Blasting Theory

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Underground Mining and Planning Methods

BLASTING THEORY

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Learning Objectives

At the end of this class, students should be able to:

Understand uses of various bulk explosives

Understand the how ore body/rock mass geometry should affect the blastdesign

Design a production blast using rule of thumb

Able to design a cut

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2 . Theory

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Explosive Characteristi cs

Explosives are defined by two strength values: Bulk Strength is energy per unit volume of rock

Weight Strength is energy per unit weight of rock

Velocity of Detonation (VOD) is the rate at which the detonation wavepasses through the explosive charge

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3 . Explosive Types & Products

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Categories of Explosives

Deflagrating Explosives Explosives initiated by a flame or spark

VOD of less than 2000m/s

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High Explosives Initiated by shock from another explosive like a detonator, primer and booster.

VOD between 2500m/s to 7500m/s

Examples are ANFO, emulsions, nitroglycerine

Initiating Explosives

VOD greater than 7500m/s

Examples are PETN in detonating cord, ASA used in detonators.

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High Explosives

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Initiating Explosives

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4 . Development Blasting

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Development Blasting

The critical drilling and blasting conditions in development or tunnel blastingare found in the following key locations:

Burn cut;

Stripping holes, or those blast holes immediately in from the perimeter charges;

Perimeter charges.

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Number of blastholes

Underground operations vary the number of blastholes, as a function of drift size.

Area of Drive (m 2)

Number of Charged Holes

Total Number of Holes

Depth of Blastholes

Diameter of Blastholes

Diameter of Uncharged

Holes


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Development Blasting Burn Cut

The success of the burn cut has the greatest impact on the performance of the remainder of the blast round.

The uncharged relief holes in the cut provide the dual purpose of anadditional free face to break towards and secondl rovide for a method of , ,ensuring some degree of looseness of the broken muck.

Interaction in the burn cut is common because of the close spacing of theblastholes, commonly resulting from inaccurate drilling or opendiscontinuities or fractures linking blastholes. Blastholes should bepositioned in the face taking account of the local structure, noting that openfractures are preferentially orientated along the strike of the structure,rather than perpendicular to it Hence, two blastholes, A and B, as shown in

e nex gure are more e y o n erac as a resu o e g pressuregases permeating through the local strocture, than blastholes A and C.Rotating cut holes

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Design o f cut

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STRIPPING HOLES

The blastholes positioned between the box cut and the perimeter chargescan be termed stripping holes and have the prime objective of breaking anddisplacing the rock towards both the void created by the burn cut, and the

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LIFTERS

The proper performance of the lifters (charges along the baseline of theround) is essential to achieve good floor control. These charges must not beadversely affected by the row of holes immediately above these (knee holes).

PERIMETER HOLES

e per me er o es are oca e on e nom na r oun ary. The optimum spacing is a function of the blasthole diameter, with trial results

showing that a spacing for the perimeter blastholes of 13 to 17 times theblasthole diameter has produced acceptable results.

To limit the damage from the breast holes, commonly the burden is keptabove 80% of the spacing,

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Explosive Used in Development

Powergel or Emulite

Detonating Cord

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Electric Detonators


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Tying In Development Faces

Cord clip development faces

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Bunch Connection development faces

5 . Product ion Blasting

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Production Blasting

The objectives of production blasting Fragmentation of ore-bearing rock.

Maximum recovery of ore with minimum dilution.

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Blast patterns vary depending on the mining methods. Benching most likely have vertical holes

Open stoping will have fanned rings

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Production Blasting

A production blast consists of A slot raise

A slot, cut-off or cut-off slot

Factors to consider with production blasting

Faults Ring orientation

Slot placement

Stope geometry

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Explosive Used in Production Blasting

Detonating Cord

Cast Primers

Ring Spider

Electronic Detonators

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Electric Detonators

Underground Charging

Explosive companieshave specialised trucksfor charging emulsion.

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Powder Factors

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Burden & Spacing

Calculating the burden and spacing

Charge Length (CL) = Avg Hole Length (L) 0.7(30 * d/1000)Where d = hole diameter

Weight of explosives (W) = CL x Loading Density

Volume of Rock (V) = W/ Powder Factor (PF)

Area of rock blasted (A) = V/L

Rule of thumb for toe spacing S = (1 to 1.8) Burdens (B)

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Ring Blasting

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6 . Secondary Breakage

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Secondary Breakage

Secondary Breakage is required when the fragmentation of the primaryblast is poor.

Two ways of undertaking secondary blasting:

Plaster blasting

Higher costs associated with secondary blasting.

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Secondary Breaking

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7 . Blasting Costs

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8. References

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References

www.oricaminingservices.com

www.dynonobel.com

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9 . Practical

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Practical Exercise

1. Design a development face with the following parameters: 5 m x 5m arched

45mm diameter holes

2. Calculate the burden and spacing for a stope with the following parameters: Level spacing 40 m

Powder factor 0.9 kg/m 3

using the following hole diameters 89, 102 and 140 mm.

. 1,500,000 tpa mine

2,400 m development per year

Production drilling density 15 t/m @ 102mm diameter

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Documents

Blasting Theory