Insulation on Water Mains Ducting

Hello. I have started a project which is being delayed by a lot more than expected. Currently I have a functioning water main sealed in a 100mm duct and buried at about 10 inches below ground. There are also two sections of the duct each about 1m long which are not buried, but visible.
As the winter comes I am concerned for the pipe freezing! I wonder if I could insulate it with some 100mm rockwool which I have or if there is any other specific insulation for ducts which I can use, please!

I've no idea what you mean but trace heating might be your solution.

Dan

Thank you dan2071!

Could you slide a split pipe insulation onto the pipe/into the duct? Or fully bury it.