TYPES OF ROLLERS AND THEIR USES
Different types of rollers used are :
a) Smooth Wheel Rollers :
These rollers can operate to and fro without turning.
These rollers are useful for compacting granular base courses of highways and runways.
They are used for finishing operations after compaction of fills.
These are not effective for compaction of deep layers of soils.
Types of Smooth Wheel Rollers :
i) Conventional three wheel type (weight 2 to 15 cm)
ii) Tendem Rollers (weight 1 to 14 ton)
iii) Three axle tendem roller (weight 12 to 18 ton)
b) Pneumatic Tyred Rollers :
Pneumatic tyred rollers use compressed air to develop the required inflation pressure.
The roller generally consists of 9 to 11 wheels fixed on two axles, with the pneumatic tyres so spaced that a complete coverage is obtained with each pass of the roller.
The gross mass of the varies from 5 to 200 ton.
The roller compacts the soil primarily by kneading action.
These rollers are effective for compacting cohesive as well as cohesionless soils.
Light rollers (up to 20 ton) are effective for compacting soil layers of small thickness up to 15 cm, where as heavy rollers are useful for layers of thickness up to 30 cm.
c) Sheep Foot Rollers :
The sheep foot roller consists of a hollow drum with a large number of small projections (known as sheep feet) on its surface.
These projections penetrate the soil layers during the rolling operations and cause compaction.
The drum can be filled with water or ballast to increase the mass.
The loaded weight per drum ranges from 1.5 to 10 ton, and the foot pressure range from 8 to 35 kg/cm².
The sheep-foot rollers are ideally suited for compaction of cohesive soils.
The rollers compact the soil by the combination of tamping and kneading action.
d) Vibratory Rollers :
These rollers are available both as pneumatic type and smooth wheel type.
In a smooth wheel type, as separate motor drives an arrangment of eccentric weight 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 vibratory unit is attached to the wheel axle.