Question

A concentrated vertical laod of 6000 lbf is applied at the ground suface most nearly what is the increase in the vertical pressure 3.5 ft below the surface and 4 ft away from a point directly below the concentrated load?
(A) 29 lbf/ft^2
(B) 36 lbf/ft^2
(C) 41 lbf/ft^2
(D) 58 lbf/ft^2

Answer 1

Answer:

the correct answer is option A

Explanation:

given,

Load = 6000 lbf            

depth = 3.5 ft                                      

distance from the load = 4 ft                  

vertical stress = $\dfrac{3Pz^3}{2\pi (r^2+z^2)^{\frac{5}{2}}}$

                        = $\dfrac{3\times 6000\times 3.5^3}{2\pi (4^2+3.5^2)^{\frac{5}{2}}}$

                        = 28.96 lbf/ft²                      

                        = 29 lbf/ft²              

hence, the correct answer is option A