Question

When a vertical face excavation was made in a clayey silt, having density of $20kN/m^3,$ it failed at a depth of excavation of 4 m. What is the cohesive strength $\left(inkN/m^2\right)$ of the soil, if its angle of internal friction was ${30}^{\circ }$?

• A. 23.1
• B. 20.0
• C. 11.6
• D. 10.2

Answer 1

The correct option is C 11.6

$H_c=\frac{4c}{\gamma \sqrt{K_a}};But{K}_a=\frac{1-\sin {30}^{\circ }}{1+\sin {30}^{\circ }}=\frac{1}{3}\therefore 4=\frac{4\times c\times \sqrt{3}}{20}\Rightarrow c=11.6kN/m^2$