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Field identification of soil | Various on-field Tests on Soil

Updated: Jun 15

Field identification of soil is one of the important steps in soil investigation. It includes visual examination, dilatancy, toughness, dry strength, organic content and shine test. Based on the size of soil particles soil can be gravel, sand, silt or clay.

Now let us see some of the steps in field identification of soil. These are

  1. visual examination

  2. dilatancy

  3. toughness

  4. dry strength

  5. organic content

  6. shine test.

Visual examination

  • Bigger the particles: coarse-grained

  • Smaller the particles: fine-grained.

Dilatancy

It is based on the water movement in the soil sample. Take a slightly wet soil, squeeze it in the hand.

  • If the water disappears immediately it is silt.

  • If it takes some time for the water to disappear or if water doesn't go back then it is clay.

Toughness

The same sample of the dilatancy test is used and dry for a while. Try to roll it into a 3 mm thread then find the plastic limit. Now after reaching the plastic limit, try to roll it by using some extra pressure.

  • if it can roll further, it implies the soil has more toughness.

  • If we cant roll it or it crumbles then it indicates low toughness.

  • If the thread starts to crumble below the plastic limit itself then it indicates the medium toughness.

Dry Strength

The same sample would be dried until it loses its water completely and then apply pressure by fingers, then if it converts into powder then it implies it has low dry strength.

  • If it requires strength from fingers it implies it has medium-dry strength.

  • If it can’t be powdered with the application of strength also, it implies it has high dry strength.

Organic content

It smells like a decomposed organic matter and it increases with an increase in heating. The Colour would be dark.


Acid test: To check whether the soil has Ca or not, tested using HCL. This soil may show extra strength due to cementing capacity.


Shine test

Take a soil sample and cut with the knife, If it looks shiny it is plastic clay. If it has a dull surface it is a low plastic clay.


This is all about this article. See you soon in the next one.


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