Execution of stone columns by the vibro-replacement technique

2 Execution of stone columns by the vibro-replacement technique 

To construct stone columns, a vibro-flot (see Section 7.5.3.3) is allowed to penetrate to the design depth and the resulting cavity is during retrieval of the probe filled with gravel or crushed rock, free of clay and silt. Several techniques have been developed to install stone columns in soils with different groundwater levels, ranging from completely saturated (wet, top-feed process) to dry (bottom-feed process). 

The dry, bottom-feed method uses a vibro-probe with a separate tremie pipe along the probe feeding the gravel to the tip of the vibrator. The probe penetrates to the required depth by vibration and air jets. Once at depth, gravel is fed into the ground through the tremie pipe and eompacted by the probe. This process is repeated while the probe is withdrawn. 

Various methods exist to eonstruct stone eolumns over water. Traditionally a blanket of gravel with a thiekness typically varying between 2 to 3 m is placed on the seabed. The vibro-probe penetrates the layer to its final depth. As with the top feed method, the hole is supported by water jets and gravel drops in the annular space between the existing ground and the probe to the bottom of the hole. The gravel is compacted by the probe. 

Nowadays systems exist that resemble the dry-feed method, feeding the gravel from a (single-batch) hopper or by a pump or compressor through a tremie pipe to the bottom of the hole. 

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