This ground improvement method has been developed in the 1950s as method that allows to improve cohesive and high silt content soils that could not be treated only by dynamic methods, now using soil reinforcement with aggregates.
A special built vibrating probe penetrates the loose ground using self-weight of vibrator and extension tubes and water and flush to the required depth. The water stabilizes the hole and flushes out the fines and loose soil. After the hole is flushed, coarse fill material (normally gravel with grain diameter of 30 to 80 mm) is introduced through the annular space surrounding the vibrator. The material drops down to the vibrator tip and is compacted to form the stone column by lifting the vibrator in stages. The gravel quantity is controlled as well as the depth of execution and energy consumption allowing a continuous control and record of the execution parameters.
This method allows the execution of stone columns to depths of 26 m.
The soil improvement with stone columns will allow an increase in the soil stiffness increasing soil bearing capacity and reducing settlements, and reducing consolidation time (when applicable). Due to the reinforcement and drainage effect combined it has also been used as a liquefaction mitigation technique. This method can be designed considering regular grids of stone columns to improve large areas with distributed loads under rafts, pavements, embankments, or can also be designed to improve soils localized under the footings only.
For the right loading and geology conditions can be a very cost/effective method when compared with indirect foundations.