Under a rigid footing on cohesive soil, the contact pressure distribution is:
Try it first: pick an option, then read the explanation.
Asked in SSC JE 30/10/2020 (Morning)
Detailed Explanation
Contact pressure is the pressure between the underside of a footing and the soil. Its shape depends on two things: whether the footing is rigid or flexible, and whether the soil is cohesive (clay) or cohesionless (sand).
Why “non-uniform, with maximum at the ends and minimum at the centre” Is Correct
A rigid footing forces the soil to settle by the same amount everywhere. Clay can carry shear stress at the edges of the loaded area, so to produce uniform settlement the edges must carry more pressure than the centre. Theoretically the edge pressure is very high; in practice it is limited by local yielding. So the distribution is non-uniform with the maximum at the ends and minimum at the centre.
Why the Other Options Are Wrong
- A. uniform: Uniform contact pressure occurs under a flexible footing, not a rigid one.
- C. linear: The distribution is curved, not linear.
- D. non-uniform, with maximum at the centre and minimum at the ends: Maximum at the centre is the pattern for a rigid footing on sand.
Key Point
Rigid on clay: max at edges. Rigid on sand: max at centre. Flexible: uniform pressure, non-uniform settlement.
Key Concepts for Students
- Flexible footing on clay: settles more at the centre (dish shape).
- Flexible footing on sand: settles more at the edges.
- For design, contact pressure is usually assumed uniform or linear.
Practice more: this is question 21 in Shallow and Deep Foundation MCQs – Part 2. Try the whole set and check every answer instantly.