SOIL MECHANICS ( MCQs)

SOIL MECHANICS ( MCQs)
📘 SSC JE | RRB JE | State AE/JE –  EXAM LEVEL

🧪 PART A – SOIL MECHANICS

Difficulty: Easy → Moderate → Tricky
Pattern: PYQ-oriented | Theory + Numericals
Each question includes Answer + Explanation

🔹 SOIL MECHANICS – MOCK TEST (Q1–Q75)

Q1. The soil which shows plasticity only within a narrow range of water content is:

1. Clay
   B. Silt
   C. Gravel
   D. Sand

✅ Answer: B
📝 Explanation: Silt has a very small plasticity range compared to clay.

Q2. Which soil property governs the behavior of soil under load?

1. Texture
   B. Structure
   C. Consistency
   D. Shear strength

✅ Answer: D
📝 Explanation: Shear strength controls failure and deformation under load.

Q3. The ratio of volume of voids to volume of solids is called:

1. Porosity
   B. Void ratio
   C. Degree of saturation
   D. Water content

✅ Answer: B
📝 Explanation:
Void ratio

Q4. Which soil is best suited for earthen dams?

1. Gravel
   B. Sand
   C. Clay
   D. Silt

✅ Answer: C
📝 Explanation: Clay has low permeability, preventing seepage.

Q5. Effective stress in soil is given by:

1. Total stress – pore pressure
   B. Total stress + pore pressure
   C. Pore pressure – total stress
   D. Depends on soil type

✅ Answer: A
📝 Explanation:

Q6. If degree of saturation is 100%, soil is:

1. Dry
   B. Partially saturated
   C. Fully saturated
   D. Impermeable

✅ Answer: C
📝 Explanation: 100% saturation means all voids are filled with water.

Q7. Which test is used to determine liquid limit?

1. Shrinkage test
   B. Casagrande test
   C. Proctor test
   D. Vane shear test

✅ Answer: B
📝 Explanation: Casagrande apparatus is used for liquid limit.

Q8. Plasticity Index (PI) is:

1. LL – PL
   B. PL – SL
   C. LL – SL
   D. PL – LL

✅ Answer: A
📝 Explanation:

Q9. Soil having PI = 0 is classified as:

1. Clay
   B. Silt
   C. Sand
   D. Non-plastic soil

✅ Answer: D
📝 Explanation: PI = 0 indicates non-plastic soil.

Q10. Which soil shows highest compressibility?

1. Sand
   B. Gravel
   C. Clay
   D. Silt

✅ Answer: C
📝 Explanation: Clay particles are small and compressible.

🔹 PERMEABILITY & SEEPAGE

Q11. Unit of coefficient of permeability is:

1. m²/s
   B. m/s
   C. m³/s
   D. Dimensionless

✅ Answer: B
📝 Explanation: Permeability is velocity (length/time).

Q12. Darcy’s law is valid for:

1. Turbulent flow
   B. Laminar flow
   C. Both
   D. No flow

✅ Answer: B
📝 Explanation: Darcy’s law applies only to laminar flow.

Q13. Which soil has maximum permeability?

1. Clay
   B. Silt
   C. Sand
   D. Gravel

✅ Answer: D
📝 Explanation: Larger particle size → higher permeability.

Q14. Critical hydraulic gradient depends upon:

1. Void ratio
   B. Particle size
   C. Specific gravity
   D. Degree of saturation

✅ Answer: C
📝 Explanation:

Q15. Seepage pressure acts:

1. Downward
   B. Upward
   C. Horizontally
   D. Randomly

✅ Answer: B
📝 Explanation: Seepage pressure acts opposite to gravity.

🔹 COMPACTION

Q16. Maximum dry density occurs at:

1. Liquid limit
   B. Plastic limit
   C. Optimum moisture content
   D. Shrinkage limit

✅ Answer: C
📝 Explanation: OMC gives maximum dry density.

Q17. Compaction increases:

1. Permeability
   B. Compressibility
   C. Shear strength
   D. Void ratio

✅ Answer: C
📝 Explanation: Compaction improves strength and reduces voids.

