Question

Consider the following statements:
1. The bulb of pressure under strip-footing forms in the lengthwise direction.
2. The bulb of pressure under a strip-footing forms in the width-wise direction.
3. Contact pressure at the edges of a rigid looting in a saturated clay is theoretically infinite.
Which of these statements are correct?

• A. 1, 2 and 3
• B. 2 and 3 only
• C. 1 and 2 only
• D. 1 and 3 only

Answer 1

The correct option is B 2 and 3 only

At a given depth and for some distance from center line of footing, pressure remains constant along the length of strip footing, hence pressure bulb forms in the width wise direction and along the length.
According to theory of elasticity, contact pressure at the edges or a rigid footing on saturated clay assuming clay to be perfectly elastic and homogenous and extending to a great depth increases from a value less than 0.7 q at the center line to an infinite value at the edges.

$\Delta \sigma =\frac{q}{\pi }[\beta +\sin \beta \cos (\beta +2\delta \left)\right]$