“The closer you look, the more complicated it gets” Interview with Prof. Marius Milatz

Marius Milatz took over as head of the Institute for Geomechanics and Geotechnics on 1 April 2024. He succeeds Prof. Dr. Joachim Stahlmann, who retired after almost 22 years. Marius Milatz graduated from the Hamburg University of Technology (TUHH) in 2011 with a degree in Civil and Environmental Engineering. After completing his doctorate in 2016, Marius Milatz was a postdoctoral researcher and successfully habilitated in 2022 in the field of soil mechanics. In March 2024, he was appointed as a university professor at TU Braunschweig. Heiko Jacobs spoke to him about computed tomography for soil analysis, the impact of climate change on soil and his love of nature.

Professor Milatz, you are taking over the Institute for Geomechanics and Geotechnics from Professor Stahlmann and even worked alongside him for a month before he left. How much tradition does the Institute have, and how much is it changing?

I took over Prof. Stahlmann’s chair on 1 March at my request. With such an overlap period, it’s good to come in and take over the Institute’s business. I received a very warm welcome from all my colleagues here and Mr. Stahlmann took a lot of time for me. We had a lot of conversations, so I got off to a good start.

I have inherited many established structures in terms of the Institute’s facilities, staff and teaching, and there is a lot of equipment available, which is a blessing. It was a very good start! The laboratory is run by very good laboratory staff and I am very grateful for that. Of course, I would also like to buy new equipment and this will be initiated in the next few weeks.

You want to use computed tomography to analyse processes in soil samples. How can we imagine this? On what scale will it be done, how big will the equipment be?

I was able to use computed tomography (CT) for the first time in 2017, very modestly, with a CT scanner at the Institute of Biomechanics in Hamburg. Bone samples were usually analysed there, and we started looking at soil samples to see what kind of images we could get. This grew over the years with a collaboration with the Université Grenoble Alpes. They have a really great scientific CT scanner and specialise in soil analysis, so I continued my research there.

At TU Braunschweig, I discovered that there is also good equipment here, for example with Prof. Ralf Jänicke, who has a high-performance CT scanner. At the iBMB, right next door, there is a scientific CT scanner that we want to continue using, which is supervised by Thorsten Leusmann. You need this infrastructure. These are typically large machines and we want to work closely with the institutes. But we can also use large research facilities such as the Deutsche Elektronen-Synchroton DESY (German Electron Synchrotron DESY) in Hamburg. There we can use the synchrotron radiation that is a by-product of the particle accelerator and generate high-resolution 3D images using brilliant X-rays with short exposure times.

The vision would be to set up a soil mechanics research laboratory for special CT experiments here in Braunschweig. Typically, you need small devices that you can put into the CT scanner. I have been working on the construction of such devices for the last few years as part of a graduate programme in Hamburg. Based on the principle of “physical computing”, you can be very creative in building your own devices that are controlled by specially developed software. The product is then a miniaturised experimental setup that can be placed in a CT scanner and, ideally, remotely controlled using a very easy-to-use programming language such as Python. My goal is to establish such techniques in research and teaching at TU Braunschweig.

The instruments are usually small because they have to fit on the turntable of a CT scanner. The last soil samples I analysed were about the size of my thumb. That’s only a few millimetres, but the samples contain thousands of grains of sand! We can study with high spatial resolution how the sand grains rub against each other, how they move and rotate, and how fluids such as water and air move between the sand grains in the pore space.

A new theme is the focus on the challenges posed by climate change. What does this mean for soil?

This is an issue that affects us all. We have all experienced the wilting of our garden plants in an extremely hot summer or the flooding of our basements. Our cities have to cope with extreme heat and extreme weather events in terms of rainfall and flooding, such as the river Oker that runs through Braunschweig.

Climate change in the area of soil affects agriculture, cities and coastal protection. The dykes become saturated during heavy rainfall and there is a risk of dyke failure. There is a great need for research into the stability of dykes, a classic topic in earthworks and geotechnics.

