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Soil Mechanics -1 Module-1 Origin of Soil Important Questions and Answers

📘 SOIL MECHANICS – MODULE 1

🌍 Origin of Soil & Weathering Actions

✍️ 1 MARK QUESTIONS (Very Short Answer)

Q1. What is soil?

Ans: Soil is the natural uncemented accumulation of mineral particles formed by weathering of rocks.

Q2. Define weathering.

Ans: Weathering is the process of breaking and decomposition of rocks into soil particles.

Q3. What is parent rock?

Ans: The original rock from which soil is formed is called parent rock.

Q4. Name types of weathering.

Ans: Physical, Chemical, and Biological weathering.

Q5. What is residual soil?

Ans: Soil formed and remaining at the same place of rock formation.

Q6. What is transported soil?

Ans: Soil moved from its origin by wind, water, ice, or gravity.

✍️ 2 MARK QUESTIONS (Short Answer)

Q1. State two differences between physical and chemical weathering.

Ans:

  • Physical weathering: No chemical change, only breaking of rock.

  • Chemical weathering: Chemical composition changes.

Q2. Define hydration.

Ans: Hydration is the chemical weathering process in which minerals absorb water and expand.

Q3. What is oxidation?

Ans: Oxidation is the reaction of oxygen with minerals, forming oxides like rust.

Q4. What is abrasion?

Ans: Abrasion is the wearing of rocks due to friction caused by wind, water, or glaciers.

Q5. Name types of transported soil.

Ans: Alluvial, Aeolian, Glacial, Marine, Lacustrine.

✍️ 5 MARK QUESTIONS (Medium Answer)

Q1. Explain physical weathering.

Ans:
Physical weathering is the breakdown of rocks into smaller particles without chemical change. It occurs due to temperature variation, frost action, abrasion, exfoliation, and pressure release. It produces coarse-grained soils and is common in deserts and cold regions.

Q2. Explain chemical weathering.

Ans:
Chemical weathering is the decomposition of rocks due to chemical reactions. It changes the mineral composition of rocks. Main types are hydration, hydrolysis, oxidation, carbonation, and solution. It produces fine-grained soils like clay.

Q3. Explain residual and transported soil.

Ans:
Residual soil remains at its place of formation. It is directly formed from parent rock. Transported soil is moved from its origin by natural agents like water, wind, and glaciers and deposited elsewhere.

Q4. Write short note on biological weathering.

Ans:
Biological weathering is caused by plants, animals, and microorganisms. Roots of plants enter cracks and break rocks. Burrowing animals loosen soil. Organic acids also contribute to rock decomposition.

Q5. State importance of soil in civil engineering.

Ans:
Soil supports foundations, acts as construction material, influences stability of structures, and is used in roads, embankments, and dams.

✍️ 10 MARK QUESTIONS (Long Answer)

Q1. Explain origin of soil in detail.

Ans:
Soil is formed by weathering of rocks over long periods. The parent rock breaks down due to physical, chemical, and biological weathering. The disintegrated material mixes with air, water, and organic matter to form soil. Factors affecting soil formation include parent material, climate, topography, biological activity, and time. Soil can be residual (formed in place) or transported (moved by agents like water, wind, ice, sea, and lakes). Soil formation is a continuous and slow geological process.

Q2. Explain physical weathering with causes.

Ans:
Physical weathering is the mechanical breakdown of rocks without chemical change. Causes include:

  • Temperature variation (expansion and contraction)

  • Frost action (freezing water expands in cracks)

  • Abrasion (wearing by wind/water/glacier)

  • Exfoliation (layer peeling)

  • Pressure release (uplift and expansion)
    It produces coarse particles and is common in dry and cold climates.

Q3. Explain chemical weathering and its types.

Ans:
Chemical weathering is the decomposition of rocks due to chemical reactions. It changes mineral composition and forms new minerals.

Types:

  • Hydration: absorption of water

  • Hydrolysis: reaction with water forming clay

  • Oxidation: reaction with oxygen forming rust

  • Carbonation: carbonic acid dissolves limestone

  • Solution: minerals dissolve in water

It produces fine soils and is common in humid climates.

Q4. Differentiate physical and chemical weathering.

Ans:
Physical weathering breaks rocks mechanically without changing composition, producing coarse particles and occurring in dry climates. Chemical weathering changes mineral composition, producing fine particles and occurring in humid climates.

Q5. Classify soil based on origin.

Ans:
Soil is classified as:

  1. Residual soil – formed at same place

  2. Transported soil – moved by agents:

    • Alluvial (river)

    • Aeolian (wind)

    • Glacial (ice)

    • Marine (sea)

    • Lacustrine (lake)

YOUTUBE : SOIL MECHANICS PLAY LIST  MODULE-1 : Origin of soil by Hasan Sir



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