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Origin of Soil
Soil

Origin and Formation of Soil

Origin and Fromation of Soil

  • Rock + Organic matter = Soil
  • The Soil is composed of particles formed from the disintegration of rocks. The void space between the particles may contain air, water, or both.
    Origin and Formation of Soil
  • The soil particles may contain organic matter.
  • The formation of soil particles takes place by two processes 
(a) Physical weathering
   
(b) Chemical weathering


A) Physical Weathering:
  • The physical weathering process is Erosion of Rock by wind, water, Glacier, etc. and penetration of plant roots
  • A disintegration of rocks due to alternate freezing and thawing cycle. Soil so formed retained the minerals that were present in the parent rock, soil so formed are coarse grain examples sand, gravel.
  •  Their shape may be angular, subangular, surrounded, and rounded.
  • Soil so formed does not have the bond between the particles and hence they are said to have a single grain structure.

B) Chemical Weathering:
  • It occurs due to the action of Acid and Alkalies present in water, air, and glacier.
  • Chemical weathering leads to the formation of crystalline particles of small size (< 2 microns) known as clay minerals. 
  • The density of these minerals is different from that of Parent Rock.
  • Clay minerals have a “Plate-like” structure having a large specific surface area (Surface area per unit mass or volume).
  • The identity of these minerals is different from Parent Rock.
  • Thus surface bonding forces are more predominant in these soil.
  • The presence of water in the soil influences the engineering properties significantly. 

 Residual or Transported Soil
  • Soils that remain at the location of their formation are called Residual Soil.
  • Soils that are transported from their place of origin by wind, water, or glacier, are called Transported Soil.
  • Most residual soils are weakly bonded, they have widely varying void ratios. They contain angular rock segments of varying sizes. Residual soils have better engineering properties.

 According to the transporting agency, soils are classified as:

1. Alluvial Deposit- Deposited by river water. 

2. Lacustrine Deposit- Deposited by still water of lakes. 

3. Marine Deposit- Deposited by seawater. 

4. Aeolian Deposit- Deposited by the wind.

5. Glacial Deposit- Deposited by ice. ex:- Drift, Tilt, and outwash.

 6. Colluvial Deposit- Deposited by gravity. ex:- Talus- found at foot of hills.

 1. Different Types of Soil
2. Soil water Relationship
3. Important Soil water Relationship
4. Water content Determination
5. Unit weight Relationship
6. Index Properties of Soil
7. Consistency Limit

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