Objective

For determination of the liquid limit of soil using cone penetrometer.

Reference Standard

IS : 2720(Part 5)-1985- Methods of test for soils : Determination of liquid and plastic limit.

Equipment & Apparatus

• Oven
• Balance (0.01g accuracy)
• Sieve [425 micron]
• Cone penetrometer

Preparation sample

After receiving the soil sample it is dried in air or in oven (maintained at a temperature of 60⁰C). If clods are there in soil sample then it is broken with the help of wooden mallet.

Procedure

1. About 150 gm. of air dried soil from thoroughly mixed portion of material passing 425 micron IS sieve is  obtained.
2. Distilled water is mixed to the soil thus obtained in a mixing disc to form a uniform paste.
3. Then the wet soil paste is transferred to the cylindrical cup of cone penetrometer apparatus, ensuring that no air is trapped in this process.
4. Finally the wet soil is leveled up to the top of the cup and placed on the base of the cone penetrometer apparatus.
5. The penetrometer is so adjusted that the cone point just touches the surface of the soil paste in the cup and the initial ready is to be taken.
6. The vertical clamp is then released allowing the cone to penetrate into soil paste under its own weight for 5 seconds. After 5 seconds the penetration of the cone is noted to the nearest millimeter.
7. The test is repeated at least to have four sets of values of penetration in the range of 14 to 28 mm.
8. The exact moisture content of each trial is determined

Calculation

• A graph representing water content on Y – axis and the cone penetration on X – axis is prepared. A best fitting straight line is then drawn.
• The moisture content corresponding to cone penetration of 20 mm. is taken as the liquid limit of the soil.

Report

The liquid limit is to be reported to the nearest first decimal place.

Safety & Precautions

• Soil used for liquid limit determination should not be oven dried prior to testing.
• After mixing the water to the soil sample , sufficient time should be given to permeate the water throughout out the soil mass
• Wet soil taken in the container for moisture content determination should not be left open in the air, the container with soil sample should either be placed in desiccators or immediately be weighed.