Q$3.(25$P$.)$ In a consolidation test with double drainage, the stress increment was from $1$ to $2k\frac{g}{c}{m}^2,$ the initial

height of specimen was $2x$ mm and the dial reading at zero loading was zero. a$)$ Calculate $c_v$ using Casagrande's

method $($Dial reading $0\mathrm{.}1mm).$ b$)$ Find the time for $70\%$ consolidation in the field under the same stress

increment assuming double and single drainage conditions $($The thick of clay layer $=3m).$ X$=2$