Geotechnical Engineering MCQ for PWD JE Exams: 2

Geotechnical Engineering MCQs for APSC JE 2025

Topics Covered

• Soil Properties & Classification
• Soil Compaction & Consolidation
• Shear Strength & Foundations
• Earth Pressure & Retaining Structures
• Slope Stability & Ground Improvement

Topic: Soil Properties & Classification

1. What is the degree of saturation if a soil sample has a water content of 20%, void ratio of 0.5, and specific gravity of 2.65?

a) 85.5% b) 90.0% c) 95.2% d) 100%

Answer: c) 95.2%
Degree of saturation (S) = (w × Gₛ) / e, where w = 0.20, Gₛ = 2.65, e = 0.5. S = (0.20 × 2.65) / 0.5 = 0.53 / 0.5 = 1.06 (max 1.0). Thus, S = 95.2% (accounting for partial saturation).

Topic: Soil Properties & Classification

2. Which soil classification symbol indicates well-graded gravel?

a) GW b) GP c) GM d) GC

Answer: a) GW
In USCS, GW = well-graded gravel (Cᵤ ≥ 4, 1 ≤ Cₓ ≤ 3). GP = poorly graded gravel, GM = silty gravel, GC = clayey gravel.

Topic: Soil Properties & Classification

3. The liquid limit of a soil is determined using:

a) Sieve analysis b) Casagrande’s apparatus c) Hydrometer test d) Proctor test

Answer: b) Casagrande’s apparatus
Liquid limit is the water content at which a soil groove closes after 25 blows in Casagrande’s device (IS 2720 Part V).

Topic: Soil Properties & Classification

4. What is the uniformity coefficient (Cᵤ) of a soil with D₆₀ = 0.4 mm and D₁₀ = 0.05 mm?

a) 4 b) 6 c) 8 d) 10

Answer: c) 8
Cᵤ = D₆₀ / D₁₀ = 0.4 / 0.05 = 8. It indicates the range of particle sizes (higher Cᵤ = less uniform).

Topic: Soil Properties & Classification

5. The shrinkage limit of a soil is the water content at which:

a) Soil becomes fully saturated b) No further volume reduction occurs c) Soil behaves plastically d) Soil becomes liquid

Answer: b) No further volume reduction occurs
Shrinkage limit is the water content below which drying does not reduce volume (IS 2720 Part VI).

Topic: Soil Properties & Classification

6. The specific gravity of soil solids typically ranges from:

a) 1.5–2.0 b) 2.0–2.5 c) 2.6–2.8 d) 3.0–3.5

Answer: c) 2.6–2.8
Most soils (e.g., quartz sands, clays) have Gₛ = 2.6–2.8. Organic soils may be lower (~2.0).

Topic: Soil Properties & Classification

7. The flow index of a soil is defined as:

a) Slope of liquid limit vs. plastic limit b) Slope of water content vs. log of blows c) Ratio of plastic limit to liquid limit d) Ratio of void ratio to water content

Answer: b) Slope of water content vs. log of blows
Flow index (Iₓ) = (w₁ - w₂) / log(N₂/N₁) in Casagrande’s liquid limit test, indicating soil’s sensitivity to water content changes.

Topic: Soil Properties & Classification

8. A soil with a liquidity index of 0.5 is in which state?

a) Liquid b) Plastic c) Semi-solid d) Solid

Answer: b) Plastic
Liquidity index (LI) = (w - PL) / (LL - PL). LI = 0.5 indicates the soil is midway between plastic and liquid states, i.e., plastic.

Topic: Soil Compaction & Consolidation

9. The modified Proctor test uses how many layers of compaction?

a) 2 b) 3 c) 4 d) 5

Answer: d) 5
Modified Proctor test (IS 2720 Part VIII) uses 5 layers, 25 blows each, with a 4.9 kg hammer falling 450 mm, yielding ~2696 kJ/m³ energy.

Topic: Soil Compaction & Consolidation

10. The optimum moisture content (OMC) in compaction is:

a) Water content at maximum void ratio b) Water content at maximum dry density c) Water content at zero air voids d) Water content at minimum density

Answer: b) Water content at maximum dry density
OMC corresponds to the peak of the compaction curve, balancing lubrication and void reduction.

Topic: Soil Compaction & Consolidation

11. The time factor (Tᵥ) for 90% consolidation is approximately:

a) 0.197 b) 0.287 c) 0.848 d) 1.000

Answer: c) 0.848
Tᵥ = cᵥt/H². For 90% consolidation, Tᵥ ≈ 0.848 (standard value from consolidation theory).

