Compaction is the process of application of mechanical energy to the soil mass so as to rearrange or resettle its particles or molecules and decrease the void ratio.
Compaction  process is applied to the entire soil mass through improve the properties of an existing soil or in the process of placing or fulfill such area or volume as in the construction of embankments, road bases, runways, earth dams, and reinforced earth, retaining walls etc. Compaction process is also used to prepare a level of surface dressing during construction of buildings, bridges, highways, railways track, airport runways etc. There is generally no change in the water content and in the size of the different soil particles and molecules.

The objectives of compaction are as follows:

  • To increase soil shear strength value and therefore its bearing capacity value.
  • To decrease the subsequent settlement or deflection under excessive working loads.
  • To decrease soil permeability making it more difficult for water penetration to flow through the soil mask.

Method of Laboratory Compaction:
The variation in compaction method with water content and compactive force need to be determined in the laboratory. There are different type of  tests with standard procedures and rules such as:

  • Indian Standard Light Compaction Test (as per to Standard Proctor Test)
  • Indian Standard Heavy Compaction Test (as per to Modified Proctor Test)
  • Indian Standard Light Compaction Test:
    Soil mask  is compacted into a 1000 cm3 steel mould in 3 equal separate layers, each layer must be compacted by 25 no of blows of a 2.6 kg rammer suddenly fall down from a height of 310 mm above the soil. The compaction process is repeated at various moisture contents with any type of soil.
  • Indian Standard Heavy Compaction Test:
    From experiment of results was found that the Light Compaction Test (Standard Test) could not reproduce the value of densities measured in the field insitu under excessive loading conditions, and after that, it is move to the development of the Heavy Compaction Test (Modified Test). The equipment, apparatus and procedure are very much essential  for the same as it is used for the Standard Test except that the soil mask is compacted in 5 different layers, each an every layers also excepting 25 no of blows. In this case the same mould is also used. To provide the increased compactive forces, a heavier rammer of 4.9 kg and a higher drop height of 450 mm are used experimental process for achievement of better compaction.