Question

Two footings, one circular and the other square, are founded on the surface of a purely cohesionless soil. The diameter of the circular footing is the same as that of the side of the square footing. The ratio between their ultimate bearing capacities will be

• A. 1.0
• B. 1.3
• C. 1.33
• D. 0.75

Answer 1

The correct option is D 0.75

Ultimate bearing capacity is given by Circular footing :

$Q_{uc}=1.3c{N}_c+\gamma D_f{N}_q+0.3b\gamma N_{\rho }$

Square footing :

$Q_{us}=1.3c{N}_c+\gamma D_f{N}_q+0.4b\gamma N_{\rho }$

For cohensionless soil : c = 0
For footing on surface of soil : $D_f=0$

$\therefore \frac{Q_{uc}}{Q_{us}}=\frac{0.3}{0.4}=0.75$