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