Atterberg Limits Test of Soil

The Atterberg Limits Test is used to determine the consistency and plasticity characteristics of fine-grained soils.

 

Objectives of Atterberg Limits Test

· Determine consistency of soil

· Classify fine-grained soil

· Measure plasticity characteristics

· Assess suitability for construction

Types of Atterberg Limits

· Liquid Limit (LL)

· Plastic Limit (PL)

· Shrinkage Limit (SL)

Apparatus Required

· Casagrande apparatus

· Grooving tool

· Glass plate

· Oven

· Weighing balance

· Moisture containers

Liquid Limit Test Procedure

1. Prepare soil paste

2. Place soil in Casagrande cup

3. Cut groove using grooving tool

4. Rotate handle at 2 revolutions per second

5. Count blows required to close groove over 12 mm length

6. Determine water content

7. Plot flow curve

Plastic Limit Test Procedure

8. Take small soil sample

9. Roll into threads on glass plate

10. Continue rolling until thread diameter becomes 3 mm

11. Determine moisture content

Formula

Plasticity Index (PI) = LL - PL

Where:

LL = Liquid Limit

PL = Plastic Limit

Example Calculation

Liquid Limit (LL) = 42%

Plastic Limit (PL) = 24%

Step 1: Calculate Plasticity Index

PI = 42 - 24

PI = 18%

Interpretation of Plasticity Index

Plasticity Index	Soil Type
0 – 5	Low Plastic
5 – 15	Medium Plastic
15 – 35	High Plastic
> 35	Very High Plastic

Final Result

Plasticity Index = 18%

Soil Type = High Plastic Soil

Advantages

· Simple laboratory test

· Useful for soil classification

· Helps in foundation design

Limitations

· Applicable mainly for fine soils

· Results depend on operator skill

Standard Codes

IS 2720 Part 5 – Liquid and Plastic Limit Test

ASTM D4318

Applications

· Road construction

· Foundation engineering

· Embankment design

· Soil classification