The actual movement of a soil mass is known as:
Try it first: pick an option, then read the explanation.
Correct answer: C. Slope failure
Asked in SSC JE 23/09/2019 (Evening)
Detailed Explanation
When the shear stresses in a sloping soil mass exceed its shear strength along some surface, a part of the mass slides down and outwards. This actual movement of the soil mass is called a slope failure (landslide or slip).
Why “Slope failure” Is Correct
Slope failure is the general name for the movement of a soil mass. Face failure, toe failure and base failure are different types of slope failure, classified by where the slip surface emerges.
| Type of slope failure | Where the slip surface passes |
|---|---|
| Face (slope) failure | Cuts the slope face above the toe |
| Toe failure | Passes through the toe of the slope |
| Base failure | Passes below the toe, into the base (common in soft clay) |
Why the Other Options Are Wrong
- A. Surface failure: ‘Surface failure’ is not the standard term for the movement of a soil mass.
- B. Collapse: Collapse refers to sudden volume reduction of certain dry soils on wetting.
- D. Base failure: Base failure is only one particular type of slope failure.
Key Point
Slope failure types: face, toe, base.
Key Concepts for Students
- FOS of a slope = shear strength available ÷ shear stress mobilised.
- Common causes: rainfall raising pore pressure, cutting at the toe, loading at the top.
- Analysed by the method of slices (Fellenius, Bishop).
Practice more: this is question 51 in Shear Strength of Soils MCQs – Part 4. Try the whole set and check every answer instantly.