The Importance of Research on Alternative and Hybrid Rock Extraction Methods
- 1.1k Downloads
Current methods of mechanical excavation of rock are limited in regard to the material which can be extracted economically. The use of roadheaders with pick tools has the advantage of high flexibility in form of turn off radii down to 1 m but is limited by rock strength to figures below 150 MPa UCS.
While mechanical rock excavation machines with disc cutters can handle rock strengths above 150 MPa, they are limited to turn off radii >12 m. This issue is discussed in detail and shown in this paper.
Therefore there is presently a significant “Gap” for a method (other than drill & blast) of rock extraction for turn off radii below 12 m and rock strengths above 150 MPa UCS.
This gives the motivation of R&D into alternative extraction methods which could lead to new combined methods covering this “Gap”.
KeywordsMechanical rock extraction Continuous mining Hard rock Alternative extraction methods Roadheader
Die Notwendigkeit, auch im Bereich der alternativen und hybriden Gesteinslöseverfahren zu forschen
Für die derzeit verfügbaren Methoden des mechanischen Lösens von Gestein gibt es in Bezug auf den ökonomischen Einsatz erhebliche Einschränkungen. Teilschnittmaschinen mit einem Schneidkopf mit Meißelbestückung sind sehr flexibel in Bezug auf den Abzweigradius, allerdings ist nach derzeitiger Entwicklung bei einer Gesteinsfestigkeit von rund 150 MPa UCS die Grenze des wirtschaftlich sinnvollen Einsatzes erreicht.
Maschinen mit Schneiddisken können zwar viel höhere Gesteinsfestigkeiten lösen, die Flexibilität in Bezug auf den Abzweigradius ist jedoch auch bei den neuesten Entwicklungen auf >12 m beschränkt. Der Stand der Technik wird ausführlich dargestellt und diskutiert.
Daher besteht derzeit eine „Lücke“ für eine Methode des kontinuierlichen Gesteinslösens (zusätzlich zum Sprengbetrieb) für Abzweigradien kleiner 12 m und in Gesteinsfestigkeiten über 150 MPa UCS.
SchlüsselwörterMechanisches Gesteinslösen Kontinuierlicher Vortrieb Hartgestein Alternative Lösemethoden Teilschnittmaschine
1 Introduction/Problem Statement
Current methods of mechanical excavation are limited by the rock strength and abrasivity on the one hand and by the machine size and capability of the tools on the other side.
Although blasting operation is the most economic for mass mining in the cyclic entry development in increasing depths in underground mines, it has severe disadvantages. Some of these are safety during blasting, need for time to ventilate the blast fumes, safety of storage, transport and handling of explosives, possible damage to entry profile; over-break and profile.
Beside research into improved drill & blast equipment and operation (e.g. mechanization and automation of the process ) there is a trend to search for continuous rock extraction methods like mechanical cutting.
Fast excavation of hard rock (UCS range from 150 to 300 MPa)
Low energy consumption
Little environmental impact
Economic rock extraction.
When it comes to flexible advance also regarding the radius of the entry development for mechanical cutting, only the roadheader concept is flexible enough to cut turnoffs etc.
But the cutting tools of the roadheader have their limits concerning rock strength and abrasivity.
Despite in-depth research by several companies, like Element 6, Kennametal or Sandvik, in the last two decades the limit of usage has only been shifted higher very slightly. Presently it cannot be predicted if and when new materials like diamond composites will lead to a break-through with this type of tools.
As there is a significant “Gap” for rock extraction in rock strength UCS higher than 150 MPa and flexibility in turn off radius <12 m, this is an important area for R&D at Montanuniversitaet Leoben and its partners.
The various existing methods shown in Fig. 1 are discussed in the following parts.
It is also essential to know that the cutting performance in m³/h is sinking with increasing UCS and abrasivity.
A roadheader can cut a 90° turnoff in entry development as long as the entry width is broad enough to allow the roadheader to manoeuvre (typically 6 to 8 m). For this reason the roadheader can swivel its cutter boom and rear conveyor in order to get around the corner.
3 Tool Development for Roadheaders
Cemented tungsten carbide pick tools have reached a certain limit regarding the rock properties they can cut economically as shown in Fig. 2. In the last 15 years R&D in this type of tools has only yielded improvements in the range of a few percents.
During cutting tests PCD tools have performed well under stable cutting conditions for UCS up to 220 MPa, but as soon as there occurred irregularities in the guidance of the PCD tool they tended to disintegrate abruptly. It seems that they are not stable against pull or impact forces.
As on the other side PCD tools produce less dust and do not generate sparks in the UCS range <120 MPa, they fit perfectly for coal mining with touching the side stones sometimes for short periods.
But for hard rock with UCS >160 MPa the PCD pick tools need more R&D and it cannot be predicted if a breakthrough can be achieved in the near future.
Consequently, the performance of roadheaders in hard rock is limited by the available tools.
4 Tunnel Boring Machines (TBM)
Tunnel boring machines with a circular full-cut cutter head equipped with disc cutters can cut rock up to 300 MPa .
