Shrinkage Limit

Published: August 10, 2020 | Last updated: July 5, 2023

What Does Shrinkage Limit Mean?

Shrinkage limit (SL) is the moisture content at which a fine-grained soil does not change the volume on drying; the moisture loss is compensated by air that enters its pores.

It can be determined in a laboratory using a disturbed or undisturbed soil sample. The volume for the soil sample at the SL equals the total volume of oven-dried soil, and the volume of soil solids is constant throughout the shrinkage process. The decrease in volume is a result of the decrease in volume of voids.


Trenchlesspedia Explains Shrinkage Limit

The shrinkage limit (SL) test of the soil determines:

  • Shrinkage limit.
  • Shrinkage ratio.
  • Shrinkage index.
  • Volumetric shrinkage of soils.

The apparatuses required for the test include:

  • Evaporating dishes.
  • Spatula.
  • Shrinkage dish.
  • Straight edge.
  • Glass plate.
  • Glass plate with metal prongs.
  • Glass cup.
  • Sieve.
  • Balance.
  • Mercury desiccator.

The shrinkage dish is cleaned, weighed, and filled with mercury. The mercury is weighed and divided by its density to obtain the volume of the dish, which is the volume of the wet soil. Next, the soil is taken in the evaporating dish and thoroughly mixed with water of an amount slightly more than the liquid limit (LL).

The shrinkage dish is coated with a thin layer of grease and filled one third with the soil-water mix. The dish is tapped and the procedure is repeated until the dish is full. Excess soil paste is removed with a straight edge. It is then air-dried till the color changes from dark to light and then dried in a temperature-controlled oven. Once dried, it is air-cooled and weighed.

The glass cup is then filled with mercury and placed in an evaporating dish and the dried soil pat is placed on the surface of the mercury. The soil pat is forced over the mercury with the glass plate with prongs so that the soil pat is completely submerged in mercury.

The displaced mercury is collected, weighed and its volume is determined, which will be the volume of the dry pat.


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