Vibro-Compaction or Vibro-Flotation is a useful method for ground improvements
Vibro-compaction alias vibro-flotation is a method that is useful for enhancing the density of granular soils with the addition of a large vibrating poker to preferred depth. This vibrating poker is also called as depth vibrator or a vibroflot or just flot. It is considered as the most recognized method that employ vibrator to improve the quality of the ground. Water flushing is performed all through the inclusion process.
Vibroflotation will be most effective for very loose sands immersed under water table. Effectiveness of densification is decreased with escalation in silt and clay content. The penetration rate is decreased if condensed sands immersed with deep water tables.
Principle: The vibroflot passes on horizontal vibrations into the ground for decomposition of the frictional contacts and operative stress among soil structures. Therefore, ground turns into a solider structure as illustrated in the following image.
Soil structure is decomposed under dynamic stresses of around 0.5 g. When acceleration becomes higher to about 1-1.5g the shear strength is reduced and ground turns into fluidised. The dilation of the soil occurs, if acceleration gets increased to 3 g.
Accelerations provided by the vibrator, reduces if the distance is raised. The level of compaction is reduced adjacent to the compaction point. To make compaction better, the ground should drain without obstruction. The lowest suggested permeability is 10-5m/s. If silt content in ground is increased, the shear stresses can’t be transmitted efficiently rather they are damped influencing the effectiveness of compaction. Likewise, greater fines decrease degree of improvement attained.
Vibro flotation Compaction points are generally arranged at gapping of 1.8 to 3.0m on square or triangular grids.
Vibrating Poker Description - The vibrating poker or vibroflot includes the following
• Vibrating unit;
• Follower sections;
• Lifting head;
An eccentric weight attached at bottom of shaft associated with hydraulic or electric motor is the origin of the vibration.
Power developed: 35 kW to 100 kW, even 160 kW for some machines;
Vibration frequencies: 30 Hz or 50 Hz;
Amplitudes of 5-10 mm, up to 23 mm;
Penetration of flot throughout preliminary boring is dependent on compressed air or water jets. Compaction of the ground is accomplished in vertical steps of around 0.3 m giving adequate time at each phase to maximize degree of compaction.