The planned underground expansions to existing mines; as well as major new underground operations being looked at means that achieving faster and more efficient development underground is as much at the fore as it has ever been. Taking Codelco El Teniente’s New Mine Level (NML) as just one example – between 2011 and 2017, the project will build 98,450 m of horizontal tunnels and 3,454 m of vertical development in the form of ventilation shafts and transfer shafts. Not only that, but access to the NML will be through two parallel tunnels, one entry and exit tunnel for employee buses, and the other for the ore conveyor belt, service track and alternative emergency route – these will be excavated using TBMs. Vinci Group announced the winning of this contract in September 2011 and has already begun the first excavation.
The contract is split 60:40 between Vinci Construction Grands Projets and Vinci subsidiary Soletanche Bachy and is valued at $400 million. There will be two interconnected tunnels, each 9 km long and 9 m high with an average sectional area of 65 m2. There are also two intermediate access tunnels each 6km long. The ground at the tunnel’s level includes strong volcanic deposits, metamorphic structures and some weak rock in fault zones. Experience with the Rio Blanco TBM water supply drive in the 1990s showed the volcanic rock to be of good quality but the presence of minerals that swelled in the presence of water caused subsequent spalling problems.
Initially two Robodrill drilling jumbos are being employed in drill-and-blast excavation in the hard, but this is due to rise to a total of twelve excavation rigs and at least one Montabert 108 dedicated rock bolting rig. Half of the drill-and-blast rigs on order are computerised Robofore three-boom units, and the others are manually operated Pantofore twin-boomers with an HL150 basket boom. The Robodrills, made near Lyon in France, feature Montabert HC 110 HF (high-frequency) hydraulic drills capable of 3.5-3.8 m/min drilling speeds on the three-boom rigs and HC 108 drills on the twin-boom rigs. Robodrill’s supply contract includes a full maintenance and support package.
The overall planning and design for development of the new level has been carried out by Hatch, supported by Mott MacDonald. Vinci is carrying out detailed design in the design-build contract. The project work is scheduled to take 40 months.
The NML project adds 2.02 billion t of reserves, with a 0.86% copper grade and an average 0.022% molybdenum grade, equivalent to more than 17 Mt of fine copper over a period of 50 years of operations, starting at the end of 2017. It will maintain the existing capacity at El Teniente of 137,000 t/d, equivalent to 430,000 t/y of fine copper. It also leaves open the option, until 2020, to start the work required to produce 180,000 t/d.
Chuquicamata underground mine is another crucial strategic project for Codelco. Under the existing open pit the amount estimated is 1.7 billion t of copper ore reserves (0.7% grade) and molybdenum (502 ppm), representing more than 60% of what has been mined during the last 90 years. The project involves ore extraction by macro blocks and block caving, in an underground mine that consists of four production levels; a main access tunnel (7.5 km); five clean air injection ramps, and two airextraction shafts, in addition to other work. Furthermore, the expected throughput rate is 140,000 t/d, which would mean production of 340,000 t/y of fine copper and more than 18,000 t/y of fine molybdenum.
A third Codelco project is the expansion of Andina, known as the Andina Phase II. Sinclair Knight Merz (SKM) was recently awarded the basic engineering contract for the tunnels, primary crushing plant and materials handling for the project. SKM’s involvement in NML was an important factor in the award as SKM has been delivering prefeasibility and feasibility studies for that project since 2006. SKM’s South American Manager, Mining, Claudio Lesch, comments: “In the competitive bidding process, we faced other Tier 1 engineering and project delivery companies, however, our experiences and the lessons learned on the work we have undertaken so far on the New Mine Level at El Teniente, along with our capabilities and experience in underground mining projects, and our use of the SmartPlant 3D platform, were crucial in the decision by Codelco to award us the work at Andina.”
SKM, together with JRI, has now completed the detailed engineering works of the $300 million project which consists of enlarging the mining and smelting capacity of Andina from 32,000 to 65,000 t/d. The enlargement includes a new underground primary crushing plant; underground crushed ore transportation system; underground silo for stockpiling crushed ore; as well as an underground SAG mill, pebble crushing plant and collective Flotation Plant.
