Vibratory Roller

The vibratory roller is a commonly used piece of equipment at construction sites around Newfoundland. It employs a steel drum that vibrates while it is pushed and pulled over the soil. It is especially effective at compacting gravel material.

POINTS TO REMEMBER:

• contains a vibratory unit that vibrates the roller as it is pulled/pushed over the soil
• vibration frequencies range from 1500-1200 cycles per minute
• effective in compacting clean sands and gravels

Sheepsfoot Roller

The sheepsfoot roller is another piece of equipment that is not common in Newfoundland as it is best used on soil types that are not present here. It gets its name from the imprint left on the soil after it has passed over; it looks like a herd of sheep had just walked over it. Working on a site where the soil is being compacted by a sheepsfoot roller makes it difficult to walk around, the indents left behind are about 6" in diameter and about 4" deep. It is like walking around on a large 'Bat the Mole' game.

POINTS TO REMEMBER:

• drum with metal knobs called feet
• feet reduce contact area and therefore increase pressure
• P=F/A
• good for compacting silts and clays

Pneumatic Roller

Pneumatic rollers are not all that common to Newfoundland; the soil types here do not often require this type of equipment. The machine is best used on clay, where the soil here in Newfoundland is rocky and gravel-like. The machine is a self-driven (has an engine) piece of equipment that uses several highly inflated rubber tires as a compaction surface. The weight of the machine is used to provide compaction and extra weight may be added by filling boxes on the ends with sand or rocks.

POINTS TO REMEMBER:

• machine consists of a number of rubber tires, highly inflates
• vary from small rollers to very large and heavy rollers
• may be self-propelled but the larger ones are usually towed
• some have boxes mounted above their wheels so that material may be added to provide more compaction
• used on 'clayey' and silty soils
• effective in compacting granular material containing small amounts of fines

Smooth Wheel Roller

Smooth wheel rollers are one of the most common types of compaction equipment used. We've all seen them in action on a highway during the summer. They are a standalone piece of equipment that have an engine, move very slowly and their weight is used to provide compaction. They are typically used for base layers of soil or for asphalt pavement.

POINTS TO REMEMBER:

• 2-3 smooth metal rollers
• useful in compacting base layers and paving mixtures
• also used to provide a smooth finished grade
• generally are self-propelled, i.e. has an engine
• compaction is provided by the weight of the machine

Tampers

Tampers are small devices used to compact soil. It is likely you've seen one before; they can be rented for a few hours at a time and are often seen where sidewalks and walkways are being built. The tamper uses a plate that is moved up and down a small amount very quickly to compact the soil.

Tampers are typically used in places where large rollers cannot be used. They are versatile machines and can fit into some tight spaces.

When soil is being compacted with a tamper, it is placed in smaller layers that are slightly thinner, 6" before compaction rather than 8" as we previously discussed.

The slides above show a heavy duty tamper that runs on gasoline or compressed air and a light duty tamper (plate tamper) that runs on gasoline.

POINTS TO REMEMBER:

• tampers are devised that compact soil by delivering a succession of light, vertical blows
• they are held in place and operated by hand
• tampers are powered pneumatically (compressed air) or by gasoline engines
• they are limited in scope and compacting ability - good for small jobs and tight spaces
• layers are limited to 6" or 150mm with a tamper

Disk Plow

A disk plow is just what it sounds like - a plow with a series of disks that churn the soil and mix it with water. It is typically an attachment that is towed by a larger piece of equipment.

STUDY QUESTION:

What is the purpose of a disk plow?

Field Compaction

It is difficult to compact all of the soil that is placed on a construction site at once. The thicker the layer, the less effect compaction has on the soil at the bottom of the layer. Soil is typically placed in layers and each layer is compacted. The layers start out at about 8" in depth and once compact it is about 6" in depth.

If the weather is warm and sunny, it is common practice to have a water truck sprinkle the soil with water. The soil is then mixed with the water using a disk plow. A disk plow will be shown and explained further in the next section.

Likewise, if the soil is too wet, a disk plow can be used to expose wet parts of the soil that are under the surface. This helps the soil to dry faster.

After each layer is compacted, it is good practice to 'rough up' the top of the smooth layer so that it bonds to the next layer of soil. Depending on the size of the area to be compacted, tampers and rollers are used.

POINTS TO REMEMBER:

• normally soil is compacted in layers
• usually each layer starts as 8" or 200mm of loose material which is then compacted to 6" or 150mm
• if the soil is too dry, water can be added with a water truck and mixed into the soil by disk plowing
• if the soil is too wet, moisture can be reduced by aeration, i.e. spreading it out, disk plowing to constantly turn out wet soil, and allowing to dry
• the surface of each layer should be 'roughed up' by disk plowing or scraping to provide bonding between the layers
• work is usually done by tampers and rollers
• tampers and rollers usually achieve their maximum compaction withing 6 - 10 complete passes over the compaction area