Quarry Southern Africa January 2017 | Page 15

BUSINESS
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
Figure 4
Figure 5
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