Granular or weakly cohesive sediments such as gravel and sand often have very uneven layer densities in their natural state. With vibro-compaction densification (VCD) this can be increased to around 80 %. In the process, the soil is "floated" by a water or air flush, the vibrator sinks and a settlement depression is formed at ground level. This is filled with added material. By extracting the vibrator in stages, a compacted zone 2 to 4 m in diameter is created.