Initial, Primary and Secondary Consolidation of Soil

Initial Consolidation
  • When a load is applied to a partially saturated soil, a decrease in volume occurs due to expulsion and compression of air in the voids.
  • A small decrease in volume occurs due to compression of solid particles.
  • The reduction in volume of the soil just after the application of the load is known as initial consolidation or initial compression. For saturated soils, the initial consolidation is mainly due to compression of solid particles.
Primary consolidation
  • Occurred due to the expulsion/extrusion of the water that occupies the void spaces.
  • Primary consolidation settlement is a result of a volume change in saturated cohesive soils.
  • Very slow and continues over a long period of time.
Secondary consolidation
  • Additional form of compression that occurs at constant effective stress at a very slow rate.
  • Observed in saturated cohesive soils.
  • Result of the plastic adjustment and rearrangement of soil fabrics.
  • Occurs after the primary consolidation settlement ended.


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