Why is it used?
This technique is used to improve the engineering characteristics of loose granular soils or soft cohesive soils and is installed in a grid pattern in order to achieve a global improvement of the soil.
How does it work?
The columns are formed by the introduction of a vibrating poker into the ground; this poker is used to create the void in the ground into which stone backfill is introduced. The construction of the columns is achieved by the gradual introduction of the stone, progressing from the base of the column to the ground surface with the vibrating poker being used to compact the stone as the column is formed.
Effect on loose granular soils vs cohesive soils:
In the loose granular soils the vibrations induce densification of the soil surrounding the poker, as well as displacing the soil laterally, to allow the placement of the stone backfill for the column formation. In soft cohesive soils the effect of the vibrations is negligible in terms of modifying the surrounding soil and is limited to achieving the lateral displacement of the soil, however, the action of the column formation, forcing the engineering characteristics.