Q18. Proctor test determines:

1. Permeability
   B. Shear strength
   C. Compaction characteristics
   D. Liquid limit

✅ Answer: C

Q19. Heavy compaction test gives:

1. Lower MDD
   B. Higher MDD
   C. Same MDD
   D. No effect

✅ Answer: B
📝 Explanation: Higher energy → higher MDD.

Q20. Which soil requires maximum compaction energy?

1. Clay
   B. Sand
   C. Silt
   D. Peat

✅ Answer: A

🔹 CONSOLIDATION

Q21. Consolidation occurs due to:

1. Expulsion of air
   B. Expulsion of water
   C. Compression of solids
   D. Chemical reaction

✅ Answer: B

Q22. Primary consolidation depends on:

1. Permeability
   B. Plasticity
   C. Particle size
   D. Temperature

✅ Answer: A

Q23. Time factor is used to calculate:

1. Settlement
   B. Degree of consolidation
   C. Void ratio
   D. Effective stress

✅ Answer: B

Q24. Normally consolidated soil has:

1. OCR < 1
   B. OCR = 1
   C. OCR > 1
   D. OCR = 0

✅ Answer: B

Q25. Secondary consolidation occurs due to:

1. Water expulsion
   B. Air expulsion
   C. Creep of soil
   D. Load increase

✅ Answer: C

🔹 SHEAR STRENGTH

Q26. Mohr-Coulomb failure criterion is:

1. Linear
   B. Parabolic
   C. Hyperbolic
   D. Exponential

✅ Answer: A

Q27. Cohesion of clean sand is:

1. High
   B. Moderate
   C. Zero
   D. Variable

✅ Answer: C

Q28. Angle of internal friction depends on:

1. Particle size
   B. Shape
   C. Arrangement
   D. All of the above

✅ Answer: D

Q29. Undrained shear strength is determined by:

1. Triaxial CD test
   B. Triaxial CU test
   C. Triaxial UU test
   D. Direct shear test

✅ Answer: C

Q30. Vane shear test is suitable for:

1. Sand
   B. Gravel
   C. Soft clay
   D. Hard rock

✅ Answer: C

🔹 SOIL CLASSIFICATION

Q31. Unified Soil Classification System is based on:

1. Plasticity
   B. Grain size
   C. Plasticity & grain size
   D. Color

✅ Answer: C

Q32. Well graded soil means:

1. Uniform size
   B. Wide range of sizes
   C. Poorly compacted
   D. Clayey soil

✅ Answer: B

Q33. Cu for well-graded sand should be:

1. < 2
   B. > 6
   C. = 1
   D. = 4

✅ Answer: B

Q34. Soil symbol “CL” represents:

1. Low plastic clay
   B. High plastic clay
   C. Silt
   D. Organic soil

✅ Answer: A

Q35. Plasticity chart was developed by:

1. Terzaghi
   B. Casagrande
   C. Rankine
   D. Coulomb

✅ Answer: B

🔹 NUMERICAL / CONCEPTUAL MIX

Q36. If void ratio = 0.6, porosity is:

37. 37.5%
    B. 60%
    C. 45%
    D. 50%

✅ Answer: A
📝 Explanation:

Q37. Dry unit weight increases when:

1. Water content increases
   B. Compaction increases
   C. Void ratio increases
   D. Saturation decreases

✅ Answer: B

Q38. Capillary rise is maximum in:

1. Sand
   B. Silt
   C. Clay
   D. Gravel

✅ Answer: C

Q39. Stress transmitted through soil skeleton is:

1. Total stress
   B. Neutral stress
   C. Effective stress
   D. Excess stress

✅ Answer: C

Q40. Which soil is most suitable for road subgrade?

1. Clay
   B. Silt
   C. Well-graded sand
   D. Peat

✅ Answer: C

🔹 SOIL MECHANICS – MOCK TEST (Q41–Q75)

Level: Moderate → Tricky | Focus: PYQs + Numericals
Each question includes Answer + Explanation

---

🔹 EFFECTIVE STRESS & SEEPAGE (ADVANCED)

Q41. A saturated soil has total unit weight = 20 kN/m³. Unit weight of water = 10 kN/m³. Submerged unit weight is:
A. 10 kN/m³
B. 20 kN/m³
C. 30 kN/m³
D. 0

✅ Answer: A
📝 Explanation:
γ′ = γ_sat − γ_w = 20 − 10 = 10 kN/m³

---

Q42. Quick sand condition occurs when:
A. Seepage force = zero
B. Effective stress = total stress
C. Effective stress = zero
D. Pore pressure = zero

✅ Answer: C
📝 Explanation:
At critical hydraulic gradient, effective stress becomes zero, causing boiling.

