Volume of rock blasted due to blasting

Surface mining or Opencast mining

Surface mining is also known as opencast mining or open-pit mining. Here, the rock or ore are extracted by creating an open-air pit. The main aim of mining is to extract valuable rock, ore, mineral, coal from the earth. There are basically two principles for rock extraction. One is blasting ( use of chemical energy), other is the mechanical cutting techniques. Among those easiest and economical ways of rock extraction is the blasting technique. Because this blasting technique is cheap as compared to other cutting technique and applicable in every type of geo-mechanical terrain.

In both opencast and underground mine, the blasting technique plays a very crucial role in the rock extraction process. Here, surface mining rock extraction through blasting is discussed.

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Notes -

Blasting is one of the rock extraction technique.
In blasting, chemical energy is used for rock extraction.
Blasting is the most suitable rock extraction technique - as it can be applied to all geo-mining condition and economical as compared to others.

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Blasting technique

In the blasting technique, explosive energy is used to generate the shock wave and gas pressure. These generated shock wave and gas pressure reduces the rockmass strength and break the rockmass.

Rock extraction through blasting Procedure:

Drilling in the rock for creating a hole, which will contain the explosive.
Charing the hole with the explosive.
Detonating the explosive for the blast.

Figure 1 Rock blasting procedure.

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Note -

Blasting is not the same as the explosion.
Blasting is a controlled process.
The explosion is an uncontrolled process.
For example - we say like, there was an oil tanker explosion on the highway.

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Surface bench blasting

Figure 2 - Surface mine bench with blastholes.

Figure 2 shows an open cast or surface mine bench with bench height or depth of the bench is H. There are 16 drill holes or blastholes with burden value B and spacing value of S. The free face is also shown in the figure.

Free face means - on that side, there is no rock.

So, the blast design parameters are -

bench height or depth : H

burden : B

spacing : S

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More details - Blast design parameters.

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The top view of the bench is like as shown in Figure 3.

Figure 3 - Top view of the bench with the blastholes.

Rock blasted per hole

Figure 4 - Rock blasted per hole.

A particular hole can blast =

Where,

Figure 5 - A blasthole layout with its blasting volume zone.

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Note -

While calculating, kindly arrange all value to the same unit. ( Burden in meter, spacing in m and depth of bench in meter).
So, the volume of rock blasted will be in cubic meter.

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If there are 'n' number of blastholes, then the volume of rock blasted will be

Unit is the cubic meter.

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Problem 1

Suppose, a surface mine bench is being extracted by drilling and blasting technique. The burden and spacing used in the blast is 3 m and 5 m respectively. If the depth of the bench is 10 m, and 40 number of holes are blasted, then calculate the volume of rock will be blasted through the blasting.

Solution:

Given, burden (B) = 3 m,

spacing (S) = 5 m

depth of bench (H) = 10 m,

number of holes (n) = 40

So, the volume of rock will blast = 𝐁 ×𝐒 ×𝐇 × n

= 3 × 5 × 10 × 40 = 6000 m3

Problem 2

Suppose, an iron ore mine bench is being extracted by drilling and blasting technique. The density of iron ore is 2.5 tonne/m3. The burden and spacing used in the blast is 3 m and 5 m respectively. If the depth of the bench is 10 m, and 40 number of holes are blasted, then calculate the tonne of rock will be blasted through the blasting.