Which of the following statements is true?
Try it first: pick an option, then read the explanation.
Asked in SSC JE 25/01/2018 (Morning)
Detailed Explanation
Contact pressure under a foundation depends on the rigidity of the foundation and on the type of soil. A flexible base gives uniform pressure with non-uniform settlement; a rigid base gives uniform settlement with non-uniform pressure.
Why “On an absolutely rigid foundation base, the pressure will not be uniform” Is Correct
A perfectly rigid base must settle by the same amount everywhere. To achieve that, the soil reaction has to vary across the base: on clay it is highest at the edges, on sand highest at the centre. Either way the pressure is not uniform. Only statement (c) is true for every soil.
Why the Other Options Are Wrong
- A. On an absolutely rigid foundation base, the pressure will be more at the edges of the foundation: True for clay only; on sand the pressure is higher at the centre.
- B. On an absolutely rigid foundation base, the pressure will be uniform: Uniform pressure occurs under a flexible base, not a rigid one.
- D. On an absolutely rigid foundation base, the pressure will be zero at the centre of the foundation: The pressure is never zero at the centre; on sand it is maximum there.
Key Point
Rigid base → uniform settlement, non-uniform pressure. Flexible base → uniform pressure, non-uniform settlement.
Key Concepts for Students
- Clay: pressure peaks at edges under a rigid base.
- Sand: pressure peaks at the centre under a rigid base.
- Real footings are between perfectly rigid and perfectly flexible.
Practice more: this is question 46 in Shallow and Deep Foundation MCQs – Part 4. Try the whole set and check every answer instantly.