---

Q43. A soil has e = 0.8 and G = 2.7. Critical hydraulic gradient is:
A. 0.95
B. 1.0
C. 0.85
D. 0.75

✅ Answer: A
📝 Explanation:

$$i_c = \frac{G-1}{1+e} = \frac{2.7-1}{1+0.8} = \frac{1.7}{1.8} \approx 0.95$$

---

Q44. Effective stress in soil increases due to:
A. Increase in pore pressure
B. Decrease in total stress
C. Lowering of water table
D. Saturation

✅ Answer: C
📝 Explanation:
Lowering water table reduces pore pressure → effective stress increases.

---

🔹 COMPACTION & FIELD CONTROL

Q45. Zero air voids curve represents:
A. Maximum void ratio
B. 100% saturation
C. Minimum dry density
D. Fully dry soil

✅ Answer: B
📝 Explanation:
Zero air voids = no air → 100% saturated soil

---

Q46. For the same soil, modified Proctor test compared to standard Proctor gives:
A. Lower OMC, lower MDD
B. Higher OMC, lower MDD
C. Lower OMC, higher MDD
D. Same OMC, same MDD

✅ Answer: C
📝 Explanation:
Higher energy → higher MDD and lower OMC

---

Q47. Relative compaction is defined as:

• A. $ \frac{\gamma_d(\text{field})}{\gamma_d(\text{lab})} $

• B. $ \frac{\gamma_d(\text{lab})}{\gamma_d(\text{field})} $

• C. $ \frac{e_{\text{field}}}{e_{\text{lab}}} $

• D. $ \frac{w_{\text{field}}}{w_{\text{lab}}} $

✅ Answer: A
📝 Explanation:
Relative compaction = field dry density / lab max dry density

---

🔹 CONSOLIDATION (NUMERICAL & CONCEPTUAL)

Q48. Primary consolidation settlement depends mainly on:
A. Void ratio
B. Compressibility of soil
C. Thickness of clay layer
D. All of the above

✅ Answer: D
📝 Explanation:
Settlement equation includes e, Cc, H

---

Q49. Degree of consolidation is 90% when time factor (Tv) is approximately:
A. 0.197
B. 0.287
C. 0.848
D. 1.0

✅ Answer: C
📝 Explanation:
From standard consolidation charts, Tv ≈ 0.848 for 90%

---

Q50. Coefficient of consolidation depends on:
A. Permeability
B. Compressibility
C. Unit weight of water
D. All of the above

✅ Answer: D
📝 Explanation:

$$C_v = \frac{k}{m_v \cdot \gamma_w}$$​

---

Q51. Double drainage condition reduces consolidation time by factor of:
A. 2
B. 4
C. 8
D. 16

✅ Answer: B
📝 Explanation:
Time ∝ (drainage path)² → H/2 gives 1/4 time

---

🔹 SHEAR STRENGTH (TRICKY PYQs)

Q52. For purely cohesive soil, angle of internal friction (ϕ) is:
A. 0°
B. 15°
C. 30°
D. 45°

✅ Answer: A
📝 Explanation:
Clay under undrained condition → ϕ = 0

---

Q53. Failure envelope in UU triaxial test is:
A. Curved
B. Horizontal
C. Inclined straight line
D. Vertical

✅ Answer: B
📝 Explanation:
Undrained test → shear strength independent of normal stress.

---

Q54. In direct shear test, failure plane is:
A. Natural
B. Predetermined
C. Random
D. Circular

✅ Answer: B
📝 Explanation:
Failure occurs along predefined horizontal plane.

---

Q55. Which test gives least reliable shear strength parameters?
A. Triaxial test
B. Direct shear test
C. Vane shear test
D. UCS test

✅ Answer: B
📝 Explanation:
Non-uniform stress distribution in direct shear test.

