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MWD optimises drill and blast techniques

AVKO Quarry Consulting Group, based in Brisbane, is  a subsidiary of AVKO Mining, which is renowned for  its underground and civil construction work in Western  Australia and more recently on the east coast. The Quarry  Consulting Group was formed in September 2008 and is headed by principal engineer Alan Robertson.

In its first 18 months, the Consulting Group has been involved in several quarrying and civil construction projects, mainly in Queensland, assisting greenfield resource programmes to plan for drilling and blasting, primarily using Measure While Drilling (MWD) techniques. MWD helps to determine accurate rock properties while measuring numerous drilling parameters, including penetration rates, rotation speed, fracture density and torque. The MWD data can then be used to calibrate a drill rig for a specific rock type and can also assist the blast engineers with input into the blast design for achieving ideal fragmentation.

?We do hard rock and sand quarry resource assessments and evaluations all over Queensland for small to medium size quarry operations,? Alan Robertson explained. ?We have done some resource assessment drilling for Holcim, but most of our work is with the smaller players.?
The AVKO Quarry Consulting Group is also involved in regional studies, 3D quarry design and geotech studies of quarries and notably in the work on Brisbane?s Northern Link Tunnel Project which Alan stated has some potentially positive benefits for quarry rehabilitation. ?We are currently involved in the feasibility of the disposal of one million bank cubic metres (BCM) of tunnel spoil from the proposed traffic tunnel in Brisbane into the Mount Coot-tha quarry for future processing or the best part of the fill for the final rehabilitation of the quarry. We are assessing the spoil specifications for this spoil to be placed into the quarry.

?A million BCM is equivalent to about two and a half million tonnes of material. This is actually six times the annual production of a quarry, so we are putting back into the quarry six years? worth of extraction. We have to do that at the same time as the quarry operations are proceeding, so it?s an interesting concept. It is not necessarily the final solution for the spoil – that depends on the tenders for final design and construction.?

MEASURE WHILE DRILLING
In 2009, the AVKO Quarry Consulting Group worked with several Queensland quarries, including the Bungil Quarry, owned by Roma Regional Council, and Boral?s Narangba and Coolum quarry operations in resource assessment and drilling for drill and blast operations. AVKO trialled the MWD approach in these quarries, drawing on Atlas Copco?s ROC Manager software to interpret the MWD data to calculate the relative hardness of the rock and  fracturing parameters and providing Orica Quarry Services with ?full in the hole? geological data for its blast design package.

Alan Robertson explained that MWD measures ?penetration rates, rotation speed, fracture density, torque and other drilling parameters. We calibrate the machine for a particular rock type. When we are doing the resource assessment, we collect the one metre samples of the drill cuttings and have them checked by a geologist. We then refer to three logs – driller?s log, geologist?s  log and MWD log – to calibrate the rig for the site. When we  return to that site we have all the data on-board, based on those parameters, to read any rock type. So, for example, if we are going from a highly weathered granite to a moderately weathered granite to a freshly weathered granite, and then into a dyke, we can actually pick up the changes in rock type. And if there are sediments above the granite, like a sandstone, we could detect that. That is really important to blast design.

?The actual process of using data from drill logs is often ignored by the blast designer,? Alan added. ?The lack of knowledge or wrong interpretation of the rock type and structures is a major issue in the blast design. MWD gives the blast designer the ?full in the hole? geological data and ideally could be downloaded to the blast design package. By having different persons carrying out the data collection activity, such as the hole marking, drilling (drill logs) and bore tracking to measure hole angle and deviation, there is increased room for error in the blast design. MWD allows this to be done by the machine and the driller. By boretracking after each hole is drilled, the driller gets an indication of his drilling accuracy rather than waiting until the hole shot is drilled out.?

Alan Robertson cited some recent work by the Quarry Consulting Group that he felt would have benefited from access to more  accurate data. ?In a recent job, it would have been nice to be able to give the blast designer the whole MWD data in a graphical form that could have made the actual blast work better than what it did. The data may have been able to improve the blast, as we had some oversize at the top of the blast. One of the issues, of course, is if you don?t know the exact rock type you are ?drilling through, once you set your burden and spacing for the blast, the only parameter of change you have is your bulk density or ?explosive weight. A knowledge of the rock conditions by each hole will determine how you distribute the explosives in the hole, whether you air deck, whether you charge and stem and then double time. MWD can help in making those decisions, especially if you have a weathered zone which varies significantly in depth over the shot –  an assumption using an ?average depth? may  result in not enough ?oomph? where the fresher rock is close to the ?surface. With MWD we have a full plot of which rock types are where so that we can change input into the blast designs.?

Alan stated that the upshot of MWD is that, combined with other software such as ROC Manager and Gemcom?s Surpac, it could lead to an optimised drill and blast process. In turn, for the quarry operator, that could mean reduced crushing and screening costs, thanks to accurate drilling (including hole length and orientation) and recorded data on rock types and fractures for input into the quarry design model.

