Principle of Vibro Compaction
The method of soil improvement whereby granular soils are compacted using depth vibrators is known as Vibro Compaction or Vibroflotation. Naturally deposited soils as well as artificially reclaimed sands can be compacted to great depths. The current depth record lies at 70 meters for reclaimed sands and at 53 meters for naturally deposited sands. The intensity of compaction can be varied in order to achieve the desired effect depending on the foundation or ground improvement purpose.
Compaction effects
- The sand and gravel particles rearrange into a denser state
- A significant increase in the horizontal to vertical effective stress ratio
- The permeability of the soil is significantly reduced
- Increased friction angle
- Settlements of the compacted soilmass (between 2% and 15%)
- Increased stiffness modulus
Compaction process
The compaction process consists of a flotation of the soil particles as a result of vibration, which then allows for a rearrangement of the particles into a denser state
Left: Uncompacted
Middle: In flotation
Right: Compacted
Improvement effects
- Increased bearing capacity
- Settlement reduction under loads
- Near–elimination of differential settlements for large foundations
- Liquefaction mitigation
- Prevention of lateral spreading
- Prevention of settlements, due to rearrangement of particles from impacts
- Prevention of (inundation) settlements
- K-value reduction (permeability of soils)
Application of the technology in an optimal manner is an art!
The challenge of optimization lies in the multiple parameters that can be varied and the narrow band in which those parameters need to be adjusted to deliver the desired results. Some of the parameters that can be varied include:
- Type of vibroflot used
- Distance between compaction points
- Hold time per depth interval
- Water pressure
- Location and type of water jets required
Penetration
By vibration and the flushing of water and/or air, the vibroflot penetrates to the desired depth.
Compaction
The vibroflot is recovered from a certain vertical distance after a verified holding time or buildup of resistance from the compacted ground.
Completion
Immediate top layers may be leveled or impact compacted or roller compacted to ensure a ready-to-build surface.
Movie of Vibro Compaction at Port of Calais, France
The following movie shows a Tandem Vibro Compaction setup during compaction works at the Port of Calais in 2017.
This movie was taken during the initial compaction trials, in which compaction grid, holding time and use of water and air are optimized by our experts.
A word on taking movies of vibroflots:
The vibroflots in this movie operate at 1800 RPM (30 Hz) while the movie is shot at 25 frames per second (= 25 Hz). The small difference between the movie frequency and the vibroflot frequency has the effect of slow motion
and hence makes the motion of the vibroflots better visible in the movie than with bare eyes on site. The differential movement of the upper, middle and lower parts of the vibroflot tube are an artifact of the scanning
made by the video recorder that sequentially scans from top to bottom. This leads to the appearance as if the very stiff steel tubes would be out of rubber.
If the movie had been shot at 30 frames per second, which is the default on mobile phones, the vibroflots in the movie would have made the appearance of standing still.
References for Vibro Compaction
The following globally recognized projects, as well as many similar medium size projects were performed by the members of Betterground in either joint ventures or equipment supply and service arrangements.
Dubai: Palm Jumeirah, Palm Jebel Ali, Dubai Maritime City, Palm Deira, World Dubai Heart of Europe and Iceland (2004 and 2010), Pearl Jumeirah Island (2012), SARB Island (2013), Container Terminal 4 (2016),
Mina Rashid Marina (2018).
Germany: Lausitz (eng. “Lusatia”) coal mine restoration slope stability projects (1994 to 2006)
Hong Kong: Chek Lap Kok Airport (1995), Central Reclamation (1994 and 2006), West Kowloon Reclamation (1991-1992),
Penny’s Bay (2001-2003)
Singapore: Pasir Panjang Container Terminal (1998 – 2000)
World Island Dubai: Vibro Compaction on first showcase island. The completed island is seen on the right.
Dredged sand keys of land reclamations are compacted from barges before the filling of embankments and land based compaction of the final fill volume.