New block cave projects such as Resolution Copper in Arizona and the Oyu Tolgoi copper-gold project in Mongolia will also require construction of significant underground infrastructure prior to ore production. As outlined in some detail in previous issues of IM, Rio Tinto Technology & Innovation has a long running development programme to improve significantly both the safety and speed of constructing underground infrastructure such as shafts and tunnels. This work also involves Canada’s Centre for Underground Mine Construction (CEMI) as a centre for excellence in the areas of deep mine geomechanics, risk mitigation and underground construction. Rio Tinto and CEMI are conducting research into mechanised excavation that consists of both a shaft boring system (SBS) from Herrenknecht and tunnel boring systems (TBS) from Aker Wirth and Atlas Copco. However, related matters such as rock mass strength at depth and pillar design will also be included in the research program. CEMI states: “An integral component in ensuring consistent advance rates is the geotechnical parameters that play a key role in ensuring successful application of these step-function technologies. CEMI’s expertise and R&D track record in this field will play a critical role in supporting this ambitious program. The initial focus of the Centre is to support the field trial of the first of two new tunnel boring systems at Northparkes, Australia.” The challenges to be overcome by the Centre include the need to develop innovative ground support systems that can be installed in parallel with rock excavation, ensuring sufficient stand up time and the proper management of strainburst potential, and identifying the means to improve construction logistics.
The field trials on the first TBS projects began earlier this year and the second TBS trial is anticipated to begin in late 2012, with the SBS trial planned to commence in 2013. All three new concepts are a result of civil tunnelling industry technologies combined with input from Rio Tinto mining experts and contractor partners Redpath and Cementation.
More vertical developments
As stated, vertical excavation is key to the rapid development of underground mine workings. The latest generation of Atlas Copco Robbins raiseborer is being used by Italian specialist contractor Edilmac to tackle demanding raise, pass and shaft tasks. Atlas Copco and Edilmac technical staff worked together with component suppliers to create an upgrade package for the company’s existing 73R raiseborer to give it more control, more power and more torque to tackle tough conditions previously only possible with larger machines. The upgrade involved close cooperation with the manufacturer of the new compact, water-cooled, electric motor manufacturer in Austria. Johnny Lyly, Atlas Copco Product Manager for raiseborers, commented: “We carried out tests with the powerpack and motor over two days including stalling, backspin and fluctuating load to simulate all the conditions that might occur with a raiseborer. The results were very good, meaning we could go ahead with the retrofit work.” Meanwhile, Edilmac was fitting a new gearbox, supplied by Atlas Copco, to suit the new variable frequency electric motor drive. One result of this work was a big increase in torque to 250 kNm. The rig could then be designated as an Atlas Copco Robbins 73RVF C. The new 73RVF C raisebore package also includes a new hydraulic powerpack, electrical transformer and switchgear unit, a special cooling unit that caters for all requirements and a compact operator control panel. After the first raise reaming task carried out with the equipment – a ventilation shaft, Adriano Facchinetti, Edilmac’s Technical Manager, commented: “With the high power of 450 kVA instead of 350 kVA we are very happy with the new rig. The new 280 kW VF motor gives a maximum torque of 250 kNm instead of the previous 180 kNM and the new console is a big improvement too. The operators like it a lot.”
Mining contractor and engineering group Redpath has just announced the latest addition to its Redbore family of raise drills – the Redbore 90. Redpath’s latest raisedrill was manufactured to address the growing demand for 4.5 m to 5.5 m diameter raises up to and in excess of 600 m in length. The company states: “Our clients quickly recognised the benefits of a new drill which utilizes the latest in modern proven technology to deliver more cost effective raise development. The Redbore 90 provides coverage in capacity between Redpath’s Redbore 70 and a Redbore 100.”
The considerably lower profile drill provides a cost effective method to bore large diameter raises underground while minimising the expensive underground excavations required by older model raisedrills. The Redbore 90 is easily dismantled and provides quicker, more efficient, equipment mobilisation whether on surface or underground; resulting in savings of time and money to ensure the capabilities of the drill are utilised sooner. Built in North Bay, Canada, the Redbore 90 offers the services of yet another large capacity conventional raisedrill, to Redpath’s extensive line of raisedrills including the Redbore 40, Redbore 50, Redbore 50MDUR, Redbore 70 and the largest capacity raisedrill package in the world – the Redbore 100.
