$2-$ A consolidated drained triaxial test on a sample of clay gives the following results:

$\backslash$table$[[$Cell pressure $(kPa)$:$,50,100,150],[$Deviator stress at failure $(kPa)$:$,105,178,251]]$

a$)$ Find $c^{\text{'}}$ and $\text{'}$ for this clay

b$)$ An identical sample of this clay is subjected to an unconsolidated undrained triaxial test using a cell pressure of $100$kPa. It is found that the deviator stress at failure is $40$kPa. What would be the average value of pore pressure in the specimen as it fails?