Question

In an unconfined compression test on saturated clay, the undrained shear strength was found to be $6t/m^2$. If a sample of the same soil is tested in an undrained condition in a triaxial compression at a cell pressure of $20t/m^2$, then the major principal stress at failure will be:

• A. $48t/m^2$
• B. $32t/m^2$
• C. $24t/m^2$
• D. $12t/m^2$

Answer 1

The correct option is B $32t/m^2$

${\sigma }_1={\sigma }_3{\tan }^2(45+\frac{\varphi }{2})+2c\tan (45+\frac{\varphi }{2})$

For saturated clay $\varphi =0^{\circ }$

${\sigma }_1=20+2\times 6$

$=32t/m^2$