Liquid Limit Test of Soil by Casagrande Apparatus | lS: 2720 Part 5

What is The Liquid Limit Test of Soil?

Liquid limit test of soil is one of the engineering laboratory tests used internationally to differentiate or classify soils into groups.

Liquid limit of soil is the water content at which soil changes from a plastic state to a liquid state or liquid state to plastic state, when the soil specimen is just fluid enough for a groove to close when jarred in a specified manner.

The liquid limit of soil is the moisture content or water content at which soil begins to behave as a liquid material and below which it stop to behave like a liquid material, but has small shear strength.

There are three methods of determining liquid limit:

• Casagrande's Method
• One Point Method
• Cone Penetrometer Method

Here we have covered the first “Casagrande's Method” in this blog post.

The liquid limit is calculated from only one soil sample test by dividing the number of blows by 25 in Casagrande's liquid limit device, raising the result to the power of 0.121 and multiplying by the percent water content.

Liquid Limit Test of Soil by Casagrande Apparatus | lS: 2720 (Part 5): 1985

Hi friend, here I have explained about Liquid Limit Test of Soil. After reading this you will be able to determine the Liquid Limit of Soil easily.

Scope: To determine the liquid limit of soils by mechanical method using Casagrande apparatus.

IS Code For Determination of Liquid Limit of Soil by Casagrande Apparatus :-

• lS:  2720 (Part 5): 1985

Apparatus Required For The Liquid Limit Test of Soil by Casagrande Method:-

• Casagrande Liquid Limit Device
• Grooving tool
• Porcelain Evaporating Dish/Aluminium bowl
• Flat Glass plate - 10 mm thick
• Spatula - flexible and with the blade about 8 cm long and 2 cm wide
• Weighing balance - sensitive to 0.01 g.
• Oven–thermostatically controlled with interior of non-corroding material to maintain the temperature between 105 ºC & 115 ºC.
• Wash Bottle or Beaker - containing distilled water.
• Non corroding containers

Procedure of The Liquid Limit Test of Soil by Casagrande Method:-

1. About 120 g of oven dry soil sample passing 425 micron IS sieve shall be mixed thoroughly with distilled water in the evaporating dish or on the fiat glass plate to form a uniform paste.
2. The paste will have a consistency that will require 30 to 35 drops of the cup to cause the required closure of the standard groove.
3. ln the case of clayey soils, the soil paste shall be left to stand for a sufficient time (24 hours) so as to ensure uniform distribution of moisture throughout the soil mass.
4. A portion of the paste shall be placed in the cup above the spot where the cup rests on the base and spread it with the help of the spatula.
5. Make a 2 mm groove using 'A' type grooving tool. In case where grooving tool, Type A does not give a clear groove as in sandy soils, grooving tool Type ‘B’ or Type ‘C’ should be use.
6. The cup will be fitted and dropped by turning the crank at the rate of two revolutions per second until the two halves of the soil cake come in contact with bottom of the groove along a distance of approximately 12 mm. The number of drops is recorded.
7. A representative slice of soil approximately shall be taken in a suitable container and its moisture content is determined.
8. The remaining soil in the cup will be transferred to the evaporating dish. Then the cup and the grooving tool will be cleaned thoroughly.
9. The operations shall be repeated for at least three more additional trails by adding sufficient water to bring the soil to a more fluid condition.

10. In each case the number of blows will be recorded and the moisture content determined.

11. The number of blows required to close the groove should be between 15 to 35 blows.

Formula to Calculate Liquid Limit of Soil:-

A flow curve will be plotted on a semi logarithmic graph representing water content on the arithmetical scale and the number of drops on the logarithmic scale.

The moisture content (water 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.

Report :-

The results of the observations of the liquid limit test of soils shall be recorded suitably. The liquid limit should be reported to the nearest to first decimal place.