Contractors like Redpath, Murray & Roberts Cementation, Dumas Contracting and others are at the forefront of vertical raising and shaft sinking. And improvements to mine development technology is just as important for coal operations as it is for metallic mines. Murray & Roberts Cementation has begun work on a contract awarded by Sasol Mining to provide a men-and-material shaft and a ventilation shaft as well as a decline and coal seam development on the No 2 and No 4 seams at Sasol Mining’s greenfields Impumelelo Mine Project. The mine, located about 50 km from Secunda and 22 km from Greylingstad in Mpumalanga, is one of the biggest coal projects that Murray & Robert Cementation has been involved with to date.
The shaft complex has been designed to operate for a minimum period of 35 years. Project duration is estimated at about 43 months, from May 2011 to Nov 2014, including site establishment and site de establishment. Excavation on the men-and-material shaft, the ventilation shaft and the decline began in July 2011 and is well within the programme schedule.
RSV Enco-Goba Coal JV, comprising RSV Enco Consulting and Goba, is also project managing Sasol’s other greenfields mine complex projects, the nearby Thubelisha coal mine, which is being developed by Grinaker-LTA.
Johann Prinsloo, senior project manager at Murray & Roberts Cementation, says that owing to the complexity of the project and in order to deliver a professional product, it was decided that Concor Civils, a Murray & Roberts Construction company, will undertake the civil construction of both shafts collars and the decline box cut, as well as portal construction with the closure of the box cut. Concor Civils will also carry out all other civil works for the site establishment.
The 11.7 m diameter men-and-material shaft will be 240 metres deep, with a four sided station on No 4 seam and a three sided station on No 2 seam being developed for access to the coal production sections that will be mined by Sasol using mechanised mining methods. The shaft will be fully lined and equipped as a service shaft with buntons and guides. Murray & Robert Cementation will also erect the permanent steel structure headgear frame, conducting the installation in two phases. Headgear structure erected during the first phase will be used for the sinking operation and the permanent arrangement will be erected during the second phase. Lifting of pre erected headgear sections will be carried out by a 750 t crawler crane. The shaft will be serviced by a 65 t payload cage and counterweight by means of a Koepe winder, which will allow Sasol Mining to lower its continuous mining equipment into the underground workings.
During the sinking process a single drum 12 t kibble winder will be used for lowering and hoisting personnel and material up and down the shaft, while a stage winder will be used to lower and raise the four-deck working stage. A five-boom drill jumbo will drill the shaft and shaft cleaning will be carried out by means of an excavator into the kibble.
The 6.7 m diameter ventilation shaft will also be sunk to 240 m, with access through the four sided station on No 4 seam and the three sided station on No 2 seam to the coal production sections. During the sinking process, a double drum 8 t kibble winder will be used for moving personnel and material up and down the shaft and a stage winder will be used for lowering and raising the five-deck working stage. A temporary steel structure headgear frame will be erected for the sinking phase of this shaft.
During pre-sinking of the ventilation shaft, a Scott derrick will be used to hoist material. Shaft drilling will be carried out using a fourboom drill jumbo and shaft cleaning will be undertaken with a cactus grab unit into the kibble. After sinking is completed, a permanent ventilation fan will be installed to service the mine.
A box cut for the 17° decline will be excavated for the construction of the portal. Once the portal is complete, the box cut will be covered with a Supercore structure and then backfilled to leave only the entrance of the decline on surface. A workshop structure will be constructed over this entrance that will be used when conveyor belting in the decline is changed out. The decline is being sunk to dimensions of 6.5 m wide and 3.3 m high. Breakaways on the No 2 seam and the No 4 seam will be carried out with a coal loading gallery and surge bins at the end of the decline. Once the holing on the No 4 seam is complete, continuous mining equipment will be lowered down the decline to the seam to begin work.
A temporary conveyor system will be installed during the sinking phase, until the continuous mining equipment has been lowered. Thereafter, a permanent conveyor belt will be installed to service this equipment during its cutting operations. Mechanised mining equipment will be harnessed to sink the decline, in order to keep the number of people at the working face to a minimum. An LHD will clean the working face and dump material onto the temporary sinking conveyor belt while a drill rig will drill the working face and the roof bolt holes.
