A special built vibrating probe penetrates the loose ground using self-weight of vibrator and extension tubes and water and/or air flush to the required depth. The vibrator is then lifted in predefined steps (normally 0.5 to 1 m) with certain time per step. During this process the vibrator will be generating lateral vibratory forces rearranging the sand particles in a denser state. In saturated cohesionless sands, vibration can generate excess pore water pressure which reduces temporarily effective stresses and shear strength allowing particle rearrangement in a denser state by gravity action. After treatment the soils will show lower void ratio and compressibility and higher angle of shear resistance. The achievable improvement depends on grain shape, soil composition and vibration intensity.
In dry cohesionless sands water is injected to provide the same effect (facilitate soil particles densification). When necessary good quality backfill can also be used to improve densification degree.
This technique has been developed in Germany in 1930s and used successfully worldwide to densify loose sands and hydraulic fill deposits or other man-made fill deposits with controlled materials, increasing bearing capacity and contributing to liquefaction mitigation.
Vibro Compaction is suitable for densifying deep deposits of cohesionless geomaterials with up to 15% fines including clay content less than 2%. For higher fines/clay content other techniques including soil reinforcement need to be considered (Stone columns, Grouting,…).
When possible to apply this is a very cost/effective method.