Success stories are not only good news to the parties involved, but to the industry as a whole. It allows the industry to learn and grow, by understanding how to achieve industry best practice in various scenarios.
Hanson’s Lysterfield quarry is a large granodiorite quarry in Melbourne. It has been able to successfully absorb a required production increase demanded by current large infrastructure projects in Melbourne. This ability has been partially linked by site personnel to the improvements in drill and blast processes. Maxam Australia became involved with supplying explosives to Hanson Lysterfield in early 2004 and was entrusted with the Rock on Ground Services (ROGS), excluding drilling, in January 2006.
Aggregate quarries have, as a fundamental requirement in the efficiency of their production process, to ensure the effective breakage of the rock mass. This primary breakage mechanism of blasting has a large influence on efficiency of the production process that can be summed up by the old saying ‘the most cost effective breakage is in the pit, not the plant’.
The breakage process represents a significant component of the entire cost of the production process, as well as overall cost structures. This is true for Lysterfield.
One key motivation in the site’s goals is to achieve industry best practice. It was and is a good site for showing the gains that can be made in cost structures, by identifying the key bottlenecks in the production process and working towards their elimination.
One bottleneck identified by Hanson at Lysterfield was the role of the rock breaker used on-site. In 2005, Lysterfield was in the process of assessing what equipment was required to replace the old 70 tonne rock breaker. It was being used for a very large percentage of its time on rock breaking and, therefore, was not available for use on other required work around the pit.
In the evaluation process conducted by Hanson, either a new 70 tonne excavator/rock breaker or a 45 tonne machine would be purchased.
One of the contributing factors identified in the decision to buy the smaller machine was that oversize had been reduced since Lysterfield had started using Maxam’s Rioflex watergel explosive in early 2004.
Oversize had decreased to a level that the newer, more efficient 45 tonne rock breaker could be purchased, within an acceptable risk margin. This margin level included some of the savings to Lysterfield in the purchase price of the smaller efficient machine, as well as the likelihood of maintaining oversize reductions due to blasting in further ongoing operations.
The machine, in fact, has been used since it was purchased to carry out site stripping and other auxiliary work for a significant amount of its operating time. The efficiency of the new machine combined with using Rioflex in the blasting operation has reduced oversize to a level, to allow it to be used for additional duties.
The other bottleneck identified was the effectiveness in blasting on achieving floor levels and oversize generation in production blasts.
When Maxam became responsible for Rock on Ground Services in January 2006, the site focused efforts into these two major problems.
Maxam, who had been supplying Rioflex and explosive accessories before January 2006, now also contributed technical service personnel to design blasts and audit blastholes, as well as operation personnel to load, stem, fire and analyse blast results. Maxam personnel had the task of removing the effects of the bottlenecks in the site process, which were:
1. Non-consistent achievement of design floor levels affecting production by:
? Generating secondary toe blasting
? Oversize generation from irregular toe
? Increasing repair and maintenance of loader and truck equipment as well as tyre wear and damage
? Road maintenance increases due to irregular surfaces with larger material
? Increased time constructing haul roads after the blast
? Decreasing loading times and therefore increased overall cost of the operation
2. Oversize percentage generated from production shots:
? Producing significant material tied up until broken by the rock breaker
? Extra production time required to separate and handle the oversize
? Increased risk to personnel and machinery in handling oversize
These two factors were having significant effects on production effectiveness and efficiencies. It was, therefore, decided to attempt a rethink of the drill and blast process with Maxam when they became involved. The process is best summarised as follows:
1. Understanding what is required of the drill and blast process for the site
2. Ensuring that the drill and blast design is optimised to the required outcome for the site
3. Auditing the drill and blast process to ensure design is implemented in the field
4. Collecting and analysing accurate information on the drill and blast process and subsequent production of the muckpile, to allow changes to be made if required
5. Feedback changes into process
These steps are not new, but it was necessary to go back to basics for a successful outcome.
Maxam and Hanson introduced changes to the blast design, auditing and loading criteria, timing design, shot firing practices and blast outcome analysis to overcome the bottlenecks, while maintaining or enhancing safety standards but minimising risk levels to acceptable standards.
Blast design
Accurate, relevant and well-planned blast designs are the basis of a good, well-
fragmented and diggable rock mass.
The blast design needs to be altered on-site to accommodate the rock mass and the required size of the rock to maximise efficiencies in the production cycle.
It was identified that the oversize was being generated from the cap region as well as from with the blast muckpile due to deviation of drill holes and changes in geology (rock structure) within blast areas.
To accommodate these deviations the previous designs were altered by:
? Reducing diameter of the blastholes from 102mm to 89mm to improve the distribution of Rioflex throughout the rock mass
? Reducing the stemming lengths from 3.5m to 2.8m, to minimise the oversize coming from the top of the blast area (this was possible due to the reduction in blasthole size)
Loading and auditing criteria
Introducing extensive auditing of drilled blastholes for deviation from design has played a key role in the reduction of oversize and blast result.
