Vibro compaction densifies clean, cohesionless granular soils with a downhole vibrator. During vibro compaction, clean sand backfill is typically added at the ground surface to compensate for the decrease in soil volume from the densification process. Vibro replacement is the construction of dense aggregate columns (stone columns) with a down-hole vibrator suspended from a crane or specially built rig. This process densifies granular soils and reinforces all soils. The improved soil characteristics depend on the soil type and gradation, spacing of the penetration points, and the time spent performing the compaction. Compaction is achieved above and below the water table.