$($a$)$ A fully saturated soft clay was tested in a triaxial apparatus. The sample was

consolidated by allowing drainage from the specimen under a cell pressure of

$550$ kPa and a back pressure $($pore water pressure$)$ of $200$ kPa. The drainage

tap was then closed and the cell pressure increased to $700$ kPa. Determine the

effective stress and pore water pressure before and after the increase of cell

pressure was applied.

$(5$ Marks$)$

$($b$)$ Comment on any changes to the shear strength of the soil that may have

occurred during the testing described in part $($a$).$

$(5$ Marks$)$

$($c$)$ A second sample of the same clay was again consolidated by allowing drainage

from the specimen under a cell pressure of $550$ kPa and a back pressure $($pore

water pressure$)$ of $200$ kPa. The drainage tap was then closed and a standard

undrained triaxial shearing test performed. At failure the axial stress had

increased by $342$ kPa and the pore water pressure had increased by $153$ kPa.

Assuming a value of c$=0$ estimate a value of $$ for this soil.