GeoCentrifuge: advanced time machine for soil processes

Background

GeoCentrifuge: advanced time machine for soil processes

Deltares in Delft started using the GeoCentrifuge in June. This makes it possible to test soil processes on a scale by increasing gravity. What can take years in the ground is thus reduced to hours. In the face of societal challenges such as climate change, subsidence and space pressure, this innovative research facility is of great importance for a robust and sustainable infrastructure.

Author: Loet van Bergen

“Putting applied research into practice usually starts with experiments,” says Suzanne van Eekelen, a researcher at Deltares. “Here you see a development of upscaling from lab scale to real scale. This is also the most cost effective. For research in and with soil, it is important that the applied forces are correct. ”

“In the soil, processes take place over a long period of time. The idea that you can scale forces by increasing gravity dates back to the 1930s. From the 1990s, this could be done better with more modern machines. Our GeoCentrifuge is modern and special because of its dimensions. Due to its size, dike, road and railway models can be scaled as a whole in order to conduct research with them. ”

“There are similar centrifuges of the same size in Cambridge and Nantes in Europe, but they are equipped for other specific applications for research, such as earthquakes. The Deltares version is mainly designed for research related to soft soil with water problems. This allows us to test infrastructure models under extreme conditions, such as extreme weather. “

“The plan for the GeoCentrifuge was developed by Deltares,” says Harm Aantjes, head of Deltares, “and is supported by the Ministry of Infrastructure and Water Management. The construction was realized through market-based procurement processes and took a total of about 10 years (from planning to realization). The unit was built in France by the French company Actidyn, the architectural part was carried out by Verbakel Bouwbedrijf bv and the building-related installations by Groen & Aldenkamp Installatietechniek. .

Operation

The GeoCentrifuge is a giant device for which a special room with a diameter of 8 meters has been built, where tests are performed under climatic conditions. The models to be tested are placed in a test tank. “This test tank hangs at the end of a 5 m metal arm, which is rotated very hard about an axis,” explains Van Eekelen. “The test box tilts like the seats in a carousel. Due to the centrifugal forces, we increase the gravity of the model. Gravity g can be increased by a factor of 150. The machine then spins at a speed of more than 347 km / h and passes three times per second. ”

“If the model consists of, for example, a small dike on a soft surface, the effect is that the pressure under the dike will be the same as under a real dike outside. This allows us to perform a series of tests relatively quickly with small-scale models, while the pressure in the ground or in the structures is the same as in reality. So reality is very well imitated. Certain processes are also accelerated, such as consolidating or spreading soil contamination. ”

“During the flight, we can measure everything, and high-speed cameras keep an eye on. Robots can also be used for extra activities. The GeoCentrifuge, where models up to 1.2 m by 1.2 m by 1.8 m can be tested, comes with a development environment that “This gives us measurement data. This allows us to validate numerical geotechnical software models. Many different types of scientific research are possible with this. The results and video images can be followed live via the Internet,” says Van Eekelen.

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HWBP test blast in GeoCentrifuge

In the pilot project Reevediep, Drents Overijsselse Delta and Delta Water Council investigate how the ground behind the dike is pushed up and ‘bursts’ at high tide. If this happens, the dike becomes unstable and the slope slides off a dike. There is still insufficient knowledge about how this blasting works exactly, says HWBP, which aims to gain more insight into what happens to the dike when it blasts with the ‘Practice study on blasting at dikes’.

In the new GeoCentrifuge, a small-scale model is tested with the aim of determining whether the model describes reality well with different variations in the soil structure (topsoil). The tests in the centrifuge serve as preparation for a large field test on Reevediep. This field experiment is expensive, which justifies a good preparation with a series of tests in the GeoCentrifuge. For a few hundred thousand euros, different variations in the soil structure (top layer) can be tested in preparation for the large field experiment on Reevediep.

Application options

The GeoCentrifuge has been thoroughly tested beforehand. In addition to the test drive to test the machine and equipment, a number of relatively simple tests have been started to examine the behavior of Dutch peat.

The most appealing example that can be tested with Deltares is probably the wind turbine. The energy transition presents unprecedented challenges. The size of the wind turbines in the North Sea is being built larger than ever, up to 300 meters high. These dimensions have never been built and it has implications for design and execution. Deltares tests the foundation for the turbines in the centrifuge. “For the tests, we installed a small version of the monopiles and loaded them in the same way as the wind turbines in the North Sea. In this way, the wind turbines’ foundation piles can be optimized. ”

Our infrastructure in the water, energy, urban and transport sectors faces major challenges, ranging from the effects of extreme weather to obsolescence and increased use. In the GeoCentrifuge, these effects can be tested on both existing and new infrastructures. “We are currently conducting experiments to investigate the infrastructure’s behavior on peat. For this we have Norwegian and Irish researchers as guests. Very soon we will start testing flood protection. Small dikes are being tested for this.”

Dikes must also be safe. In the GeoCentrifuge, it can be tested under extreme conditions that almost never occur in real life, such as high water levels or extreme rainfall alternating with drought. Due to the changing climate, we would like to know more about this.

Chancer

Aantjes sees many possibilities for the GeoCentrifuge. “Partly in the light of the interest of governments, engineering firms, knowledge institutes and the offshore industry in the uses of the GeoCentrifuge. You can look for effects of circumstances that are extreme but with little chance of happening or that are still thought to be far ahead of us. “

“In a European context (during the opening, European partners are working on this research) the vulnerability of our (critical) infrastructure (roads, railways, pipelines) to climate change is examined. Here, the remaining life of structures in the replacement and renovation task also plays a role. ”

“The effect of new innovative ideas is also being investigated. For example, to make infrastructure less sensitive to extreme weather (methods to reduce the effects of softening or erosion due to excessive rainfall, or methods to build with less nitrogen production (for example, a certain type of road (violence) on peat, where peat not to be dug).

Van Eekelen adds: “For flood risk management, the direct reinforcement task for the flood protection program for the coming years looks at modeling eruptions. In addition to centrifuge research, all other research will be performed, such as a field trial. The result is expected to optimize the task.”

“The interventions in our delta must be balanced. Due to intensive use, these affect each other (more and more). Landslides and climate change are putting even more pressure on this. Understanding the behavior of the (often soft) subsoil in the Netherlands better and being able to simulate it in models means that we can do this in balance and will / will be able to limit effects / nuisances. ”

Strategic value
At the opening, Minister Harbers spoke about the ‘enormous strategic value’ of the GeoCentrifuge. According to the Minister, the new test facility can make an important contribution to the tasks facing the Cabinet, such as risk management of floods, energy conversion and climate-safe construction.

“The knowledge and data gathered here is absolutely necessary for these tasks. Think of dam reinforcement, coastal protection, offshore infrastructure. Think also of earthquakes, dry and wet infrastructure. And think of our giant housing subsidy. In addition, GeoCentrifuge also contributes to another ambition in the cabinet, namely that water and soil are included earlier and more urgently needed in physical plans. ”

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