LIQUID LIMIT TEST OF SOIL BY CASAGRANDE'S DEVICE.

Definition :-
Liquid limit is the water content where the soil starts to behave as a liquid.

Aim :-   
To determine the liquid limit of soil as per IS 2720-1985.

Principle :-
The liquid limit of fine grained soil at which soil behaves practically like a liquid, but has small shear strength . It's flow closes the groove in just 25 blows in casagrande's liquid limit device.

Liquid Limit Test Of Soil - Engineering Discoveries

Apparatus :-  
1. Casagrande's liquid limit device
2. Grooving tools of both standard and ASTM types
3. Oven
4. Evaporating dish
5. Spatula 
6. Is sieve of size 425 micron.
7. Weighing balance with 0.01 gm accuracy
8. Wash bottle
9. Air-tight and non-corrodible container

Atterberg Limits: Determination of Plastic, Liquid, & Shrinkage ...


Preparation of sample:- 

1. Air dry the soil sample and break the clods. Remove the organic matters like roots, pieces of bark, etc.
2. About 100 gm of the specimen passing through 425 micron IS sieve and mixed through lt with distilled water in the evaporating dish and left for 24 hours for soaking.


Procedure :-

1. Place a portion of the paste in the cup of the liquid limit device.

2. Level the mix so as to have a maximum depth of 1 cm.

3. Draw the grooving tool through the sample along the symmetrical axis of the cup, holding the tool perpendicula to the cup.

4. For normal fine grained soil , The casagrande's tool is used to cut a groove 2 mm wide at the bottom, 11 mm wide at the top and 8 mm deep.

5.For sandy soil, The ASTM tool is used to cut a groove 2 mm wide at the bottom, 13.6 mm wide at top and 10 mm deep.

6. After the soil has been cut by a proper grooving tool, the handle is rotated at the rate of about 2 revolution per second and the the no. of blows counted till the two part of the soil sample come into contact for about 10 mm length.

7. Take about 10 gm of soil near the closed groove and determine its water content.

8. The soil of the cup is transferred to the dish containing the soil paste and mixed throughly after adding a little more water. Repeat the test.

9. By altering the water content of the soil and repeating the foregoing operations obtain atleast 5 reading in the range of 15 to 35 blows. Don't mix dry soil to change its consistency.

10. Liquid limit is determine by plotting a curve 'Flow curve' on a semi-log graph with no. of lows as log scale and the water content as ordinate and drawing the best straight line through the plotted points.

11. Water content corresponding to 25 blows, is the value of liquid limit.

How to Determine the Liquid Limit of Soils?

As you see in above image, The liquid limit of soil at 25 blows is 50%.

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