Question

For a sample of dry, cohesionless soil with friction angle $\varphi$, the failure plane will be inclined to the major principal plane by an angle equal to

• A. $\varphi$
• B. ${45}^{\circ }$
• C. ${45}^{\circ }-\varphi /2$
• D. ${45}^{\circ }+\varphi /2$

Answer 1

The correct option is D ${45}^{\circ }+\varphi /2$

For cohesionless soil,

c = 0

$\text{Angle between major principal plane and failure plane}={\theta }_f$

$\text{From Mohr circle},2{\theta }_f=90+\varphi$

${\theta }_f=45+\frac{\varphi }{2}$