Overview
A leading soil improvement contractor in Germany initiated a project to replace an aging bridge located in a region characterized by poor subsoil conditions. The bridge, no longer structurally suitable for current traffic loads, required not only a new superstructure but also a significant ground engineering intervention to support the new ramp foundations.
Given the poor ground conditions near the riverbed and the structural demands of modern vehicular loads, the client opted for ground improvement solutions via Geosynthetic Encased Columns (GECs) using the vibro displacement method. This technique was chosen for both its technical performance and economic efficiency in soft soil applications. The approach allowed the contractor to leverage locally available sand and reduce dependence on cement, aggregates, steel and concrete, further aligning with sustainability and logistics goals.
Spanning over a multi-year period, the scope of works covered the installation and consolidation of the bridge ramp foundation. Solmax worked in close collaboration with the design-and-construct contractor, an engineering office, a certified project checker, and relevant public authorities to ensure regulatory compliance, structural integrity, and optimal performance of the ground improvement solution. The result is a durable and cost-effective foundation solution that benefits not only the client but also local communities and the environment by reducing carbon footprint and extending infrastructure lifespan.
Challenge
The primary engineering challenge lay in the poor native soil along the riverbanks, which lacked sufficient load-bearing capacity to support traditional bridge ramp structures. These subsoil conditions required a solution capable of redistributing loads effectively and preventing differential settlement, which could compromise long-term structural performance and safety.
An additional constraint was timing. The consolidation and settlement period of the ramp foundations had to align precisely with the bridge construction schedule. Conventional soil improvement methods would have required long waiting periods for settlement to complete, potentially delaying subsequent phases of the project. Predictability of settlement behaviour was therefore a critical design factor.
Another layer of complexity was introduced by the separation of contracts for the bridge structure and the earthworks in the tender process. This required careful integration and communication between parties to ensure that the foundation solution would not only meet load-bearing requirements but also fit the bridge construction timeline and cost constraints.
Precise coordination and project oversight were essential to manage logistics, including material delivery and equipment mobilization. Furthermore, the installation technique demanded specialized expertise to ensure accurate placement and performance of the geosynthetic components that bridged the GECs and reinforced the foundation layers. Extensive monitoring equipment was also deployed to measure and verify settlement behaviour during and after installation, ensuring compliance with design parameters and validating the performance of the ground improvement system.
Solmax’s role was to provide technical expertise throughout the design, material specification, and installation process. The knowledge required to properly engineer the load transfer platform and specify reinforcement materials at varying stiffness levels is not widely available in the market, which positioned Solmax as a critical technical partner. By maintaining close contact with all project stakeholders, Solmax ensured the implementation of a robust, predictable, and time-efficient ground improvement solution.
Solution
The core of the foundation solution was built around Solmax’s high-performance geosynthetics, including MIRAFI® Mirapile and MIRAFI Geolon PET series. These products were specifically selected based on load transfer requirements, long-term performance characteristics, and compatibility with the vibro displacement installation method.
The primary reinforcement product used for the column encasement was MIRAFI Mirapile in three variants: 100/300, 100/400, and 100/500. These geosynthetics offer optimal stiffness and durability for vertical load distribution and lateral confinement of sand columns. Above the column heads, MIRAFI Geolon PET reinforcement in varying grades – PET 400, PET 600, PET 800, and PET 1000 – was installed to create an effective bridging layer, ensuring even load transfer from the embankment structure to the GEC foundation system.
One of the key advantages of using the GEC system via the vibro displacement method is that it improves the bearing capacity of the existing ground without removing or replacing weak soils. This not only reduces excavation, transport, and disposal but also allows construction to proceed more efficiently. In this project, the consolidation and settlement period of the ramp foundations was a critical factor in aligning with the bridge construction schedule. Using GECs provided a faster, more predictable consolidation phase compared to conventional soil improvement methods. Extensive settlement monitoring instrumentation was installed to measure and verify performance, confirming that actual settlement matched design expectations and validating the choice of GECs as a technically robust, time-efficient foundation solution.
Additional reinforcement and filtration layers across the broader site terrain included MIRAFI Polyfelt TS 30 and TS 65 nonwoven geotextiles for separation and filtration, MIRAFI Geolon PP 60 for drainage and reinforcement, and MIRAGRID GX 55/55 biaxial geogrid for secondary stabilization of temporary haul roads and working platforms.
The choice of materials was governed by a combination of engineering design and practical considerations. The geosynthetics selected were certified for use in critical infrastructure projects and known for their proven performance in load-bearing applications. The MIRAFI Mirapile and MIRAFI Geolon PET products offer high tensile strength and low creep under long-term load, making them ideal for permanent foundation works.
Material availability and logistics were key success factors. Solmax ensured that reinforcement materials were available on site in the required quantities and formats to prevent delays during installation. The vibro equipment used for column installation operates on a tight schedule, and any shortage of material would result in costly idle time.
The experience also provided valuable insights into the practical implementation of GEC systems in European soil conditions. One of the key learnings was the importance of close collaboration between material suppliers, contractors, and engineers to ensure the compatibility of installation techniques with design requirements.
Ultimately, this transportation infrastructure project exemplifies the effective use of geosynthetics in modern foundation engineering. The successful deployment of GECs using MIRAFI Mirapile and MIRAFI Geolon PET products not only met engineering demands but also contributed to a more sustainable and cost-effective construction process. With long-term performance and reduced environmental impact, the project stands as a model for future ground improvement applications in soft soil environments.
