UNDERGROUND BLAST TECHNIQUES- PART-II

13-06-2023
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Burn cut
A series of parallel holes are drilled closely spaced at right angles to the face. One hole or more at the centre of the face are uncharged. This is called the burn cut

The uncharged holes are often of larger diameter than the charged holes and form zones of weakness that assist the adjacent charged holes in breaking out the ground.

Since all holes are at right angles to the face, hole placement and alignment are easier than in other types of cuts. The burn cut is particularly suitable for use in massive rock such as granite, basalt etc.

Short-hole blasting
The diameter and length of shot holes are usually limited to 43 mm and 4 m respectively.
Short-hole blasting is usually used in breast stoping for narrow, tubular orebodies such as gold or platinum reefs.
Figure 6 is an example of blasting arrangement in breast stoping in a gold mine in South Africa. Capped safety fuse and igniter cord (burning speed of 18 s/m) make the carrier of the initiating system.
The igniter cord is usually fired by an electric starter for igniter cord.

Long hole blasting
Basically, there are three long hole blasting systems:
ring blasting
bench blasting
vertical crater retreat (VCR).

Ring blasting
This technique involves drilling a series of blastholes in a circular pattern within each sublevel. The name "ring drilling" refers to the circular arrangement of the blastholes resembling a ring. This technique is commonly used in sublevel stopping.
It allows for efficient and systematic ore extraction, providing a high degree of control over the fragmentation process.
Additionally, ring drilling enables safe and effective extraction in steeply dipping ore bodies, minimizing the risk of instability or cave-ins during the mining process.