Drums are conquering the earth.

Roads require a stable foundation to be built on. That is why earthmoving operations need to be carried out prior to paving a road’s base, binder and surface course layers. What are the rolling techniques used in soil compaction? In which way will the ground structure influence compaction results?

Nature doesn’t always provide the ideal foundation for the construction of roads: natural rock. In the majority of cases, the ground is unstable, offering insufficient bearing capacity. Earthmoving operations are therefore usually the first step in the construction of a new road. When the course has been defined and set out, the ground underlying the new road needs to be prepared.

Stable ground will carry the road

Compaction is the single most important process in soil construction. Its job is to reduce the volume of pores in the soil to be compacted, which are filled with water and air. Compaction will give soil the desired properties: Its resistance to stresses induced by traffic and climate will be improved by increasing its stability while simultaneously reducing its tendency to swell due to water absorption. The latter will additionally make the soil resistant to frost.

Cohesive and non-cohesive soils

The process is different for different types of soil. Experts distinguish between cohesive and non-cohesive soils. In cohesive soils like loam, clay or silt, the particles in the soil bond to one another. In non-cohesive soils like gravel or sand, the particles lie side by side without bonding. Soil types can be distinguished as follows in terms of compactability: water-retaining soils, fine grained cohesive soils, coarse grained non-cohesive soils, fine and coarse grained mixed soils, and rock.

Dynamic compaction is highly effective

Dynamic compaction of soils by means of vibrating or oscillating compaction equipment has proved to be particularly effective in earthmoving operations. Compaction is generated by the combined action of the vibrating or oscillating roller drum and the weight of the machine itself. Applying a dynamic load achieves significantly higher compaction effects than applying just the weight force.

Compaction requires more than just weight

The intensity of compaction is governed by three influencing factors: displacement of the roller drum, meaning the amplitude of the vibration or oscillation, rate of recurrence of the vibration or oscillation, meaning the frequency, and duration, meaning the roller’s travel speed. When these parameters are set correctly, the specified density can be achieved in considerably less roller passes.

The right technique for any type of soil

Cohesive soils are compacted most effectively using single-drum compactors with padfoot drums applying high amplitudes of approx. 1.8 mm. Non-cohesive soils are best compacted using smooth drums and low amplitudes of between 0.5 mm and 1 mm. The ground has now been prepared to serve as a base for the upper road structure – unless its moisture content is too high. Excessively wet soils require additional stabilizing.