Rock Blasting Technology and Techniques
In the year 2000, it was estimated that over 1.1 billion kilograms of explosives were being used annually. These were for commercial purposes. This would mean that over 3.1 million kilograms were being discharged each day. Each hour over 129 000 kilograms were being detonated. And the amount was growing.
Blasting is the process of reducing a solid body to fragments by using an explosive. Rock blasting is specifically blowing up solid rock. It is necessary in construction and in mining projects. It requires the use of controlled explosives. It takes very precise preparation and skill.
Blasting Technology
Blasting technology has come a long way since the use of gunpowder. The first recorded instance of using explosives to blast rock was in Hungary. This was in the year 1627.
Alfred Nobel, famous today for the five Nobel Prizes, was the inventor of dynamite. He patented it in 1867. It was the first “safe” high explosive.
Today a variety of explosives are used, depending on the specifics of the project. There is also the option in certain scenarios to use air blasting. This is one way to reduce the noise of an operation.
Drilling technology has also advanced. Mechanised drilling uses various machines. Jumbo drills are used to bore directly into the hardest rock. They are pneumatic, which means that the machines both drill and hammer. Pneumatic technology continues to develop and improve.
Blasting Explosives
The basic idea of explosives is that large amounts of energy are released extremely quickly. This is accomplished when the chemical compounds of the explosive rapidly decompose, leading to heated gas at a high pressure. This is the explosion.
There are basically two types of explosives. Low explosives have reaction velocities of about between 600 meters per second and to less than 915 meters per second. High explosives, by contrast, have a reaction velocity of over 1500 meters per second.
When an explosive detonates, hole pressure exceeds the atmospheric pressure. This is at a rate of between 20 thousand to 100 thousand times. This also causes stress waves, which can travel at a velocity of 5000 meters per second.
Common explosives used are ANFO, slurries, and emulsions. ANFO is ammonium nitrate/fuel oil. It is a dry blasting explosive. It is often mixed with aluminium powder. This is because its density needs to be increased. It is very useful in blasting very large and tough rocks.
Slurries are based on aqueous solutions of ammonium nitrate. Emulsions are quite new to the explosives industry. They have the same properties as slurries, but with high strength. They are also water resistant.
Combining ANFO with a base emulsion produces heavy ANFO. It produces more energy and has better sensitivity. It is also highly water resistant.
Gelatine and granular dynamites are also used when appropriate. Black powder explosives are also sometimes an option, though their strength is less than a third of gelatine dynamites.
Rock Blasting Techniques
Techniques of rock blasting vary depending on the task. Various factors influence the specifics. These include whether the blast is above ground or underneath the surface.
The most common technique for rock blasting is to drill holes at precise points in the rock face. Explosives with detonators are placed in the drilled holes. The charges are then detonated. After the explosion, the broken material is cleared away. This process is repeated until it removes enough of the rock for mining or construction to be carried out.
Blasting Preparation
While it might sound straightforward, rock blasting requires meticulous planning. Before undertaking any project, many factors are analysed and accounted for.
The blast patterns and blast-holes are calculated. This takes into account the position and type of rock that will be blasted. Possible deviations from the initial measurements are also taken into account. Even the way the rock will move from the stress waves is known before any detonation takes place. Explosive loading can be performed to a higher degree of accuracy than ever before.
Done properly, this means more effective blasting leading to higher productivity. These calculations also play a big part in ensuring the safety of those involved in blasting projects.
Three-dimensional imaging in Rock Blasting
The latest developments in three-dimensional imaging have been impressive. These have meant much greater precision in rock blasting planning. Photogrammetry is the surveying and mapping to establish measurements between objects. It has been used since the 1850s. Thanks to advances since the 1990s, precision in the blast pattern computations has increased. This is thanks to the use of computer imaging and sophisticated algorithms.
Advances in unmanned aerial vehicles have been significant in the last two decades. Combining them with the 3-D imaging has been invaluable. The combination has led to blasting survey and profiling technology that is far more accurate than anything seen before. This is isn’t just above the ground, but also for any explosives that need to be set underground.
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Bibliography/Further Reading
https://www.onepetro.org/conference-paper/ASSE-00-005
https://www.britannica.com/technology/blasting
https://curiosity.com/topics/pacifist-alfred-nobel-invented-dynamite-on-accident-curiosity/
https://nptel.ac.in/courses/105106055/Mod11/Lecture36.pdf
https://m.miningweekly.com/article/3d-blasting-method-achieves-safe-and-effective-results-2015-11-20
https://m.miningweekly.com/article/uavs-to-streamline-blasting-technology-2012-11-30
https://www.researchgate.net/publication/261992940_Blasting_Optimization_using_3D_Photogrammetry_in_a_South_Brazilian_Quarry
https://www.mining-technology.com/contractors/drilling/
https://www.omicsonline.org/open-access/new-trends-in-economical-and-safe-rock-blasting-2168-9806.1000e104.php?aid=8140
https://www.osmre.gov/resources/blasting/btm/Module1.pdf
file:///Users/macintoshhd/Downloads/Methodology_for_Characterizing_the_Efficacy_of_Blasting_in_O.pdf
