The research project comprehensively investigates the interaction between tension steel piles and surrounding soil. The main goal is to explain the significant discrepancies between the expected and actually measured load-bearing capacity of tension piles. Through detailed laboratory experiments and simulations, the frictional behaviour at the contact surface between pile and soil is examined as a function of factors such as surface texture and soil type. With the help of computed tomography, the processes can be observed on the smallest scale of individual soil particles. Further goals are to gain a better understanding of the influence of thinly inter-layered soils as well as the pile installation method on the later load-bearing capacity. In addition, innovative approaches such as bio-inspired surface structures will be tested for their potential to improve the load-bearing capacity. The research findings will help to better understand the complexity of the pile-soil interaction and develop more realistic calculation models and optimized solutions for the design and construction of tension piles.