PEBSTER Project

Project Scope

Reinforced piled embankments make infrastructure projects on soft soils feasible. Current design practice assumes a perfectly rigid pile behaviour and uses analytical design methods that were developed for geosynthetic reinforcement. However, piles usually show some settlement. Welded steel mesh reinforcement is applied sometimes instead of geosynthetics, especially for high embankments. The PEBSTER test program addresses knowledge gaps in the load transfer mechanism of steel-reinforced piled embankments, and the difference between rigid and flexible piles. Therefore, model tests at two scales were planned: small-scale model tests at Deltares and large-scale model tests at TU Darmstadt. The research program was developed in close cooperation with the research group led by Keller.

The small-scale test set-up consisted of an embankment founded on four piles with a basal steel reinforcement. The consolidation of the soft soil between the piles was simulated by draining a saturated foam cushion. Surcharge loads up to 100 kPa were applied, to match the prototype stress in an embankment with a height of about 5 m.
In the four small–scale tests, the following variations were made:

• Steel reinforcement or no steel reinforcement;
• Rigid piles or piles on springs, comparing the theoretical model with a more realistic behaviour;
• Stepwise or continuous consolidation, emulating different construction sequences.

Force and pressure cells were used to capture the load distribution. Steel and soil strains as well as 3D soil displacements were measured using innovative Distributed Fibre Optic Sensing (DFOS) technology.

In a follow-up, the large-scale test at TU Darmstadt will serve to verify and translate the findings to an almost true scale.

Innovative Aspects and Main Results

This research project introduces innovative approaches to enhancing the resilience and sustainability of piled embankments through the application of welded steel mesh as basal reinforcement, a departure from the traditional use of geosynthetic geogrids. The project aims to explore the load transfer mechanisms facilitated by the steel mesh, and to explore, if existing analytical models for geosynthetic geogrids can be applied for steel meshes as well. Additionally, it seeks to understand the impact of pile flexibility and soft soil consolidation on these mechanisms. Employing cutting-edge distributed fiber optic sensing (DFOS) technology across small-scale and large-scale tests, the project will offer comprehensive insights into the fill-reinforcement-piles-soil interaction, enabling a significant leap forward in the design and construction of more resilient piled embankments. These innovations have been made possible through the joint efforts of the global building company Keller, the construction monitoring firm SHM System (Poland), the Dutch knowledge institute for water and the subsurface Deltares, and the Technical University of Darmstadt (Germany), within the framework of GEOLAB.

Publications from PEBSTER:

• M. Schneider, M. Hel, P. Pandrea, B. Wittekoek, S.J.M. van Eekelen,M. Topolnicki, K. Makowska, R. Sieńko, & H. Zachert (2024). High-density spatial measurements on a 3D large-scale model of a basal steel-reinforced piled embankment. Proceedings of the 5th European Conference on Physical Modelling in Geotechnics, 2-4 October 2024, Delft, The Netherlands.
• S.J.M. van Eekelen, M. Schneider, M. Hell, K. Makowska, K. Zdanowicz, B. Wittekoek, P. Pandrea, R. Sieńko, P. Schauber, M. Topolnicki, H. Zachert (2024). Distributed Fibre Optic Sensing (DFOS) in 3D small-scale tests on steel-reinforced piled embankments. Proceedings of the 5th European Conference on Physical Modelling in Geotechnics, 2-4 October 2024, Delft, The Netherlands.
• M Schneider, M. Hell, B. Wittekoek, S. van Eekelen, P. Schauber, P. Pandrea, M. Topolnicki, K. Makowska, & H. Zachert. Untersuchungen zum Tragverhalten von Piled Embankments im
• Großversuch (Investigations into the load-bearing behaviour of piled embankments in large-scale test). Darmstädter Geotechnik-Kolloqium, 7 March 2024, Darmstadt, Germany.