Question Bank • QB_SWCE_EXP_072 NAT • 2 Marks

Section 4: Soil and Water Conservation Engineering

Soil Mechanics

Subtopic: Shear strength

Question Statement:

A direct shear test on a sandy soil sample under a normal stress of $\sigma = 150\text{ kPa}$ gave a shear stress at failure of $\tau = 90\text{ kPa}$. Assuming effective cohesion $c = 0$, calculate the angle of internal shearing resistance $\phi$ in $\text{degrees}$.

Answer Key:

30.96

Step-by-Step Solution & Explanation

Mohr-Coulomb failure criterion for cohesionless soil ($c = 0$): $\tau = \sigma \tan\phi$ $\tan\phi = \frac{\tau}{\sigma} = \frac{90}{150} = 0.60$ $\phi = \arctan(0.60) \approx 30.964^\circ$
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