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Optimisation programme – Phase Two
Phase Two of the drill and blast optimisation programme consisted of monitoring the blast patterns, powder factors and drilling accuracy. Prior to implementing the photogrammetric face profiling, the operation used a 2-D laser profiler to lay out the front row of boreholes whenever possible. Often times, however, the shot was laid out using the method of setback markers because the blast faces were not cleared of muck prior to the pattern being drilled, making custom face row placement virtually impossible. Due to the inconsistencies of the blast face, a 2-D system did not prove adequate to provide a high level of detail for an optimized blast design. To ensure more accurate measurements, the quarry implemented both the 3GSM BlastMetriX3-D photogrammetric face profiling with advanced blast design software as well as a full-time RTK capable GPS and base station. Additionally, a cabled borehole survey system was used to update blast face profiles and check the accuracy of drilling. Several faces were profiled using the 3-D photogrammetric profiling system to audit current blasting patterns and compare against the design.
Figure 4 is an example of a borehole survey from a blast. Borehole surveys of blasts were used to check drilling accuracy and update blast face profiles for more accurate loading.
Figure 5 shows evidence of inaccurate drilling. A change in drilling azimuth may cause the boreholes to diverge, which will significantly increase the powder factor in that area and increase the chance of highwall damage.
The standard pattern design for the operation is an 11’ × 13’( 3.35 × 3.96m) drill pattern with a 5”( 127mm) borehole on a 50’( 15.2m) bench. The blast audits showed significant variations in face row burdens, with some shots having minimum burdens that ranged from 3.6ft to 24.8ft( 1.1 – 7.6m).
Figure 6 details two boreholes with varying burdens taken from an audited blast. Angled boreholes were used when necessary, but most boreholes were drilled vertically. These profiles were used to both determine the burden of the face row and to assist with borehole loading.
During the second phase, the quarry began proactively profiling the blast face and designing a blast pattern based on highwall conditions. When implementing a profiling programme, it is beneficial to clear the entire blast face of muck prior to profiling. This allows for every borehole in the face row to be custom designed and positioned using the blast design software within the programme. Pattern modifications can then be made as necessary. Pattern modifications are crucial
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Figure 6
when toe or high bottom is encountered in front of the blast face, increasing the burden. Designing blasts to ensure that the burden and spacing are correct allows for better explosives distribution and produces more uniform fragmentation. Additionally, maintaining the proper face row burden significantly reduces the potential for flyrock or airblasts, while also allowing for controlled shot movement. This helps maintain muckpile configuration, floor grade and reduces highwall damage for the next shot.
Knowing the burdens for the face row of a blast is just one aspect of a good blast design. Determining the actual bench height, before the blast has been designed, ensures that boreholes can be drilled to the appropriate depth, reducing any over or under drilling. This will reduce bench damage to the next level down, as well as assist with eliminating
QUARRY SA | JANUARY 2017 _ 13