Determination Of Liquid Limit By Casagrande Apparatus

 

STANDARD

• IS: 2720 (Part 5)1985.

DEFINITION

•  Liquid Limit is defined as the water content at which the groove in soil pat cut by standard tool  flows together through 12 mm under an impact of  25 blows imparted by Casagrande apparatus.

APPARATUS

• Casagrande apparatus confirming to IS: 9259-1979.
• Grooving tool.
• Balance of capacity 500 grams and sensitivity 0.01 gram.
• Thermostatically controlled oven with capacity up to 250°C.
• Porcelain evaporating dish about 12 to 15 cm in diameter.
• Spatula flexible with blade about 8 cm long and 2 cm wide.
• Palette knives with the blade about 20 cm long and 3 cm wide.
• Wash bottle or beaker containing distilled water.
• Containers airtight and non- corrodible for determination of moisture content.
  PROCEDURE
•  Take representative soil sample of approximately 120 gms passing through 425 micron IS sieve and mix thoroughly with distilled water in the evaporating dish to a uniform paste. The paste shall have a consistency that will require 30 to 35 drops of the cup to cause the required closure  of the standard groove.
• Remix the soil thoroughly before the test.
• Place a portion of the paste in the cup above the spot where the cup rests on the base, squeeze down and spread in to position with a few strokes of the spatula as possible and at the same time trim to a depth of 1 cm at the point of maximum thickness.
• Make a clean, sharp groove by a grooving tool along the diameter through the center line of the cam follower.
• Drop the cup from a height of 10 ± 0.25 mm by turning the crank at the rate of two-revolutions/ sec, until  the two halves of the soil cake come in contact with the bottom of the groove along the distance of about   12 mm.
• Record the number of drops required to cause the groove close for the length of 12 mm.
• Collect a representative slice of sample of soil approximately the width of spatula, extending from about edge to edge of the soil cake at right angle to the groove in to an air tight container and keep in the oven for  24 hrs ,maintained at a temperature of 105˚C to 110°C and express its moisture content as the percentage of the oven dried weight.
• Transfer the remaining soil in the cup to the evaporating dish and clean the cup and the grooving tool thoroughly.
• Repeat the operation specified above for at least three more additional trials (minimum of four in all) with soil collected in evaporating dish to which sufficient water has been added to bring the soil to more fluid condition.
• In each case record the number of blows and determine the moisture content as before.
• The specimens shall be of such consistency that the number of drops required to close the groove shall not be less than 15 or more than 35.

REPORT

• Plot a flow curve with the points obtained from each determination on a semi logarithmic graph representing water content on the arithmetical scale and the no 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  second decimal and is reported as liquid limit of the soil.
  PRECAUTIONS
• This test should proceed from the drier (more drops) to the wetter (less drops) condition of the soil.
• This test may also be conducted from wetter to drier condition provided drying is achieved by kneading the wet soil and not by adding dry soil. 

Graph

DETERMINATION OF LIQUID LIMIT AND PLASTIC LIMIT
IS:2720 (Part 5)1970

Description	Liquid Limit				Plastic Limit
Observation No.	1	2	3	4	1	2
No. of Blows
Container No.
Weight of container(W1)
Weight of container +wet soil(W2)
Weight of container +wet soil(W3)
Weight of Water(W2-W3)
Weight of dried soil(W3-W1)
Water Content= ( (W2-W3)/(W3-W1))x100

 

Result from Graph
Liquid Limit(%)
Plastic Limit(%)
Plasticity Index(%)

 Specified Limits 

Activity	L.L.(Max)	P.I.(Max.)
EMB./SGD	70	45
GSB	25	6
WMM	–	6