Example $2$:

Using the Fellenius method of slices, determine the factor of safety, in terms of effective stress, of the slope shown in Figure $9\mathrm{.}6$ for the given failure surface $($a$)$ using peak strength parameters $c^{\text{'}}=10k\frac{N}{m^2}$ and ${}^{\text{'}}=29$ and $($b$)$ using critical$-$state parameter ${}_{cv}^{\text{'}}=31.$ The unit weight of the soil both above and below the water table is $20k\frac{N}{m^3}.$

Figure $9\mathrm{.}6$