CONTINUOUS CUTTING dimensions of the required excavation in this trial , with the machine development rates proving very competitive when compared with the conventional roadheaders the contractor was using alongside the MC51 .”
He concluded : “ There are some benefits of this machine that we haven ’ t been able to measure yet ; ventilation engineers have viewed the MC51 excavations and are excited about the potential to create a much more efficient ventilation system based on its work . We are also seeing an up to 25 % decrease in ground support installation times , plus there is no need to fill the floor with crushed material – the flat floor excavation is already fit-for-purpose .
“ These characteristics are only becoming more important as the industry looks to mine orebodies at increasing depths , encounters more complex conditions and , as a result , has to reconsider conventional mine development means .”
Accelerating first ore
Robbins is world-renowned in tunnelling circles , with a name that has over 70 years of innovation behind it .
Some of this innovation has been directly applicable to the mining sector , with the company trialling a Mobile Miner with Mount Isa all the way back in the 1980s and being the first to introduce raiseboring to mines .
In terms of MRE in hard-rock mining today , most of the buzz is focused on its MDM5000 machine , which uses disc cutter technology proven on traditional circular machines to excavate rock up to 200 MPa in rectangular cross section tunnels with dimensions of 5 m x 4.5 m . This is thanks to a reciprocating cutterhead able to exhibit a swinging cutterhead motion .
In addition to the cutting element , continuous ground support is placed immediately behind the cutterhead in a pattern that is mine-standard , according to Robbins . Ground support and installation of utilities such as piping , ventilation and lighting are carried out simultaneously to boring , with the MDM5000 providing a complete mechanical rock excavation system .
The ability to excavate a flat tunnel invert for immediate use by rubber-tyred vehicles is a key selling point of the technology , as well as a major differentiator to standard TBMs .
Robbins has been able to put this into practice during a trial with Fresnillo at its flagship mine in Mexico , which saw the company clock up more than 1,700 m of advance up to September 2021 at rates up to 52 m in one week and 191 m in a month .
“ We learned that the fastest the Fresnillo team had ever achieved in a blind heading with drill & blast was 120 m / mth ,” Lok Home , President of Fresnillo , told IM . “ To get to that 191 m rate was
deemed very good from their perspective and , from how we look at it , has shown that you can get to your first mineralisation with the MDM5000 sooner than you can with drill & blast methods .”
One of the other benefits that has been shown during this trial is the “ controlled muck ” output : a result of the consistent cutting process and internal conveyor mechanism on the MDM5000 unit .
“ Such characteristics mean you could easily send the material to surface , or , in certain applications , even consider the option of bolting on a bulk sorter underground ,” Home said .
The big and impressive statistics from mine development using the MDM5000 have been circulating for at least two years , with Brad Grothen , VP of Engineering for Robbins , explaining that a diversion from the original development plan at Fresnillo caused some unwanted delays to the wider 5,000 m program .
“ The MDM was making pretty good progress on a straight alignment and then the Fresnillo team decided to put the machine into a curve ,” he said . “ They hit faults they weren ’ t expecting – one of these being the biggest the mine had ever experienced – and also came into problems with hot water inflows .”
As a result of this , both parties agreed to pause development .
“ We are now in the process of resetting the machine after carrying out some modifications with a re-launch scheduled for December ,” Grothen added .
Robbins is expecting to continue the 5,000 m plan the parties originally agreed on for the Mexico mine , meaning there is plenty more development ahead of the MDM5000 .
Into 2024 , the company will continue to work on slight modifications to the existing MDM5000 design that could appear on any machines being deployed in the near-future .
And , in terms of a second-generation machine , Robbins already has some concepts in mind .
“ We currently have the square / rectangular profile , but we are looking at other machine types , not exactly like the MDM , which could offer alternative profiles , such as the horseshoe type , depending on what a mine would be looking for ,” Grothen said .
“ And , of course , all the mines want to excavate with tight turning radiuses . The MDM was designed around a development drift with conveyors , but we are also looking at what we could offer for excavations on curves .
“ Another consideration is also quick tramming for relocating the machine from one heading to the next .”
The Robbins MDM5000 is capable of cutting hard rock up to 200 MPa UCS while creating a flat invert for access by rubber-tyred vehicles
In its current form , the MDM5000 still has plenty of potential applications for the mining sector , Grothen says .
“ People like TBMs where they can excavate quickly and handle the material ,” he said . “ Some of the challenges associated with using roadheaders and partial face cutting technology are tied to sacrificing speed for mobility and potentially having issues with material handling . With the MDM5000 , we ’ re looking to give them the best of both worlds by being able to attack the entirety of the face as much as possible while having a proven material handling philosophy .”
Mining companies are more readily familiarising themselves with MRE options at the early stages of projects , he added , with Robbins having been called upon for input on studies relating to TBM and drill & blast tradeoffs .
Home and Grothen have also witnessed more interest from the contractor side of the mining business , with several companies looking to understand the process and the systems-based approach to mine development with TBMs .
“ Cutting technology is , for sure , important , but you also need to consider the muck removal , the ground support and logistics ,” Grothen said . “ You have to manage this system and have a scalable technology in play where no one element becomes a bottleneck .”
Taking a systems approach
Master Drilling Group has also been looking to dispel the associations of inflexibility often levelled at TBM companies from the mining community .
Its Mobile Tunnel Borer ( MTB ) is equipped with a full-face cutter head with disc cutters adapted from traditional TBMs . Unlike these traditional machines , it is designed to work both on inclines and declines , with the first-generation machine
NOVEMBER / DECEMBER 2023 | International Mining