1. Light Compaction Equipment
Technology
Welcome remarks TBD.

2. 4 processes producing compaction
Impacting
Compaction is the result of material compression under relatively low frequency impacts with significant amplitude.
Static (pressure) compaction
Static rollers compact the material by their dead weight alone. These machines tend to « surface compact » only. They achieve higher density near the surface.
Vibratory compaction
The vibrations create motion of the particles in depth. They rearrange and the compaction occurs from bottom to top.
Kneading
The material undergoes a shearing force that creates particles motion toward interlocking.
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3. 4 types of soil vs 4 compaction processes
Rammer
Vibr. Sheepfoot
Static Sheepfoot
Grid Roller
Scraper
Vibrating Plate
Vibrating Roller
Rubber-tired roll.
Loader
Grid roller
Soils
Lift Thickness
Impact
Pressure (with kneading)
Vibration
Kneading (with pressure)
Gravel
>=30cm
Poor No
Good
Very Good
Sand
~25cm
Excellent
Silt
~15cm
Clay
Very good
Compaction equipment usually consists in a combination of these 4 compaction processes.
In practice, the most important process is probably the compaction through vibrations. But it is still not the most obvious to understand.
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4. Families of equipment Family Compaction process Application Frequency
Impact force concentr.
Rammers
Impact + Kneading
Cohesive soils
700 BPM
High
Forward plates
Vibration
Granular soils – Asphalt
BPM
Low
Reversible plates
Vibration + Impact
Gravels – Semi cohesive soils
3000 – 4000 BPM
Medium
Double-drum rollers
Static weight + Vibration
Asphalt – Granular soils
BPM
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5. 1 Rammers
Technology Rammers get compaction force from a small gasoline engine powering a large piston set with two sets of springs. Frequency range is 500 to 750 blows per minute. The rammer is inclined at a forward angle to allow forward travel as the machine jumps.
Application Rammers deliver a high impact force (high amplitude) on a small shoe surface. It makes them an excellent choice for cohesive and semi-cohesive soils. They are perfect for backfilling and narrow trench compaction applications. Rammers cover three types of compaction: impact, vibration and kneading.
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6. 1 Rammers The 4 stroke engine runs the big green gear at 700 rpm.
The blue crank drives the orange piston up and down.
The piston is activating the rammer foot through a set of springs. Hard spring for hammering down, softer spring for bringing it up.
The bottom part is dipping in oil.
The purple bellows protects the mechanics against dirt.
The forward motion is created by the angle between the ground and the oscillating movements.
Rammers are characterized by their impact force and shoe width.
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7. 2 Vibratory Plates
Technology Gasoline engines drive one eccentric weight at a high speed to develop compaction force. Frequency range is usually 2500 to 6000 vpm. The resulting vibrations cause forward motion. The engine and handle are vibration-isolated from the vibrating plate.
Application Vibratory plates are low amplitude and high frequency, designed to compact granular soils and asphalt. The heavier the plate, the more compaction force it generates. Plates used for asphalt have a water tank and sprinkler system to prevent asphalt from sticking to the bottom of the base plate. Vibration is the one principal compaction effect.
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8. 2 Vibratory plates
A 4 stroke engine drives an eccentric shaft through a belt transmission equipped with a centrifugal clutch.
The shaft is strongly connected to the base plate with bearings in such a way that the centrifugal force will result into vibrating the plate.
The engine is isolated from the plate thanks to silent blocks.
The vibrations naturally result into a forward motion by small jumps.
A plate compactor is characterized by its
Impact force
Contact surface, plate width
Weight [kg]
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9. Impact force [kN]
Eccentric shaft design & frequency The impact force of a compaction unit depends on the design of the eccentric weight (mass m and eccentricity R) and on the rotation speed (frequency).
High frequency – Small eccentricity: Vibratory plates Low frequency – High eccentricity: Rammers
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10. 3 Reversible Vibratory Plates
Technology In addition to some of the standard vibratory plate features, reversible plates have two eccentric weights that allow smooth transition for forward or reverse travel, plus increased compaction force as the result of dual weights.
Application Due to their weight and force, reversible plates are ideal for semi-cohesive soils or crushed stones, which require high compaction energy. Heavy plates with high compaction energy are good for trench works. Unlike standard plates, the reversible forward travel may be stopped and the machine will maintain its force for « spot » compaction.
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11. 3 Reversible Vibratory Plates
Reversible plates have 2 eccentric shafts connected by gears and turning in opposite directions.
The 2 weights will be at the same angle twice per revolution. By changing the relative position of the weights on their shafts with the lever, the operator will change the motion from forward to neutral and further, backward.
The weight position modification is done through a sliding helicoidal spring system.
