3. (5 pts) A Douglas electric power transmission pole is embedded into the ground. The weight of the

pole is 7500 lb. If the pole transmits the load as a point load, determine the vertical stress increase

at x=2 ft, y=3 ft, and various depths of z = 0, 2, 4, 6, and 8 ft by using both Boussinesq's and

Westergaard equations (Show one sample calculation). Plot the changes of the vertical stress

increase over depth from the two tables. Use MS Excel (x-axis: stress increase, y-axis: depth).

At what depth, the vertical stress increase is the largest?

From Boussinesq's Equation:

r (mt)

z (ft)

0

From Westergaard's Equation (Assume the Poisson's ratio is 0.3)

r (ft)

2

z (ft)

0

2

4

6

1/z

n

Influential Factor Stress Increase (ib/ft²)

(2) Influential Factor Stress Increase (ib/ft²)