Padfoot vs Smooth Rollers: Choosing the Right Compaction Equipment for Your Project
As the main component of a roller, drum design will have a huge impact on the quality of your soil and aggregate compaction. Considering soil type, compaction capabilities, and the job site will all inform the choice between smooth and padfoot rollers.
Understanding the Functions and Applications of Padfoot and Smooth Rollers
Single-drum rollers, also known as soil compactors or vibratory rollers, are a type of heavy equipment that compacts soil, asphalt, and other aggregates. A roller's structure is made up of a seat, back wheels, and a metal drum. They can be an open cab or a little cabin. The metal drum flattens the ground beneath it as it repeatedly passes over the area, like passing a rolling pin over some dough.
Compacting is important because it increases the load-bearing capacity of the ground, making the amount of weight the ground can safely support higher. This is especially important when building structures and foundations.
There are two main types of soil compactors: smooth rollers and padfoot rollers, which are identified by the design of their drum. Smooth rollers have flat, smooth drums while padfoot rollers have drums studded with metal knobs. Padfoot rollers can also be commonly referred to as sheepsfoot rollers. Although these terms are used interchangeably, sheepsfoot rollers differ slightly from padfoot rollers in knob size and soil compaction.
Both smooth and padfoot rollers are commonly used to prepare a job site before construction starts. They ensure that previously excavated and surrounding soil has the adequate load-bearing capacity and that the surface is primed and smooth.
Typical applications of rollers include compacting the bases of driveways, sidewalks, parking lots, trails, and roads. They're also found on industrial construction sites, compacting soil before foundation construction, and compacting trenches.
Key Differences Between Padfoot and Smooth Rollers
Roller Design and Compaction Mechanism
Roller design is the most noticeable difference between smooth and padfoot rollers. Smooth rollers have flat, smooth-surfaced drums that resemble smooth metal. Padfoot rollers have studded drums with multiple metal knobs attached to the surface. As a padfoot drum rolls, additional force is centralized beneath each knob, which enables better compaction.
Both smooth and padfoot rollers have similar compaction mechanisms. Depending on the model, rollers compact soil and other aggregates with static or vibratory compaction. The static compaction mechanism uses the machine's own weight to compact material as the drum flattens it with multiple passes. This reduces the air content and space between particulates.
In comparison, vibratory compaction mechanisms provide greater compaction because the drum vibrates as it rolls. This exerts more pressure on the ground below and can reduce the number of passes needed.
Static and vibrating soil compactor models can be outfitted with either a smooth or padfoot drum, so the compaction mechanisms on both roller types are very similar but the operating weight will change.
Soil Type and Compaction Requirements
Each roller design is best suited to compacting certain soil types. Smooth rollers are better at compacting grainy materials like sand, gravel, limestone, and asphalt. These materials are non-cohesive, meaning their particulates don't stick to each other and form clumps.
Padfoot rollers work best when compacting semi-cohesive soils whose particles stick together, such as clay, silt, and mud. This is why padfoot rollers are great at compacting soil on job sites with high water tables that are located near dams and other bodies of water.
You shouldn't try to use one type of roller to compact the opposite soil type it was designed for. The knobs of metal on a padfoot roller will churn granular soils as opposed to flattening them whereas smooth drums aren't able to provide enough force to flatten semi-cohesive materials. The soil will simply stick to the drum's surface and unevenly compact the earth.
Operating Weight and Pressure Distribution
The operating weights for soil compactors vary between models and manufacturers. Smooth and padfoot rollers have similar operating weights, but there will be slight variations between models.
Smooth drum soil compactors distribute pressure evenly as they roll. This allows them to compact larger areas more efficiently than padfoot rollers can. They also make the compaction surface more flat and level, since they don't have knobs that dig into the ground.
Even though smooth rollers distribute force evenly, padfoot rollers have more compaction strength. Pressure is distributed at the base of each metal stud on the drum. This helps concentrate more force onto smaller areas.
In addition to static compaction, padfoot drums knead sticky soils like you would knead some dough. This process, which smooth rollers can't perform, compacts the soil further. This allows them to compact more quickly compared to a smooth roller.
Maneuverability
Both roller types have similar degrees of maneuverability. Padfoot rollers are often used to compact the bottom of trenches since they easily move around and within tight, deep areas, and because deeper soil is usually a bit damper.
Smooth rollers tend to have slightly narrower bodies than padfoot rollers. This allows them to fit through restricted areas and compact material along paths and other narrow areas. Safely maneuvering rollers in all environments is incredibly important, as risk increases in narrower, rough terrain environments.
