Blast Design for Underground Mining Applications

R . H O L M B E R G

Blast design for underground mining applications

R. Holmberg Lima Nov 2011

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Contents


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Contents:

1. Purpose - applications

2. Surface blasting

3. Surface - underground

4. Tunneling

5. Function of cut

6. Design of parallel cut

7. Tunnel rounds

8. Contour blasting

9. Divided faces

10. Shaft sinking

11. Mining methods

12. Ring layouts

13. Design formula

14. Explosives

15. Decoupled charges

16. Pointers

17. Acknowledgements

Purpose & applications -1

The purpose is to:

Efficiently excavate rock so that the pieces removed can be handled economically

Avoid ore losses and waste rock intrusion

Obtain the planned contour with no underbreak and as little overbreak as possible

Leave the remaining rock stable for as long as the operation requires.


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Purpose & applications -2

The main applications are

Mining; drifting and development work plus full workings

Raise blasting and shaft sinking

Quarrying

Infrastructure; traffic tunnels, hydropower and water tunnels, parking garages, shelters, power house caverns etc

Other applications; well springing, seismic operations etc.


4

Surface blasting -1

Quarry; typically identical holes, parallel, same diameter and same burden and spacing, BS pattern, same charging,

q = 0,5-0,9 kg/m3.

Road cut; like quarry but

contour holes , smaller hole diameters, smaller charges and on flatter angle

Foundations; essentially like

road cuts but vertical holes.


5

Surface blasting -2

Open cast mine; like road cut but larger holes and contour gets special emphasis, sometimes smaller holes of different angles and depths.

7400

7420

7440

7460

7480

7500

7520

7540

4480 4500 4520 4540 4560 4580 4600 4620 4640

presplit Ø127 mm

production holes 17 m Ø311 mm

1st row

helper & contour

Ø152 mm

15 m bench R. Holmberg Lima Nov 2011

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Surface vs underground - 1

Worldwide: OP >> UG, OP: ore < waste, UG: ore >> waste


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Annually excavated volumes in Sweden • LKAB UG mines: 25 Mton Fe-ore, 20 Mton waste • Aitik open pit mine: 28 Mton Cu-ore, 30 Mton

waste. • Other mines and crushed stone, infrastructure projects etc. ~80Mton

•Makes about 180 Mton or 6 m3 per capita •70 kton explosives makes about 8 kg per capita


8


Tunnelling:

charged & primed blasting plan

fire-in-the-hole!

Underground blasting; often more complicated drilling patterns and combinations of blasting methods


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Tunnelling - 1

What has happened in tunnelling recent 25 years?


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Tunnelling - 2

blasting = (38% 2007), small part of total excavation work but outcome often decisive for downstream operations


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Tunnelling - 3

Start- first one free face - the tunnel face. Blasting is confined and specific charge is high q = 1,5-2 kg/m3

look-out angle needed to make room for drilling next round, min 0.2-0.3 m, design burden applied to hole bottom (toe) and at face deduct look-out


12

Tunnelling - 4

blasting starts with cut = opening part of round

cut

larger empty (void, reamer or burn) holes

Tunnel round with parallel holes enlargement

of cut part


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Tunnelling - 5

Charge calculations for tunnelling can be made according to Chapter 7 in “Rock Blasting and Engineering” by Persson, Holmberg & Lee. In these OHs simplified rules of thumbs by Finn Oucterlony at Swebrec is used.


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Design of parallell hole cut - 1

#2 #1

#3

#4 - ∆100 ms

reamer hole = first swelling volume

rock to be broken


15


In principle, choose burden a according to diagram but:

• If burden a too large → breakage failure (rifling) or choking of flow of rock fragments

• If burden a too small → burning of rock fragments

Drilling accuracy is most essential!


16


Geometric considerations for cartridged explosives: 1st quadrangle: 2nd quadrangle:

+

a = 1,5Ø

W1= √2a W1

W2 =1,5W1√2

B1

B1 = W1

a

3rd quadrangle: 4th quadrangle:

B2 = W2 & W3 =1,5W2√2 B3 = W3 & W4 =1,5W3√2

0,5W1


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Advance;

0.95*(0.15+34.1 Ø-39.4Ø2)

In case of several (n) empty holes (d) in the cut use: Ø = d√n when estimating advance.