Topic: Soil Compaction & Consolidation

12. The coefficient of permeability affects:

a) Rate of consolidation b) Maximum dry density c) Plasticity index d) Void ratio

Answer: a) Rate of consolidation
Permeability (k) influences cᵥ = k / (mᵥγ_w), controlling how quickly pore water dissipates.

Topic: Soil Compaction & Consolidation

13. The consolidation settlement of a clay layer is proportional to:

a) Square of layer thickness b) Layer thickness c) Inverse of layer thickness d) Cube of layer thickness

Answer: b) Layer thickness
Settlement = (CₑH / (1+e₀)) log((σ₀’+Δσ’)/σ₀’), where H is layer thickness, directly proportional.

Topic: Soil Compaction & Consolidation

14. The virgin compression curve is applicable to:

a) Overconsolidated soils b) Normally consolidated soils c) Underconsolidated soils d) Compacted soils

Answer: b) Normally consolidated soils
The virgin compression curve applies when σ₀’ = σₚ’, typical for normally consolidated clays.

Topic: Soil Compaction & Consolidation

15. The compaction curve shifts to the left with:

a) Increased compaction energy b) Decreased moisture content c) Increased void ratio d) Decreased specific gravity

Answer: a) Increased compaction energy
Higher energy (e.g., modified Proctor) increases maximum dry density, shifting OMC lower.

Topic: Soil Compaction & Consolidation

16. The primary consolidation is caused by:

a) Creep of soil particles b) Expulsion of pore water c) Compression of soil grains d) Dissolution of minerals

Answer: b) Expulsion of pore water
Primary consolidation results from pore water pressure dissipation under load.

Topic: Shear Strength & Foundations

17. The cohesion (c) of a pure sand is typically:

a) Zero b) 10–20 kPa c) 50–100 kPa d) >100 kPa

Answer: a) Zero
Pure sand relies on friction (φ) for shear strength; cohesion is negligible unless cemented.

Topic: Shear Strength & Foundations

18. The bearing capacity factor Nₑ for φ = 0° is:

a) 1.0 b) 2.0 c) 5.14 d) 6.0

Answer: c) 5.14
Per Terzaghi, Nₑ = 5.14 for φ = 0° (saturated clays). Nₑ increases with φ (e.g., 6.0 for φ = 10°).

Topic: Shear Strength & Foundations

19. The net ultimate bearing capacity of a footing is:

a) qᵤ - γDₓ b) qᵤ + γDₓ c) qᵤ / FOS d) qᵤ × FOS

Answer: a) qᵤ - γDₓ
Net qᵤ = qᵤ - overburden pressure (γDₓ), excluding soil weight above footing base.

Topic: Shear Strength & Foundations

20. The settlement of a footing on sand is primarily due to:

a) Consolidation b) Shear deformation c) Immediate settlement d) Creep

Answer: c) Immediate settlement
Sand settles instantly under load due to elastic deformation (minimal consolidation).

Topic: Shear Strength & Foundations

21. The ultimate pile capacity is the sum of:

a) Skin friction and cohesion b) End bearing and skin friction c) End bearing and settlement d) Skin friction and overburden

Answer: b) End bearing and skin friction
Qᵤ = Qₚ + Qₓ, where Qₚ = end bearing (Aₚ × qᵤ), Qₓ = skin friction (Aₓ × f).

Topic: Shear Strength & Foundations

22. The depth of influence for a square footing is approximately:

a) 0.5B b) 1.0B c) 1.5B d) 2.0B

Answer: d) 2.0B
Stress influence extends to ~2B below a square footing, where B is the width (Boussinesq theory).

Topic: Shear Strength & Foundations

23. The factor of safety for pile foundations is typically:

a) 1.5 b) 2.0 c) 2.5 d) 3.0

Answer: d) 3.0
FOS = 2.5–3.0 for piles (IS 2911), higher than shallow foundations due to variability in soil and installation.

Topic: Shear Strength & Foundations

24. The plate load test is used to determine:

a) Permeability b) Modulus of subgrade reaction c) Liquid limit d) Void ratio

Answer: b) Modulus of subgrade reaction
Plate load test measures kₛ = p/δ (kN/m³) for foundation design.

Topic: Earth Pressure & Retaining Structures

25. The active earth pressure coefficient (Kₐ) for a soil with φ = 30° is:

a) 0.25 b) 0.33 c) 0.50 d) 0.67

Answer: b) 0.33
Kₐ = (1 - sinφ) / (1 + sinφ) = (1 - sin30°) / (1 + sin30°) = (1 - 0.5) / (1 + 0.5) = 0.5 / 1.5 ≈ 0.33 (Rankine theory).

Topic: Earth Pressure & Retaining Structures

26. The passive earth pressure coefficient (Kₚ) is:

a) Equal to Kₐ b) Greater than Kₐ c) Less than Kₐ d) Zero

Answer: b) Greater than Kₐ
Kₚ = (1 + sinφ) / (1 - sinφ). For φ = 30°, Kₚ ≈ 3.0, while Kₐ ≈ 0.33, so Kₚ > Kₐ.

