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What is rock blasting?

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Rock blasting is the process of drilling holes in a rock mass at depths, and spacing to allow an explosive to fracture the rock.  In this process, the rock must fracture enough to be broken down to the size intended.

It is practiced most often in mining, quarrying, and civil engineering such as dam, tunnel, or road construction.

But how exactly does this process work and what does it involve?

Let's dive into everything you need to know about rock blasting.

How does rock blasting occur?

After detonating, chemical energy from the explosive is released, causing the explosive to transform into a glowing gas with large amounts of pressure. In a densely packed hole, this pressure can exceed 1,500,000 psi.

The high pressure released is what shatters the area surrounding the drill hole and exposes the rock beyond to high levels of stresses (and strains), stresses, and strains that cause the rock to crack.

While under pressure, the cracks in the rock extend, and the rock in front of the drill hole yields and move forward. If the distance of the hole to the closest surface is not too great, the rock in front of the hole will break free.

How is rock blasting performed?

Rock blasting is performed to fracture rocks so that these can be excavated for construction, or quarried for processing.

This process is completed by discharging explosives in a confined manner (for instance mud capping) or confined in a borehole.

Is rock blasting precise?

Rock blasting's design is not an exact process, but an iterative process of designing the blast hole layout and estimating the number of explosives needed to blast the rocks.  This process requires professional assistance and experience. 

Therefore, it is possible to produce the desired result in all rock blasting situations (considering the unique rock formations).

What explosive is used for rock blasting?

Ammonium nitrate fuel oil (ANFO) is used as an explosive in mining, quarrying, and tunneling construction.

Ammonium nitrate can be transported and stored and mixed with fuel oil when needed. ANFO is made of about 94% ammonium nitrate and 6% fuel oil.

Over the years, consumption of ammonium nitrate explosives has grown because of its safety advantage over other products such as dynamite.

Is rock blasting safe?

Over the years, the United States Bureau of Mines (USBM) and the Office of Surface Mining (OSM), universities, and private groups have conducted extensive research about rock blasting.

Research findings have led to the development of acceptable vibration standards that greatly reduce the risk of off-site impacts. Ground vibration levels have been set by law to avoid off-site damage and should feel the same as a loaded truck or bus going 50 to 100 feet away.

One of the greatest challenges of rock blasting is to accurately determine the bounds of the blast area. This is particularly true in geologically disturbed rock that is to be blasted. The determination of the bounds of the blast area is the first step in ensuring safety.

Mine operators prevent injury to people or damage to equipment when a scheduled blast is detonated by having a blast area security system. Most blasting accidents occur during scheduled blasting and are due to inadequate blast area security. 

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References

Blasting - https://www.britannica.com/technology/blasting

Explosives and Blasting Agents - https://ihsmarkit.com/products/explosives-and-blasting-chemical-economics-handbook.html

208 Rock Blasting - https://www.dot.state.oh.us/Divisions/ConstructionMgt/OnlineDocs/2009MOP/200%20Earthwork/208/208%20Rock%20Blasting.htm

Blasting Safety – Revisiting Site Security - https://www.cdc.gov/niosh/mining/userfiles/works/pdfs/bsrss.pdf