Geotechnical engineers at the University of Siegen are working with construction companies to develop a new system for pile foundations. The aim is to save concrete in the piles and thus significantly reduce CO2 emissions in construction projects.
If a building is to be erected, the ground must be safe, i.e. load-bearing. If this is not the case, piles can help. They are driven into the ground to transfer high loads to deeper layers. Scientists from the Department of Geotechnical Engineering at the University of Siegen are currently working with construction companies to develop a new pile system. The aim of the project is to increase the load-bearing capacity of the individual piles. The piles would then no longer have to be as long as before. This would save concrete and therefore CO2. The project is being funded by the Federal Ministry for Economic Affairs and Climate Protection with a total of 1.5 million euros, of which around 407,000 euros will go to the University of Siegen.
"Concrete is one of the biggest CO2 drivers in the construction sector. If we succeed in developing shorter piles with the same load-bearing capacity, we could make an important contribution to sustainable and climate-friendly construction," says Siegen geotechnical engineer Prof. Dr.-Ing. Initial calculations using the example of a fictitious construction project with 1,000 piles are promising: according to these calculations, an optimized pile system could save between 20 and 50 percent CO2 compared to conventional systems.
The Siegen project is using an established drilling technique to develop the new pile system: In so-called full displacement bored piles, a special auger is screwed into the ground to the required depth. The auger then slowly withdraws again. At the same time, liquid concrete is pressed into the hole through the hollow shaft. The hole fills with concrete until the auger is pulled out completely. Within a short time, a stable concrete pile is created in the ground. The special screwing in of the drilling tool pushes the soil to the side and compacts it - increasing the load-bearing capacity of the pile.
In order to investigate this principle on a smaller scale, the Siegen geotechnical engineers set up some technology in the test pit: At the bottom of the pit is a tank almost two meters high, filled to the top with test soil. Above the test tank: a drilling rig, albeit much smaller than the original rigs used on construction sites. Next to the drilling rig are various model drilling tools, all produced on a scale of 1:10 using a 3D printer. These are systems that were developed by the project partners Jacbo Pfahlgründungen and Otto Quast and are already being used in practice.
"Just like on the construction site, we screw the different drilling tools into our test tank. We then test the load-bearing capacity of each pile. To do this, we apply a load to the pile head using a hydraulic cylinder, which we increase in stages," explains project team member Johannes Kuhlmann from the Chair of Geotechnical Engineering. A sophisticated measuring concept records the loads that the piles can bear and the mechanical changes that occur in the soil.
Parallel to the practical tests, the team is developing a numerical calculation method in order to be able to simulate different pile systems on the computer. "Based on the simulations and our tests in the tank, we can model optimized pile variants through targeted modifications," says Kuhlmann. The most promising candidates are then tested again in practice: first on a smaller scale in the test pit in the university laboratory. The final step is a large-scale test in close cooperation with Jacbo Pfahlgründungen and Otto Quast: the developed piles are then placed in the ground in their original size and tested again for their load-bearing capacity under real conditions.
"We are delighted to be able to contribute our expertise to the project. At the same time, of course, we hope to be able to use the system developed as part of the project in the future and thus realize our construction projects in a more climate-friendly way," say Philipp Dietrich from Otto Quast and Andreas Reinfeld from Jacbo Pfahlgründungen. For both of them, the collaboration with the Siegen Geotechnics Department is also a kind of "home game": before their professional careers in the construction industry, they studied here themselves and each graduated in civil engineering.
Background:
The joint project "LeVoresT - Efficiency-enhanced lightweight full displacement bored piles as resource-optimized deep foundation elements in the construction industry" was launched in December 2023 and will run until the end of November 2026. The project partners are the companies Jacbo Pfahlgründungen GmbH and Otto Quast Bauunternehmen GmbH & Co. KG. The Federal Institute for Materials Research and Testing, the German Institute for Building Technology, Goldbeck Nord GmbH, Baugrund Dresden Ingenieurgesellschaft mbH and Dr. Ingo Hylla are involved as associated partners.
