The shrinkage limit of soil is the water content of the soil when the water is just sufficient to fill all the pores of the soil and the soil is just saturated. The volume of the soil does not decrease when the water content is reduced below the shrinkage limit.
Shrinkage limit can be determined from the relation
Where M1= initial wet mass,
V1= initial volume
Ms = dry mass of soil
V2 = volume after drying.
Determination of Shrinkage Limit of Remoulded Soil
Equipment for Shrinkage Limit Test
- Shrinkage dish having flat bottom, 45mm diameter and 15 mm height
- Two large evaporating dishes about 120mm diameter with a pour out and flat bottom.
- One small mercury dish 60mm diameter
- Two glass plate, one plain and one with prongs, 75mm x 75mm x 3mm size.
- Glass cup 50mm diameter and 25mm height
- IS sieve 425micron
- Weighing balance accuracy 0.01 g.
- Straight edge
Procedure of Shrinkage Limit Test
1. Take a sample of mass about 100g from a thoroughly mixed soil passing 425 micron sieve.
2. Take about 30g of soil sample in a large evaporating dish. Mix it with distilled water to make a creamy paste which can be readily worked without entrapping the air bubbles.
3. Take the shrinkage dish. Clean it and determine its mass.
4. Fill the mercury in the shrinkage dish. Remove the excess mercury by pressing the plain glass plate over the top of the shrinkage dish. The plate should be flush with the top of the dish. And no air should be entrapped.
5. Transfer the mercury of the shrinkage dish to a mercury weighing dish and determine the mass of the mercury to an accuracy of 0.1g. the volume of the shrinkage dish is equal to the mass of mercury in grams divided by the specific gravity of the mercury (i.e. 13.6)
6. Coat the inside of the shrinkage dish with a thin layer of silicon grease or Vaseline. Place the soil specimen in the center of the shrinkage dish equal to about one-third the volume of the shrinkage dish. Tap the shrinkage dish on a firm cushioned surface and allow the paste to flow to the edges.
7. Add more soil and continue the tapping till the shrinkage dish is completely filled and excess soil paste projects out about its edge. Strike out the top surface of the plate with a straight edge. Wipe of all soil adhering to the outside of the shrinkage dish. Determine the mass of the we soil (M1).
8. Dry the soil in the shrinkage dish in air until the colour of the pat turns from dark to light. Then dry the pat in the oven at 105 to 110 0C to constant mass.
9. Cool the dry pat in a desiccator. Remove the dry pat from the desiccator after cooling, and weight the shrinkage dish with the dry pat to determine the dry mass of the soil (Ms).
10. Place a glass cup in a large evaporating dish and fill it with mercury. Remove the excess mercury by pressing the glass plate with prongs firmly over the top of the cup. Wipe off any mercury adhering to the outside of the cup. Remove the glass cup full of mercury and place it in another evaporating dish taking care not to spill any mercury from the cup.
11. Take out the dry pat of the soil from the shrinkage dish and immerse it in the glass cup full of mercury. Take care not to entrap air under the pat. Press the plate with prongs on the top of the cup firmly.
12. Collect the mercury displaced by the dry pat in the evaporating dish and transfer it to the mercury weighing dish. Determine the mass of the mercury to an accuracy of 0.1g. The volume of the dry pat (V2) is equal to the mass of the mercury divided by the specific gravity of the mercury.
13. Repeat the test atleast 3 times.
Fig: Stages for derivation of Shrinkage Limit
Fig: Determination of volume of dry pat
Data Sheet for Shrinkage Limit Test
|Sl. No.||Observations and Calculations||Determination No.|
|1||Mass of empty mercury dish|
|2||Mass of mercury dish, with mercury equal to volume of the shrinkage dish|
|3||Mass of mercury = (2) – (1)|
|4||Volume of shrinkage dish V1= (3)/13.6|
|5||Mass of shrinkage dish|
|6||Mass of shrinkage dish + wet soil|
|7||Mass of wet soil M1= (6) – (5)|
|8||Mass of shrinkage dish + dry soil|
|9||Mass of dry soil Ms= (8) – (5)|
|10||Mass of mercury dish + mercury equal to in volume of dry pat|
|11||Mass of mercury displaced by dry pat|
=(10) – (1)
|12||Volume of dry pat V2= (11)/13.6|
Results of Shrinkage Limit Test
Shrinkage limit = _____%.