Geotextile Encased Columns (GEC) as Pile-Similar Foundation Elements: Basics, Specifies, Case Studies
The Geotextile Encased Columns (GEC) deep foundation system for embankments and dikes on soft soils was introduced some 20 years ago and is now considered State-of-the-art in Germany, Europe ans, step by step, worldwide. The GECs consist of compacted non-cohesive granular fill similar e.g. to common garval columns with one decisive deifference: they are confined in a high-strength, high-modulus, flexible geotextile "cylinder" (encasement. This engineered element with parameters being adaptable in a wide range provides a decisive tool to control and optimize the behavior of the GEC foundation system. Consequently, the GECs work properly even in extremely soft soils, and a wide range of fills inclusive of sands can be used. In the meantime vast design and technological experience is available and codified design methods exist. Initially the paper briefly describes the general idea, the basics and specifics of design, construction technology, materials, restrictions and optimal application areas. Then it focuses on three informative case studies. They are briefly presented focusing for brevity only on the most important facts and experience inclusive of the most meaningful data of short- and lon-term measurement programs.
Due to space reasons neither more case studies nor corresponding details can eb included herein. They can be found e.g. in Kempfert(1996), Kempfert & Raithel (2002), De Mello et al. (2008), Alexiew et al. (2010), Raithel et al. (2012), Schnaid et al. (2014), Alexiew & Raithel (2015). The GEC foundation system has reached the stage of maturity. Projects have been successfully executes worldwide. At least one verified and codified design procedure is available (EBGEO 2011) (may be a bit conservative overestimating sometimes settlements and underestimating global stability) and two approved by practise installation options are established as well. Installation techniques and equipment are quite simple.and accessible for everyone, GEC lengths of up to 29 m have been installedand it seems to be not the limit. A wide range of non-cohesive fills can be used including sand (in fact the most used fill until today); the lattercan be a significant advantage e.g. in lowlands and/or on seashores, where other fills are rare or expensive. A wide range of geotextile seamless encasements from two poymers and with diameters from 0.4 to 1.0 m is available. They are easy to transport made-in-plant engineered controlled elements. Consequently an optimized solution is possible whatever the project circumstances are. In all the projects completed herein many competent colleagues (designers, owners, supervisors, installers etc.) have been active, flexible and enthusiastic. Their succesful efforts are strongly appreciated.