Types of rollers and their functionalities
Rollers are mainly utilized for the compaction of soil, gravel, sand, crushed stone layers, etc. The functionality of roller is primarily dependent on vibration, impact loading, kneading as well as direct pressure on the relevant layer. The following types of rollers are mostly recognized:
1. Vibratory Roller 2. Tamping roller/ sheep foot rolle 3. Smooth wheel rollers 4. Pneumatic tired roller
VIBRATORY ROLLER: Vibratory type rollers comprise of two smooth wheels/ drums along with the vibrators. One is set at the front and the other one is on the back side of vibratory roller. Both wheels/drums have equivalent diameter, length and weight. Vibratory roller covers the entire area under wheel.
To improve the functionality of vibratory roller, vibrators are also set with smooth wheel rollers. Vibration of vibrators places the particles by initially distressing even the arranged ones. Conversely, the weight of wheels employs direct pressure on the layer. Vibrators are deactivated throughout the reversed motion of roller meanwhile only static weight directly operates on the soil layer.
Vibration facilitates decreasing the air voids as well as inducing condensation of granular soils. In the vibration process of soil layer, the particles are reorganized for deformation of the granular soil caused by oscillation of the roller in a cycle.
SHEEP FOOT ROLLER/ TAMPING ROLLER: Sheep foot roller also known as tamping roller. Front steel drum of sheep foot roller contains several rectangular shaped boots having same size which are settled in a hexagonal pattern.
Coverage area of sheep foot roller remains less i.e., about 8- 12% due to the boots on drums. Sheep foot roller executes compaction with static weight and kneading of relevant layer. It prepares tamping roller suitable for clay soils. Contact pressure of sheep foot roller differs from 1200- 7000Kpa.
Tamping foot roller comprises of four wheels and on each wheel kneading boots/feet are settled. There are more coverage area for tamping roller i.e., about 40- 50%. Contact pressure of tamping roller differs from 1400 – 8500KPa. It is ideal for fine grained soils.
SMOOTH WHEEL ROLLER: Both smooth wheel roller and vibratory rollers are similar. Both contain similar properties. The variation lies with vibratory equipment. Smooth wheel roller does not include any vibrator secured with the drum. In this way, smooth wheel roller becomes perfect for rolling of weaker aggregates, proof rolling of subgrades and in compacting asphalt pavements. Compaction of clay or sand is not recommended for smooth wheel roller sine there are several empty voids in clay soil and sand, which cannot be reduced without vibrators.
PNEUMATIC TIRED ROLLER: Pneumatic tired roller contains a number of rubber tires at the front and at the rear end. Empty spaces exist among the two tires which produce 80% coverage area under the wheels. Pneumatic roller is capable of employing contact pressure ranges from 500 – 700Kpa. Pneumatic tired roller is effective for highways, construction of dams and for both fine grained and non-cohesive soils. It can also be applied for flattening of finishing bitumen layer on highways, roads, streets etc.