There are two methods of ground improvement, i.e. by using surface rolling and by using vibro-stabilization methods. While surface rolling method is used for stabilizing or compacting soils on the top layer, vibro-stabilization method is used for compacting deep layers of loose granular materials beyond the range of surface vibrations.
Vibro-stabilization is the method used for ground improvement using a vibrating poker to achieve deep compaction of soil.
Methods of vibro-stabilization for ground improvement:
1. Vibro-Compaction Method:
This method is used for stabilization or compaction of deep layers of non-cohesive soils. When vibration is applied to such soils, they rearrange themselves under gravitational forces and become denser by reducing the void ratio and compressibility of soil. This density of soil thus achieved is permanent. This process can be used in both dry and wet condition of soil.
2. Vibro-Displacement Method:
Vibro-displacement method is used for compacting layers of cohesive soil. The process involves the penetration of the vibrator into partially saturated soils resulting in shear failure of the soil, which then gets displaced forming a cylindrically compacted zone.
3. Vibro-Replacement Method:
Vibro-replacement method is used for compaction of cohesive soils which are more sensitive, saturated silts and alluvial soils which have undrained shear strength of less than 20 kN/m2. This method uses the wet process, in which the disturbed soils are washed away and are replaced by compacted stone columns.
The process involves of penetrating the poker into the soil using water jets to cut an over-sized hole to the required depth of treatment. The vibro-float is kept in the hole while selected backfill of granular material is placed in the hole.