmore precise timing

But many good reasons to choose ED’s,other than precision

October 202



Claude Cunningham: Blasting Investigations and Consultancy $

Vibration amplitude and frequency

Airblast amplitude and frequency

Fragmentation size range Overbreak and depth of damage

Movement direction and range

Drilling/ Powder factor needed

- cost and productivity

All affected to some degree by timing…

%ey blasting results

October 202



Claude Cunningham: Blasting Investigations and Consultancy &

Blasting mechanisms governed by:

Explosives characteristics

Energy, sensitivity, VoD

Ground reaction to detonation impulse

Strength, rigidity, structure

Blast Layout

Drilling pattern

Free Faces Timing of holes…

October 202



Claude Cunningham: Blasting Investigations and Consultancy '

()plosive*Roc+ Interaction

The initial ground conditions are FIXED

They determine how the available energy is partitioned.

Strong rock: 40 – 60% shock energy.Resists shock mechanisms

• Less expansion of the hole• Greater transmission of strain waves• Greater displacement of burden.

Weak rock: 60 – 90% shock energy.Absorbs shock mechanisms

• More expansion of the hole• Reduced transmission of strain waves• Reduced displacement of burden.

Shock phase:Plastic distension,

Weakening of mass

Heave/Gas phase:Loosening of weakened mass,

Expansion/ movement

October 202



Hard rocks

Claude Cunningham: Blasting Investigations and Consultancy ,

Weak rocks

Mechanisms in blasting

Radial expansion/ compressive failure

Transmission of strain waves Extension of microcracks weakens mass

Tensile failure by reflected strain waves

Tensile failure by gas expansion in cracks Displacement of burden rock

Shear failure by displacement between holes

Fragmentation by autogenous attrition

October 202



Claude Cunningham: Blasting Investigations and Consultancy -

Timing in.luence

Ground condition and geometry determine if timing caninfluence hole interaction. Holes too far apart cannot influence each other

Fractured, weak ground limits benefits of precise timing

For holes that can influence each other, timingdetermines whether they interact well, badly, or not at all. Strong rock – strain interaction – quick timing

Weak rock – gas interaction – slow timing…

October 202



Claude Cunningham: Blasting Investigations and Consultancy /

%ey needs o. timing

Sequencing:

holes firing in wrong sequence tend to be catastrophicto efficiency, effectiveness and safety.

Interval:

given a critical interval, the physics of too-short or too-long will give sub-optimal outcome.

Priority:

Timing that favours one outcome might degrade

another outcome: e.g., movement vs fragmentation.

October 202



Claude Cunningham: Blasting Investigations

and Consultancy 0

ibration Control

Frequency ~ 1000/dt

Vibration Frequency vs Row Interval

0

10

20

30

40

50

60

70

80

90

100

0 50 100 150 200

ms Interval

R e s p o n d i n g F e q u e n c

y H z

Hard rock,close up

Weak rock,far off.

October 202




and Consultancy

1ragmentation * intervals

Timing for Fragmentation in different rock types

0

10

20

30

40

50

60

70

80

90

100

0 2 4 6 8 10 12

Burden m

m s i n t r a - r o w

i n t e r v a l

2000

3000

4000

5000

6000

Soundspeed,

m/sInter-row ~ 3 x Intra-row interval

October 202




and Consultancy 2

elay vs Interval: easy to con.use

200 300 400

Interval 100ms

TIME, msDelay

Delay determines Scatter

Delay

Scatter5%

20 ms

range

Scatter range on interval - 20%Blastholes

Interval determines Effect

Scatter influences Effect

15 ms10 ms

Scatter affects Interval

90 – 110 ms

October 202



Claude Cunningham: Blasting Investigations and Consultancy !

Basis o. Precision:

3ormal istribution

Normal Distribution - 500 ms Shock Tube Delays, 7.5ms SD

0

1

2

3

4

5

6

4 7 7

4 7 9

4 8 1

4 8 3

4 8 5

4 8 7

4 8 9

4 9 1

4 9 3

4 9 5

4 9 7

4 9 9

5 0 1

5 0 3

5 0 5

5 0 7

5 0 9

5 1 1

5 1 3

5 1 5

5 1 7

5 1 9

5 2 1

5 2 3

Delay ms

P e r c e n t

34% 34%

13.8% 13.8%2.1%2.1%

500 507.5 515 522.5 492.5 485 477.5

Only 3/1000 shots fall outside this envelope

1/20 shots fall outside 2σσσσ

October 202




and Consultancy $

Real vs Modelled 4catter

500ms Shock tube Delay Stats

0%

10%

20%

30%

40%

50%

60%

470 480 490 500 510 520 530

5ms Delay Range

D

i s t r i b

u

t i o n All

03-Feb

28-Feb

06-Mar

500ms Shock tube - Normal Distribution

0

5

10

15

20

25

30

35

40

45

460 470 480 490 500 510 520 530 540

Delay ms (5ms bins)

% i n B i n

03-Feb

28-Feb

6-Mar

All

Actuals are notsymmetrical

Batches have differentMeans and SD’s

But we can only workwith modelled stats

October 202



Claude Cunningham: Blasting Investigations and Consultancy &

Normal distribution

SD σ for Mean time Tm

Range = + 6σ

Range vs delay

Coefficient of Variance

CoV = σ / Tm x 100%

Shock tube CoV 1.5% to 2% down hole ED CoV <0.1% (old systems only?)

