CONTINUOUS CUTTING
The aim is to boost single face advance by at least 50 % compared with traditional drill and blast applications , according to Jordaan .
One specific adaptation to the MTB at Mogalakwena is a change to broader , smooth conveyor belts with primary and secondary scrapers and hot splicing to alleviate the problems previously experienced operating on steep angles where wet material and belt scrapers with excessive spillage hindered operation .
“ Many technical improvements , such as this example , were done from technical and operational data recorded during the previous project and addressed through a root cause analysis process ,” Jordaan said .
And , while one MTB may be the order of the day at Mogalakwena , Jordaan and Master Drilling are looking at second-generation MTB developments that could see two units being used in tandem for twin-decline access .
“ Many mines going underground require tunnel access ,” Jordaan explained . “ Twin access supports flexibility in the ventilation and tunnelling design and provides a means of second egress . Master Drilling sees this as a significant market within the mining industry .”
With a new contract in the bag and interest on the up , Jordaan has high hopes for the company ’ s MTB and tunnelling strategy .
“ At Master Drilling , we are confident that the MTB concept machine and service will provide quick , safe and high-quality excavation access from point A to B ,” he said . “ Considering industry developments in the rock-cutting field as well as a proven track record from a well matured drill and blast excavation business , we consider the MTB ’ s characteristics to be very relevant and with the potential to prove very competitive .”
The company is in the process of addressing some of the drawbacks that have , traditionally , come with the use of TBMs in mining projects . This is on top of the ability for the MTB to tunnel with tighter turning radiuses .
“ Historically , with TBMs ( which part of the
MTB concept is based on …), round profile tunnels were seen as a challenging geometrical profile to accommodate a traditional mine layout configuration with a flat roof and floor to cater for vehicles and roof-mounted services ,” Jordaan said . “ Master Drilling is developing a solution to provide a flat floor for logistical purposes and a curved roof for structural integrity to be integrated with the MTB application in the future .
“ This will provide a more optimised excavation in terms of size , cost , energy and quality for certain applications .”
Progressive excavation
One company to have already solved the flat floor problem typically associated with the application of traditional TBM technology in mining is Robbins .
The US-based company has come up with a novel TBM that uses disc cutter technology proven on traditional , circular machines to excavate rock with a reciprocating cutterhead and swinging cutterhead motion to create a rectangular cross section tunnel .
The MDM5000 ( standing for Mine Development Machine ) has been designed for use in underground mining in rock up to 200 MPa UCS , making it particularly useful for long access tunnels and development drifts . It has dimensions of 5 m x 4.5 m and is capable of excavating a flat tunnel invert for immediate use by rubber-tyred vehicles , according to the company .
Robbins has gone further than most in the continuous cutting game to prove the MDM5000 ’ s application in mining , having , by September , clocked up more than 1,700 m of advance at rates up to 52 m in one week and 191 m in one month at the Fresnillo silver mine in
The Robbins MDM5000 uses disc cutter technology proven on traditional , circular machines to excavate rock with a reciprocating cutterhead and swinging cutterhead motion to create a rectangular cross section tunnel , as pictured at the Fresnillo mine here ( left )
Mexico . Such numbers make it significantly faster than the equivalent drill and blast excavation method , which is all the more impressive considering it has been excavating in andesites and shales with quartz intrusions that , according to the company , have defeated earlier attempts to excavate these tunnels with heavy roadheaders .
Fidel Morin , Projects Superintendent for Fresnillo Mine , said the company chose to work with Robbins for its experience applying TBMs in mining applications .
This experience includes the application of a TBM in a decline project at Anglo American ’ s Grosvenor coal mine in Australia , which involved an 8 m diameter Robbins Dual Mode ‘ Crossover ’ TBM and continuous conveyor system . The Robbins TBM at Grosvenor bored two decline access tunnels at grades of 1:6 and 1:8 , one for conveyors and another for personnel and equipment .
Robbins has also used variations of traditional TBM technology in extensive work over the years at the Stillwater platinum and palladium mine in the US and excavating dewatering tunnels at the Ok Tedi copper-gold mine in Papua New Guinea .
Robbins Owner and CEO , Lok Home , said the company ’ s legacy in mining is vast .
“ Even in the 1980s at Robbins we were trialling a Mobile Miner with Mount Isa ,” he told IM at the recent MINExpo event in Las Vegas . “ We also had shaft boring machines and the main achievement was introducing raiseboring to mines . The raiseboring business was later sold to Epiroc .
“ As a result of this historic business , we are very mine-savvy , I would say , as a company . That said , despite over 40 years of experience , neither we nor the other players have managed to make a really big impact in mining with mechanical mining methods . Finally , I think we are seeing a switch in attitudes with the mining companies with it becoming more accepted , but at the same time it is still largely limited to trials .”
Instead of viewing these machines as an “ experimental tool ” – where the first reaction to a
72 International Mining | NOVEMBER / DECEMBER 2021