Mining Engineering

Mining Engineering

Question no. 1

An open pit mine employs ANFO at a density of 0.85 g/cc as its explosive. Given the following details, determine the Blasthole spacing.



Blastholes are vertical and bench height is 11m.

Burden and spacing of blastholes are the same, i.e. B = S.

The specific gravity of the rock is 2.5.

The powder factor is 0.5 kg of explosive per m3 of rock.

Hole diameter is 225 mm.

Stemming column length is 3 m and subdrill is 2m.

Data:

Blastholes are vertical and bench height is 11m.

Burden and spacing of blastholes are the same, i.e. B = S.

The specific gravity of the rock is 2.5.

The powder factor is 0.5 kg of explosive per m3 of rock.

 Hole diameter is 225 mm.                         

Stemming column length is 3 m and subdrill is 2m.

Based on the specific gravity of the rock the material is BASALT which has a broken density of 2.36-2.53

Solid Density = 3.0

Unconfined Compressive Strength (MPa) = 78-412

Young's Modulus = 20-100

Poisson's Ratio =0.14-0.25

ANFO density = 0.85 g/cc

Blast holes = vertical

Bench height = 11m

Burden and spacing = B=S

Powder factor = 0.5 kg/m3 of rock

Hole diameter = D = 225

Solution:

To calculate the Burden we use the formula (2 SGe/SGr + 1.5) De

Where SGe is the specific gravity of the explosive

SGr is the specific gravity of the rock

De is the diameter of the explosive

(2 0.85/2.5 +1.5) 225

Burden = 4.9

Blast hole spacing can be given by L + 2B/ 3

= 11 + 2 (4.9)/ 3

= 6.9

BLAST HOLE SPACING = 6.9

Question no. 2

An open pit blast consists of 120 vertical blastholes. Bench height is 10m and 1m of sub drilling is undertaken. The holes have 2.5m of stemming. Blasthole diameter is 200mm, the burden is 6 m and spacing is 7 m. An emulsion explosive of specific gravity 1.1 is used. What is the powder factor? (Note consider the emulsion only, i.e. do not consider primers)

Solution:

Blast hole depth = bench height + sub drilling

Blast hole depth = L = 11

Powder column - blast hole depth - stemming

= 11 - 2.5

= 8.5

The spacing pattern can be determined by the values of burden and spacing

Therefore the pattern can be given as 6 x 7

Blast volume = B x S x BH x N

= 6 x 7 x 10 x 120

= 15372 ft

Mass of explosive per hole = volume of hole length x explosive density

= 11 x 1.1

= 12.1 kg per hole

Stemming (T) = 2.5 m

Sub drilling (J) = 1 m

Powder column length = (L + J) - T

= (11 + 1) - 2.5

= 1.9 kg

Total weight per column = 102.6 kg

The powder factor can be given as

Powder factor = total weight of explosive

Volume of rock fractured

= 102.6 ÷ 6 x 7 x 11/11

Powder factor = 2.44

Question No. 3

What range of application of blast monitoring is available?

Answer

Range of Applications

Blast monitoring for compliance

Near-field blast analysis

Pile driving

Construction activity

Demolition activity

Heavy transportation monitoring

Bridge monitoring

Structural monitoring and analysis

Underwater blast monitoring

4 or 8 channel data acquisition

Remote monitoring

Multi-point monitoring (8 channel)

Low frequency monitoring

Sensor category: ...