Question

A sample of saturated cohesionless soil tested in a drained triaxial compression test showed an angle of internal friction of ${30}^{\circ }$. The deviator stress at failure for the sample at a confining pressure of 200 kPa is equal to

• A. 200 kPa
• B. 400 kPa
• C. 600 kPa
• D. 800 kPa

Answer 1

The correct option is B 400 kPa

Angle of internal friction,

$\varphi ={30}^{\circ }$

Confining pressure,

${\sigma }_3=200kPa$

C = 0

${\sigma }_1={\sigma }_{3}ta{n}^2(45+\varphi /2)$

$+2Ctan(45+\varphi /2)$

$\Rightarrow {\sigma }_1=200ta{n}^2(45+\frac{30}{2})$

= 600 kPa

Deviatoric stress = ${\sigma }_1-{\sigma }_3$

= 600 - 200 = 400 kPa