Objective

For determination of the shrinkage limit of soil.

Reference Standards

IS : 2720(Part 6)-1972  Methods of test for soils : Determination of shrinkage factor.

Equipment & Apparatus

• Oven
• Balance
• Sieve
• Mercury
• Desiccator

Preparation sample

The soil passing 425 micron sieve is used in this test.

Procedure

1. 100 gm. of soil sample from a thoroughly mixed portion of the material passing through 425 micron IS sieve is  taken.
2. About 30 gm. of above soil sample is placed in the evaporating dish and thoroughly mixed with distilled water to make a paste.
3. The weight of the clean empty shrinkage dish is determined and recorded.
4. The dish is filled in three layers by placing approximately 1/3^rd of the amount of wet soil with the help of spatula.
5. Then the dish with wet soil is weighed and recorded immediately.
6. The wet soil cake is air dried until the colour of the pat turns from dark to light. Then it is oven dried at a temperature of 105⁰ C to 110⁰ C for 12 to 16 hours. The weight of the dish with dry sample is determined and recorded. Then the weight of oven dry soil pat is  calculated (W₀).
7. The shrinkage dish is placed in the evaporating dish and the dish is filled with mercury, till it overflows slightly. Then it is be pressed with plain glass plate firmly on its top to remove excess mercury. The mercury from the shrinkage dish is poured into a measuring jar and the volume of the shrinkage dish is calculated. This volume is recorded as the volume of the wet soil pat (V).
8. A glass cup is placed in a suitable large container and the glass cup removed by covering the cup with glass plate with prongs and pressing it. The outside of the glass cup is wiped to remove the adhering mercury. Then it is placed in the evaporating dish which is clean and empty.
9. Then the oven dried soil pat is placed on the surface of the mercury in the cup and pressed by means of the glass plate with prongs, the displaced mercury being collected in the evaporating dish.
10. The mercury so displaced by the dry soil pat is weighed and its volume (V_o) is calculated by dividing this weight by unit weight of mercury.

Calculation

The shrinkage limit is to be calculated by using the following formula

Where W = Moisture content of wet soil pat

Report

The test is repeated at least 3 times for each soil sample and the average of the result is reported.

Safety & Precautions

• Clean the sieves with the help of a brush, after sieving
• While weighing put the sieve with soil sample on the balance in a concentric position.
• Check the electric connection of the sieve shaker before conducting the test.