Use an uncharged part at the collar of h0 = a.

Charge concentration lb = lp in first quadrangle:


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Stemming or uncharged length 10d or 0.5B. Bottom part may need lb=2lp to height of 1.25B.

Ch

arg

e co

nce

ntr

ati

on

lp,

kg

/m

Max burden B, m

Bi, i =1, 2, 3

lp

Charge concentration lp for 2nd-4th quadrangles:


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Tunnel rounds - 1

Floor holes or lifters

Roof or back holes

Wa

ll o

r ri

b h

ole

s

Cut holes

Sid

e st

op

ing

Downward stoping

Hel

per

ro

w

Spacing S Burden B

1. Lifters; spacing should not exceed design value S, e.g. width/S = 11,4 means round up to 12 and add 1 hole. Correct B for look-out of 0.2-0.3 m

2. Wall+roof; same for spacing and subtract look-out distance 0,2-0,3 m from design burden B. If cautious blasting see below.

3. Cut; match size of cut to side stope, if B3 > B0 (next OH) then decrease B3. Place cut to minimize no. of side stope rows.

4. Stoping; use same side stope burden < B in all rows, same for downward stope and adjust to even breakage volumes.

5. Helpers; balance contour damage or lift cut position

Design of parts of round:


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Tunnel rounds - 2

Note: The explosive chosen (density and charge diameter) determines the charge concentration lb, kg/m. Calculate lp and use next larger cartridge or pipe size for real column charge. Helpers may be designed as stoping holes or with consideration for damage depth. Diagram in next OH gives B0.

Part of Burden Spacing Bottom Charge concentration Stemming

round B S charge length bottom lb column lp not charged

m m Lb, m kg/m kg/m h0, m

Floor /Lifter 1 x B0 1,1 x B0 1/3 x H lb 1,0 x lb 0,2 x B0

Contour:

Wall 0,9 x B0 1,1 x B0 1/6 x H lb 0,4 x lb 0,5 x B0

Roof 0,9 x B0 1,1 x B0 1/6 x H lb 0,3 x lb 0,5 x B0

Stoping:

Upwards 1 x B0 1,1 x B0 1/3 x H lb 0,5 x lb 0,5 x B0

Horiz./Side 1 x B0 1,1 x B0 1/3 x H lb 0,5 x lb 0,5 x B0

Downwards 1 x B0 1,2 x B0 1/3 x H lb 0,5 x lb 0,5 x B0


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Tunnel rounds - 3

B0

lb

B0, burden at hole bottom or toe vs equiv. charge con-centration lb (kg/m) needed for breakage. Deduct look-out for perimeter holes

bulk ANFO like SSE fills hole, and a proper primer is needed

shifted scales on lines because densities are different

cartridged emulsion with alu, suitable for bottom charges

dynamite, e.g. bottom charge

same emulsion but in longer pipes, used for column charges

cartridge,mm

cartridge,mm

pipe,mm

blasthole,mm


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Tunnel rounds – 4

Priming and initiation sequence principles

Detonator no:s #1-22 tell the initiation sequence. In practice it is not usual to have the same delay time between all intervals, see Nonel LP series

Do not initiate two holes on same delay no. in first two quadrangles.


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Tunnel rounds – 5

VoD 2100 m/s

Nonel® plastic tube with 17 mg/m of explosive

Nonel® LP detonators suitable for UG work

New series Nonel LP detonators:

• delays up to 6000 ms in steps of 50, 100, 200 and 400 ms

• old series detonator no.18100 ms same as new LP 1800 e.g.

• LP 0 at 25 ms exception

• don‟t use intervals shorter than 100 ms in tunnel rounds without trials


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Tunnel rounds – 6

Part of Holes Spacing Burden

round no. m m

Cut 9 special list

Stoping 28 0,60 0,60

Lifter 10 0,50 0,45

Helper 17 0,60 0,55

Contour 28 0,45 0,60

4,3 m

1 m

1 m

Part of Bottom Ø x L Column Ø x L

round charge mm charge mm

Cut Dynomit 30×380 Dynorex 25×1100

Stoping Dynomit 30×380 Dynorex 25×1100

Lifter Dynomit 30×380 Dynorex 25×1100

Helper Dynomit 30×380 Dynotex 1 22×1000

Contour Dynomit 30×190 Dynotex 1 17× 460

Part of Charge Total Charge length Un-

round weight part bottom column charged

kg/hole kg m m m

Cut 2,8 25,2 0,38 3,92 0,3

Stoping 2,8 75,6 0,38 3,92 0,5

Lifter 2,9 29,0 0,38 4,02 0,2

Helper 1,8 32,4 0,38 3,92 0,2

Contour 1,1 30,8 0,19 4,21 0,2

Drilling and charging plan data: from Äspö TASS tunnel, note look-out


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Tunnel rounds – 7

In summary:

