A $72-$in$.$ diameter, $2-$mile$-$long steel pipeline is required to be placed in dry clay soil as shown. The contractor plans to excavate a trench with $1$ to $1\mathrm{.}5$ slope walls to build this trench.

$[50$ points$]$

Specifications:

a$.$ Placement of $12$ in $.$ sand bedding $(C={12}^{\text{'}\text{'}})$

b$.$ Depth of pipe crown $($top$)$ from ground level is $9$ ft

c$.$ Soil Swell $-20\%$

d$.$ Allow $18"$ of working space on both sides of pipe