Shrinkage Limit of Soil | IS 2720 Part 6

What is The Shrinkage Limit of Soil?

The shrinkage limit of soil is the water content (or moisture content) of the soil when the water is just sufficient to fill all the pores of the soil and the soil is just saturated. Beyond the shrinkage limit of soil; decrease in moisture content does not cause any further decrease in volume of soil.

Shrinkage limit can be determined from the relation. Commonly the shrinkage limit of soil test is much less used than the liquid limit and plastic limit test.

Shrinkage Limit of Soil, lS: 2720 Part-6

Hi friend, here I have explained about shrinkage limit of soil. After reading this you will be able to determine the shrinkage limit of soil easily.

Scope: To determine the shrinkage limit of soil.

IS Code For Determination of Shrinkage Limit of Soil:-

• IS:  2720 (Part 6): 1972, Methods of tests for soil: Determination of shrinkage limit or shrinkage factor

Apparatus Required For Shrinkage Limit Test of Soil:-

• Evaporating dish
• Spatula–flexible, with the blade about 8 cm length and 2 cm width.
• Shrinkage Dish–circular porcelain having a flat bottom and 45 mm in diameter and 15 mm height internally.
• Straight Edge–of stainless steel, about 15 cm in length.
• Glass Cup–50 mm to 55 mm in diameter and 25 mm in height.
• Glass plates–two, each 73 mm × 73 mm, 3 mm thick. One plate will be of main glass and the other having three metal prongs insert.
• Oven–thermostatically controlled with interior of non-corroding material to maintain the temperature between 105ºC & 115ºC.
• Sieve–425 micron IS Sieves.
• Balances–sensitive to 0.1 g and 0.01 g.
• Mercury–clean and sufficient to fill the glass cup to overflowing.
• Desiccator–with any desiccating agent other than Sulphuric acid (H₂SO₄).

Procedure For Shrinkage Limit of Soil Test:-

1. Take oven dry sample weighing about 100 g from the thoroughly mixed portion of the material passing the 425 micron IS Sieve.
2. Place approximately 30 g of the soil specimens in the evaporating dish and mix thoroughly with distilled water in an amount sufficient to fill the soil voids completely and to make the soil pasty enough to be easily worked into the shrinkage dish without entrapping air bubbles.
3. Determine the weight of the cleaned empty shrinkage dish and record it.
4. Calculate the volume of the shrinkage dish. This volume will be recorded as the volume of the wet soil pat (V).
5. Coat the inside of the shrinkage dish with a thin layer of grease to prevent the adhesion of soil to the dish.
6. Place an amount of the soil paste equal to about one-third the volume of the shrinkage dish in the centre of the shrinkage dish and allow the paste to flow to the edges by tapping the shrinkage dish on a firm surface cushioned by several layers of rubber sheet.
7. Add an amount of the soil paste approx. equal to the first portion and tap the shrinkage dish as before until the soil paste is thoroughly compacted and all the included air has been brought to the surface.
8. Add more soil paste and continue the tapping until the shrinkage dish is completely filled and excess soil paste stand out about its edge.
9. Then strike off the excess soil paste with a straight edge, wipe of all soil adhering to the outside of the shrinkage dish and weight it immediately.

10. Allow the soil pat for drying in air until the colour of the soil pat turns from dark to light.

11. Oven-dry the soil pat in the shrinkage dish at a temperature of 105 ºC to 110 ºC for 12 to 16 hours, cool in a desiccators and weight it, record this weight as the weight of shrinkage dish and dry soil. This is the weight of dry soil pat (Wₒ).

12. Fill the glass cup with mercury; press the glass cup with three prongs firmly over the top of the cup, collecting the excess mercury in a suitable container.

13. Carefully wipe off any mercury which may be adhering to the outside of the glass cup and place the cup in the evaporating dish taking care not to spill any mercury from the glass cup and place the oven-dried soil pat on the surface of the mercury in the glass cup.

14. Then carefully force the pat under the mercury by means of the glass plate with the same prongs and press the plate firmly over the top of the cup.

15. Collect the displaced mercury in the evaporating dish without spilling out of it.

16. Weigh the mercury displaced by the dry soil pat to an accuracy of 0.1 g and determine its volume (Vₒ) by dividing this weight by the unit weight of mercury.

17. This volume will be recorded as the volume of the oven-dry soil pat (Vₒ).

Calculations:-

Formula for shrinkage limit of soil

Where W = Moisture content (or water content) of wet soil pat.

What is the shrinkage factor of soil?

Table: Soil Property

Report:-

The observations and results of the test will be reported suitably. If any value varies from the average by more than ±2 percent, it shall be discarded and the test repeated.