GEOLAB - ELURPGEC: Effect of loading, unloading and reloading on the performance of foundation systems with geosynthetic encased columns

GEOLAB: GEOLAB is a project of the European Union’s Horizon 2020 research and innovation program under Grant Agreement No. 101006512, addressing Europe's Critical Infrastructure (CI) challenges in the water, energy, urban, and transport sectors.

The GEOLAB Research Infrastructure (RI) consists of 11 unique installations across Europe to study subsurface behavior and its interaction with structural CI elements and the environment. During the GEOLAB Transnational Access (TA), users outside the consortium gained access to the GEOLAB installations to perform research and innovation.

Research group: The project was conducted by a research group that includes Deltares (Netherlands), Huesker Synthetic GmbH (Germany), Ed. Züblin AG (Germany) and Ruhr University Bochum (Germany).

Project Title: Effect of loading, unloading and reloading on the performance of foundation systems with geosynthetic encased columns

Project Acronym: ELURPGEC

Project Overview: This project investigated the load-bearing behavior of Geosynthetic Encased Columns (GEC) foundation systems during unloading and reloading phases. Building upon prior research that identified increased vertical stiffness during reloading cycles, the study focused on how the stiffness ratio between GEC and the surrounding soft stratum evolved. By addressing these changes, the project aimed to enhance the effectiveness and sustainability of infrastructure foundations on soft subsoils.

Background and Motivation: Previous studies had concentrated on high-frequency cyclic loading scenarios typical of traffic and seismic activities. In contrast, this project explored single-cycle loading, unloading, and reloading conditions, which mirrored the construction process involving preloading, surcharge removal, and final embankment loading. This alternative approach provided insights into long-term settlement and stiffness variations, crucial for transport infrastructure such as roads, railways, and ports.

Methodology: The project utilized the Actidyn C72-3 beam centrifuge at Deltares, Delft (NL), to simulate real-world stress conditions. Two experimental setups with 10% and 20% area replacement ratios were constructed in strongcylinders, each measuring 590 mm in diameter. The GECs, encased in seamless textile encasements and installed using a replacement method, were filled with sand and compacted layer by layer. Instrumentation monitored vertical displacements, pore water pressures, vertical forces, and stress distribution.

Key Finding: The study highlighted how changes in the stiffness ratio between GEC and soft surrounding soil was affected by loading cycles. The experiment showed that the GECs not only attract more load during the consolidation phase after each loading cycle, even though the settlements of both the columns and the surrounding clay remain approximately equal, but they also exhibit increased stiffness upon reloading compared to their state after the initial loading phase. 

Applications and Impact: The findings provided valuable insights for civil infrastructure projects, enabling engineers to design more efficient foundation systems for sites with limited space and challenging soil conditions. By optimizing GEC configurations, the project supported the development of durable, cost-effective, and sustainable infrastructure solutions, addressing critical challenges in transport networks and urban development.