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Drilling campaign Einstein Telescope EMR: ‘promising results’

The results of the drilling campaign are ‘promising’. This preliminary conclusion generated enthusiasm during the ministerial summit. From the Einstein Telescope EMR project office, director Hans Plets and technical manager Wim Walk explain the significance of that preliminary conclusion.

To start with: how was the ministerial conference?

Hans Plets: ‘These are always important moments. Lots of people from our project office, from universities, companies, knowledge institutes and local authorities are busy every day investigating the feasibility of the Einstein Telescope in this area. The ministerial conference is one of those moments when all the lines at the top of our organisational tree come together. For us then, it is always a bit exciting how people react to the progress.’

And?

Hans Plets: ‘Positive. Satisfied and actually quite enthusiastic. Certainly also about the Flemish cabinet’s announcement of an initial reservation of 200 million for the Einstein Telescope. As a Fleming, I think this is obviously a good signal. Together with Arjen van Rijn, I myself had the opportunity to outline a number of developments from the project office. Of course, it was not all completely new to the ministers. We regularly discuss progress with their officials.’

As a preliminary conclusion of the drilling campaign, it has been announced that the deep subsurface is suitable. What does that mean?

Wim Walk: ‘Actually exactly as the press release says: that the initial results are promising. Indeed, the preliminary conclusion is that the subsurface in the border area of Belgium, the Netherlands and Germany is sufficiently stable and offers possibilities for building the underground telescope. But it should be added that this is an intermediate conclusion: not all analyses have been carried out yet and the last of 11 borings is currently ongoing.’

So why draw a preliminary conclusion and not wait for the final results?

Wim Walk: ‘We have agreed that we will take stock at regular intervals. Then we will see whether we run into issues that would make the construction of the Einstein Telescope impossible. We call them ‘showstoppers’. After all, we are working with taxpayers’ money. It would be wrong to keep drilling or exploring when you actually already know it’s all impossible.’

Photo of dark grey drilling cores. Source: ET-EMR
Cores from the 2024 drilling campaign for the Einstein Telescope EMR. Photo: ET-EMR
Is there more to say?

Wim Walk: ‘The drilling campaign is obviously important because the deeper subsurface has to be stable enough to be able to drill tunnels into it. What layers will you encounter and what rocks do those layers consist of? Geology, in other words. But also: are these rocks suitable for drilling a tunnel into? That is civil engineering. Another aspect being investigated is whether it is all hydrologically possible. But so the preliminary conclusion is that we have not encountered any showstoppers. In other words, we dare to say as an interim conclusion that – when it comes to the deeper subsurface, it should work. And we are not just saying that; we have also asked an independent body to do a review.’

Who exactly?

Wim Walk: ‘That’s TNO, the Netherlands Organisation for Applied Scientific Research. In a review, the head of TNO’s geological department says he agrees with our research team’s conclusion. Namely, that based on the results obtained so far, no factors have been identified that would make the ET-EMR project unfeasible. That is not just about soil stability, but also questions like where and how to build the tunnels.’

Boorstelling uit de boorcampagne 2024 van Einstein Telescope EMR. Bron: ET-EMR
Drilling site in the 2024 drilling campaign for Einstein Telescope EMR. Photo: ET-EMR
Who are responsible for those drillings?

Wim Walk: ‘The drilling was carried out by the Swiss company Stump, which has a lot of experience in this field. Steered by our project office, a partnership was set up between organisations from industry, research institutes, universities and companies. For instance, Bjorn Vink from Nikhef Amsterdam led the drilling campaign with important support from Marius Waldvogel from RWTH, Aachen. From the University of Liège, Philippe Orban was responsible for the initial hydrological measurements. The geological survey was led by Geert-Jan Vis from the Geological Survey of the Netherlands with important support from geologists Yves Vanbrabant from federal Belgium and Rudy Swennen from KU Leuven.

A long list

Wim Walk: ‘Actually, it is even longer. Companies supported us in specific technical areas. We needed permits, of course. The environment had to be informed, including with 10 public meetings in full halls. At the drilling sites, viewing moments were organised for interested members of the public. Many people attended. At some sites, specific nature and environmental surveys were carried out first. In Obsinnich in Flanders, for instance, it was checked whether the habitat of the protected hazel mouse was at a sufficient distance. And on the advice of an ecologist called in, we postponed the drilling at the Vijlenerbos car park until after the breeding season. That drilling is currently ongoing. All the drill rods will eventually be taken to our special shed in Aubel for registration and geological analysis.’

A big step, then?

Wim Walk: ‘Yes, but immediately with the note that it is an interim step and a lot still needs to be done. We are investigating whether additional drilling is needed. That chance is real. But not only in the geological field is there still a lot to do. The hydrological situation in the subsurface needs to be measured and evaluated in detail. Seismic studies must also show whether too many above-ground vibrations, say noise, do not penetrate into the deeper soil. We can only make good measurements of gravity waves if it is almost completely noise-free at a depth of 250 metres.’

The ministry’s press release said that this does not yet say anything about the three corner points of the Einstein Telescope.

Hans Plets: ‘That’s right. That deep subsurface has to be OK, of course, but it also has to be right in many other areas. Think about how we can build the telescope. Think about the effects on the environment and how you deal with that. Think about how we plan to organise the logistics during the construction phase. Think about the degree of sustainability. Etcetera, etcetera. We are optimistic, but we also want to be realistic. So: yes, we have taken a step, but a lot of other steps with a good result still have to follow to reach the finish line.’

This was a preliminary conclusion. When will the final one follow?

Hans Plets: ‘Tricky question. Studies sometimes run in parallel. The outcome of one study may mean that another study is no longer needed or should be extended. It all hangs together. I cannot give a hard date, however much I would like to.’

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