TECHNOLOGY
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Drilling and blasting are increasingly seen as a single tailored activity .
accuracy : the fragmentation is uniform . “ It also controls the ground vibrations . We have a lot of communities around the quarries , so you want to control the mass per delay ( kilograms of explosives all firing at the same time , which control ground vibration air blast ) without creating inefficiency in bringing down a bench . You still want to fire your big benches from a productivity point of view , so what you do effectively is divide your blast into two , so you put a detonator in the top half and a detonator in the bottom half , fire the top half and then fire the bottom half . To all intents it ’ s a single blast , but in reality , you ’ re able to control the mass per delay .”
What automation means for a quarry is that you can now have an automated drill rig next to the high wall — this addresses the risk of things falling off the face and landing on people , so you ’ re removing people out of the danger zone .
A major factor in blasting — whether surface or underground — is the reef size , which affects the hole size . In the underground environment , it is approximately 23kg to 42kg per hole ; in civils , it is 42 to 89 ; in a quarry , it is 89 to 127 ; and above 127 in large-scale mining and up to 311kg per hole in coal mining . In opencast mining , you can get up to one and a half tons per hole . Tose has a specialised team that monitors such holes — size and location — and how the explosive is likely to perform in that hole , looking at how the rock is actually breaking .
This has equal applicability in quarrying , and in China they are looking at not blasting an entire bench but cutting it to the exact size , and having it fall directly onto a conveyor that takes it to a crushing plant — but there ’ s a substantial capital cost to that type of equipment . But once you ’ ve got over the capital cost , the cost of a conveyor is about a third of transporting it by road .
“ This means the job of a geologist is changing , as the drilling rigs are able to determine what is happening below ground and your ground plan suddenly becomes a thousand times more accurate .
“ A blaster is now able to successfully initiate a blast up to 2km away from the actual event , offering much safer operating conditions . The pre- and post-blast capability of the system enables a user to prevent a misfire from occurring , or to at
20 _ QUARRY SA | SEPTEMBER / OCTOBER 2018