1. Light Compaction Equipment
About compaction
Welcome remarks TBD.

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 erosion due to sweeping water
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 leaves voids in the ground that will either:
Let water come in the ground, create cavities and destroy it when freezing.
Be weaknesses in case heavy loads are coming over: collapsing.
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 bitumen 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. 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. Ideal soil frequency: 2450 RPM (32 Hz)
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11. 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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12. 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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13. 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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14. 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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