$18\mathrm{.}4($a$)$ A $10ft$ deep basement is constructed with reinforced concrete walls on a large unob$-$

structed site. Although the final choice of excavation support system is up to the general

contractor $($GC$),$ your opinion, as an experienced construction contract administrator for

the project, has been sought by the $GC,$ who is relatively new to the field. What is your

suggestion to the $GC$ as the most suitable excavation support system? Explain.

$($b$)$ If the basement described above exists on a relatively restricted site, which excavation

support system would you suggest? Explain.

$($c$)$ If the basement is $50ft$ deep below the ground, which excavation support system would

you suggest? Explain.