Q$2.$

In a triaxial test a soil specimen is allowed to consolidate fully under $600$ kPa cell pressure and $400$ kPa back pressure. Under undrained conditions the cell pressure is increased to $800$ kPa $,$ resulting in a pore water pressure increase of $150$ kPa $.$ Axial load is then applied under undrained conditions until failure takes place. The variation of Skempton's A$-$value with axial strain is illustrated in the Figure. Determine

a$)$ The value of the pore pressure coefficient $B.$

b$)$ The effective major principal stress at failure when the deviator stress at failure is $283$ kPa $.$

c$)$ The friction angle $({}^{\text{'}}).($Assuming $($:$c^{\text{'}}=0$