Question

Find the influence factor for the vertical pressure at depth 5m for a uniformly loaded circular area of 80 kN/m^2 load and radius of 1m.

(a) 0.6212

(b) 0.0571

(c) 0.0328

(d) 0.0624

I had been asked this question in an internship interview.

The question is from Stress Distribution in portion Stress Distribution of Geotechnical Engineering I

Answer 1

Right choice is (b) 0.0571

To explain I would say: Given,

uniformly loaded circular area of radius a=1m

depth z=5m

load q=80 kN/m^2

The Boussinesq’s vertical pressure σz under a uniformly loaded circular area is given by,

\(σ_z=q\left[1-\left[\frac{1}{1+(\frac{a}{z})^2}\right]^\frac{3}{2} \right] \)

∴ σz=kq

∴ \(k=\left[1-\left[\frac{1}{1+(\frac{a}{z})^2}\right]^\frac{3}{2}\right] \)

\(K=\left[1-\left[\frac{1}{1+(\frac{1}{5})^2}\right]^\frac{3}{2} \right] \)

k=0.0571.