$\text{1.}$ A big hole is having to be digged.

$\text{→}$ Modal V: S + modal V + be + Ved/ P2

$\text{2.}$ Windy is said to be a spy.

$\text{→}$ S + be + Ved/ P2 + to-V/ to have + Ved/ P2

$\text{3.}$ It's possible to have this water porified.

$\text{→}$ It's + adj (for sb) to-V

$\text{4.}$ It's impossible to have her replaced.

$\text{5.}$ It's necessary to have your feet kept warm.

$\text{6.}$ It is understood that knowledge is power.

$\text{→}$ It + be + Ved/ P2 + (that) + S + V.

$\text{7.}$ I am thought to be very lazy.

$\text{8.}$ Children used to be taught at home.

$\text{9.}$ He won't let you have that silly thing done again.

$\text{10.}$ It must be seen to believe by Timmy.