$17)$ a$)(10$ points$)$ A $200$ mm diameter pipe is placed in a $3$ m deep, $0\mathrm{.}9$ m wide trench and backfilled with sand. Using the safety factor of $1\mathrm{.}5,$ select an appropriate class of bedding for the pipe if it is standard strength VCP$.$

b$)(5$ points$)$ What would be a suitable type of bedding for the pipe in the above problem if it were extra$-$strength VCP instead of standard strength?