CONTINUOUS CUTTING
TBM world record
Anglo American recently set a World Record for the longest tunnel developed by a single TBM in a soft-rock environment . The record – previously set at 25.8 km – was surpassed by the Woodsmith project team in the UK in late October , when the owner , Anglo American , declared it had reached the 25.9-km mark . This development is part of a 37-km-long mineral transport tunnel to service its 5 Mt / y polyhalite mine .
The machine used at Woodsmith is a Herrenknecht hard-rock TBM that , Tom McCulley , CEO of Anglo American ’ s Crop Nutrients division , says works in a similar fashion to the Herrenknecht Shaft Boring Roadheaders being used at Woodsmith for shaft sinking operations in that it cuts the soils , without blasting , and the material is transported through the machine and out of the tunnel via a conveyor that is part of the TBM .
“ In addition to excavating the material , the TBM also simultaneously lines the tunnel via precast concrete segments ( six segments make up a ring around the circumference of the tunnel ); these concrete segments are fabricated at the Teesside port by a project dedicated facility ,” McCulley said during a recent analyst and investor visit .
He said in every measure the tunnelling on the project to date has been an amazing success , aided by a solid team performance . This team is made up of contractors from STRABAG , Herrenknecht and Anglo American . Progress has been aided by
The Woodsmith tunnel boring team is made up of consistent ground conditions across the contractors from STRABAG , Herrenknecht and Anglo
tunnel within Mudstone strata , McCulley American said .
“ These conditions are very predictable , and cutting is easy for the machine which minimises the bearing wear , which is a key risk area for the TBM ,” he said . “ This consistent strata has allowed us to switch our strategy from three TBMs to one TBM for the entire 37 km , which means we will not only pass the World Record , but we will also smash it when we reach Woodsmith in late 2026 .
“ This reduction in TBMs had a knock-on impact of saving significant capital over what was originally planned .”
Anglo is consistently seeing average rates increase to over 20 m / d and trending closer to 25 m / d , which compares favourably with about 16-17 m / d in late 2021 , it noted .
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
44 International Mining | NOVEMBER / DECEMBER 2023