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The application of Geotextile Encased Columns (GEC) beneath water in a highly seismic area for the construction of an up to 22 m high embankment

A geotechnical construction project in the central Turkish region of Kirsehir is described. It comprises the construction of a highway link incorporating the re-establishment of a connection between two towns interrupted due to the reservoir of the Hirfanli dam. For this purpose an embankment of 430 m length was constructed across an existing reservoir. This embankment had to be formed over deep, soft deposits of clay, silts and sand lenses and is supported on a Geotextile Encased Columns (GECs). The unique aspect of the project is that this is the first time anywhere in the world that GEC construction has been carried out from and installed below water.
The construction of this section of highway has been a historically challenging one due to the difficulty in crossing the section of open water as well as the potential earthquake hazard. Previous designs had proposed either a bridge structure on pile foundations or an end tipped rock fill embankment. The design of pile foundations was not possible because the extremely soft alluvial deposit could not provide the necessary lateral stability. As a result both proposals were found to be either too expensive or technically inadequate for the constraints of the site.
The project environment, construction problems and typical solutions are described, as well as design and calculation philosophy and methods, with typical cross-sections and photographs illustrating the specific points. In respect to the hazard of earthquake loading, the behavior of GEC’s under seismic loading will be discussed and research results presented.