According to research by TU Delft and TNO, deep subsidence is not the cause of damage to buildings in Groningen. What is the matter then, Delta asked researcher Jan Rots.
Inspection of the damage to a house in Warffum. ( Photo: Kees van de Veen/Hollandse Hoogte)

According to research by TU Delft and TNO, deep subsidence is not the cause of damage to buildings in Groningen. What is the matter then, Delta asked researcher Jan Rots.

Lees in het Nederlands

A motion by Pieter Grinwis (ChristenUnie) and Agnes Mulder (CDA) was supported by the entire House of Representatives during the vote on 5 October. They called on the Government not to allow the Institute for Mining Damage in Groningen (IMG) to exclude areas in the provinces of Groningen and North Drenthe from submitting damage claims.

In doing so, the House of Representatives dismissed two research reports used by the IMG. The first report (in Dutch) by TNO and TU Delft from March 2021 about the direct consequences of deep subsidence concludes ‘that deep subsidence (and rising) in the gas storage facility Norg and the Groningen field does not lead nor has led to damage to buildings’. There is more documentation on this on an IMG webpage (in Dutch). The other report (in Dutch), published last September, is about the indirect effects of deep subsidence. Deltares, a hydro engineering research institute, explains that this mostly concerns changing groundwater levels and their effects on the subsurface and foundations. Based on the first report, the IMG rejected 1,800 claims, 300 of which it reconsidered on the grounds of the second report. Nonsense, said the Lower House on 5 October, let us first see what the cause is.

Thousands of houses in Groningen started to show cracks in the aftermath of gas extraction beneath their homes. It sounds plausible that the gas extraction has something to do with it, but proving it scientifically or legally is very difficult.

Delta rang Prof. Jan Rots about the work on the emotionally charged Groningen dossier. Prof. Rots is the co-author of the report on the direct effects of deep subsidence and Professor of Structural Mechanics at the Faculty of Civil Engineering and Geosciences.

In the study, you write ‘deep subsidence does not lead and has not led to damage to buildings’. Yet there are thousands of reports of damage. If it is not because of the deep subsidence, what is going on?
“That is not the question we were asked, so I can't answer that. We know that cracks in masonry can be caused by a multitude of things. A building can subside unevenly over time because the soil or the pressure on the foundation is uneven. What also frequently happens is that sand-lime walls shrink. If this is impeded in any way, tension builds up and they crack.”

Of course, you have also read about farms that have been there for more than a century and that have only started to subside in recent decades. That‘s strange, isn’t it?
“That question didn‘t come to us, so we didn’t investigate it.”

You have investigated deep subsidence. Did you also look at earthquakes whereby changes are spasmodic?
“We didn't do that in this study because the question here was only about the direct effects of deep subsidence. But we are investigating the effects of earthquake vibrations on buildings. We are carrying out tests in the lab and using mathematical models. We are also investigating the cumulation, the influence of new vibrations on existing damage. One question that Groningen residents are rightly concerned about is whether cracks will grow.”

Is there anything to say about that yet?
“No, not yet. The investigation has not yet been completed, so the announcement will still take some time.”

The Institute of Mining Damage in Groningen has tried to narrow down the area in which it can be held liable for damages. They used both your research and that of Deltares for this. Were you aware of this intention behind the research?
“We were aware of the background to the evidence presumption, but I dispute that it was the intention to narrow down the area. That was not a preconceived intention. At least, not that I know of. We were simply asked if deep subsidence can have a direct effect on damage.”

Now the House of Representatives has unanimously passed a motion prohibiting the IMG from reducing the area of liability. What do you think about this?
“I cannot comment on this.”

There are research reports and there are thousands of angry Groningen residents with damaged houses. How can it be that science cannot provide a satisfactory answer to the cause of the damage?
“If you have done a study and it shows that, in this case, deep subsidence cannot be the cause, the question is what is the cause then? We were not asked that question now, but we were asked it in a study (in Dutch) we did in 2018. At the time, we examined 69 buildings with 2,400 pieces of damage to find out the cause of the damage. The result was a nuanced story with different probabilities of various causes. We wrote then that the effects of tremors is difficult to exclude, but equally difficult to prove. If you want to refute the suspicion of proof, as lawyers call it, you also have to be able to point to another cause.”

Is it still possible to do objective scientific work in such a legally charged environment?
“Yes. I have never felt impeded because the work we have been asked to do has always been pure and objective. We gather objective knowledge to help people who need to award damages. I have no problem with that. We have been working on ‘Groningen' for a long time, since 2013. I can’t remember it causing us any difficult situations. You just have to stick to your role as a researcher and not make statements about politics or governance.”

Do you also read the reactions that people post in response to your research reports? They express little faith in ‘the Delft gentlemen’.
“Of course there are people who react positively and others who are distrustful. That is no reason for me to stop researching. Indeed, and this applies to other TU Delft scientists too, we want to be socially relevant. That is why we work on safety in Groningen, and that is why we contribute objective knowledge about possible causes of damage to buildings. I believe this is a good thing for the people. We have also entered into dialogue with them and explained the research in a webinar (in Dutch) organised by IMG.”

And that some people are unhappy about this?
“That is not up to us. Ultimately, we provide knowledge that damage experts, lawyers and administrators use to take decisions. The rest is not up to the researchers. We provide them with building blocks to take more objective decisions than in the past.”