Consolidation Test

When a compressive load is applied on a soil mass, its volume decreases and this decrease is known as compression and the property of soil mass pertaining to its tendency to decrease in volume under pressure is known as compressibility. In a saturated soil mass having its voids filled with compressible water, a decrease in volume, i.e, compression can take place when water is expelled out of the voids. Compression resulting from a long time static load and the consequent escape of pore water is termed as consolidation.

When the load is applied on the saturated soil mass, the entire load is carried by the porewater initially. As the water starts escaping from the voids, the hydrostatic pressure in water gradually dissipates and the load is gradually shifted to the soil solids and as a result the soil decreases in volume. The rate of escape of water depends on the permeability of the soil.

A major problem in soil is the soil subsidence caused by pressure or weight of construction trucks on the surface, which may be divided into three categories.

  1. Elastic Deformation
  2. Primary Consolidation
  3. Secondary Consolidation

This test is performed to determine the magnitude and rate of volume decrease that a laterally confined soil specimen undergoes when subjected to different vertical pressures. From the measured data, the consolidation curve (pressure-void ratio relationship) can be plotted. This data is useful in determining the compression index, the recompression index and the preconsolidation pressure (or maximum past pressure) of the soil. In addition, the data obtained can also be used to determine the coefficient of consolidation and the coefficient of secondary compression of the soil.

From this test, it will be possible for us to predict the time rate and extent of settlement of structures founded on fine-grained soils. It is also helpful in analyzing the stress history of soil. Since the settlement analysis of the foundation depends mainly on the values determined by the test, this test is very important for foundation design.