Vibro-Replacement (VR) (Stone Columns)

Vibro-repalcement (VR) also known as stone columns, is well-known soil improvement technique used in soft soils as kind of replacement by good material such as aggregate.

The stone column is constructed using vibro float attached to a crane by
following the process of penetration, replacement by filling, and compaction of aggregate.

Following penetration of the vibrator and its withdrawal after reaching the required depth the resulting cavity is filled with coarse-grained materials (stone).
This supply of material is itself in turn compacted. A stone column is thus formed in which the stone is laterally pressed into the soil. The stone column and the in-situ soil form an integrated system having low compressibility and high shear strength. The excess pore water can readily dissipate through the stone columns that act simultaneously as drains. For this reason, settlement occurs faster than normal in cohesive soils.

Vibro replacement stone columns are constructed with either the dry bottom-
feed process or the wet top-feed process.

In the top-feed process, the vibrator penetrates to the design depth using the vibrator’s weight and vibrations, as well as air jets located in the tip. The stone (crushed stone or recycled concrete) is then added at ground level to the space created around the vibrator. The stone falls through the space to the vibrator tip, and fills the void created as the vibrator is lifted a few hundred millimetres. The vibrator is then lowered, densifying and displacing the underlying stone. This vibro replacement process is repeated in lifts until a dense stone column is constructed to the ground surface.

The bottom-feed process is similar, except that the stone is fed to the vibrator tip through an attached feed pipe. Pre-drilling of dense strata may be required for the vibrator to penetrate to the design depth.