Methods of test for soils, Part 1: Preparation of dry soil samples for various tests
1983 Edition

Soil samples should generally be oven-dried at temperatures between 10561106C for a period of 24 hours. For soils containing organic matter or calcareous content, drying should not exceed 606C to prevent alteration. Air drying is advised for such soils or where oven drying is unsuitable. Chemical drying is discouraged. Typical tests involving oven drying at 10561106C include calcium carbonate content, cation exchange capacity, and permeability, each requiring about 24 hours of drying.

Representative soil samples are obtained by reducing bulk soil via quartering or riffling methods. For coarse gravel or gravelly soils, avoid forming a cone during quartering. Instead, mix the entire sample thoroughly, spread it evenly, divide into four quadrants, and mix diagonally opposite sections repeatedly until the desired sample size is achieved. This approach ensures homogeneity and precision in subsequent testing.

Sample quantities vary depending on the test: for water content, quantities depend on particle size (e.g., 25 g for 425 micron particles, up to 1000 g for 37.5 mm particles). Specific gravity tests require 50 g for fine soils and 400 g for coarser soils. Grain size analysis samples depend on test specifications. Liquid limit tests need about 270 g, plastic limit 60 g, compaction tests range from 6 to 15 kg depending on soil type, and unconfined compressive strength tests require around 1 kg. Detailed quantities and pulverization sieve sizes correspond to each test as per the standard.

Pulverization involves breaking large clods with a wooden mallet, followed by grinding with a mortar and rubber-covered pestle, either manually or mechanically. The pulverized soil is then passed through specified sieves, re-pulverizing any retained material until minimal soil passes through. Sieving sizes range from 75 mm down to 425 microns, consistent with IS 460 Part 1. Drying prior to pulverization is done by air drying or at temperatures not exceeding 606C when necessary.

Yes, soils with organic or calcareous components must not be oven-dried above 606C to avoid degradation or alteration of material properties. Air drying or oven drying at or below 606C is recommended for these soils. Chemical drying methods are prohibited for all soil types. Such precautions ensure the integrity and accuracy of test results involving organic or lime content analyses.