Re-drilling of blastholes is mandatory if blastholes are not drilled according to the drill plan (given the small percentage of deviation allowed). This has allowed for the loading criteria to be designed so the numbers of inert decks (below minimum burden) and stemming heights have been reduced.
The auditing has allowed not only front row burdens to be designed for minimisation of oversize, but also for control of venting of explosion gasses through the face.
Auditing is also carried out on a random selection of blastholes in the body of the blast, to ensure drilling is to specification.
All blastholes are dipped within a short time before blasting (in addition to after drilling) to ensure that correct depth is maintained (blocked holes, short or over drilling) which has largely led to floor levels being achieved, as well as reduction (near elimination) of toe on excavation floors. This step is simple, but as shown at Lysterfield, this was often difficult to achieve in blast preparation due to the organisation’s previous goal of very large shot tonnages.
Timing design
The timing used at Lysterfield has been modified to accommodate the changed pattern dimensions and blast outcomes required.
Timing designs are currently designed according to the pattern, characteristics of Rioflex explosive and the environmental constraints applicable to the Lysterfield site.
Timing designs are kept as simple as possible, but do change depending on which bench is being blasted, with more conservative designs on the upper, more weathered benches that are more likely to push environmental constraints.
Shot firing practises
Control of blasthole depth and pattern dimensions is mandatory before the blast, normally when the drill rig is still on-site.
Blocked or short blastholes are redrilled to ensure that oversize and design bench levels are not affected.
This does take extra time and expense, but the analysis by Hanson of the overall cost structure downstream has shown that it is a required step.
Loading densities of Rioflex are always controlled by the blasthole depth and the area of the quarry the blasting is to occur. This is especially applicable in the upper benches of the site, due to environmental constraints that apply to Lysterfield by its commitment to reducing its impact on neighbours as much as practicable.
Safety
Safety is not compromised by the increased emphasis on the changed drill and blast process at Lysterfield.
Maxam technical services personnel conduct a risk assessment before the designing of the blast is started. This risk assessment is conducted in conjunction with the quarry manager or the Hanson Lysterfield representative, to ensure that all parties understand and have contributed to the safe execution of the process.
Items such as the blast outcome required, environmental constraints, rock type, access for personnel, trucks and drills, equipment and personnel working in the vicinity of the blast area are all considered.
In addition, the Maxam loading crew conducts a further risk assessment before loading is commenced on the blast. This risk assessment is signed off by the shotfirer prior to starting the loading operations.
Outcomes
The outcomes of the process change at Hanson Lysterfield are evident and sustainable. The bottlenecks in the production side of the operation have been largely removed. The efficiency drive outcomes for achievement of floor levels can be summarised as follows:
? Savings on repair and maintenance of loader and truck
? Road maintenance decrease
? Significant saving time in constructing haul roads after the blast
? The absence of toe led to improving loading times
? Reduction in the overall risk and cost of the operation due to safe, smoother and level floors.
The oversize at Hanson Lysterfield has been reduced to a level that is affecting the production process less. This has occurred since the emphasis on drill and blast process was applied, as well as the introduction of Maxam products to Lysterfield.
Reduction of oversize has led to:
? A reduction of secondary breakage
? Increase of production rates overall due to a better fragmentation sizing and diggability of muckpile. This has led to the increased production consistency from the primary crusher.
? Improved blast designs and their execution in the pit have led to the grading of the muckpile changing, with product now coming from the pit closer to specification.
These positive outcomes have contributed to Hanson Lysterfield’s ability to meet increased market demands. It must also be emphasised that this has come at no increased risk of safety to personnel or equipment.
The commitment to neighbours has also been met, with all blasts monitored for vibration and airblast, and no blast exceeding set limits. Hanson has achieved consistent high production rates through the primary due to muckpile grading and reduction in oversize handling.
Better muckpile grading has allowed them to produce a consistent A-grade crusher run. This has resulted in evening tertiary production being possible, without the need to employ a second shift (partly due to Lysterfield’s plant configuration).
Reduced oversize handling and better floors have reduced risks. The blast designs are analysed for improvements, and are implemented and monitored in consultation with Hanson personnel.
The technical services personnel also work closely with the field delivery teams so that any information is shared for the benefit of improved service and utilisation of explosive products. These on-the-ground services are backed up by safety, training and administrative teams that use Maxam’s U-Safe as their standard.
Mark Morse is quarry manager at Hanson Lysterfield, Paul Klaric, David Fernandez and Shane Slaughter work for Maxam as services technician, blast engineer and technical manager, respectively.