Atterberg Limits (Liquid & Plastic Limit) — Lab Manual

Objective & standard

Liquid limit, plastic limit and plasticity index of the fine fraction (passing 425 µm).

Standard: ASTM D4318 / BS 1377-2

Apparatus

• Casagrande cup & grooving tool (or cone penetrometer)
• Glass plate, spatula
• Moisture tins, oven, balance
• 3 mm rod for PL

Procedure

1. Mix about 150 g soil passing 425 µm with water to a paste.
2. Place in the cup, cut a groove and count the blows to close it over 13 mm.
3. Take a moisture sample; repeat at 4 water contents with blows between 15 and 35.
4. Plastic limit: roll threads on glass until they crumble at 3 mm; take moisture.
5. Plot water content vs log blows — the water content at 25 blows is the LL.

Calculations

• PI = LL − PL
• A-line: PI = 0.73 (LL − 20)
• Liquidity index LI = (w − PL) ÷ PI

Typical values: Low plasticity CL: LL < 50; high plasticity CH: LL > 50. PI > 25 indicates expansive behaviour.

Open the Atterberg Limits (LL, PL, PI) calculator →

Data sheet (print this page)

Project: ____________________   Sample: __________   Date: __________   Tested by: __________

🖨 Print lab sheet