Here we go again?

20 May 2021

First, there was Elon Musk who claimed to be able to increase the speed of TBM tunnelling by ten.

Greeted mostly with a degree of skepticism – some in the industry even felt insulted by the claims – it was nevertheless accepted that he was in his own way raising the profile of tunnelling. But it’s currently gone quiet on that particular front.

But now, claims of a similar nature have surfaced, not from Musk but from a trio of companies who claim TBM boring speeds can be increased by up to ten times the current rates – through hard rock even. Some of you at this point may be forgiven for having those recurring feelings of déjà-vu, but please cast these aside for now and read on.

What is interesting about the claims of Slovakiabased GA Drilling, development company Callio and Finnish company Finest Bay Area Development (the company leading the proposed Helsinki-Tallin undersea tunnel) is that they involve what could be a promising new boring technology that they plan to trial at a deep mine in northern Finland. The ‘Plasmabit’ geothermal solution will be tested at the Pyhäsalmi mine which, at over 1,400m deep, is the deepest base-metals mine in Europe and includes more than 100km of tunnels.

Plasmabit is the brainchild of GA Drilling and involves a ‘pulse-plasma’ drilling bit which neither rotates nor requires direct contact and is able to disintegrate any material – or so the trio claim. So it really is stuff of the future, the sort of thing we used to see on the TV serial Dr Who: I remember the Daleks had such a device mounted on their heads which would be activated whenever they cried “exterminate”.

But seriously, the important point is that the technology can be conceivably used for horizontal excavation. An array of these devices on a TBM cutterhead could obviate the need for disc cutters, scrapers and the associated requirement to stop for routine tool changes.

It sounds exciting but how seriously should we take all this? As it has yet to be tested, we must wait to see the outcome of first, the geothermal borehole trials, and then of any tests that are applied to tunnel excavation. But it is very interesting to note the involvement of Finest Bay Area Development.

Whether the technology will really increase excavation speeds as claimed remains to be seen. My guess is that the trio’s claims are wildly optimistic as other variables in tunnelling must also increase in tandem.

But even if the claimed speeds are not achievable, the ability to break rock without the need for conventional cutterhead action (with the associated maintenance stops and resulting delays) could be something worth waiting for. Let’s wait to see how the trio progresses.