What is Liquid limit of soil, properties of soil

SCOPE: 

To determine water absorption of Liquid Limit of soil by Casagrande’s liquid limit device. 

 The liquid limit is the moisture content at which the groove formed by a standard tool into the sample of soil taken in the standard cup, closes for 12 mm on being given 25 blows in a standard manner. At this limit, the soil possess low shear strength

    IS CODE:

 IS: 2720 (Part 5) – 1985 

 APPARATUS: 

 1. Casagrande’s liquid limit device 

 2. Grooving tools 

 3. Oven 

 4. Evaporating dish 

 5. Spatula 

 6. IS Sieve of size 425 µm 

 7. Weighing balance 

 8. Wash bottle 

 PROCEDURE: 

 1. Take 120g of the oven Dry soil passing through 425micron IS Sieve is mixed thoroughly with distilled water in the evaporating dish. 

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

 3. Level the soil in the device as maximum depth of 1cm. 

 4. Draw the grooving tool through the sample along the symmetrical axis of the cup, holding the tool perpendicular to the cup. 

 5. After the soil has been cut by a proper grooving tool, the handle is rotated at the rate of about 2 revolutions per second and the no. of blows counted, till the two parts of the soil sample come into contact for about 12mm length.

 6. Take some soil near the closed groove and determine its water content. 

 7. The soil in the cup is transferred to the evaporating dish and mixed thoroughly after adding a little more water. 

 8. Repeat the test.By change the water content of the soil and repeating the process, obtain at least 5 readings in the range of 15 to 35 blows. Don’t mix dry soil to change its consistency.

 9. Liquid limit is determined by plotting a ‘flow curve’ on a semi-log graph with no. of blow in x axis and the water content in y axis. 

 10. Plot the straight line for 25 blows and the value is liquid limit of soil. 

 CALCULATIONS: 

 Liquid Limit ‘A flow curve’ shall be plotted on a semi- logarithmic graph representing water content on the arithmetical scale and the number of drops on the logarithmic scale. 

 The flow curve is a straight line drawn as nearly as possible through the four or more plotted points. The moisture content corresponding to 25 drops as read from the curve shall be rounded off to the nearest whole number and reported as the liquid limit of the soil.