Operating Costs and Maintenance
The mechanics behind soil compactors are relatively simple compared to other machines, as the main functions performed by the machine are driving and rolling. Smooth and padfoot rollers will require preventative maintenance and routine inspections. This includes checking to see that the drum's bearings are lubricated, cleaning the drum and checking its scrapers, checking engine fluid levels, and other tasks.
Overall, operating and maintenance costs are constant between the two roller types, since the only major change between each machine is the drum itself.
Benefits of Using a Padfoot Roller
Effective Compaction of Cohesive Soils: The knobs on a padfoot roller knead cohesive soil, which further compacts and prevents the soil from sticking to the drum.
Larger Surface Area for Improved Compaction: The ends of each knob create an additional surface area on a padfoot drum. Pressure is concentrated at each of those points, which improves overall compaction.
Better Traction on Slopes and Uneven Terrain: Cohesive soils clump together, which creates a non-level compaction surface. So, padfoot rollers have decent gradeability and traction in order to operate on uneven terrain.
Versatility with Vibratory Options: The kneading motion caused by studded drums enhances the static and vibratory compaction mechanisms found on rollers.
Enhanced Compaction Speed: Padfoot rollers can compact areas faster than smooth rollers can.
Benefits of Using a Smooth Roller
Effective Compaction of Non-Cohesive Soils: Smooth drum rollers compact non-cohesive soils by flattening particulates and eliminating air pockets between materials and aggregates.
Efficiently Compact Large, Shallow Areas: Smooth drums distribute force evenly across their drums, allowing them to flatten larger, shallow areas more effectively than padfoot rollers.
Narrow Machine Widths: Padfoot rollers are often slightly wider machines than smooth rollers. Smooth rollers are able to fit through restricted spaces better than a padfoot roller can.
Creates Smooth, Even Passes: Smooth drums create a level, polished compaction surface. Padfoot roller knobs dig into the surface, so the soil is compacted but not perfectly flattened.
Benefits of Using a Sheepsfoot Roller
Padfoot vs Sheepsfoot Rollers
Even though padfoot and sheepsfoot rollers are seen as synonymous, there are slight differences between the two. The knobs on a sheepsfoot roller are cylinders that can be up to 8 inches long. Because of their length, sheepsfoot knobs can till the top layer of soil whilst compacting the layer directly below it.
In contrast, padfoot knobs are shorter and can be rectangular, oval, or hexagonal shaped. They still knead the soil in the same way sheepsfoot rollers do, but they don't lift topsoil in the same way. Generally, padfoot rollers are better at compacting wet, cohesive soils, while sheepsfoot rollers compact semi-cohesive soils with finer grains. Then, smooth rollers are designed to compact coarse-grain materials.
These are the main benefits of using a sheepsfoot roller:
- Effective compaction of finer, semi-cohesive soils
- Exerts the most pressure at the end of each knob
- Knobs penetrate deeply into the soil
Factors to Consider When Choosing Between a Padfoot and Smooth Roller
It's important to evaluate the following factors when choosing between a padfoot and a smooth roller.
- Required specs for your project (drum width, horsepower, max. operating weight)
- Soil type, or other material that requires compaction
- Desired results post-compaction
- Job site conditions and accessibility considerations
- Budget constraints
Renting vs Buying: Making the Best Choice for Your Compaction Needs
Several factors affect the choice between renting and buying soil compactors. Renting is more cost-friendly, especially when you aren't using the equipment for an extended period that would justify a purchase.
When renting compaction equipment, there are generally more options to consider compared to buying. Among multiple rental opportunities, there's a greater variety of equipment models, new technologies, and rates. Overall, renting compaction equipment is a sound decision for short-term projects, constrained budgets, and when you want to shop around between offers.
Finding the Most Competitive Rental Offers With DOZR
DOZR is a rental equipment marketplace that facilitates rentals for 18 types of heavy equipment. Our online marketplace provides multiple rental opportunities for contractors to evaluate. For each rental opportunity, you can compare the rates and real-time availability offered by different suppliers.
Choosing Your Soil Compactor
It's best to use each type of roller in its recommended soil type. Use smooth rollers on coarse materials like sand and asphalt, use sheepsfoot rollers on fine, semi-cohesive soils like silt, and use padfoot rollers on wet, cohesive soils like clay. If you base your decision on soil type and desired compaction results, you'll be sure to choose the best soil compactor for your project!
For your next compaction project, check out DOZR's equipment marketplace for padfoot, sheepsfoot, and smooth roller rentals!
