In granular materials, the resistance to sliding on any plane within the soil mass depends upon the ______.
Try it first: pick an option, then read the explanation.
Correct answer: D. normal force and angle of internal friction
Asked in SSC JE 15/11/2022 (Shift-I)
Detailed Explanation
Granular soils behave like a block on a rough surface: the force needed to make it slide is proportional to how hard it is pressed against the surface. In soil terms, the shear strength on a plane is
\[ \tau_f = \sigma\tan\phi \]
Why “normal force and angle of internal friction” Is Correct
Two things appear in that equation: the normal stress σ (the normal force over the area) and the angle of internal friction φ. So the resistance to sliding depends on the normal force and φ.
Why the Other Options Are Wrong
- A. normal force only: Normal force alone is not enough; the friction angle sets how much resistance each unit of normal force gives.
- B. tangential force only: The tangential force is the applied shear, not the resistance.
- C. tangential force and angle of sliding friction: Again the tangential force is the load, not what the resistance depends on.
Key Point
Friction resistance = normal force × tan φ.
Key Concepts for Students
- Increasing confining pressure increases sand strength.
- Effective normal stress must be used when pore water is present.
- Interlocking in dense sands adds to the measured φ.
Practice more: this is question 18 in Shear Strength of Soils MCQs – Part 2. Try the whole set and check every answer instantly.