A 1,500 t circular surge bunker will be constructed by means of a raisebore hole that will be pilot drilled from surface to the coal loading gallery in the decline. The hole will be reamed to 7.1 m from the coal loading gallery through the No 2 seam to the No 4 seam. The surge bunker between the coal loading gallery and No 2 seam will be enlarged to 10 m using conventional drill and blasting methods, while the bunker between No 2 and No 4 seams will remain at 7.1 m. The total length of the surge bunker will be supported and lined to last the lifetime of the mine.
An access adit between the coal loading gallery and No 2 seam will be developed at 9° degrees from the No 2 seam elevation. On completion of the surge bunker, the coal loading gallery will be equipped with a steel construction tipping arrangement onto the permanent conveyor belt.
A total of 550 m conventional drill and blast development on No 2 seam will open up the mining area and connect the shafts with each other, with 4,660 m of coal cutting on No 4 seam being undertaken to open up the area for establishing continuous mining sections.
Horizontal development
Record development speeds are also being achieved in horizontal development. The Barminco-Ausdrill JV, African Underground Mining Services (AUMS), recently announced that it has broken the world mining advance record. At the Randgold Resources Gara project based at the Loulo mine in Mali, West Africa, AUMS has achieved over 5 km of development in a single jumbo operation since commencement of works in April 2010. In July 2011, three crews operating a Sandvik jumbo, fully bolted and meshed as per Australian standards in 5 m by 5 m headings achieved 603.1 m of advance in a single month. In doing so, AUMS believes it has achieved a world record result for development mining in this application. Barminco Business Development and Commercial Manager David Noort said in his 25 years of experience in international mining operations he has yet to see a result come close to this achievement. “One jumbo installing its own rockbolts and full mesh to achieve this advance within one month is singularly one of the most spectacular feats of development mining performance I have come across. The fact the team did it in Mali, in one of the poorest and most remote countries in the world and despite considerable cultural and language barriers, demonstrates exceptional capability and leadership by AUMS and their crews”. AUMS commenced operations in Ghana in 2008, bringing much needed underground mining expertise into an area largely dominated by open pit mining. Today AUMS boasts five major mining contracts and a workforce of 700 comprising 80% local workers, many of whom joined the team as unskilled labour and have undergone an intensive training program. The team responsible for delivering the record at Loulo was comprised of 15 expatriate AUMS operators and 30 local operators.
According to AUMS Operations Manager Kevin Flynn the result was made possible through a combination of operator expertise, quality machinery and a mutual respect between all crew members to get the job done. “Our teams in Mali contain some of the best class jumbo operators in the world, some are 20 or 30 year veterans in their field,” he said. On the back of the success at Gara, AUMS has been awarded a further development mining contract at Randgold’s Yalea project, also at Loulo. The Yalea project will see AUMS construct a portal and decline designed to access the orebody below the company’s existing mining operations, in what will be a new and improved approach to underground mining for this orebody.
In soft rock mining, Sandvik Borer Miner range is the machine of choice for many of the world’s major potash operations and work on new technology on the Borer Miner designs is ongoing. The company this year entered into an agreement with BHP Billiton for the conceptual design of a new mechanical cutting system for use at BHP Billiton’s Jansen potash project. The project, located near Saskatoon, Saskatchewan in Canada will employ Sandvik Borer Miners designed and developed under the agreement. The Sandvik Borer Miners will incorporate the latest technology available for enhancement of automation, production, life cycle costs and safety. Sandvik Borer Miners (including the former Marietta Borer) are used around the world for mining potash and trona and are well known for their high production rates and low life cycle costs.
In June this year, BHPB announced an additional approval for $488 million of further investment to support development of the Jansen project. This additional pre-commitment capital is funding site preparation and the procurement of long lead time items during the project’s feasibility study. The funding is enabling BHP Billiton to develop the first 350 m of the production and service shafts following conformation of governmental approval for the project. This announcement took BHP Billiton’s investment in Jansen to $1.2 billion. In February 2011, BHP Billiton had announced progression of Jansen into the feasibility study phase. On site, the company had already constructed the refrigeration centre and drilled more than 55,000 m of wells to complete the 89 freeze holes and monitoring wells required for the production and service shafts. Based on the current schedule, Jansen is expected to start producing saleable potash from its 3,370 Mt insitu Mineral Resource in 2015. The project is designed to ultimately produce approximately 8 Mt/y of agricultural grade potash with an estimated 70 year mine life.