5 New Types of Hardrock Mining Machines
5.1 Aker Wirth
The Mobile Tunnel Miner is designed for rock UCS from 50 to 260 MPa and the MTM 4 model has a 12 m turning radius. The planned advance rate in development is up to 12 m per day.
In February 2013 it was announced that a Mobile Tunnel Miner was intended for a test operation in 2014 at Chuquicamata mine in Chile . This test operation was never accomplished due to the changes at Aker Wirth.
5.2 Atlas Copco
So the Atlas Copco Mobile Miner as built today has a turning radius of 65 m, and practical operation will show the upper economical limit in regard to cuttable rock strength. A big advantage is that the results of the Robins Mobile Miner operation in Broken Hill in the 1990s were taken into consideration.
The Rock Straight System is designed for reef mining in abrasive material and is therefore not suitable for the development of roadways. From the cutter head design it will be interesting to see the size of the cut material and the tear and wear for rock with UCS >150 MPa.
5.4 Joy Mining
The roadheader concept gives this system a high flexibility. But the application of a single oscillating cutting disc raises questions regarding the amount of extracted material per hour. In road development the question how to achieve the undercut free space to start is not solved. It will be interesting to see the results of the planned tests in this regard.
Around 2004, Sandvik Mining and Construction developed the Reef Miner ARM 1100, which was operationally tested in the abrasive platinum reef in South Africa and in copper mining in Poland. In the beginning, the lifetime of the cutter discs was a limiting factor. ARM1100 is designed for following the reef, so the flexibility is low and the cutting discs are built to withstand a high abrasivity and rock strength >200 MPa.
6 Alternative Methods of Rock Extraction
So closing this present “Gap” above 150 MPa rock strength and entry development radii <12 m is not possible with a “simple” improvement of the tools in operation.
Beside R&D aiming at “mechanizing and automation” of drill&blast to make it more flexible and “micro blasting” methods using LOX (liquid oxygen), new combined methods as listed in Fig. 16 are under development.
The goal of alternative and hybrid combinations of alternative and classical rock extraction methods is therefore to artificially alter the RMR in a favourable way. This can be done by introducing artificial crack networks, generating slots/free surfaces or applying additional stresses on the rock surface by means of microwave irradiation, microblasting with LOX, activated cutting tools, high pressure water jets or Lasers.
Open access funding provided by Montanuniversität Leoben.
- 1.Nordic Rock Tech Centre Project: Safer Charging of Bulk Explosives in Entry development, 2015, http://www.rocktechcentre.se/core-business/projects/ (3.9.2016)Google Scholar
- 2.Restner, U.; Plinninger, R. J.: Rock Mechanical Aspects of Roadheader Excavation, EUROCK 15, 64th Geomechanical Colloquium, Salzburg 2015Google Scholar
- 3.Girmscheid, G.: Baubetrieb und Bauverfahren im Tunnelbau, Table 7.9-1, Klassifizierung der TSM, 3. Auflage, Ernst & Sohn, 2013Google Scholar
- 4.Sandvik –MGT Product Catalogue http://mining.sandvik.com/SiteCollectionDocuments/products/tools/Sandvik-MGT-catalouge.pdf (3.9.2016)
- 7.Bilgin, N.; Copur, H.; Balci, C.: Mechanical Excavation in Mining and Civil Industries, Boca Raton, Florida: Taylor&Francis, 2014Google Scholar
- 8.Herrenknecht Gripper-TBM Catalogue, https://www.herrenknecht.com/de/produkte/kernprodukte/tunnelling/gripper-tbm.html (2. 9. 2016)
- 9.Cigla, M.; Yagiz, S.; Ozdemir L.: Application of Tunnel Boring Machines in Underground Mine Development, http://inside.mines.edu/UserFiles/File/earthMechanics/tbm/tbm3.pdf (25.12.2016)Google Scholar
- 11.Aker Wirth Designing Mobile Tunnel Miner for Chilean Copper Mine, http://www.oemoffhighway.com/press_release/10874235/aker-wirth-designing-mobile-tunnel-miner-for-chilean-copper- mine (2.9.2016)
- 12.Ramström, M.: A Mining industry game changer, Atlas Copco News, 25 May 2016, http://www.atlascopco.com.au/auus/news/companynews/a-mining-industry-game-change.aspx. (25.12.2016)Google Scholar
- 13.Caterpillar, Rock Straight System, http://www.cat.com/en_ZA/campaigns/awareness/rock-straight-system.html (3.9.2016)
- 14.CDC Technology, https://www.australianmining.com.au/features/dynacut-oscillating-disc-cutter-technology-achieving-breakthroughs/. (16.01.2017)
- 15.Leonida, C.: Making hard-rock history, Mining Magazine July/August 2016, p. 52-61Google Scholar
- 16.Wohlmeyer, J.: Machine for Boring Galleries, Tunnels, Channels and the Like by Cutting Action, US Patent US 2,758,825, Aug.14, 1956Google Scholar
Open Access This article is distributed under the terms of the Creative Commons Attribution 4.0 International License (http://creativecommons.org/licenses/by/4.0/), which permits unrestricted use, distribution, and reproduction in any medium, provided you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons license, and indicate if changes were made.