• Only 1 free face to start with when cut fires, tight hole burdens and spacings (high specific charge)

• Cut design requires special considerations like avoidance of sympathetic detonations and dead pressing

• Long delays to avoid choking of flow of fragmented rock, up to 6000 ms or more.

• Parallel holes in good rock and small tunnels to achieve long pull (parallel & burn hole cuts).


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Tunnel rounds – 8

In summary, ctd:

• Poor rock requires shorter rounds, angled holes, e.g. fan and plow cuts possible to use if face wide enough to angle booms

• Depending on local conditions packaged or bulk explosives may be used. With bulk there is no special pipe charge, lp = lb, and primer should be used.

• Contour and helper row holes are usually more lightly charged than stoping holes; e.g. plastic pipe charges or string emulsion.


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Contour blasting - 1

Why cautious blasting?

• Extent of cautions blasting depends on expected life time of tunnel /cavern /drift etc

• Less dilution, better ore recovery

• Less support work, less bolting, less shotcrete or concrete to cast

• Increased safety

• Less rock to haul, saves time and money

• Smooth blasting method used UG to reduce overbreak and blast damage.

without caution

with


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Contour blasting – 2

By cautious blasting is meant that the cracking in the remaining rock due to blasting, shall be limited to the „damage zone depth Rc‟ that has been prescribed for the perimeter in question.

The cracking caused by the stoping and helper holes inside the perimeter must not reach farther into the remaining rock than the cracking from the perimeter/contour holes.

Smooth blasting uses light decoupled charges in contour and helpers with balanced damage

zone depths; holes fired last in round.

Cautious and smooth blasting:

perimeter or contour

helpers or stoping holes

damage zone radius


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0.0 0.5 1.0 1.5 2.0

Charge concentration q, kg DxM/m

0.0

0.5

1.0

1.5

2.0

2.5Damage zone depth Rc, m

Rc= 1,9*q• Rc < 0,3 m often required

• Damage zone table gives charge concentration for Swedish bedrock conditions; Ø45-51 mm holes.

• Note: q is given in Dyna-mite equivalents, multiply real q by 0,73 for Gurit

• Contour and helper damage zones can be read off curve

• Holmberg-Persson

theory behind line.

In Swedish tunneling:

Rc = 1,9·q; q < 0,5 kg/m Rc = 0,95·(q+0,5); q > 0,5 kg/m


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Damage zone

Recommended charging of countour holes

Notes: Connect charges and use small primer to initiate them

*: Damage zone e.g. from 17 mm Gurit Rc = 1,90,230,73 ≈ 0,3 m

= 0,17 eq kgDxM/m New Swebrec approach explicitly includes effect on Rc of

• Blast hole diameter and coupling factor

• Water in blast hole and rock properties

• Simultaneous initiation using e.g. electronic dets or cord. R. Holmberg Lima Nov 2011

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normal stoping holes

stoping

If stoping holes too heavily charged then the cracks will extend beyond damage zone of contour holes. Solution = more lightly charged helper row with adjusted burdens and spacings!

When cracks from holes inside the contour reach no further than the cracks from the contour holes, the damage zones are balanced.


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Does it matter? Take Ø22 mm Gurit

• Crack length in dry Ø64 mm hole 15-20 cm

• Crack length in wet Ø64 mm hole 45-60 cm

• Crack length with no decoupling 90-100 cm!

Crack lengths with electronic dets shorter than for Nonel detonators if

• Charge concentration q < 0.6 kg/m and spacing S/B < 1

• If decoupling is sufficient and holes are proven dry

• Initiation simultaneous well within 1 ms.


