Formation of Soils- Physical and Chemical Disintegration | Type of Soils- Residual and Transported Soils

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In this article, we will discuss the formation of soils.


  1. Introduction  

Soil is defined as an unconsolidated material that comprises solid particles and voids. The void may comprise either air only, water, or both air and water. If the void is totally occupied by water, then the soil is said to be saturated soil and if the voids are totally occupied by air, then the soils are said to be dry soil.

Soil is used as construction material in various civil engineering projects and it supports structural foundations.

Rock is defined as a natural aggregate of mineralogical composition bounded by strong and cohesive force.


Formation of Soils


  2. Formation of Soils  

The soils are formed by the disintegration of rocks either physical disintegration or chemical disintegration.


  a. Physical disintegration  

Mechanical disintegration of rocks into small fragments due to different actions of geological agents is called physical disintegration. It occurs due to the following physical disintegration that is as follows:

1. Temperature change

Due to different coefficients of thermal expansion, expansion and contraction of minerals occur due to changes in temperature.

2. Wedging of Ice

Water in the pores and small cracks of rock gets frozen in cold climates. The disintegration of rocks takes place due to an increase in volume.

3. Spreading of roots

When the roots of trees grow up inside cracks and fissures, a force acts on rock and breaks it down.

4. Abrasion 

Due to abrasion, the rocks are disintegrated into soils. Abrasion is due to the movement of the geological agents over the surface of rocks.


  b. Chemical Disintegration  

Chemical disintegration/ Decomposition of rocks due to different chemical processes such as hydration, carbocation, oxidation, solution, hydrolysis, etc.

The soil formed by chemical disintegration doesn’t have the properties of parent rocks.

1. Hydration

Water combined with rock results in the formation of new chemical compounds.


2. Carbocation

Carbon dioxide reacts with water to form carbonic acid. This combines with rocks and disintegrates the rock into soil mass.


3. Oxidation

Oxygen ions combine with rock minerals. For example, the Formation of rush.


4. Solution

Some of the rock minerals form minerals from a solution with water when they get dissolved in water. A chemical reaction takes place in the solution and soils are formed.


5. Hydrolysis

In this process, water gets dissociated into H+ and OH ions.


  2. Type of Soils  

On the basis of the formation of soils, it can be divided into residual soils and transported soils.


  a. Residual Soils  

The soils remain at the place of formation of soils after the disintegration of rocks. The characteristics of residual soil are similar to parent rock characteristics.


  b. Transported soils  

The soils are transported a far distance from the place of formation due to the action of different geological agents such as wind, water, glacier, etc.

The characteristics of transported soil are different from parent rock characteristics. Soil deposits after transportation by a geological agent.


Read Also: How much Does Dirt Weight?


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