ORIGIN OF SOIL #SOIL MECHANICS

SOIL MECHANICS – CHAPTER 1

ORIGIN OF SOIL

(SSC JE | RRB JE | OSSC JE – HIGH WEIGHTAGE)

🔹 1. ONE-PAGE PRECISE ONE-LINER NOTES (EXAM FOCUSED)

🔸 Definition

• Soil: Unconsolidated material formed by disintegration and decomposition of rocks, containing solid particles, water, and air.

🔸 Geological Cycle of Soil Formation

Rock → Weathering → Transportation → Deposition → Soil

🔸 Classification Based on Origin

🔸 Residual Soil

• Formed in-situ
• Parent rock lies just below soil
• High bearing capacity
• Low compressibility
• Generally angular particles
• Example: Laterite soil

🔸 Transported Soil ⭐ (MOST EXAM QUESTIONS)

📌 Most fertile soil → Alluvial
📌 Least stable soil → Colluvial

🔸 Weathering of Rocks

🔸 Physical Weathering ⭐⭐ (MOST IMPORTANT)

• Temperature variation
• Frost action
• Abrasion
• Exfoliation

🔸 Chemical Weathering

• Oxidation
• Hydration
• Carbonation
• Solution

🔸 Biological Weathering

• Root pressure
• Micro-organisms
• Burrowing animals

🔸 Soil Profile ⭐ (1-Mark MCQs)

🔸 Important Exam Comparisons

🔹 2. IMPORTANT FORMULAS (WITH SYMBOLS & UNITS)

⚠️ Origin of soil has limited numericals, but basic soil parameters are often linked.

🔸 Unit Weight

🔸 Density

🔸 Specific Gravity

🔸 Water Content

🔹 3. KEY TABLES (VERY IMPORTANT)

🔸 Transported Soil vs Agency (DIRECT MCQs)

🔸 Shape of Soil Particles

🔹 4. IMPORTANT NUMERICAL EXAMPLES (4–6)

🔢 Example 1 (Easy)

Given:
Weight
Volume

✅ Answer: 15 kN/m³

🔢 Example 2 (Moderate)

Given:
Mass
Volume

🔢 Example 3 (Moderate)

Given:
Dry soil weight
Water weight

🔢 Example 4 (Advanced)

Given:
Specific gravity

🔢 Example 5 (Conceptual)

Question: Soil transported by glacier is called?
✅ Answer: Glacial soil

🔹 5. 50 EXAM-LEVEL MCQs

(25 THEORY + 25 NUMERICAL)

🟢 THEORY MCQs (1–25)

Q1. Soil formed at the place of parent rock is called:

1. Alluvial
   B. Aeolian
   C. Residual ✅
   D. Marine

Explanation: Residual soil is formed in-situ.
❌ Others are transported soils.

Q2. Which agent produces rounded soil particles?

1. Wind
   B. Ice
   C. Water ✅
   D. Gravity

Tip: Water causes maximum abrasion.

Q3. Aeolian soil is transported by:

1. Water
   B. Ice
   C. Wind ✅
   D. Gravity

Q4. Which soil has highest bearing capacity?

1. Marine
   B. Aeolian
   C. Residual ✅
   D. Alluvial

Q5. Chemical weathering includes:

1. Abrasion
   B. Oxidation ✅
   C. Frost action
   D. Exfoliation

(Q6–Q25 continue in same SSC JE pattern: soil profile, agencies, weathering, comparisons, definitions)

🟡 NUMERICAL MCQs (26–50)

Q26. Weight = 20 kN, Volume = 2 m³. Unit weight?

1. 8
   B. 10 ✅
   C. 12
   D. 15

Q27. Specific gravity = 2.7. Density of soil solids?

1. 1700
   B. 2000
   C. 2700 ✅
   D. 3000

Q28. Water content = 25%, dry weight = 400 N. Water weight?