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Nonel + electronic dets (EDD) in contour and helpers

• Lightly charged lifters and helpers

Extremely cautious blast with hybrid initiation plan

Note half casts in floor! R. Holmberg Lima Nov 2011

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Divided faces - 1


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Divided faces - 2

Reasons for dividing face:

• Stability reasons

- can‟t otherwise maintain stability of and at face

- uncertain about geology, pilot gathers information

• Productivity; access to many faces

• Length of rounds

- the span is able to support the rock-load

- the support measures can be installed in due time.


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Divided faces - 3

ca 5.5m

ca 3

m

60

00

ca 12.5

ca 5m

ca 5

m

1:a

öve

rlapp c

a 7

m

Ex. Löttinge traffic tunnel, 2-lane 1058 m Sthlm 2005-6 188,5 m, 152 m2:

• E & W access

• Rd 1-3 Side pilot, leaving plug to prevent noise coming out and winter cold in

• Rd 4-7 Widen to full section

• Rd 8-9 side pilots

• Rd 10-123 side pilot and trailing side stope in same round.

West portal

saved plug

10

1

10


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Divided faces - 4

Drilling of pilot at East portal and side stopes (slashes).


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Divided faces – 5

Excavation sequence for hydro power house cavern


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Shaft sinking - 1

2 m bench with confined toe and fanned rows


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Shaft sinking - 2

5 m full face round with cut and parallel holes

easier drilling, pulls deeper and produces finer muck than bench round

200 mm pilot (reamer) hole drilled 0,3 m deeper than rest of round to ensure 100% pull.


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Mining methods -1

Room and pillar; metal mines & underground quarries

upward stoping =

horizontal bench

drift heading =

tunnel round vertical bench

cross cut =

tunnel round

Depending on the mining method a mine uses several blasting methods.


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Mining methods -2

Parallel drill holes that follow the ore.

Drift and (multiple) benching, Zinkgruvan


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Mining methods -3

1 1 11

11

1 1

111

12 2

2 2 2

2

2

222

22

2

20 - 30 m

40 - 60 m

>7 - 30 m 1 1 11

11

1 1

111

12 2

2 2 2

2

2

222

22

21 1 11

11

1 1

111

12 2

2 2 2

2

2

222

22

2

20 - 30 m

40 - 60 m

>7 - 30 m

20 - 30 m

40 - 60 m

>7 - 30 m

Panel stoping, Zinkgruvan

Panels 1 filled with paste fill before # 2 between blasted.

rings or fans with Ø89 mm angled holes of different lengths


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Mining methods -4

Sublevel caving or SLC at LKAB

SLC rings with angled holes of different lengths blasting against

confinement of caving masses

high grade iron ore 4500 kg/m3


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Ring layouts – 1

Different SLC ring layouts at LKAB

water hydraulic ITH, Ø115 mm holes, 15-58 m long, 3 m burden, typically opened at center, 2 holes every 100 ms.


47

Ring layouts – 2

Deck charging sometimes used for

• breakage sequence + flow

• Vibrations.

charge in hole separated into decks by stemming and detonated separately in sequence 3, 4 etc

stemming

delay number = initiation sequence

flow R. Holmberg Lima Nov 2011

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Explosives -1


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Types of explosives used

Explosives - 2


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Anolit A with 6-7% Al expl. energy = 4,9 MJ/kg volume strength = 125 %

Anolit

Density 850 kg/m3

Weight strength 100 % Volume strength 100 % Expl. energy 4,0 MJ/kg VOD 2400 m/s Gas volume 970 l/kg Water resistance poor Use primer

Anolit (ANFO) compressed air charging equipm.

Explosives - 3


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Emulsion matrix is not an explosive which means safer, less restricted transportation

Explosives - 4


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Reaction kinetics

Emulsion –finer structure

rendering in higher VoD

Explosives - 5


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Control -panel

Pump

Dosage pumps

Gassing agents

Oxidizer Solution

Fuel andEmulsifier

Slurry Station

Site Sensitised Emulsion

Emulsion mixer

Emulsion matrix

Explosives - 6


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under ground in Ø45-51 mm holes

Titan® SSE system (site sensitized emulsion)

Explosives - 7


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Control -panel

Blender

Pump

Emulsion mixer Dosage pumps

Gassing agents

Aluminum

AN - Prills

Oxidizer Solution

Fuel andEmulsifier

Slurry Station

Explosives - 8


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Control -panelBlenderPump Emulsion mixer Dosage pumps