Safer development and monitoring
Speeding up underground development also means improvements are required in the areas of ground support, especially as many of the planned underground mines and expansions are at greater depths. ROCK Australia has successfully developed the ROCK MESHATM (mechanised mesh handler) for the application of Tecco and Deltax roll mesh products. MESHATM has been successfully tested in Australia and is available for use in underground mining ground support applications. The system requires minimum manual handling for installation of mesh to underground backs and walls. There is no requirement for the operator to be out in unsupported ground. The product is delivered in cassettes, which are mechanically handled into position for installation. Mesh can be installed up to 30% faster than the standard practice of sheet meshing in the underground environment. Lower development costs will be achieved due to the faster installation cycle times. Correspondingly, material savings are gained due to less overlaps, plus a reduced overlap requirement as a result of the mesh dimensions and characteristics. In turn, this also has the potential for bolt spacings to be optimised, resulting in further savings in reduced bolt quantities.
Canada’s Dux Machinery has launched a new shotcreting platform for underground mines. Measuring only 1.83 m wide, the S1-Remix Truck forms part of Dux line of S1-Series utility trucks equipped with 148 HP Cummins 4.5 l engine and heavy-duty DANA SOH powertrain. The S1-Remix drum has a 4.5 m3 shotcrete/concrete volume capacity and come with optional tilt cylinders for positioning the drum when loading. The article on German mining technology in this issue has details of Putzmeister`s most advanced model to date for shotcrete spraying in lower mine sections – the Sika-PM 4210, a further development of the well-known Sika-PM 4207. The series includes a version which allows dual operation, both diesel and electric, to facilitate its use in any work environment independently of a power source.
Normet introduced its new Alpha series concrete sprayer, the Semmco Alpha 30, at the recent XXIX Mining Convention in Acapulco, Mexico. The Semmco Alpha 30 is a dieselhydraulic mobile concrete sprayer designed for tunnel profiles up to 7 m in height and 9 m in width. The new NSP 30 concrete pump has a maximum pumping capacity of 30 m3/h. The accelerator dosing system with a total 550 liter accelerator volume is designed for a variety of modern accelerators. The spraying operation is controlled with a radio or wired remote control.
Marcelo Anabalon, COO of Normet Chile comments: “The new Semmco Alpha 30 is designed to meet the latest market and customer needs with more emphasis on enviromental and safety issues. Therefore it has a Tier III diesel engine and a FOPS and ROPS canopy. Its four wheel drive and four wheel steering makes for easier manoeuvering in narrow tunnels”. The Alpha 30 is now available for customer orders with earliest deliveries available in January 2012.
Mining groups also want to better understand the dynamic ore and rock movement processes in their underground operations. Lundin Mining’s Neves Corvo, also discussed in this month’s Great Mines piece, has recently installed the first Metso SmartTag system in Europe. The SmartTag system was developed by Metso Process Technology and Innovation (PTI) to track ore and/or waste from mines to the plant using Radio Frequency Identification (RFID) technology. The RFID tags have been designed to withstand blasting, handling by mining equipment, and passing through primary and sometimes secondary crushers. Neves Corvo is using the SmartTag system to track ore and waste from post-blast muck piles through underground loading, hauling, ore passes, crushing, storage, and finally hoisting and conveying to surface stockpiles. The information will be used to better understand and improve ore and waste handling logistics. Elsewhere, Boliden-owned Tara Mines in Ireland has also placed an order for the SmartTag system. Tara processes around 2.6 Mt/y of ore using Metso equipment, such as a C200 jaw crusher, and VPA filters and pumps. The main objective of the SmartTag system at this site will be to track ore being mined from diff erent stopes and headings as part of their reconciliation process. Waste in ore streams can increase transport and processing costs, reduce the head grade, and produce additional waste tailings. IM
