For any applied stress, zone of influence refers to isobar corresponding to

Question

Question

This question was previously asked in

UPPSC AE Civil 2019 Official Paper I (Held on 13 Dec 2020)

Answer 1

Concept:

An isobar or pressure bulb is a stress contour or a line that connects all points below the ground surface at which the vertical pressure is the same.
Pressure at points inside the bulb is greater than that at a point on the surface of the bulb and pressures at points outside the bulb are smaller than that value.

An isobar of n% represents that the vertical pressure at all points of isobar is n% of load applied.

5% isobar means, vertical stress = 5% of load applied

10% isobar means, vertical stress = 10% of load applied

It is evident from the diagram that vertical stress reduces with increasing depth.

Effect of vertical stress beyond the zone of 0.2Q (vertical stress is 20% of applied load) isobar is neglected.

Zone of influence refers to zone within which the stresses have a significant effect on the settlement of the structure

Zone of influence is assumed to an isobar corresponding to 20% of the applied load.