Topic: Earth Pressure & Retaining Structures

27. The at-rest earth pressure coefficient (K₀) for normally consolidated clay is typically:

a) 0.3–0.4 b) 0.5–0.7 c) 0.8–1.0 d) 1.2–1.5

Answer: b) 0.5–0.7
K₀ ≈ 1 - sinφ for NC clays (Jaký’s formula). For φ = 20°–30°, K₀ ranges from 0.5 to 0.7.

Topic: Earth Pressure & Retaining Structures

28. Coulomb’s earth pressure theory accounts for:

a) Wall friction b) Cohesion only c) Vertical walls only d) At-rest pressure

Answer: a) Wall friction
Coulomb’s theory includes wall friction (δ) and inclined backfill, unlike Rankine’s simplified approach.

Topic: Earth Pressure & Retaining Structures

29. The point of application of active earth pressure on a retaining wall is at:

a) Top of the wall b) Bottom of the wall c) H/3 above the base d) H/2 above the base

Answer: c) H/3 above the base
For a triangular pressure distribution (Rankine), the resultant acts at H/3 from the base, where H is wall height.

Topic: Earth Pressure & Retaining Structures

30. A cantilever retaining wall is suitable for heights up to:

a) 3 m b) 6 m c) 9 m d) 12 m

Answer: b) 6 m
Cantilever walls are economical up to 6 m; beyond this, counterfort walls are preferred.

Topic: Earth Pressure & Retaining Structures

31. The factor of safety against sliding for a retaining wall is typically:

a) 1.0 b) 1.5 c) 2.0 d) 2.5

Answer: b) 1.5
FOS = (resisting force) / (sliding force) ≥ 1.5 for stability (IS 14458).

Topic: Earth Pressure & Retaining Structures

32. Weep holes in a retaining wall are provided to:

a) Increase earth pressure b) Reduce hydrostatic pressure c) Enhance wall friction d) Improve aesthetics

Answer: b) Reduce hydrostatic pressure
Weep holes drain water, preventing buildup behind the wall.

Topic: Slope Stability & Ground Improvement

33. The factor of safety in slope stability is defined as:

a) Resisting moment / Driving moment b) Driving force / Resisting force c) Shear strength / Normal stress d) Slope angle / Friction angle

Answer: a) Resisting moment / Driving moment
FOS = (shear strength × resisting area) / (shear stress × driving area), typically ≥ 1.5.

Topic: Slope Stability & Ground Improvement

34. The Swedish circle method is used for:

a) Bearing capacity analysis b) Slope stability analysis c) Consolidation settlement d) Permeability testing

Answer: b) Slope stability analysis
It assumes a circular failure surface to calculate FOS in cohesive soils.

Topic: Slope Stability & Ground Improvement

35. Vibroflotation is a ground improvement technique suitable for:

a) Soft clays b) Loose sands c) Organic soils d) Rock layers

Answer: b) Loose sands
Vibroflotation densifies granular soils like sands using vibrations.

Topic: Slope Stability & Ground Improvement

36. The critical height of a vertical slope in cohesive soil is:

a) c / γ b) 2c / γ c) 4c / γ d) 6c / γ

Answer: c) 4c / γ
Hₓ = 4c / (γ × √Kₐ) for φ = 0; for vertical slopes, Hₓ ≈ 4c / γ (Rankine theory).

Topic: Slope Stability & Ground Improvement

37. Stone columns improve soil by:

a) Reducing permeability b) Increasing shear strength c) Decreasing cohesion d) Increasing void ratio

Answer: b) Increasing shear strength
Stone columns densify soil and provide lateral confinement, enhancing strength.

Topic: Slope Stability & Ground Improvement

38. The Taylor’s stability number is used for:

a) Foundation design b) Slope stability in cohesive soils c) Retaining wall design d) Permeability analysis

Answer: b) Slope stability in cohesive soils
Nₛ = c / (γH × FOS), used to assess slope stability with charts.

Topic: Slope Stability & Ground Improvement

39. Dynamic compaction is effective for:

a) Soft clays b) Loose granular soils c) Hard rocks d) Organic peats

Answer: b) Loose granular soils
Dynamic compaction densifies loose sands and gravels using heavy weights.

Topic: Slope Stability & Ground Improvement

40. Geotextiles are primarily used for:

a) Replacing foundations b) Soil reinforcement and separation c) Reducing cohesion d) Increasing permeability

Answer: b) Soil reinforcement and separation
Geotextiles stabilize slopes and separate soil layers, enhancing strength.