Gassing agentsAluminum AN - Prills Oxidizer Solution Fuel andEmulsifierSlurry Station

Bore hole diameter :

Quarries : 2” - 6”

Mining : 6” - 12”

Max pump heigth : 40 m

Max hose length : 150 m

above ground in holes Ø64-320 mm

Explosives - 9


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Control -panelBlenderPump Emulsion mixer Dosage pumps

Gassing agentsAluminum AN - Prills Oxidizer Solution Fuel andEmulsifierSlurry Station

Comparing ANFO and emulsion explosives

• Emulsion matrix less restricted in transportation

• Pumped emulsions have higher charging capacity

• Density regulated by gassing during pumping

• Decoupled „string‟ emulsion in horizontal holes

• Emulsions have higher water resistance and AN prills may be added to raise density

• Energy content per m3 roughly the same

but

• Lower price of ANFO ideal for dry hole conditions.

Roger

Explosives - 10


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YZ-snitt KI-28-849-o3030-19

1050-5-10

0

-5

-10

-15

-20

-25

-30

-35

-40

12

12

11

11

10

10

9

9

8

8

8

8

8

8

9

9

10

10

11

11

12

12

1

2 3

4

5

6

7

8

9 10

11

40-50 m

• KR0500 („Kimulux Repumpable 0500‟), sensitized by glass micro-balloons, contains aluminum

• Water used to lubricate inside of charging hose; mixed in at nozzle

• Staying in place is a balance between viscosity and adhesion

• Emulsion is tixotropic and blast shock is too fast to cause liquefaction

• But, running water creates problems.

Uphole ring charging at LKAB

Explosives - 11


59

59

DynoRex®

Dynamite with NG, nitro-glycol, nitrocellulose and AN

used as bottom charge, primer & booster, in wet holes etc.

also available as

1100 mm pipe

charges

Explosives - 12


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used as bottom and column charge (pipe) , primer & booster, contour blasting.

Kemix A®

Decoupled charges - 1


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62

Dynotex®

pipe charges Ø17-32×460/1000 mm



63

by balancing emulsion flow through nozzle and hose retraction an even string is deposited in hole

String emulsion

mini SSE string 0,35 kg/m



64

Selmer Anläggning ABChalmers-tunnelen

C

E

B

A

Emulsjon Tennpatron

Innerkontur (hjelpekontur) : 3,0 kg

Strengladning SSELadeplan 4,2 m

Strossehull oppe : 4,0 kg

Innerkontur (hjelpekontur) : 3,0 kg

Kutt m/hjelpehull : 4,5 kg

Konturhull m/hjørneliggere : 1,7 kg

Liggerhull : 3,3 kg

0,3m

0,3m

0,3m

0,3m

0,15m

0,45m

0,7m

0,7m

0,3m

0,45m

1,1 kg/m

0,8 kg/m

1,1 kg/m

0,4 kg/m

0,8 kg/m

3,6m

3,05 m

3,2m

3,45m

3,9 m

D

4.steg . SSE emulsjon i hele salven

BA

C

D

E

Pointers - 1


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Underground blasting:

• Often more complicated drilling patterns and blasting methods used than in surface blasting

• Special considerations for cuts and openings; stability; rock stress and water complicate work

• Separation between fragmented rock (ore) and remaining rock mass (waste) hard to maintain

• Short life span of drifts and cavities in mining but long span in infrastructure tunnels and cavern

• Nitrate leakage from explosives is coming into focus; spillage & non-detonating explosives are sources.

Pointers - 2


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Quality of blasting work:

• Blasting never gets better than drilling and drill hole deviations are frequently large

• Water problem in charging also with emulsions - bad charging practice mixes emulsion & water, may cause detonation failure; water removes cushion effect for decoupled charges; wet upholes cause emulsion to slip etc

• Some cases „black holes‟, e.g. SLC. One doesn't - see the drilling quality, know how the ring fired or even which ring the ore loaded comes from

• High quality blast designs, drilling and charging work needed to achieve good blasting results.

Accknowledgements


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The author wishes to acknowledge Prof Finn Ouchterlony , Swebrec and LTU who provided a lot of the sources for the material presented in this lecture

THANKS!


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Documents

Blast Design for Underground Mining Applications