Method For Preparation Of Dry Soil Samples For Various Tests

STANDARD

• IS: 2720 (Part 1)1983.

OBJECTIVE

• To prepare dry soil samples from the field for various laboratory tests.

APPARATUS

• Wooden Mallet.
• Non-corrodible trays.
• Pulverizing apparatus such as mortar and a rubber covered pestle or a mechanical device consisting of mortar and a power driven rubber covered pestle.
• A suitable riffle sampler or sample splitter for quartering the samples.
• Thermostatically controlled oven of capacity 250 °C.
• Balance of capacity 500 grams and sensitivity 0.01 gram.
• Balance of capacity 10 kgs and sensitivity 0.5 gram.
• Balance of capacity 15 Kgs and sensitivity 1 gram.

PROCEDURE

• Dry the soil sample as received from the field in the air or under the sun.
• Remove the organic matter like tree roots and pieces of bark from the sample.
• Separate matter other than soil, like shells from the soil mass.
• Break the clods with a wooden mallet to hasten drying.
• In wet weather a drying apparatus may be used but the temperature of the sample during heating shall not exceed 60 °C.
• When an oven is used for drying, the temperature in the oven shall not exceed 110 °C.
• The amount of drying depends upon the proposed test to be conducted on the particular sample.
• The type, temperature and duration of drying of soil samples for different tests are given in Table: 1.
• After the specified period of drying, cool the material to the room temperature.
• Break the big clods with the help of wooden mallet.
• Pulverize the soil sample to pass through the specified sieves of the particular test to be conducted.
• Mix the entire soil thoroughly and spread on a flat surface.
• Divide the sample into four quadrants and mix the diagonally opposite quadrants.
• Repeat the process till the desired quantity of sample is obtained.

Method for Quartering

The quartering method shall be used when splitters are not available. Quartering simply requires a quartering cloth and a stick or rod and is done as follows

1. Pour contents from sample bucket on to the quartering cloth.
2.   Level sample on quartering cloth using a rod.
3. Insert rod under the middle of the quartering cloth and lift both  ends of rod to divide the sample into two equal parts.
4. Repeat step 3, dividing the sample in to four quarters.
5. Retain any two diagonally opposite parts for testing.
6. If the sample is still not small enough, repeat the quartering procedure using either of the two diagonally opposite halves.

PRECAUTIONS

• Care shall be taken not to break individual grains during pulverization of soil.
• Soils containing organic or calcareous matter should not be dried at a temperature above 60°C.
• In the case of coarse gravels or gravelly soils quartering by forming a cone shall not be done.

Table: 1 Quantity of soil sample required for conducting various tests

Test	Type of drying and temperature	Duration of drying	Amount of sample required for test	Passing IS sieve
Water content	Air dried/oven dried at 105 to 110°C	24 Hours	• As per Table: 2.2.1	–
Compaction	Air dried/oven dried at 105 °C to 110 °C	24 Hours	6 Kgs (Not Susceptible to rushing) 15 Kgs (Susceptible to Crushing)	1 9mm •
Free Swell Index	Air dried/oven dried at 105 to 110 °C	24 Hours	20 Grams	425 Microns
Liquid Limit	Air dried/oven dried at 105 to 110 °C	24 Hours	120 Grams	425 Microns
Plastic Limit	Air dried/oven dried at 105 to 110 °C	24 Hours	20 grams	425 Microns
CBR	Air dried/oven dried at 105 to 110°C	24 Hours	15 Kgs	19 mm
Specific Gravity	Air dried/oven dried at 105 to 110 °C	24 Hours	50 Grams (Fine Grained Soils) 400 Grams (Medium& Coarse Grained Soils)	2 mm
Grain Size Analysis	Air dried/oven dried at 105 to 110 °C	24 Hours	As per Table	–