In my research I also look at partially saturated soils, which we have everywhere near the surface. In partially saturated soils, the pores between the grains are not completely dry and not completely filled with water. This leads to capillary action. The water is subjected to tensile or suction stress, which contributes to the soil’s bearing capacity. When the soil dries out or becomes completely saturated, it loses its bearing capacity. We all know this from sandcastles: if we build a sandcastle and the sun dries it out completely, it will break, but so will a wave. Dykes are also usually partially saturated, if they lose this property, they no longer hold.

This is what we want to investigate here together with the neighbouring institutes, including the large wave channel (GWK), where I am now also co-director. The interaction of structure, soil and water is an area where we can do joint research, also in the GWK, where we can test structures in the wave channel at different scales. We would provide the soil component.

So far, the IGG has also focused on the final disposal of radioactive waste. Will you continue this work?

We have the Asse mine here on the outskirts of Braunschweig, where many tests have already been carried out and many problems have arisen. I find the subject very exciting, it was Mr. Stahlmann’s hobby horse and a flagship project here. It’s a task that will take millions of years; we have to find a solution. The research topic is currently being continued at the Institute in the SEMOTI project, which Mr. Stahlmann is completing. How can we operate the repository safely over time, how can we calculate this? This is a major task that we want to solve, also with a view to retrievability. As a geotechnical engineer, I would focus on the host rock. What happens when brine or fresh water flows through rock salt, how does it dissolve? We want to study this with new methods. We want to continue the seminar on deep geological disposal.

Another traditional topic at the IGG is tunnel construction. In view of the immense costs and material consumption in times of climate change, under what parameters is tunnel construction for transport routes still sustainable? What are the potential savings?

I have been interested in tunnel construction for many years; I have also had a lectureship in Hamburg on “Introduction to Tunnel Construction “, from the history of mining to the latest tunnelling technology. Of course, it is resource intensive and produces a lot of spoil, sometimes spoil that is modified in such a way that it has to be deposited or reprocessed. This is where spoil management can be used to ensure that the material can be reused as a building material.

I still think tunnel construction is important and we can still do a lot of research in this area. Also in cooperation with the Herrenknecht company, which also supports us here with scholarships for students.

What are your plans for teaching?

Among other things, there are new trends in the area of tension between basic knowledge and digitalisation. It is important to me that students acquire a solid grounding in soil mechanics, foundation engineering, the specialisms of excavation, civil engineering and, of course, the use of numerical methods. It is important to me that students learn programming, which has been neglected in Civil Engineering in recent years. Students can learn to program a mini-computer to control an experiment, for example, to control motors that load a soil sample and sensors that collect data.

You describe yourself as down-to-earth and North German – so you should find it easy to settle into Braunschweig. Have you arrived well in Braunschweig?

During the application phase, I got to know the city and came to love it. Compared to Hamburg, it is clearer in a positive sense, you can reach everything quickly, but there are also lots of green spaces and water – just like in Hamburg. I really like that. I’ve already found a flat in a good location.

I grew up in Norderstedt, in the suburbs of Hamburg, in Schleswig-Holstein between the seas. I’ve also done a lot of hiking in northern Germany.

I can imagine that if you’re a soil scientist, you walk in a different way when you know what’s underneath you.

Yes, Braunschweig is also very interesting geologically. I’ve always had a natural interest in geology, I wanted to study palaeontology, and now I can see that it’s a good combination when I look for fossils as a hobby in my work. There are so-called key fossils, which are representative of certain layers of the earth and ages. I can use my love of nature here.

We have different geomaterials here, I have samples of different sands in front of me, from Iceland with volcanic components, from the Great Lakes in Canada and a sample from Santorini in Greece where the individual grains are porous. These sands have very different properties. Understanding this better and making it more predictable is one of our visions. The closer you look, the more complicated it gets. That fascinates me.

Thank you very much for the interview!

The interview was conducted by Heiko Jacobs and first appeared in the Alumni-Bau Newsletter 01/2024.