Question

The contact pressure distribution below a rigid footing on the surface of a clay soil is

• A. Uniform for the full width
• B. Maximum at the edges and minimum at the center
• C. Maximum at the center and minimum at the edges
• D. Maximum at half of the length

Hint:

For rigid footings: \[ \begin{array}{ll} \textbf{Clay (Cohesive Soil)} &\rightarrow \text{Maximum pressure at edges} \textbf{Sand (Cohesionless Soil)} &\rightarrow \text{Maximum pressure at center} \end{array} \] This is one of the most frequently asked concepts in Foundation Engineering.

Answer 1

The Correct Option is B

Concept: The contact pressure distribution beneath a footing depends on both the rigidity of the footing and the nature of the supporting soil. For a rigid footing:
• On sand (cohesionless soil), the pressure is maximum at the center.
• On clay (cohesive soil), the pressure is maximum at the edges and minimum at the center. This occurs because a rigid footing undergoes uniform settlement, whereas the soil reaction varies with the soil type.

Step 1: Identify the footing and soil type. The footing is rigid and rests on clay soil. Clay is a cohesive soil that tends to deform more near the center under a rigid footing.

Step 2: Determine the pressure distribution. To achieve uniform settlement, the soil reaction becomes greater near the edges and smaller at the center. Hence, \[ \boxed{\text{Contact pressure is maximum at the edges and minimum at the center}.} \] Therefore, the correct option is \[ \boxed{(B)\;\text{Maximum at the edges and minimum at the center}.} \]