Rock fragmentation by mining

Rock fragmentation by explosivesin mines and quarries aims“to access the desired resource and separate it from the unwanted material (waste) with which it is mixed, using the least energy or expenditure possible”, as already stated in a previous article. The explosives basically replaced the use of human or mechanical strength aiming at fragmenting the rock in order to access the desired material. The explosives significantly upgrade the efficiency ratio during the extraction and beneficiation stages of the mining cycle.A Typical Blasting Operation To keep it simple, to mine an area (or more likely a volume of rock) in a surface mine or in a quarry, you will: *.Drill holes regularly along a selected pattern (depending on hole diameter, on rock characteristics, amongst others) *.Locate a detonator down the hole. Whatever the selected technology (non electric, electric, electronic detonators), don’t forget to keep the extremity of the cable (or of the tube) on the surface *.Fill the holes with a certain quantity of explosive product (in bulk or/and in cartridges) in line with your operational objectives, context and constraints (safety, legal compliance with environmental regulations) *.Tap the holes with a certain quantity of drilling cuttings, sand or gravel: this is the stemming stage ; a critical step in the loading process, mitigating fly-rocks risk, crater effect, noise and allowing a better concentration of the energy inside and around the hole *.Start then another critical step: the connection of the detonators (the wiring). Detonators are connected in a predefined order which is decided during the sequence creation step *.A large area around the blast is cleared of all people, mobile equipment and vehicles. Safety distance is defined by legal regulations and site rules which are often stricter *.A programming step starts when electronic detonators are used. The non electric and electric detonators are pre-set timing devices and consequently don’t require any programming action *.After the site alarm has been rung, the blast is triggered from a safe distance by the chief blaster, usually protected by a shelter *.The site alarm is rung again along a different sequence to inform the blast operation is overEffects of an Explosion & Rock Fragmentation Mechanism As described to About Mining by Dr. Thierry Bernard, a worldwide renowned blasting consultant and inventor of unique blasting simulation engineering software:“Without going into details, the description of the effects of an explosion can be split up as follows: 1.The charge explodes and it is split up into high-pressure, high-temperature gases 2.The gases are applied to the borehole, which contains them and creates a strain field in the rock 3.This strain field, due to its impulse nature, creates a strain wave that is propagated in the rock and damages it 4.This damage is the centre of the cracks in the rock 5.The gas pressure is reduced via the cracks thus separating the rock fragments 6.The pressure of these gases applied to the face of the fragments, produces forces that propel the fragments 7.The fragments adopt a ballistic trajectory 1.In areas where the damage to the rock was not sufficient to create fragments, the strain wave continues its trajectory until it runs out of energy that dissipates by making the rock vibrate.”Measuring Rock Fragmentation Fragmentation analysis software tools allow the quantification and size estimation of the fragmentation and deliver a size distribution of rock either from sample images taken on a muck pile, a truck tipper or a conveyor belt.