As against conventional columns foundations, coated columns can be used as ground improvement in very soft soils. The radial support is guaranteed through the composite between the geo-textile coating and the surrounding soil, while the geo-textile is under ring tension forces. Therefore this foundation system will be employed widely to found buildings, especially embankments on very soft or organic soils like peat. Numerical and analytical models for calculation and design of the new foundation system will be reflected.
By the foundation of buildings on soft soils often an improvement of the soft soil with the already known column foundations was carried out for example compacted sand columns or vibro displacement granular piles. In very soft soils like peat this columns normally cannot be used, because the horizontal support in this soils is not sufficient. These columns are coated with a geo-textile of polyster threads, which guarantees the filter effect and the horizontal support. By using this new developed system a safe and flexible foundation on very soft soils with low settlements, especially for dams or traffic roads embankments, can be achieved.
Two constructions methods are developed by the Josef Möbius Baugesellschaft GmbH, Hamburg, Germany, which are called the excavation method and the displacement method. By the excavation method a casing with a diameter between 0,8 m and 1,5 m is vibrated into the ground and after that the soil in the casing is excavated. Opposite to that by the displacement method a steel tube with a much smaller diameter of about 0,6 m to 0,8 m is placed into the subsoil. According to the displacement principle, the two base flaps of the casing are closed and displaces the soft soil to the sides of the casing.