Question

A triaxial test was conducted on a granular soil. At failure $\frac{{\sigma }_1}{{\sigma }_3}=4$. The effective minor principal stress at failure was $100kPa$. The values of approximate $\Phi$ and the principal stress difference at failure are, respectively

• A. ${45}^o$ and $570kPa$
• B. ${40}^o$ and $400kPa$
• C. ${37}^o$ and $300kPa$
• D. ${30}^o$ and $200kPa$

Answer 1

The correct option is C ${37}^o$ and $300kPa$

${\sigma }_{3f}^{\prime }=100kPa$
$\therefore {\sigma }_{11}^{\prime }=4{\sigma }_{3f}^{\prime }=400kPa$
Principal stress difference
$={\sigma }_{1f}^{\prime }-{\sigma }_{3f}^{\prime }=300kPa$
$andsin\varphi =\frac{{\sigma }_{1f}^{\prime }-{\sigma }_{3f}^{\prime }}{{\sigma }_{1f}^{\prime }+{\sigma }_{3f}^{\prime }}=\frac{300}{500}=0.6$
$\varphi ={36.86}^o\simeq {37}^o$