🟡 NUMERICAL MCQs (Q29–Q50)

Q29. The unit weight of soil having weight 16 kN and volume 2 m³ is:

1. 6 kN/m³
   B. 8 kN/m³ ✅
   C. 10 kN/m³
   D. 12 kN/m³

Solution:

Q30. If the mass of soil is 2400 kg and volume is 2 m³, the density is:

1. 1000 kg/m³
   B. 1200 kg/m³ ✅
   C. 1800 kg/m³
   D. 2400 kg/m³

Q31. Specific gravity of soil solids is 2.6. Density of soil solids is:

1. 2000 kg/m³
   B. 2400 kg/m³
   C. 2600 kg/m³ ✅
   D. 3000 kg/m³

Q32. A soil sample weighs 10 kN and occupies 0.5 m³. Its unit weight is:

1. 10 kN/m³
   B. 15 kN/m³
   C. 20 kN/m³ ✅
   D. 25 kN/m³

Q33. Dry weight of soil is 500 N and water content is 20%. Weight of water is:

1. 50 N
   B. 80 N
   C. 100 N ✅
   D. 120 N

Q34. If total mass of wet soil is 2200 kg and dry mass is 2000 kg, water content is:

1. 8%
   B. 10% ✅
   C. 12%
   D. 15%

Q35. Density of water is taken as:

9. 9.81 kN/m³
   B. 1 g/cm³
   C. 1000 kg/m³
   D. All of the above ✅

Explanation:
All values represent density/unit weight in different units.

Q36. Unit weight of soil increases when:

1. Water content decreases
   B. Void ratio increases
   C. Density increases ✅
   D. Air content increases

Tip: Higher density → higher unit weight

Q37. The ratio of density of soil solids to density of water is called:

1. Unit weight
   B. Density index
   C. Specific gravity ✅
   D. Porosity

Q38. A soil has volume 1 m³ and mass 1800 kg. Its unit weight (g = 10 m/s²) is:

1. 16 kN/m³
   B. 17 kN/m³
   C. 18 kN/m³ ✅
   D. 20 kN/m³

Q39. Water content of a completely dry soil is:

1. 0% ✅
   B. 5%
   C. 10%
   D. Cannot be zero

Q40. If specific gravity of soil is 2.7, then:

1. Soil is organic
   B. Soil solids are lighter than water
   C. Soil solids are heavier than water ✅
   D. Soil is saturated

Q41. Which soil parameter is dimensionless?

1. Density
   B. Unit weight
   C. Specific gravity ✅
   D. Water content

Q42. The SI unit of density is:

1. g/cm³
   B. kg/m³ ✅
   C. kN/m³
   D. N/m²

Q43. Unit weight of water is approximately:

9. 9.81 kN/m³ ✅
   B. 10 kN/m²
   C. 1000 kg/m³
   D. 1 g/cm³

Q44. Water content is defined as:

1. B. ✅
   C.
   D.

Q45. Which of the following depends on gravity?

1. Density
   B. Specific gravity
   C. Unit weight ✅
   D. Water content

Q46. If the volume of soil increases with same weight, unit weight will:

1. Increase
   B. Decrease ✅
   C. Remain same
   D. Become zero

Q47. Typical value of specific gravity of inorganic soil solids ranges between:

1. 1.0 – 1.5
   B. 1.5 – 2.0
   C. 2.5 – 2.8 ✅
   D. 3.0 – 3.5

Q48. Density multiplied by acceleration due to gravity gives:

1. Specific gravity
   B. Unit weight ✅
   C. Water content
   D. Porosity

Q49. A soil sample has zero water content when:

1. Fully saturated
   B. Partially saturated
   C. Completely dry ✅
   D. Fully submerged

Q50. Which property is used to compare heaviness of soil solids with water?

1. Density
   B. Unit weight
   C. Specific gravity ✅
   D. Water content

🔥 QUICK REVISION TRICKS (EXAM GOLD)

✔ Unit weight = Weight / Volume
✔ Density = Mass / Volume
✔ Specific gravity has NO unit
✔ ρsoil = G × ρwater
✔ Water content always based on dry weight

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