Problem $5$

An excavation $25-$feet deep will be performed at a soft clay site where bedrock is present at a

depth of $100-$feet $($i$.$e$.,75-$feet below the floor of the excavation$).$ The slope has an angle of

$26\mathrm{.}7,$ and the soft clay has the following properties:

$=119\mathrm{.}2pcf,c^{\text{'}}=380psf,{}^{\text{'}}=25,Su=1800psf,C_{V}120c\frac{m^2}{h}r$

Please provide:

a$)$ the short$-$term Factor of Safety of the slope.

b$)$ the long$-$term Factor of Safety of the slope

c$)$ If the excavation is performed during a period of $3$ months and backfilled immediately

afterwards, what is its factor of safety, and can it be performed without triggering a deep

slope failure?