Filling with extraneous material with subsequent stuffing creates a load-bearing gravel column with a greater strength than the untreated ground.

The so-called bottom feed vibrator which penetrates a fine grained, non-compactable soil is fitted with a device for addition of material.

Vibration is carried out under addition of compressed air emerging at the vibrator tip and supporting the vacated space.

After the final depth has been reached the vibrator is systematically hoisted. Gravel or crushed stone are filled in through the material feeder and emerge at the vibrator tip under addition of compressed air.

Repeated lowering of the vibrator compacts the added material. Moreover, it is densely pressed and/or stuffed into the adjacent soil.

Alternating hoisting and lowering of the vibrator combined with batch filling with material produces a so-called vibro-replacement column.

Smaller groups of columns result in a selected soil improvement. An area-wide improvement with extensive column grids is applied, for example, under dams or foundation plates.