EARTH COMPACTING EQUIPMENTS- TYPES OF ROLLERS

Following are the equipments used for the compaction of earth:

1. Smooth Wheel Roller

2. Sheep Foot Roller

3. Pneumatic Roller

4. Tamping Roller

5. Grid Roller

6. Vibratory Roller

1. SMOOTH WHEEL ROLLER:

This types of roller incorporates a large steel drum at the front and one or two wheels or drums at the rear.
If their is one wheel at the rear they are known as Tandem roller, and Three wheeled roller if there are two wheels at the rear.
The weight of tandem roller varies from 2-8 tonnes and three wheeled roller varies from 8-10 tonnes.
The ground pressure exerted by tandem roller is typically around 10-17 kg/cm2.
The weight of roller increased by blasting with sand, water or pig iron.
Smooth wheel roller are most suitable for consolidating stone, gravel, sand, hardcore and ballast but are not suitable for embankments, soft sub-grades or uniform sand.
The Speed and number of passes of a smooth wheel roller depends on the types of soil to be compacted and project requirements.
The optimum working speed has found to be 3-6 km/h and about 8 passes are adequate for compacting 20 cm layer.
The smooth wheel roller leaves the surface smooth after compaction.

Sheep foot roller consist of a steel drum on which round or rectangular protrusions known as lugs or feet are fixed.
There are different types of lugs such as spindle shaped with widened base, prismatic and clubfoot.
Sheep foot roller are used for compacting fine grained soil such as heavy clay and silty clay. They are used for compaction of soils in dam, embankments, sub-grade layers in pavements and rail road construction projects.
Coverage area of sheep foot roller is less about 8-12 % because of the boots on drums.
Contact pressure of this type roller varies from 1200-7000 Kpa.
Area of each protrusions in sheep foot roller varies from 30-80 cm2.
Generally 10-20 passes are required to provide complete coverage on the soil and top layer of consolidated soil finished by smooth wheel roller.
Factors that governs the amount of compaction of soil are-

1- Weight of roller

2- Area of each lugs

3- No. of lugs in contact with the ground

4- No. of lugs per drum

Pneumatic roller consist of a heavily loaded wagon with with several rows of closely spaced tyres. They are also known as rubber tyred roller.
They provide uniform contact pressure through out the width covered and are often used in pavement sub-grade works.
They are suitable for compacting uniform coarse soil and rock. They are also used to finish embankment compacted by sheep foot roller.
The factors which affect the amount of compaction that can be achieved are the weight, tyre inflation pressure and the area of contact.
Coverage area of pneumatic roller is about 80%.
Contact pressure of pneumatic roller ranges from 500-700 Kpa.
The optimum speed of roller is between 6-24 km/h and maximum density can be achieved by 8 passes of the roller.
The gross weight of roller 6-10 tonnes which can be increased to 25 tonnes by ballasting.

The tamping rollers are similar to sheep foot roller.
Tamping roller consist of four wheels and one each wheel kneading boots/feet are fixed.
These roller also consist of leveling blades to spread the material.
Tamping roller has more coverage area about 40-50%.
Contact pressure of tamping roller varies from 1400-8500 Kpa.
Tamping roller is best dedicated for fine grained soils.
Tamping roller have static weight in the range of 15-40 tonnes and their static linear drum loads are between 30-80 kg/cm.
The degree of compaction achieved is more than sheep foot roller and density achieved by tamping roller after compaction is more uniform.

Vibratory roller have fitted with one or two smooth surfaced steel drums measuring 0.9-1.5 in diameter and 1.2-1.8 in width.
The drum vibrates by the rotation of an electric shaft inside.
Vibratory roller are commonly used for compacting granular base course and some times for asphalt.
Tamping roller have higher output and improved performance compared to other rollers.

Grid roller have a cylindrical heavy steel surface comprising a network of steel bars which form a grid with square shaped holes.
They are typically used for the compaction of well graded coarse soil and weathered rocks, often in sub-grades and sub-base road projects.
They are not suitable for clayey soil, silty clay or uniform soil.
The weight of grid roller con be increased by ballasting with concrete blocks.
Typical weight of grid roller vary between 5.5 tonnes net and 15 tonnes ballasted.
This roller provides higher contact pressure but little kneading action.