Versuche zur optimierung des Coplan-stabilisierungs-verfahrens (CSV)

The Combined soil Stabilization with Vertical columns (CSV) is used to increase the bearing capacity of soft soils. For that purpose small diameter displacement columns are installed by forcing a dry mixture of sand and cement into the soil by a continuous flight auger. The installation and the cementation processes as well as the mechanisms controlling the bearing behaviour during monotonic and alternating loading are not well understood. For this reason the improvement of the mechanical properties of the soil is not considered in the design. In order to quantify soil improvement and to better understand the bearing behaviour of CSV-columns large scale laboratory tests were performed. In this paper, the most relevant results of this laboratory investigation are reported. It is shown that the rotation, penetration and pull-out velocities of the auger have a significant influence on the diameter of the columns. During the installation the soil is displaced under undrained conditions. Thereafter it consolidates, pore water flows into the column and causes its cementation. The increase of density and effective stresses associated with this consolidation causes an important increase of the shear resistance of the soil. During stress-controlled cyclic loading the columns showed a stepwise failure for a maximum force which was significantly lower than the static bearing capacity.