Timing 4catter

October 202



Claude Cunningham: Blasting Investigations and Consultancy '

Pyrotechnic delay precision

0

2

4

6

8

10

12

14

0 50 100 150 200 250 300 350 400 450 500

Nominal delay, ms

Standard deviation, msCoV, %

Main source of interval error

Surface delays

October 202




and Consultancy ,

Ris+ o. .alling outside range:

Co 5&6 and 26

Risk vs Range of Delay, SD varying

0.1

1.0

10.0

100.0

0 5 10 15 20 25 30 35

ms outside Nominal Delay

% R i s k o f f a l l i n g o u t s i d e r a n g

e

SD 7.5

SD = 10

10% >13ms out

10% >17ms out

Does it matter if 10% of the intervals are more than 13,or 17 ms out?

October 202



Claude Cunningham: Blasting Investigations and Consultancy -

4catter Ratio R 4

σσσσ = Standard deviation of timing

e.g., 10 ms

6σσσσ = Range of deviation

60 ms

Tw = Interval desired

e.g., 25 ms, < Range! Rs = 6σσσσ / Tw x 100%

60 / 25 = 204%

As Rs>100% control is lost

non-sequential firing,

inconsistent intervals

σ

Tm

Tw

October 202



Claude Cunningham: Blasting Investigations and Consultancy /

Achieved Interval: 25 ms nominal

-50

0

50

100

0 20 40 60 80 100 120 140 160 180

m s

Rs 154% Rs 211% Rs 108% ED

(..ect o. R 4

on timing uni.ormity


0

50

100

0 20 40 60 80 100 120 140 160 180

m

s

Rs 91% Rs 126% Rs 64% ED


0

100

200

0 20 40 60 80 100 120 140 160 180

m s

Rs 32% Rs 44% Rs 22% ED

MeanCoV

4941.3

4971.8

4980.9

October 202




4o 7hat value o. R 4#

33% will ensure very steady breaking results.

Anything more than 100% is “very irregular” In between, OK for weak ground or where

focus is more on unit input cost than on

quality of blast. Vibration control is most critical application:

but weak ground loses frequency control

anyway. Unplanned reversals = backbreak, vibration.

October 202




"hat delays are needed#

Heavy, enduring debate with strong positions.

ED’s have enabled delays never attainable before inproduction.

Colliding shock waves theorists vs holistic realitiesdoubters.

Comparative trials very seldom done properly.

By and large, try (a) effect of precision, (b) variationof delays.

In weak rock, quick delays can work for reasonsother than precision…

October 202




Timing Precision: t7o systems

Pyrotechnic

Electronic

Shock tube: 500ms in-hole with pre-set sur!ce "el!#s

0 to $0000ms in-hole% in & ms pro'r!mm!ble steps

October 202



Claude Cunningham: Blasting Investigations and Consultancy 2$

( precision

Dependent on capacitor power and time

Typically two influences

Fusehead jitter – constant ~ 0.1-2 ms SD

Delay circuit jitter – depends on delay <0.1%

For 1000 ms delay, SD ~ 1 ms, range ~ 6 ms.

Can be big if delay is say 10 000 ms. In general far better than shock tube

ST Range ~ 35 ms for 500 ms delay.

ED Range ~ 3 ms for 500 ms delay.

But for very long delay, ED intervals can be worse than shocktube.

And doubtful for inter/intra-millisecond apps.

October 202



Claude Cunningham: Blasting Investigations and Consultancy 2&

3ormal distribution timing curves

Normal Distribution of 500ms Delay Detonators and Low Precision ED's

0

5

10

15

20

25

30

35

40

470 480 490 500 510 520 530

Time ms

P r o b a b i l i t y

S/T SD, ms 7.5ED1 SD, ms 1.1

October 202



Claude Cunningham: Blasting Investigations and Consultancy 2'

8imits o. Precision

Total Delay Range from ED and Shock Tube Systems

0

10

20

30

40

50

60

70

0 1000 2000 3000 4000 5000 6000 7000 8000 9000 10000

R a n g e m s ( 6

S D ' s )

Total ED

ED circuit 0.10% SD

ED fusehead 1 ms SD

Shock tube 1.5% SD

October 202



Claude Cunningham: Blasting Investigationsand Consultancy 2,

Effect of Delay on ED Precision.

0

5

10

15

20

25

30

35

40

0 1000 2000 3000 4000 5000

Delay ms

P r

o b a b i l i t y

(..ect o. delay on Precision

As delay increases

Precision decreases

October 202



Claude Cunningham: Blasting Investigations and Consultancy 2-

4ummary

Weak and highly jointed rock masses dissipate shock energy. Less need for precision

Strong, intact rock masses benefit from precision

All rock masses are variable Extreme caution in modeling vibration, fragmentation

Vital to test out effect of precision before changing delays

Scatter ratio is key to grasping timing issues

Timing precision is not the only criterion in choosing between

ED’s and shock tube.

October 202



Claude Cunningham: Blasting Investigations and Consultancy 2/

The end

Questions?

October 202

03 Timing Precision ASIEX Workshop-C Cunningham

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