---

🔹 SOIL CLASSIFICATION & INDEX PROPERTIES

Q56. A soil has LL = 40% and PI = 10%. It lies:
A. Above A-line
B. Below A-line
C. On A-line
D. Organic soil zone

✅ Answer: B
📝 Explanation:
Low PI → silt zone (below A-line)

---

Q57. Which soil shows maximum swelling?
A. Kaolinite
B. Illite
C. Montmorillonite
D. Quartz

✅ Answer: C
📝 Explanation:
Montmorillonite has high surface area & water absorption

---

Q58. Activity of soil is defined as:
A. PI / clay fraction
B. LL / PL
C. PI / sand content
D. Void ratio / water content

✅ Answer: A
📝 Explanation:
Activity = PI / % clay fraction

---

🔹 MIXED NUMERICAL PYQs

Q59. If water content = 20%, G = 2.7, e = 0.6, degree of saturation is:
A. 60%
B. 75%
C. 90%
D. 100%

✅ Answer: B
📝 Explanation:

$$S = \frac{w \cdot G}{e} = \frac{0.2 \times 2.7}{0.6} = 0.75 = 75\%$$

---

Q60. Bulking of sand is maximum at water content of about:
A. 0%
B. 5–8%
C. 15–20%
D. 30%

✅ Answer: B
📝 Explanation:
Bulking peaks at low moisture (~5–8%)

---

Q61. Which soil property is most affected by structure?
A. Specific gravity
B. Permeability
C. Water content
D. Particle size

✅ Answer: B

---

Q62. Stress at a point in soil due to surface load is calculated using:
A. Rankine theory
B. Coulomb theory
C. Boussinesq equation
D. Darcy law

✅ Answer: C

---

Q63. Negative pore water pressure occurs in:
A. Saturated soil
B. Dry soil
C. Capillary zone
D. Quick sand

✅ Answer: C

---

Q64. Which soil is least suitable for foundation?
A. Dense sand
B. Gravel
C. Soft clay
D. Hard clay

✅ Answer: C

---

Q65. A soil sample fails in UCS test at 100 kN/m². Undrained shear strength is:
A. 50 kN/m²
B. 100 kN/m²
C. 200 kN/m²
D. 25 kN/m²

✅ Answer: A
📝 Explanation:

$$q_u = 2c_u \implies c_u = \frac{q_u}{2}$$

---

🔹 HIGH-LEVEL TRICKY PYQs

Q66. Consolidation settlement is fastest in:
A. Clay
B. Silt
C. Sand
D. Peat

✅ Answer: C

---

Q67. Which test directly gives coefficient of permeability in lab?
A. Falling head test
B. Proctor test
C. Consolidation test
D. Triaxial test

✅ Answer: A

---

Q68. Increase in effective stress causes:
A. Increase in void ratio
B. Decrease in shear strength
C. Increase in shear strength
D. Soil liquefaction

✅ Answer: C

---

Q69. For cohesionless soil, bearing capacity depends mainly on:
A. Cohesion
B. Angle of friction
C. Water content
D. Plasticity

✅ Answer: B

---

Q70. Which condition is assumed in Terzaghi’s consolidation theory?
A. Soil is isotropic
B. Flow is laminar
C. Darcy’s law is valid
D. All of the above

✅ Answer: D

---

🔹 FINAL PYQ-LEVEL QUESTIONS

Q71. Which soil shows collapse on wetting?
A. Clay
B. Loess
C. Sand
D. Gravel

✅ Answer: B

---

Q72. Liquefaction occurs mainly in:
A. Dry sand
B. Saturated sand
C. Clay
D. Gravel

✅ Answer: B

---

Q73. The failure surface in triaxial compression is inclined at:
A. 30°
B. 45°
C. 45° + ϕ/2
D. 45° − ϕ/2

✅ Answer: D

---

Q74. Which soil parameter is independent of sample size?
A. Void ratio
B. Water content
C. Density
D. Permeability

✅ Answer: B

---

Q75. Best soil for retaining wall backfill is:
A. Clay
B. Silt
C. Well-graded sand
D. Peat

✅ Answer: C