blasting technology - blast design

7/31/2019 Blasting Technology - Blast Design

1/36

Blasting Course

Designing BlastsDesigning Blasts


2/36

Two important aims in blasting.

To fragment the rock to a desirable size and

To displace the fragments a desirable distance


3/36

At the best overall cost

0

1

2

3

4

5

6

0.5 0.7 0.9 1.1

Powder Factor (kg/m3)

Cos

t/m3

Explosive

Drilling

Load & Haul

Crushing & Milling

Overall Cost


4/36

Three things that affect outcome

ExplosiveRock

Blast Geometry


5/36

Rock

Rock StrengthRock Strength

Rock DensityRock Density

Rock StructureRock Structure


6/36

Rock Strength and elasticity

UCS and Tensile Strength

Has an influence on creation of cracks during blasting

Measured in MPa

Tensile strength about 1/10th UCS


7/36

Rock Density

Influences the displacement distance during a blast

Influences fragmentation

Higher density = higher energy for same end result


8/36

Rock Structure

Rock Structure has largest influence on fragmentation results.

Sometimes fragmentation completely controlled by structure


9/36

Rock Structure


10/36

Rock Structure


11/36

Rock Blastability Index

Rock UCS

Rock density

Joint Spacing

Joint Orientation

RMDJPSJPODensityRockUCSRBI ++++

+=

6.477.235.0


12/36

Blast Geometry


13/36

Burden and Spacing

Hoof vrye front

Breeklas

Effektiewe breeklas Spasiring

BreeklasInterimvryefront


14/36

Equilateral Pattern

A B

C

A = B =Cor

Base = 1.15 x height


15/36

Spacing = 1.15 x Burden(in plan, energy distributed evenly.)

Spacing > 1.15 x Burden

(in plan, energy not distributed evenly

and more overlap can be seen in the

energy contours in one direction.)

Red circles represent

contours of equal energy

around each borehole.


16/36

Staggered Pattern

Wherever possible use a

staggered pattern. A

square pattern is only

suitable for narrow box-

cut blasts


17/36

Deciding on Burden - Scaled Burden

cM

BurdenBurdenScaled =

cMBurdenScaledBurden =


18/36

Scaled Burden

RBI = 20 to 40 RBI = 40 to 60 RBI = 60 to 80

Shale/Mudstone 1.3 1.2 1.1

Sandstone 1.2 1.1 1

Limestone/Dolomite 1.2 1 1

Granite 1.2 1 0.9

Dolerite 1.1 1 0.9

RBI = 20 to 40 RBI = 40 to 60 RBI = 60 to 80

Shale/Mudstone 1 0.8 0.7Sandstone 1 0.8 0.7

Limestone/Dolomite 0.9 0.75 0.65

Granite 0.9 0.7 0.6

Dolerite 0.8 0.7 0.6

For Reduced Heave or coarser fragmentation

For increased heave or finer fragmentation


19/36

Burden Stiffness

5.2= burden

heightbench

Sb


20/36

Burden Stiffness - Matching bench height to hole diameter

Poor explosive distribution. Only the bottom half of the benchcontains explosive.

Tendency to crater because the surface is closer than thevertical free face. This results in

A tendency for uncontrolled fly rock

Poor fragmentation in top half of bench

Uneven floors

Very little muckpile movement


21/36

Explosives Energy

HeightBenchSpacingBurden

holeperkgFactorPowderDesign =

RWSFactorPowderFactorEnergy =

volumeblockkgtotalFactorPowderActual =


22/36

Stemming

Stemming affects the following results in a blast:

Fly rock

Air blast

Fragmentation

HeaveAll blasts require stemming


23/36

Ineffective Stemming

Excessive Fly

Excessive Noise

Poor Fragmentation

Poor Heave


24/36

Effective Stemming

Fly rock controlAir blast control

Optimal fragmentation

Optimal heave


25/36

Air

Water

Drill cuttings in water

ClayDrill cuttings in dry hole

Crushed aggregate - ungraded

Crushed aggregate - graded

Worst

Best

Stemming Effectiveness:


26/36

Factors affecting stemming performance

Stemming material

Stemming length

Rock strength

Explosive energy

Stemming length = 15 to 30 x diameter


27/36

Scaled Depth of Burial

= 1000

4

1000

833.0

cs

MDS

Scaled

Depth of

Burial

0.7 1 1.2 1.5 1.7

Hard rock much fly normal fly little fly no flyno surface

ex ression

Soft rock much fly much fly normal fly little fly no fly


28/36

Crater tests to determine site specific

values

Scale depth of burial

Maximum Burdens

Explosives performance and comparisons


29/36

Crater tests:

Surface ExpressionFragmentation

Crater Volume

Vertical Displacement Velocity


30/36

Sub-drill

Uneven floors with high bottoms

Difficult digging conditions at the bottom of the muckpile

Insufficient Sub-drill =


31/36

Sub-drill

Usually set at 20 to 50% of burden

BMQc

39.0=


32/36


33/36

Uniformity

1 10 100 1000 10000

Fragment Size (mm)

0

20

40

60

80

100

%

Passing

uniformity = 1.4

uniformity = 0.8

uniformity = 0.4


34/36

The final fragmentation influences:

Diggability: Impacts loading rates and wear and tear onequipment

Coal exposure rates: Impacts mine profitability


35/36

Kuzram model

Explosive Energy

Explosive distribution (burden, spacing, hole diameter, sub-drill,stemming length)

Bench Geometry

Rock Blastability


36/36

Kuzram

633.0

6/1

8.0

50115

100

=

RWSMEFRx cf

1.0

5.0

1.01001

2

1

142.2

+

=

c

c

b

c

h

c L

SubL

H

SubL

b

bb

s

bn

blasting technology - blast design

Documents