To determine the shrinkage limit of the soil.
The value of shrinkage limit is used for understanding the swelling and shrinkage properties of cohesive soils. It is used for calculating the shrinkage factors which helps in the design problems of the structures made up of the soils or/and resting on soil. It gives an idea about the suitability of the soil as a construction material in foundations, roads, embankments anddams.
The test is specified in IS: 2720(Part 6)-1972. The 30 g soil passing 425 micron sieve is used for the test.
As the soil loses moisture, either in its natural environment, or by
artificial means in laboratory, it changes from liquid state to plastic
state to semi-solid state and then to solid state. The volume is also
reduced by the decrease in water content. But, at a particular limit the
moisture reduction causes no further volume change. A shrinkage limit
test gives a quantitative indication of how much moisture can change
before any significant volume change and to also indication of change in
volume. The shrinkage limit is useful in areas where soils undergo large
volume changes when going through wet and dry cycles (e.g. earthdams).
Shrinkage limits are required to be determined on two types of soils,
they are
i. Remoulded soil.
ii. Undisturbed soil.
Other shrinkage factors i.e. shrinkage ratio, volumetric shrinkage may also be calculated from the test data of shrinkage limit.
Shrinkage ratio is the ratio of a given volume change expressed as a percentage of dry volume to the corresponding change in water content above the shrinkage limit.
Volumetric Shrinkage is the decrease in volume of a soil mass when the water content is reduced from given percentage to the shrinkage limit and which is expressed as percentage of dry volume of the soil mass.