Question $2-$ Shear Strength $($Trial Test$)$

The results below were obtained at failure in a series of consolidated$-$undrained triaxial tests, with pore water pressure measurement, on specimens of a fully saturated clay:

$\backslash$table$[[$Sample No$.,,$I,II$,$III$],[$All$-$round pressure, ${}_3,(k\frac{N}{m^2}),200,300,400],[$Deviator stress, ${}_1-{}_3,(k\frac{N}{m^2}),244,314,384],[$Pore$-$water pressure, u$,(k\frac{N}{m^2}),55,107,159]]$

a$)$ Determine the effective shear strength parameters c$\text{'}$ and ${}^{\text{'}}($Mohr circles must be properly drawn$).$

b$)$ Find the effective stress ${}_3$ if the specimen of the same soil was loaded to failure under a ${}_1$ stress of $650k\frac{N}{m^2}.$

Hint: Refer to the formula

$p_a=K_a{}_z^{\text{'}}-2c^{\text{'}}\sqrt[\phantom{2}]{K_a}$