Alan Robertson said that just a $1 increase – or about five cents per tonne ($0.05/t) – in drilling prices toward MWD could result in better fragmentation. ?That could be a significant saving in crushing and screening down the track,? he explained. ?Where crushing and screening costs between $4/t to $6/t in most plants, MWD could provide a ten per cent saving in crushing and screening costs. Rather than spending $1/t to $2/t using rock breakers for breaking oversize or spending more in the size ?reduction process, quarry plants could potentially save $0.60/t  in crushing and screening costs using MWD.?

Alan Robertson said he felt that the larger quarry companies will appreciate the benefits of these savings, rather than ?focusing on the lowest drilling cost. ?That is a big change in focus, it is a whole of quarry approach to fragmentation. What it requires is working together with the various parties such as the modern quarry operator, the blasting contractor and the driller to ensure that the transfer of data is done most efficiently and the on-board computer system on the drill rig allows that to proceed.?

THE ?SILENCED? APPROACH

AVKO utilises a fleet of drill rigs, spearheaded by Atlas Copco?s D9C ROC Silenced Smart Rig. It also uses an Atlas Copco ECM 660 III drill rig and two Sandvik Commando rigs for its work in the quarrying and construction industries. The D9C Silenced Smart Rig had already been employed by AKVO Mining as part of its shaft sinking of the Kangaroo Point Ventilation Shaft on the Clem 7 tunnel project, to be opened in early 2010. Its silenced mast reduces noise by up to 10 dBA compared with conventional drills and its quieter mode enables it to work up to one ?kilometre closer to urban population centres than other unsilenced rigs. In late 2009, AVKO Mining used the silenced D9C to drill a hard ?sandstone cap for the Kennedy Group at its noise sensitive ?operation at Clutha Creek Sands, Mt Tamborine.

The D9C comes equipped with the capacity for MWD and also features a Hole Navigation System (HNS) that enables automated hole drilling after initial set-up. The D9C also has an automatic feed alignment and automatic rod adding system which set the feed to pre-defined angles and drill automatically to a given depth.

The D9C is, according to Alan Robertson, one of only two silenced rigs currently operating on Australia?s east coast and the drill mast and drifter is ?fully encapsulated to reduce noise level from drilling in the ground and also from the rod string?.

Alan stressed that the application of MWD, particularly with the D9C, is still in the trial stage. AVKO?s rig fleet is not GPS-controlled and will not have that capacity until mid-2010. Alan predicted that once the GPS facility is installed, the driller should be able to ?track the holes while drilling – he can get out of the cabin and bore track the previous hole and that data gets downloaded straight into the on-board computer. We will be able to load that data as we go, it won?t require someone to come back and bore track. Also there is less chance of getting information mismatched by bore tracking the wrong hole?.

Alan said that MWD has been very successful in Scandinavia, ?where there are 40 or 50 of these GPS controlled rigs operating. There are simple savings like not, for example, having to mark out the shot. You basically bring the rig over the hole location if you want to drill and just move the feed beam until the co-ordinates and  mast orientation match those for the hole design and off you go. With automatic drilling, the hole is already set and it is in automatic so you have already pre-programmed your hole information and the rig stops automatically and then pulls the rods?.

AVKO has also been liaising with Atlas Copco about adapting the D9C Smart Rig for more depth capacity for resource drilling, as it will drill to 28 metres on the carousel before a manual rod change is required (some rigs can potentially drill to up to 32 metres – the equivalent of just over two benches of 15 metres length each, plus an additional two metres). Alan explains that ideally, a conventional exploration reverse circulation (RC) or in the hole hammer (IHH) drill rig is more suitable for exploration drilling for greater than 30 metres, but stated that a major advantage of the D9C for MWD was that it was more cost-effective and manoeuvrable than a regular RC rig ?where the rates per metre are higher. Ideally, it is a matter of maximising our capacity of automated drilling depth?.

SCOPE FOR FUTURE ANALYSIS
While it does not have MWD data from Scandinavia to refer to as a benchmark, the AVKO Quarry Consulting Group supported a research project by Rubik Ghosh, a University of Queensland  undergraduate, in 2009 to analyse MWD exploration data and the potential impact of MWD systems as a cost saving component on the quarry drill and blast optimisation process. The study concluded that MWD data analysis could be used as an aid to the driller?s and geologist?s logs for correlation (when identifying a change of hardness in the rock) and that incorporating MWD and bore tracking into current drill and blast practices would lead to fewer steps in the quarry to processing cycle. The study proposed further research avenues, including the development of a MWD interface link between available software, implementation of topographical surveying in current practices, optimum stemming material determination, fragmentation monitoring studies and blast design modification studies.

Nevertheless, despite being in a formative stage, Alan Robertson said that other drill and blast suppliers have expressed their  interest in MWD. He also predicted that the Australian quarry industry would embrace MWD within two years.

?Drill and blast in Australia is all about what it costs, not  necessarily that the lowest cost gives the best result,? he said.  ?You can?t use the lowest cost to get the best results and you can?t get the best results if you don?t have some engineering inputs. Boosting up the powder factor does not necessarily give you the best result. I know that some companies agree that MWD fits in with their quality management systems. We see the advantage of this system in the longer term, but I think it has still to be proven to be robust in Australian conditions.?

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