Problem $1$: Design a braced excavation for a large sanitary sewer force$-$main, which is a reinforced concrete pipe with a diameter of $3m.$ The trench should be $5m$ deep and $5m$ wide. The phreatic surface is below bottom of excavation. The undrained cohesion for the silty clay is $C_u=70$kPa, and $=17k\frac{N}{m^2}.$ Assume $=0.$