Question

The reason(s) of the nonuniform elastic settlement profile below a flexible footing, resting on a cohesionless soil while subjected to uniform loading, is/are:

• A. Variation of friction angle along the width of the footing
• B. Variation of soil stiffness along the width of the footing
• C. Variation of friction angle along the depth of the footing
• D. Variation of soil stiffness along the depth of the footing

Hint:

Remember: For flexible footings, the nonuniform settlement profile is controlled by lateral variation in soil stiffness across the footing width, while depth variation controls overall magnitude.

Answer 1

The Correct Option is B

Step 1: Recall settlement characteristics of flexible footing.
When a rigid footing is loaded, the settlement is uniform since the load distribution is rigid.
However, for a flexible footing, the settlement can vary along the width due to variations in subgrade stiffness.

Step 2: Effect of soil stiffness.
The elastic settlement depends on the modulus of subgrade reaction (soil stiffness).
If the stiffness varies along the width of the footing, the settlement will also be nonuniform even under uniform loading.

Step 3: Eliminate incorrect options.
- (A) Variation of friction angle along the width: Not a primary factor for elastic settlement under uniform load. ✘
- (C) Variation of friction angle with depth: This affects bearing capacity, not directly the nonuniform settlement pattern. ✘
- (D) Variation of stiffness with depth: Influences total magnitude of settlement, but not the nonuniform distribution along the width. ✘
Hence, the correct cause is (B).
\[ \boxed{\text{Nonuniform elastic settlement occurs due to variation of soil stiffness along the width of the footing.}} \]