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Soil Compaction in Action
Best Practices

Sean O'Halloran, The Toro Company


One of the last steps in a paver installation is running a plate compactor over the stones. According to hardscape materials manufacturer Pavestone, this process settles them into the base sand evenly, dropping them approximately 1/4", and vibrates joint sand into the entire joint, locking the stones into place. To ensure a solid foundation with which to build on, one of the first steps should be compacting the soil.

It's no secret that landscape contractors face a myriad of unique tasks on a weekly basis. Those involved in hardscaping and installation face several more. One key process that is extremely important when it comes to hardscaping and outdoor construction is soil compaction. This process helps set the foundation for anything that is being built above it and requires keen attention to detail to ensure a successful installation.


Compaction increases the density of a dirt bed, making it a more stable base. Soil type - whether cohesive (clay) or granular (sand, gravel and silt) - and soil moisture should be identified to help determine what piece of equipment to use.


For granular soils, plate compacters work best because their actions, reaching 6,000 vibrations per minute, causing soil particles to fall into a stable position beneath the surface, eliminating air pockets.

Simply put, compaction increases the density of the dirt bed and provides a more stable base on which to build. Savvy landscape contractors should identify both soil type and moisture levels before determining what piece of equipment to use. Cohesive (clay) and granular (sand, gravel and silt) are both typical types of soil that a landscape contractor would come into contact with during the compaction process. In terms of moisture, too much can compromise the integrity of the foundation, and too little moisture can result in poor compaction results. These factors are important in determining whether to use a plate compactor or rammer for compaction purposes. Both offer unique advantages, and are crucial to achieving a solid foundation upon which to work.


In clay soil, rammers are recommended over plate compactors because their amplitude, the maximum movement of a vibrating body from its axis in one direction, is higher. Rammers have lower vibration frequency but can generally cover more ground in a shorter amount of time.

For any soil classified cohesive, rammers are a preferable equipment solution. Generally speaking, if the soil composition is more than 30 percent clay, it's considered cohesive. Amplitude, which is the maximum movement of a vibrating body from its axis in one direction, is important to consider when determining which compaction equipment will best fit the application. Rammers have higher amplitude than their plate compactor counterparts, which is one of the primary reasons why they do so well in cohesive soil. The repeated impact force essentially forces air and water up and out of the soil beneath. Rammers have lower vibration frequency when compared to plate compactors, but can generally cover more ground in a shorter amount of time. In this category, there are varying ranges of blows per minute, but Toro rammers can provide anywhere from 650-750 blows per minute, and can exert forces of up to 3,500 pounds. Rammers are easily handled by one worker, and can be transported with relative ease. Additionally, a rammer may be able to fit in tight areas a plate compactor or trench roller would be unable to reach.


This is a forward/reverse model but plate compactors are available in forward-only models too. According to Sean O'Halloran of The Toro Company, changing direction and concentrating compaction in one area is simple with most forward/reverse plate compactors. Slower when compared to rammers, the added weight and larger surface areas of both types of plate compactors can produce results that are smoother overall.

Plate compactors are available in forward-only and forward/reverse models, and can reach levels of 6,000 vibrations per minute. They're typically larger than rammers, but the increased weight of the machine and larger surface area can contribute to a smoother overall compaction. These machines are ideal for granular soils, as the vibratory nature of the machine encourages particles to fall into a stable position beneath the soil's surface, eliminating air pockets. Changing direction and even concentrating compaction in one area is simple with most forward/reversible plate compactors models. What plate compactors lack in ground speed, they make up for with vibration frequency levels.


Providing hundreds of blows per minute and exerting thousands of pounds of force, rammers can be transported easily and they are able to fit in tighter areas than a plate compactor or trench roller.

For landscape contractors, it's vital to first understand the terrain, soil composition and moisture levels before selecting a piece of equipment. Regardless of equipment selection, the operator should make sure to wear approved personal protective equipment (PPE), and take frequent breaks to avoid operator fatigue. Compaction is a key part of the installation process, and with the right equipment, a savvy contractor can make quick work of even the largest installation projects. Sean O'Halloran is the marketing manager at The Toro Company, based in Bloomington, Minnesota.

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September 24, 2018, 8:57 pm PDT

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