Last edited 18 Jan 2019

Soil compaction

Soil compaction is the removal of pore spaces within soil structures and drainage channels between soil structures. This inhibits root penetration and the movement of air and water in soil. Ref The HS2 London-West Midlands Environmental Statement, Glossary of terms and list of abbreviations, DETR 2013.

Soil compaction can be purposeful (intentional) or consequential (unintentional) such as settlement that might occur due to vehicle movement.

Intentional soil compaction produces an increase in soil density and a decrease in air volume without producing a decrease in water content. It can improve shear strength, stiffness, bearing capacity and stability, reducing settlement and frost heave. This may be necessary in the construction of bases for highways, embankments and so on, or to create a suitable level base for the construction of a building. Existing soil can be compacted, or layers of new soil can be compacted, taking a site to the required level.

For effective compaction to take place, there must be a mixture of particle sizes so that smaller particles can fill the voids between larger particles. Soils with smooth, spherical particles are easier to compact than soils with irregular particles, although their load-bearing capacity can be lower.

Soils are typically categorised as cohesive soils, granular soils or mixed soils. Cohesive soils can be compacted effectively by impact, such as by rammers or sheepsfoot rollers (tamping rollers). Granular soils can be compacted effectively by vibratory plates and smooth-drum vibratory rollers.

The use of vibrating or oscillating rollers is sometimes referred to as dynamic compaction.

Excessive compaction can lead to soils breaking down and separating. This can cause compacted layers to weaken.