A specimen prepared from an undisturbed sample $($assume perfect sampling$)$ obtained from a saturated normally consolidated clayey soil deposit when tested in unconfined compression resulted in a deviator stress at failure of $455$kPa. The testing work conducted on the same soil from another series of consolidated undrained triaxial $($CU$)$ tests yielded the following: effective friction angle $({}^{\text{'}})=30$; Skempton's pore water pressure parameter at failure $(A_f)=1\mathrm{.}0.$ Incorporating the idea of Mohr circle at failure, for the unconfined compression test, determine:

$($a$)$ the effective stress of the sample at the beginning of the test.

$($b$)$ the pore water pressure at the beginning of the test.

$($c$)$ the pore water pressure at failure.

$($d$)$ the estimated effective overburden stress in the field soil deposit.