Factors Affecting Compaction of Soil

Updated: Jun 24

Compaction of soil means increasing the density and decreasing the air voids. It is the densification of soil by application of mechanical energy which occurs when soil particles are pressed together, reducing pore space between them. This compaction of soil depends on many factors like water content, compaction effort, type of soil, method of compaction etc.

Now let us see in detail important factors which affect soil compaction.


The compaction of soil depends on many factors. A few important factors are:

  1. Water content

  2. Compaction effort

  3. Soil type

  4. Method of compaction

Let us now see each of them in detail.

Water content

Water content is one of the important factors determining the compaction of the soil. Effects of water content are as follows:

At lower water content-

  • Vander Waal forces between two clay particles exist.

  • Adsorbed water layer around the clay particles is not fully developed.

  • The net force between the particles is attraction so a flocculated structure would form, so more voids so mess density.

At higher water content

  • The net force between the particles becomes repulsive.

  • The dispersive structure would form.

  • The void ratio decreases as the particles are arranged in a particular manner.

If we further increase the water content the place occupied by the soil particles will be replaced by water. Unit weight of water is less than the unit weight of solids, hence dry unit weight keeps decreasing.

Compaction effort

An increase in the Factors Affecting Compaction of Soil effort increases the density on the dry of optimum whereas the increase on the wet side of optimum is not that significant. Whatever method of the compact we use, still the air voids exist.

Type of soil

Type of soil also affect the soil compaction in the following way:

  • Fines in the gravel affect the compaction.

  • In the case of sands, when some water is added then due to capillary tension, even if we give the compactive effort the particles will not move closer. This tension would be maximum when the water content is 4-5% where the dry unit weight is minimum at that time

  • If we further increase the water content, the capillary effect would be reduced and the water will start entering into the voids. Then sand particles would move freely into the spaces and occupy the better alignment, after which the dry unit weight starts increasing but in later stages like in previous cases the dry unit weight starts reducing again. This phenomenon is called “Bulking of sand”

Method of compaction

Different rollers are used in the field for compaction. Sheepsfoot rollers are used for clayey soils and plastic soils. Vibratory rollers are used for cohesionless soils. Results from the lab and field would always be different.

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