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.GEOLAB: GEOLAB项目是欧盟“地平线2020”研究与创新框架计划下的资助项目，项目资助协议编号为101006512，旨在应对欧洲水务、能源、城市与交通领域的关键基础设施（Critical Infrastructure, CI）挑战。 GEOLAB研究基础设施（Research Infrastructure, RI）在欧洲范围内拥有11处独特的实验装置，用于研究地下行为及其与结构性关键基础设施单元和环境的相互作用。在GEOLAB跨国访问（Transnational Access, TA）计划期间，项目联盟外的研究人员可使用该项目的实验装置开展研究与创新工作。 研究团队：本项目由包含以下机构的研究团队牵头完成：荷兰代尔夫特水力研究所（Deltares）、德国胡斯克合成材料有限公司（Huesker Synthetic GmbH）、德国祖布林股份公司（Ed. Züblin AG）以及德国波鸿鲁尔大学（Ruhr University Bochum）。 项目名称：加卸载与往复加载对土工合成材料包裹桩（Geosynthetic Encased Columns, GEC）基础体系性能的影响 项目缩写：ELURPGEC 项目概述：本项目针对土工合成材料包裹桩（GEC）基础体系在卸载与往复加载阶段的承载性能展开研究。此前已有研究发现往复加载循环中竖向刚度会出现提升，本项目在此基础上，重点探究GEC与周围软弱土层的刚度比变化规律。通过厘清该变化机制，本项目旨在提升软弱地基上基础设施基础体系的效能与可持续性。 背景与研究动机：过往研究多聚焦于交通与地震活动中常见的高频循环加载场景，而本项目则探索了单周期加载、卸载与往复加载工况，该工况可模拟预压、卸除超载及最终路堤加载的实际施工过程。该研究视角为道路、铁路、港口等交通基础设施的长期沉降与刚度变化分析提供了新的参考依据。 研究方法：本项目依托荷兰代尔夫特Deltares研究所的Actidyn C72-3型梁式离心机，模拟实际工程应力条件。实验分别设置面积置换率为10%与20%的两组试验方案，均在直径590 mm的高强度试验圆筒中开展。GEC采用无缝织物包裹，通过置换法施工，内部填充砂土并逐层压实。试验通过各类监测仪器记录竖向位移、孔隙水压力、竖向荷载及应力分布情况。 核心研究发现：本研究阐明了加载循环对GEC与周围软弱土层刚度比的影响机制。试验结果表明，尽管GEC与周围黏土的沉降量基本一致，但在每次加载后的固结阶段，GEC承担的荷载占比会更高；同时，相较于初始加载完成后的状态，GEC在往复加载阶段的刚度有所提升。 应用与影响：本研究成果为土木基础设施工程提供了重要参考，可帮助工程师针对空间受限与土质条件复杂的场地设计更高效的基础体系。通过优化GEC的配置方案，本项目助力研发出耐久、经济且可持续的基础设施解决方案，以应对交通网络与城市发展中的关键挑战。