Lab Manual for Liquid Limit Determination Using Casagrande Apparatus

 

Lab Manual for Liquid Limit Determination Using Casagrande Apparatus

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Objective

To determine the Liquid Limit of soil using the Casagrande Apparatus and understand its significance in classifying fine-grained soils.

Apparatus Required

1. Casagrande Apparatus (with a crank and a cup)
2. Grooving Tool
3. Spatula
4. Sieve (425 micron)
5. Evaporating Dish
6. Weighing Balance
7. Mixing Tools
8. Water Content Containers
9. Oven
10. Stopwatch

Casagrande Apparatus Dimensions

• Cup Diameter: 54 mm
• Cup Height: 10 mm
• Grooving Tool: ASTM standard with a width of 2 mm and depth of 8 mm
• Crank: Should provide 2 revolutions per second

Theory

The Liquid Limit (LL) is the water content at which the soil changes from a plastic state to a liquid state. It is determined by measuring the water content at which a groove cut in the soil sample closes after being subjected to 25 blows from the Casagrande cup.

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Procedure

1. Soil Preparation

   • Take about 120g of soil sample that passes through the 425-micron IS sieve.
   • Mix the soil thoroughly with distilled water to form a uniform paste.

2. Setting Up the Apparatus

   • Place a portion of the soil paste in the Casagrande cup.
   • Using the grooving tool, cut a groove along the centerline of the soil in the cup.

3. Operating the Casagrande Apparatus

   • Rotate the crank at 2 revolutions per second.
   • Count the number of blows until the groove closes for a length of about 12 mm.

4. Recording Observations

   • Record the number of blows (N) and collect a sample of the soil from the cup for water content determination.
   • Repeat the process at least three times with different water contents, adjusting the water in the soil paste to obtain data points for a range of 10 to 40 blows.

5. Water Content Determination

   • Collect the soil samples after each test and place them in moisture containers.
   • Determine the water content (w) using the formula:
   $$w = \frac{(W_{wet} - W_{dry})}{(W_{dry})} \times 100$$

   Where,

   • $W_{wet}$ = weight of the wet soil sample
   • $W_{dry}$ = weight of the dry soil sample

6. Plotting the Flow Curve

   • Plot the number of blows (N) on a logarithmic scale against the corresponding water content (w%) on an arithmetic scale.
   • The Liquid Limit is the water content corresponding to 25 blows.

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Observation Table

Sample No.	Water Content (w%)	No. of Blows (N)	Water Content Container No.
1
2
3

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Result

The Liquid Limit (LL) of the given soil sample is calculated from the graph and recorded.

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Sketch of Casagrande Apparatus

(Draw a neat sketch with labeled parts: Cup, Grooving Tool, Crank Handle, Base, etc.)

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Conclusion

The Liquid Limit is a key parameter in classifying fine-grained soils and understanding their behavior under varying moisture conditions.

Liquid Limit of soil using the Casagrande Apparatus method, according to the Indian Standard IS: 2720 (Part 5) – 1985.