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Updated: Apr 1, 2020


To determine the liquid limit of soil as per IS: 2720 (Part 5)

- 1985.


The liquid limit of fine-grained soil is the water content 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.



i) Casagrande’s liquid limit device

ii) Grooving tools of both standard and ASTM types

iii) Oven

iv) Evaporating dish

v) Spatula

vi) IS Sieve of size 425µm

vii) Weighing balance, with 0.01g accuracy

viii) Wash bottle

ix) Air-tight and non-corrodible container for determination of

moisture content


i) Air-dry the soil sample and break the clods. Remove the

organic matter like tree roots, pieces of bark, etc.

ii) About 100g of the specimen passing through 425µm IS

Sieve is mixed thoroughly with distilled water in the

evaporating dish and left for 24hrs. for soaking.


i) Place a portion of the paste in the cup of the liquid limit


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

iii) Draw the grooving tool through the sample along the

symmetrical axis of the cup, holding the tool perpendicular

to the cup.

iv) For normal fine grained soil: The Casagrande's tool is used

to cut a groove 2mm wide at the bottom, 11mm wide at the

top and 8mm deep.

v) For sandy soil: The ASTM tool is used to cut a groove 2mm

wide at the bottom, 13.6mm wide at the top and 10mm


vi) After the soil pat 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 10mm length.

vii) Take about 10g of soil near the closed groove and determine

its water content (see Para 5.1).

viii) The soil of the cup is transferred to the dish containing the

soil paste and mixed thoroughly after adding a little more

water. Repeat the test.

ix) By altering the water content of the soil and repeating the

foregoing operations, obtain at least 5 readings in the range

of 15 to 35 blows. Don’t mix dry soil to change its


x) Liquid limit is determined by plotting a ‘flow curve’ on a

semi-log graph, with no. of blows as abscissa (log scale)

and the water content as ordinate and drawing the best

straight line through the plotted points.

xi) Water content corresponding to 25 blows, is the value of the

liquid limit.


Report the water content corresponding to 25 blows, read from

the 'flow curve' as the liquid limit.

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