Origin of Soil: Detailed Explanation in Civil Engineering
In geotechnical engineering (a branch of civil
engineering), understanding the origin of soil is fundamental because it
influences soil properties like strength, compressibility, permeability, and
behavior under loads. This affects foundation design, slope stability, and
earthwork.
Soil originates primarily from the weathering
(breakdown) of parent rocks, followed by transportation and deposition in some
cases.
1. Process of Soil Formation (Pedogenesis)
Soil forms through the gradual breakdown of rocks into
smaller particles, influenced by environmental factors over thousands of years.
1 Diagrammatic representation of soil formation processes
...
Caption: Diagrammatic representation of the overall
soil formation processes, showing weathering of parent rock leading to soil
profile development.
Soil Formation (Pedogenesis)- Factors, Process/Steps,
Examples
Caption: Step-by-step illustration of pedogenesis,
including additions, losses, translocations, and transformations in soil
horizons.
Caption: Diagram depicting soil structure formation
through various physical, chemical, and biological processes.
2. Types of Weathering
Weathering is the initial breakdown of rocks:
- Physical
(Mechanical): Disintegration without chemical change (e.g.,
freeze-thaw, thermal expansion).
- Chemical:
Alteration of mineral composition (e.g., oxidation, hydrolysis,
carbonation).
- Biological:
Action of plants, animals, and microorganisms.
Soil Weathering Processes
Caption: Rock cycle illustration highlighting
weathering processes contributing to soil formation.
2.1 - Processes of Weathering - Introduction | Soil Genesis
and ...
Caption: Detailed processes of physical, chemical,
and biological weathering.
Caption: Comprehensive illustration of different
weathering types and their effects on rock disintegration.
3. Factors Influencing Soil Formation (CLORPT)
Proposed by Hans Jenny, the five main factors are:
- Climate
(temperature and rainfall – most influential).
- Living
Organisms (vegetation, microbes).
- Relief
(topography).
- Parent
Material (original rock type).
- Time.
Factors that influence soil formation in Indian Conditions -
PMF IAS
Caption: Infographic showing key factors influencing
soil formation, particularly in specific regional conditions.
4. Classification Based on Origin
Soils are broadly classified into two types based on mode of
formation:
- Residual
Soils: Formed in place by weathering of parent rock (no
transportation). Common in tropical regions; often deep profiles with
gradual transition to bedrock.
- Transported
Soils: Weathered material transported by agents (wind, water, gravity,
glaciers) and deposited elsewhere. Most soils worldwide are transported.
What is Residual Soil and Transported Soil?
Caption: Comparison diagram of residual soil (in-situ
weathering) versus transported soil.
Residual Soil and Transported Soil -
Caption: Illustrative cross-section showing residual
soil profile overlying bedrock and examples of transported deposits.
Common Types of Transported Soils
- Alluvial
(river-deposited) → Often silty/clayey, good for foundations if compacted.
- Aeolian
(wind) → Loess; uniform, collapsible.
- Glacial
→ Till; dense, mixed sizes.
- Lacustrine/Marine
→ Fine-grained, compressible.
- Colluvial
(gravity) → At hill bases, unstable.
This origin classification helps civil engineers predict
soil behavior—e.g., residual soils may have variable strength with depth, while
transported soils depend on deposition environment