METHODS OF FIELD COMPACTION
The various methods of field compaction are
1) Rolling :
Different types of rollers are used for compaction of soils.
The compaction depends upon the following factors :
- Contact pressure
- Number of passes (normally 5 to 15)
- Layer thickness (less than 15 cm)
- Speed of roller
Different types of rollers used are,
i) Smooth wheel rollers
ii) Pneumatic tyred rollers
iii) Sheep foot rollers
iv) Track laying vehicles
2) Ramming :
A hand operated rammer (tamper) consists of a block of iron, about 3 to 5 kg in mass, attached to a wooden rod.
The rammer is lifted for about 0.30 m and dropped on the soil to be compacted.
A mechanical rammer is operated by compressed air or gasoline power. It is much heavier, about 30 to 150 kg.
Mechanical rammers have been used up to a mass of 1000 kg in some special cases.
Tampers are used to compact soils adjacent to existing structures or confined areas such as trenches, within plinth of building etc.
3) Vibrations :
In vibratory compactors, vibrations are induced in the soil during compaction.
The compactors are available in a variety of forms.
When the vibrator is mounted on a drum, it is called a vibratory roller.
These rollers are available both as pneumatic type and the smooth wheel type.
In a smooth wheel type, a separate motor drives an arrangement of eccentric weights to create high frequency, low-amplitude, up and down oscillations of the drum.
These rollers are suitable for compacting granular soils.
In a pneumatic tyred vibratory compactor, a separate vibrating unit is attached to the wheel axle.
Another form of vibratory compactor is a vibrating plate compactor.
Hand operated vibrating plates are also available.
The effect of the vibrating plates is limited to small depths.
Their main use is to compact granular base courses for highway and runways, where thickness of layers is small.