the rise in the floor. Good floor control will reduce the overall maintenance cost on equipment and reduce load out time.
As with most quarry operations in the region, the quarry was using primarily vertical boreholes in their blast design, with the occasional angled borehole to assist with heavy face row burdens and toe. Despite attempts to get a‘ vertical’ blast face, the quarry was still experiencing extensive highwall damage.
Figure 7
Figure 7 depicts the resulting highwall after excavating a blast that was designed using set back markers and a 2-D laser profiler. Pre-conditioning of the highwall left overhangs due to back break and back shatter caused from the blast. The highwall was then profiled using the photogrammetric system and a blast was designed using the advanced blast design software.
The 3-D photogrammetric profiling system and advanced blast design software allowed engineers to quantify the existing average blast face angle and determine the most effective borehole angle for their blast design. Following a series of test blasts, it was determined that a 12-degree borehole angle provided a significant improvement in highwall stability and reduced the amount of back break and back shatter, as seen in Figure 8.
they also experienced an increase in crusher throughput. As mentioned previously, primary crusher throughput was monitored prior to the implementation of the proactive blast design and quality control programme. The results showed an average primary crusher throughput of 932 short tons( 845.5 metric tons) per hour. Once the new programme was put in place, data collected for five months demonstrated an increase in crusher throughput.
The post implementation tons per hour average was 990 short tons( 898.1 metric tons), which reduced the required time to obtain the 65 000 short ton( 58 967 metric ton) goal by 4.1 hours per week. With an average cost for the primary crusher of USD950 / hour, the cost savings for the crusher would be USD202 540 / year based on the same rock volume per year. The increase in crusher throughput efficiency also provides the option for the quarry to increase their production without increasing crusher hours.
* Data from 1 July to 31 August was not included in tonnage calculation. During this period, the quarry had one of their loaders down. Figure 9
Figure 9 contains the pre- and postprogramme implementation data for primary crusher throughput in tons per hour. The data represented by the orange line is the daily average tons per hour crusher throughput prior to implementing the optimisation programme, while the data represented by the grey line is the data collected following the implementation.
In addition to the increase in crusher throughput, the quarry also experienced a reduction in oversize and an increase in loader efficiency. The quarry tracked their cost for secondary breakage both prior to and following the programme implementation and realized a savings in secondary rock breakage cost of USD97 894 over the five months following the programme’ s initiation. This equates to an average savings of USD243 000 per year. Due to the reduction in oversize and more consistent fragmentation, the quarry also measured a decrease in the haul truck loading time. However, since the operation is truck limited, they believed that an increase in truck availability would help them realize the added benefits of decreased loading time.
Technology integration
The systems and technology used in the optimisation programme were originally introduced short term to address the issues in the pit. However, due to the success of the optimisation programme, the quarry realized that the continued use of these systems would be required to maintain field controls to support this level of production. Due to the benefits seen at the quarry, it was decided that the introduction of additional technology could further improve their drilling and blasting programme.
As an extension of the original optimisation programme, the quarry decided to integrate a specialised drill that has the capability of importing a georeferenced blast design exported from the photogrammetric blast design software. The proactive blast design can then be imported into the drill navigation system for automated borehole layout.
Figure 10 depicts the specialised drill and GPS systems that were implemented during the second phase of the optimisation programme.
Benefits of this drill system include saving time and reducing potential inaccuracies in pattern layout. The drill navigation system allows for the exportation of an‘ as drilled’ borehole pattern, which can be imported back into the blast design software and used to update borehole profiles, resulting in increased accuracy. If borehole surveys are conducted on the drilled boreholes, the survey can then be imported into the blast design software, resulting in a‘ true minimum
Figure 8
Figure 8 is the resultant highwall once the custom blast design was fired and excavated.
While the highwall stability significantly improved the safety for quarry employees, it also made blast design and blast layout much more efficient. Not only did the quarry see an improvement in highwall stability, but
Figure 10
14 _ QUARRY SA | JANUARY 2017