geotextile encased columns 

Hum? Not sure what a floating column is, but since you are just pretending I guess it doesn't matter. All snarkiness aside, explain what your intent is, ie. a floating column.

@@SteveMillerhuntingforfood by floating columns i mean those that does not reach the bearing stratum (e.g a rock).

@@SteveMillerhuntingforfood in cases of a very thick soft soil layer, say 40meters, using a GEC that goes over 40m may become less cost-effective, so, u might want to think on floating columns.

what do you understand under "floating" columns? Do you mean the columns are not "embedded" within the "stable" soil stratum?

@@hansdete I'd call that a column supported by skin friction versus an end bearing pile.