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Blast Control (Open-cut Mine Surveying Duties)

Machines can't dig through solid rock, therefore blasting is required prior to excavation. This process involves the use of overburden drills to drill a pattern of holes, which are then loaded with explosives and detonated. Surveyors are involved in this process by setting out pegs for an area to be prepared for drilling, pegs for drill operators to know where to drill, as well as surveying the material once it has been blasted. In some mines, drills have GPS attached and are able to drill a pattern without the use of pegs.

Example #1: Pre-split drill holes

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To achieve a flat or smooth high wall, a 'pre-split' blast must be completed prior to blasting the rest of the material. A pre-split comprises of a single continuous row of drill holes which are packed with explosives and blasted; it splits the material prior to a full blast, hence the name 'pre-split'. Once this process is complete a full drill pattern is drilled in front of the pre-split and blasted. This causes the rest of the material to be blasted away from the pre-split line without damaging the wall behind the shot.

Example #2: Smooth high wall

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In the photo above you can see the effect of a successful pre-split blast. Notice that you can see the drill holes along the wall from the pre-split.

Example #3: Drill pattern

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Using survey pegs placed for the drills or GPS, the drill operators will drill an evenly spaced pattern as per a drill and blast engineering design. In the event that an explosive or series of explosives haven't detonated in a blast, surveyors will place pegs on the shot ground where at the coordinates of where the hole was initially drilled. Before normal excavations can commence, the explosives need to be located and removed safely by delicately digging around the suspected area. When an explosive is located, surveyors will keep a record of its final position on permanent plans.

Example #4: Shot ground after a blast

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Once a blast is complete, the blasted material needs to be surveyed. This process can be done by walking over the material and surveying it using GPS, or by the use of reflector-less lasers, automated scanners or aerial lasers. As blasted material expands, calculations need to be completed to determine the amount of swell created from the blast. The swell factor will have an effect on volume figures and therefore change the amount paid to contractors. Some surveying operations will have swell factors calculated for each blast, while others will determine an average swell factor to apply to all calculations when using shot-ground for volume calculations.

Example #5: Shot ground pickup from reflector-less laser

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Using a reflector-less laser to pickup shotground will result in a pickup similar to the above. The surveyor will generally try and take as many points as required to depict an accurate representation of the profile of the material. Depending on machine schedules, it may be planned for excavations to commence shortly after the blast is complete - so surveyors will sometimes have to collect this data as soon as possible.

Example #6: Shot ground pickup from automated scanner

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Using an automated scanner for the collection of data in shot ground is a time saving operation. It also provides an accurate profile of the ground which leads to more accurate volumes. As the automated scanner will pickup whatever it can see, the surveyor still needs to consider how many setups are required, as well as the best position for each setup to ensure adequate data is collected.

For examples of surface creation using shot ground, refer to the volume calculation section.

Blast Video

Watching blasts is not only exciting, but it provides you with a better understanding of the mining process and what's involved. See the video below for examples of typical blasts.

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Open-cut Mine Surveying Duties