Slope Stability

Question 1

1. Slope stability analysis deals with ___.
   A. Soil permeability B. Resistance of slopes against failure C. Compaction D. Lateral movement of walls

Answer 1

✅ Answer: B – Resistance of slopes against failure
Focuses on equilibrium and shear strength.

Question 2

2. The main cause of slope failure is ___.
   A. Excessive shear stress B. Lack of cohesion C. Heavy equipment D. Rock structure

Answer 2

✅ Answer: A – Excessive shear stress
Failure when τ > τ_max = c + σ′tanφ.

Question 3

3. The most common type of slope failure in homogeneous soil is ___.
   A. Plane failure B. Circular (rotational) failure C. Flow slide D. Wedge failure

Answer 3

✅ Answer: B – Circular failure
Typical for cohesive soils.

Question 4

4. Plane failure is common in ___.
   A. Homogeneous clay slopes B. Layered or jointed rock slopes C. Embankment soils D. Compacted fills

Answer 4

✅ Answer: B – Layered or jointed rock slopes
Failure along weak planes.

Question 5

5. The factor of safety (F.S.) for slope stability is ___.
   A. Shear strength / shear stress B. Stress / strain C. Load / strength D. Force × distance

Answer 5

✅ Answer: A – Shear strength / shear stress
Measures margin against failure.

Question 6

6. A slope is safe if the factor of safety is ___.
   A. <1 B. =1 C. >1 D. 0

Answer 6

✅ Answer: C – >1
Usually F.S. = 1.3–1.5 for long-term.

Question 7

7. The method of slices is used in ___.
   A. Earth pressure B. Slope stability analysis C. Compaction test D. Consolidation test

Answer 7

✅ Answer: B – Slope stability analysis
Divides slip surface into slices for computation.

Question 8

8. The Swedish slip circle method is also called ___.
   A. Fellenius method B. Bishop’s method C. Taylor’s method D. Rankine’s method

Answer 8

✅ Answer: A – Fellenius method
Simplified method assuming circular failure.

Question 9

9. Bishop’s method of slices differs by considering ___.
   A. Inter-slice shear forces B. Plane surfaces C. Ignoring water D. Only cohesion

Answer 9

✅ Answer: A – Inter-slice shear forces
Improves accuracy over Fellenius.

Question 10

10. The factor of safety in terms of moment equilibrium is ___.
    A. ΣM_resisting / ΣM_driving B. ΣM_driving / ΣM_resisting C. ΣF_resisting / ΣF_driving D. Σσ / Στ

Answer 10

✅ Answer: A – ΣM_resisting / ΣM_driving
Standard approach for rotational failures.

Question 11

11. The critical slip surface is the one with ___.
    A. Minimum F.S. B. Maximum F.S. C. Maximum area D. Minimum depth

Answer 11

✅ Answer: A – Minimum factor of safety
Represents probable failure surface.

Question 12

12. The main resisting force in slope stability is ___.
    A. Gravity B. Cohesion + friction C. Pore pressure D. External load

Answer 12

✅ Answer: B – Cohesion + friction
Shear strength of soil.

Question 13

13. The main driving force in slope failure is ___.
    A. Soil weight component parallel to slope B. Cohesion C. Friction D. Pore pressure only

Answer 13

✅ Answer: A – Soil weight component parallel to slope
Downslope component of gravity.

Question 14

14. Increasing the slope angle generally ___.
    A. Increases F.S. B. Decreases F.S. C. No effect D. Doubles F.S.

Answer 14

✅ Answer: B – Decreases factor of safety
Steeper slope = higher driving force.

Question 15

15. Increasing soil cohesion or φ ___.
    A. Decreases stability B. Increases stability C. No change D. Random effect

Answer 15

✅ Answer: B – Increases stability
Higher shear strength = more resistance.

Question 16

16. The presence of water in slope pores generally ___.
    A. Increases stability B. Reduces stability C. No effect D. Stabilizes cohesion

Answer 16

✅ Answer: B – Reduces stability
Raises pore pressure → lowers σ′.

Question 17

17. The pore pressure ratio (r_u) = ___.
    A. u / (γH) B. u / (γHcosβ) C. u / (γz) D. u / σ_total

Answer 17

✅ Answer: D – r_u = u / σ_total
Used to estimate pore pressure effects.

Question 18

18. The Taylor stability number (N_s) = ___.
    A. c / (γH) B. (γH)/c C. tanφ D. c / (H tanφ)

Answer 18

✅ Answer: A – N_s = c / (γH)
Non-dimensional slope stability parameter.

Question 19

19. For a given φ, the critical stability number (N_cr) is obtained from ___.
    A. Taylor’s chart B. Rankine’s table C. Mohr’s circle D. e–log p curve

Answer 19

✅ Answer: A – Taylor’s chart
Graphical design aid for slope stability.

Question 20

20. Factor of safety in terms of cohesion = ___.
    A. c / c_required B. c / (N_crγH) C. (N_crγH)/c D. N_s / N_cr

Answer 20

✅ Answer: D – F.S. = N_cr / N_s = (c_req / c)
Relates actual stability to critical.

Question 21

21. The typical F.S. used for slope design in clays is ___.
    A. 1.1 B. 1.3–1.5 C. 2.0 D. 3.0

Answer 21

✅ Answer: B – 1.3–1.5
For long-term stability.

Question 22

22. Rapid drawdown failure occurs in ___.
    A. Embankment slopes with sudden lowering of water level B. Dry slopes C. Compacted fills D. Retaining walls

Answer 22

✅ Answer: A – Rapid drawdown in reservoirs
Pore pressure remains high = reduced stability.

Question 23

23. Infinite slope analysis assumes ___.
    A. Finite height B. Infinite extent, parallel planes C. Circular surface D. Rock slope

Answer 23

✅ Answer: B – Infinite extent, parallel planes
Used for long uniform slopes.

Question 24

24. For an infinite slope in cohesionless soil, factor of safety = ___.
    A. tanφ / tanβ B. tanβ / tanφ C. c / γH D. 1 – sinφ

Answer 24

✅ Answer: A – F.S. = tanφ / tanβ
Stability depends purely on slope angle.

Question 25

25. For purely cohesive soil slope (φ=0), F.S. = ___. A. c / (γH N_cr) B. N_cr / N_s C. N_s / N_cr D. γH / c

Answer 25

✅ Answer: A – F.S. = c / (γH N_cr) From Taylor’s stability concept.