The Difference Between a Smooth Drum Roller and a Padfoot Roller

30/08/19

Compaction rollers also known as vibratory compactors are used to rearrange soil particles to increase density and decrease void, providing the soil with load-bearing strength. When filling an area to be rolled, the layers of soil beneath the working area are called lifts. The ability of the first few lifts to be compacted depends on the composition of the materials within the soil. If these are not compacted adequately, settlement cracks will occur in the fill and the surface above, or any structure that is supported by the surface. 

You may have seen a roller in action when a road is being resurfaced. You may recall the wheel at the front (the drum) crushes and flattens the surface. Depending on the job that is to be undertaken, along with how big the project is and the type of soil that is being compacted, the type of roller will vary. The two most common rollers are the smooth roller and the padfoot roller.

What is a smooth roller?

The smooth roller is used most frequently on road construction, to create smooth and flat surfaces. They are one of the most common types of road rollers as they combine impact, along with static pressure and vibration to compress and compact gravel, asphalt, rocks and sand. When the composition of the soil consists of materials in a granular form, the smooth roller is best suited to lock these pieces together. Keep in mind that if the soil consists of large rocks, the thickness of the lift should be twelve inches more than the biggest rock size.

There are two types of smooth rollers. The single-drum roller is also known as a steamroller and has one steel drum at the front and tires at the back moving the roller. The double-drum roller has two steel drums, one located at the front, and the other at the back, meaning the roller moves due to the twin drums rather than tires like a single-drum.

What is a padfoot roller?

Padfoot rollers are also called tamping foot rollers as they have tapered pads that compact and penetrate the soil to build up its strength. The padfoot roller creates the same pressure, vibration and impact as a smooth roller, however they also create manipulative force which allows for uniform compaction during the entire process. When the pad penetrates the surface of the lift it breaks the bonds between the particles, making it more effective in compaction. There are two different types of pad shapes for a padfoot roller. A square pad is effective for smoothing the surface and compacting semi-cohesive soils with lifts of less than six inches. An oval pad is effective for cohesive soils with a thicker lift compared to the square pad (between six to eighteen inches). Whilst this pad is smaller and does not seal the surface as well as the square pad, it does apply more pressure. This roller is best suited when the soil needs to be compacted at a greater depth, and has a composition of clay, loam and/or silt.