1. Light Compaction Equipment
About compaction
Welcome remarks TBD.
01/12/06

2. History of compaction
Ancient technique: Herds of cattle or sheep were used to compact soil for road construction. Their weight on small hoof used to make an effective compaction.
18th century Horses or oxen drawn rollers
19th century First steam roller in France
1905 First sheep foot roller for dam construction in California
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3. History of compaction
1930’s First use of vibratory compactors in Germany for highway construction.
1940’s Tow behind vibratory roller in the USA.
1950 – 1960’s First self-propelled units. Fast development started by the end of the 60’s because of the popularity of self-propelled units in highway construction.
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4. What is compaction? Rearranging the particles.
Removing voids (increasing the density [kg/dm³]).
Interlocking the particles.
Compacting freshly dropped soil will generally double its density.
The action of compacting can be measured by
The density increase.
The soil hardness increase.
The particles arrangement on a sample.
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5. Compaction objectives
Reducing soil compressibility and therefore reducing further deformation:
Increasing soil strength
Improving stability and load bearing capacity
Reducing water absorption
Increasing impermeability
No soil swelling and contraction due to water seepage
Reducing frost damage
Hardening and flattening the surface
Reducing erosion
Improving the grip
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6. Importance of ground compaction
The building itself can be as strong as possible.
If the ground below cannot bear the building weight, serious problems will arise!
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7. Why does efficient compaction make the difference?
Poor compaction results into cavities and ground permeability.
A quality work requires performing proper compaction at all levels of the layers structure.
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8. Materials: usual road layers
Shear resistance
Asphalt wearing course
Asphalt binder course
Asphalt base course
Subbase
Capping
layer
Loam
Bearing capacity
Pavement
Different materials require different compaction parameters.
For light compaction, asphalt can be seen like a material mix + a binder.
Ground
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9. Soil and Asphalt
In the prospect of light compaction, asphalt can be seen as a particular case.
Asphalt: On low traffic ways: Small stones – High sand content – Liquid bitumen On high traffic ways: Large aggregates – Low sand content – Thick bitumen
Asphalt specificities:
Must be worked when hot.
Water is necessary to prevent asphalt from sticking to the compacting machine
Compaction control is performed by core sampling.
The information that follows is focused on soil compaction +
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10. Material parameters Particle size Coarse granular soil
Fine sands & silts.
Coarse grains can be seen. Feels gritty when rubbed between fingers.
When moist, very little or no plasticity.
Little or no cohesive strength when dry.  Soil sample will crumble easily.
Relatively easy to compact
Fine cohesive soil
Mixes & clays
Particles stick together
Grains cannot be seen by naked eye. Feels smooth and greasy when rubbed between fingers.
When moist, Plastic and sticky. Can be rolled.
Has high strength when dry. Crumbles with difficulty. Slow saturation in water.
Requires high compaction energy
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11. Material parameters Particle shape Rolled aggregates
Compaction properties of granular soils will vary as according to their particle shape.
Rolled aggregates
E.g.: River gravel
Particles easily slide on each other.
Low shear resistance.
Relatively easy to compact
Static compaction can be enough.
Crushed aggregates
E.g.: Crushed granite
Lots of grip on the particle contacts: they don’t move easily.
High shear resistance.
Requires high compaction energy
Requires vibration
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12. Material parameters Size mix
The size distribution of the particles has a strong effect over the long term stability of the compacted soils.
Mixed aggregate sizes allow to achieve better mechanical properties of the compacted layer because of
better interlocking
more contact points
fewer voids
It is not allowed to backfill trenches or road support with any kind of soil.
Poor mix
Good mix
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13. Material parameters Water content
There is an optimum water content that will reduce aggregate friction and therefore maximize the compaction ability: ~11%
Dry
Ideal moisture ~11%
High water pressure
Hand test: Pick up a handful of soil, squeeze it in your hand and open.
If the soil is powdery and will not retain the hand shape, it is too dry: add water.
If the soil is moldable and breaks into only a couple of pieces when dropped, it has the right moisture content for compaction.
If the soil is plastic in your hand and stays in one piece when dropped, it is too wet for compaction.
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14. 4 compaction processes 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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15. 4 compaction processes Soils Impact Pressure (with kneading) Vibration
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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16. Compacting by vibrations
The vibrations are induced by the rotation of one or more eccentric shafts. The energy comes from the centrifugal force.
A compactor is characterized by its
Contact surface [m²]
Weight [kg]
Eccentric shaft design
Other parameters are
Frequency [Hz]
Advance rate [m/s]
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17. Compacting by vibrations
The eccentric shaft design together with the total weight of the compactor and the working frequency [vpm] will determine the vibration amplitude [cm] and the impact force [kN].
The « compaction energy » of an equipment is directly proportional to its impact force and to its working frequency.
Each compaction machine is designed to operate at an optimum frequency to supply the maximum force.
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18. Frequency effect
High frequencies are suitable for compacting a thin layer of asphalt* or small particles granular soil. Small particles also require more energy as more particles mean more friction.
Lower frequencies will work best to put big aggregates into motion on a thicker layer.
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19. 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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20. 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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21. Pay attention
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.
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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22. 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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23. 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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24. 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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25. 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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26. 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 eccentric shafts placed in 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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27. Trench Padded Rollers Not available in Europe
Technology The trench roller feature hydrostatic drive and skid-steering. Powered by a diesel engine, the trench roller is built to withstand the rigors of confined compaction.
Application This equipment has a high productivity in trenches and excavations, even on highly cohesive soils. For added safety in shored and unshored trenches, the equipment is operated by means of a remote control. Large eccentric units provide high impact force and high amplitude that are appropriate for cohesive soils. The drum pads provide a kneading action on soil.
Not available
in Europe
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28. 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…
Water content
Labor requirements
Number of operators available
Safety of operators
Required productivity
Size of the job…
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29. Equipment Applications
Granular Soils
Sand and Clay
Cohesive Clay
Asphalt
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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30. 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 pieces of 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.
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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