Vibroflotation is a ground improvement technique used at a considerable depth that by using a powered electrically or hydraulically probe, it strengthens the soil. The vibroflotation will compact the soil making it suitable to support design loads. It involves the introduction of granular soil to form interlocking columns with surrounding soil.
The technique is used to improve bearing capacity and reduce the possibility of differential settlements that might be allowed for the proposed loads. Sometimes it is also referred to as Vibrocompaction and the ultimate concept is to repack soil particles by joining them together improving soil's bearing capacity. The compaction of soil can be obtained in soils as deep as 200 feet. The risk of liquefaction in an earthquake prone area is also drastically reduced.
Vibroflotation can be obtained by using three different techniques:
- Vibro Compaction method- This method allows granular soils to be compacted. This method is only used to compact sandy soils.
- Vibro Replacement method- The technique is used to replace poor or inadequate soil material by flushing out the soil with air or water and replacing it with granular soil. This can be used in various soil types such as clay and sandy soils.
- Vibro Displacement method- This procedure is used with no or small amounts of water used during the technique. The probe is inserted into the soil and it will displace it laterally as the new soil column is being formed and compacted.
Vibroflotation is one affordable way to improve ground conditions when a deep layer of inadequate soil is found. The technique is so simple that will not require the delivery of additional materials or additional equipment other than the probe and the equipment that has it installed. The vibroflotation process can offer the following benefits:
- When the process is done properly, it will reduce the possibility of differential settlements that will improve the foundation condition of the proposed structure.
- It is the fastest and easiest way to improve soil when bottom layers of soil will not provide good load bearing capacity.
- It is a great technology to improve harbor bottoms
- On a cost-related standpoint, it helps improve thousands of cubic meters per day. It is faster than piling.
- It can be done around existing structures without damaging them.
- It does not harm the environment
- It improves the soil strata using its own characteristic
- No excavations are needed, reducing the hazards, contamination of soils and hauling material out from the site
- No need to manage table water issues, neither the permits required to manage water discharge and dewatering issues.
- The technique of vibroflotation can be adapted to each scenario and site
- When vibroflotation is performed at a site, it will reduce the possibility of liquefaction during an earthquake
How Vibroflotation Works
The process of vibroflotation is really simple as you will see in the following short description. The depth probe is located over the compaction point. Flushing water or air is expelled through jets in the tip of the probe. These induced injected vibrations will liquefy the soil temporarily allowing the probe a continuous penetration under its own weight.
Once the probe has reached the strata or poor soil, the water and air injections is stopped. At this point the soil is densified by the probe vibrations causing a crater around the vibrator, that should be backfilled with granular material.
Once the process has been completed, the probe is slowly withdrawn usually in stages of 12 inches. A cylindrical compaction zone is formed around the probe, and the achieved degree of compaction is indicated by an increase in oil pressure. The area around the probe is backfilled with granular material that will auto-consolidate, as the probe is begin brought up. The material used to backfill should be free of silt, gravel or crushed stone.