15 years of experience with geotextile encased granular columns as foundation system
The Geotextile Encased Column (GEC) foundation system for earthwork structures built on soils of low bearing capacity was launched onto geotechnical engineering some 15 years ago and is now considered state-of-the-art in Germany. The GEC system provides a geotechnical foundation solution for weak and very weak soils where more traditional ground improvement techniques are unlikely to be viable. This paper provides a system description, the required design procedure and details of ongoing long-term monitoring. Information is also included on the continuous improvements which have been made to the GEC system in response to the technical and financial requirements of large civil engineering projects as well as current potential and research directions and the current regulations and guidelines governing use of the system in Germany. In the future, GECs are likely to be used world-wide for water and land engineering projects in very soft soils.
Some 15 years after their market launch, geotextile-encased columns (GEC) have evolved into a sophisticated and absolutely reliable earthwork foundation system, underpinned by both theory and practice. Due to the confining encasement of the columns in the GEC-system it can be applied even in extremely soft soils with e.g. su < 2 kPa, which is in fact more a suspension than a soil. In particular, the system's long-term behaviour can now be accurately predicted, subject to the usual tolerances applicable to creep settlement calculations for foundations on organic soils.
In Germany, GEC foundation systems are governed by Section 10 of the current edition of the EBGEO (Recommendations for Design and Analysis of Earth Structures using Geosynthetic Reinforcements) issued by the German Geotechnical Society (DGGT). This describes the associated terminology, mechanisms, applications, production methods, design recommendations, materials, computational procedures and test criteria. In Germany, then, GECs have been definitively acknowledged as state-of-the-art technology.
The advantages of the GEC system, particularly for soft strata with extremely low shear resistances, are not only demonstrable by computational methods, but have also been substantiated by measurement results.
Ongoing refinements to the system are based on the standard EBGEO guidelines effective in Germany. Various research and development projects are currently in progress with the aim of improving the reliability of on-site installation and widening the scope of application of the GEC foundation system.