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12. 4 Double-drum Walk-behind Rollers
Technology Dual steel drum are mounted on a rigid frame and powered by a diesel engine. Steering is done manually with the machine handle. Frequency is 3300 vpm and amplitude is around 0.5 mm. Vibration is provided by one eccentric shafts placed between the drums.
Application A popular design for many years, the smooth-drum machine is ideal for both soil and asphalt. Its frequency and amplitude make it optimized for small particles material. High productivity is achieved as the double-drum works twice in one pass.
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13. 4 Double-drum Walk-behind Rollers
A diesel engine drives both the hydrostatic pump for smooth propulsion and the eccentric shaft for vibration.
The shaft is located on top between the drums; it is dipping into oil and there is a clutch system allowing the operator to put it on/off.
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14. When choosing the equipment, keep in mind
Physical constraint of the jobsite
Dimension of the trench…
Obstacles
Compaction requirements
Requested relative density
Type of soil
Granular, Cohesive… Particle shape, Particle distribution, Water content
Labor requirements
Number of operators available
Safety of operators
Required productivity
Size of the job…
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15. Equipment Applications
Asphalt
Granular Soils
Sand and Clay
Cohesive Clay
Ideal vibration frequency:
6000 RPM
4500 RPM
 2500 RPM
 750 RPM
Rammers
Not Recommended
Testing Recommended
Best Application
Forward Plates
Reversible Plates
Double-drum Rollers
Trench Rollers
Ground composition is not always easy to tell. Therefore it is wise sometimes to test the efficiency of different machines.
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16. Alternative applications
Vibratory plates of all sizes are used to settle paving stones. For this purpose, a polyurethane mattress can be fixed on the unit in order to prevent the steel plate from breaking the paving stones.
Another paving technique consists of imprinting fresh concrete with a plate mold. This gives the concrete a pattern and a color. Vibratory plates are used to press the mold onto the fresh concrete.
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17. Working parameters
The machines are always optimized to be operated at full engine load: this will provide the proper frequency.
Other parameters are controlled by the operator:
Lift thickness
Number of passes
Traveling speed
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18. Lift thickness
The fresh soil layer to be compacted, also called the lift thickness should not be too big at a time: there is a danger that an intermediate layer will stay loose, which can generate problems in the future.
Manufacturers of compaction equipment usually specify a maximum lift depth. This is measured in ideal conditions. In real jobsite conditions, you may consider that the lift thickness is 75% of this value.
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19. Number of passes
Multiple passes are necessary to optimize the compaction. For a good result, it will be necessary to perform typically from 3 to 5 passes, depending on the soil properties.
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20. Traveling speed
With reversible plates and duplex rollers, it is possible to adjust accurately the travel speed. Working at 1/2 speed will have the same effect as making 2 passes.
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21. Traveling too fast or too low vibration frequency
Traveling speed
With vibratory rollers, the machine speed must be settled in adequate relation with the vibration frequency.
A typical objective for impact spacing is at least 30 to 40 impacts per meter. A high vibration frequency of 3300 vpm (55 Hz) allows traveling at up to 1.8 m/s.
Rough surface finish:
LOW HIGH
Impact spacing
Traveling too fast or too low vibration frequency
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22. Pay attention
As the soil becomes compacted, more energy returns to the compactor. This makes the apparent amplitude (as felt by the operator) grow bigger.
Over-compaction
Making too many passes can result into over-compaction. It is like constantly hitting concrete with a sledgehammer. Cracks will eventually appear, reducing density and the ground stability.
Over-compaction is a waste of time and adds unnecessary wear to the machine.
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23. Job site specifications
The general contractor can ensure the compaction performances on a jobsite in two ways: Method Specification Detailed instructions specify machine type, lift depths, number of passes, machine speed and moisture content. End result Specification Engineers indicate final compaction requirements: soil density to a specified depth, ground hardness.
The second method is better as it gives the contractor the opportunity to the choose the most economic and flexible way to do the job, taking advantage of the latest technology
Choosing the right equipment for the right application.
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24. Jobsite observations
Construction compaction equipment can be highly dangerous. Every operator must conform to the safety instructions, wear the proper protection equipment and be trained to a safe usage of the machinery.
Some job situations require using complementary compaction equipment. For instance, when a picket is standing in the way of a double-drum roller compacting asphalt, this one cannot operate very next to the picket foot because of the side-clearance. Therefore it is compulsory to finish the work with a vibratory plate.
Organic soils should never be used for backfilling. As they will decay further, voids will appear, making it unstable.
It is possible to increase the compaction pressure of a light forward vibratory plate by forcing it to rear up by pushing the handle downward. This trick helps when leveling asphalt.
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